共查询到20条相似文献,搜索用时 0 毫秒
1.
G Ramallo 《Canadian Metallurgical Quarterly》1997,52(3-4):67-70
Spirocamallanus hilarii (Nematoda, Camallanidae) is cited parasitizing five fresh water fish species: Salminus maxillosus Leporinus obtusidens, Hoplias malabaricus malabaricus, Oligosarcus jenynsii and Pimelodus albicans, captured in Termas de Río Hondo pond, province of Santiago del Estero, Argentina. Morphologic and morphometric parasitological studies were done. The specimens described were drawned and photographed. In addition, the following parasitic infection indexes were calculated: Prevalence 26.5%, Mean 6.6 and Maximum Intensity 27. 相似文献
2.
P Klein R Béliard A Glacet S Moitel T Ducrot D Bourel 《Canadian Metallurgical Quarterly》1997,8(1):17-25
The aim of this study was to investigate how intrauterine growth retardation affects body proportions in VLBW infants. The cohort consisted of 135 surviving and 80 deceased preterm infants weighing less than 1250 grams at birth. Gestational age varied between 24 and 36 weeks (mean age 29.7 and 27.5 weeks, respectively). Birth weight was more than 2 SD below the mean birth standard values in 32% of the surviving, and in 27% of the deceased infants. Reduction of weight, length and head circumference at birth was analysed using Z scores based on Swedish birth standards. Z scores of weight, length and head circumference were highly correlated in the surviving and the deceased infants (r = 0.78 to 0.94 and 0.65 to 0.97, respectively). Length was significantly more affected by growth retardation than weight. Weight and head circumference were proportionately reduced. Intrauterine growth retardation influences body proportions in VLBW infants differently than in larger preterm and term infants. 相似文献
3.
Cephalobium magdalensis n. sp. (Rhabditida: Diplogasteridae) found in Magdalena, Buenos Aires, and Cruznema lincolnensis n. sp. (Rhabditida: Rhabditidae) found in Lincoln, Buenos Aires, parasitizing the cricket Gryllodes laplatae (Orthoptera: Gryllidae) are described and illustrated. C. magdalensis n. sp. is characterized by having the excretory pore between the pseudobulb and the basal bulb and seven pairs of postanal papillae in the male. C. lincolnensis n. sp. can be distiguished by having meanly two pairs of preanal papillae, one pair of adanal papillae and six pairs of postanal papillae in the male. 相似文献
4.
IA Vasconcelos AW Vasconcelos NM Fe Filho RG Queiroz EW Santana M Bozza SM Sallenave C Valim JR David UG Lopes 《Canadian Metallurgical Quarterly》1994,50(2):158-164
The oxidation states of intracellular myoglobin and cytochrome oxidase aa3 were monitored by reflectance spectrophotometry in isolated perfused rat hearts subjected to an acutely magnesium deficient environment. After exposure to low extracellular [Mg2+]o (i.e., 0.3 mM) for 30 min, more than 80% of the oxymyoglobin converted to its deoxygenated form. The level of reduced cytochrome oxidase aa3 also increased about 80% in low [Mg2+]o. The deoxymyoglobin was converted further to a species identified as ferrylmyoglobin by its reaction with Na2S to form ferrous sulfmyoglobin which was optically visible. This process, set into motion by acute Mg deficiency, resulted from a direct accessibility of the exogenous peroxide to the cytosolic protein. The results suggest that a pathway leading to cardiac tissue damage, induced by magnesium deficiency, is probably involved in the generation of a ferrylmyoglobin radical which could be prevented by addition of ascorbate, which is known to be a one-electron reductant of this hypervalent form of myoglobin. In further studies, we also investigated whether addition of different concentrations of ascorbic acid (AA) to the perfusate could enhance myocardial function after exposure to low [Mg2+]o perfusion. Four concentrations of AA (0.5, 1, 5, 10 mM) were tested, and the results indicate that they exert their effects in a concentration-dependent manner; 1 mM AA was the most effective dose in improving aortic output in a Mg-deficient heart. Ferrylmyoglobin formation was found to be formed considerably before intracellular release of either creatine phosphokinase or lactic dehydrogenase. These studies may have wide implications as a new mechanism by which low extracellular Mg2+ can induce myocardial injury and subsequent cardiac failure. 相似文献
5.
S Daba NS Mansour FG Youssef NM Shanbaky MG Shehata BM el Sawaf 《Canadian Metallurgical Quarterly》1997,27(3):629-637
Phlebotomus langeroni collected from a leishmaniasis endemic focus at Et Agamy, Alexandria, Egypt, were found to have fed on blood from man, dogs (Canis familiaris) and rats (Rattus rattus). The effect of the kind of blood meal on the development and the life-cycle of L. infantum and L. major in laboratory reared P. langeroni was therefore investigated. A membrane feeding technique was used to infect sand flies. Gut smears of infected females were examined immediately after feeding and daily for 16 days. Nectomonads and short promastigote forms of L. infantum or L. major were detected in females fed on human, dog and rat bloods at all intervals. Paramastigotes (infective stage) were present only in females fed on dog blood containing L. infantum or L. major and in those fed on rat blood containing L. major. It is concluded that among the factors influencing the Leishmania-phlebotomus relationship is the natural medium in which the parasite is present in vivo. The blood of the natural reservoir host(s) is the key factor for the development of the infective parasite form in the sand fly and P. langeroni could be considered a potential vector for transmitting L. infantum from dogs and L. major from rats and dogs but not from man. This investigation offers a new concept for the study of interactions among vector, host and parasites in Leishmania transmission. 相似文献
6.
The metabolic effects of sodium restriction, alone or with thiazide, were studied in 12 healthy subjects, in 24 tetraplegics during the intial 8 months of paralysis (early) and in 16 others during the subsequent period (late). The diuresis caused by both treatments led to more haemoconcentration in early than in late patients. In contrast with the healthy subjects on low sodium, the tetraplegics had a delayed urinary sodium retention and no fall in calciuria. During thiazide, urinary sodium depletion occurred early and the urine calcium fell after 3 days in all tetraplegics. During both treatments, aldosterone and renin increased more in early patients than in the other groups. The clinical implications of inducing dehydration and a sustained stimulation of the renin-angiotensin-aldosterone axis in recently injured tetraplegics with severe orthostatic hypotension are discussed. 相似文献
7.
CS Foster CA Smith EA Dinsdale P Monaghan AM Neville 《Canadian Metallurgical Quarterly》1983,96(1):197-216
8.
MD Feliciangeli 《Canadian Metallurgical Quarterly》1997,34(2):110-115
Random amplified polymorphic DNA (RAPD) analysis was used to amplify the genome of black tiger prawns (Penaeus monodon) to detect DNA markers and assess the utility of the RAPD method for investigating genetic variation in wild P. monodon in Thailand. A total of 200 ten-base primers were screened, and 84 primers yielded amplification products. Six positive primers that gave highly reproducible RAPD patterns were selected for the analysis of three geographically different samples of Thai P. monodon. A total of 70 reproducible RAPD fragments ranging in size from 200 to 2000 bp were scored, and 40 fragments (57%) were polymorphic. The RAPD analysis of broodstocks from three different locales, Satun-Trang, Trat, and Angsila, revealed different levels of genetic variability among the samples. The percentages of polymorphic bands were 48% and 45% in Satun-Trang and Trat, respectively, suggesting a high genetic variability of the two samples to be used in selective breeding programs. Only 25% polymorphic bands were found in the Angsila sample, indicating the lowest polymorphic level among the three samples examined. Primer 428 detected a RAPD marker that was found only in P. monodon originating from Satun-Trang, suggesting the potential use of this marker as a population-specific marker in this species. 相似文献
9.
C Funke DP King RM Brotheridge D Adelung JL Stott 《Canadian Metallurgical Quarterly》1997,59(1-2):151-162
C-reactive protein (C-RP) was purified from harbor seal (Phoca vitulina) serum by calcium dependant phosphoryl-choline and protein A affinity chromatography. Polyacrylamide gel electrophoresis under reducing conditions revealed a single protein moiety with a molecular weight of approximately 25 kDa. An internal peptide derived from this purified protein was subjected to N-terminal amino acid sequencing. A high amino acid sequence similarity was obtained with other published mammalian C-RP molecules confirming that the purified protein was a C-RP homologue. Eight specific monoclonal antibodies (P13, P51, P87, P101, P106, P130, P157 and P219) were raised against this purified protein. All 8 monoclonal antibodies immunoblotted with the 25 kDa C-RP subunit under reducing conditions. A competitive immunoassay was developed identifying elevated C-RP concentrations in harbor seal serum samples with clinical evidence of inflammatory disease. Application of this immunoassay for the measurement C-RP may provide valuable information for the clinical assessment of harbor seal health. 相似文献
10.
PSP94 has shown potential to be a serum biomarker for evaluating prostate cancer. Studies of the epitope structure is crucial for this endeavour. In this article, we have used 15 different monoclonal antibodies (MAb) to analyse the epitope structure of PSP94 and to compare with the results obtained from our previous work using polyclonal antibody and recombinant PSP94. Firstly, we determined the relative activities of the 15 MAb population by direct and competitive ELISA. The two predominant MAbs (MAb PSP-6 and -19) in 15 MAbs were selected for further studies of the epitope structure. By comparing the binding activities of recombinant GST-PSP94 and natural PSP94 with MAbs, and by comparing their affinity with MAbs in an in vitro denaturing experiment, PSP94 was shown to have a similar, prevalently linear epitope structure as we demonstrated by polyclonal antibody. Using recombinant GST fusion protein with PSP94 and with each half of the N- and C-terminal 47 amino acids (GST-PSP-N47/C47) in E. coli cells, the different epitopes recognized by 15 monoclonal antibodies were delineated and the polar distribution of the epitope structure of PSP94 was characterized. Results of direct ELISA of recombinant N47 and C47 and their competitive binding against natural PSP94 (competitive ELISA) showed that the N- and C-termini represent the immuno-dominant and immuno-recessive area separately. A majority of the monoclonal antibodies (12/15) showed preferential binding of the N-terminal sequence of the PSP94 protein. Using GST-PSP-N47 as a standard protein, an epitope map of the 15 monoclonal antibodies was obtained. The results of this study will help to define the clinical utility of PSP94. 相似文献
11.
FM Apter P Michetti LS Winner JA Mack JJ Mekalanos MR Neutra 《Canadian Metallurgical Quarterly》1993,61(12):5279-5285
Secretory immunoglobulin A (IgA) antibodies (sIgA) directed against cholera toxin (CT) and surface components of Vibrio cholerae are associated with protection against cholera, but the relative importance of specific sIgAs in protection is unknown. A monoclonal IgA directed against the V. cholerae lipopolysaccharide (LPS), secreted into the intestines of neonatal mice bearing hybridoma tumors, was previously shown to provide protection against a lethal oral dose of 10(7) V. cholerae cells. We show here that a single oral dose of 5 to 50 micrograms of the monoclonal anti-LPS IgA, given within 2 h before V. cholerae challenge, protected neonatal mice against challenge. In contrast, an oral dose of 80 micrograms of monoclonal IgA directed against CT B subunit (CTB) failed to protect against V. cholerae challenge. A total of 80 micrograms of monoclonal anti-CTB IgA given orally protected neonatal mice from a lethal (5-micrograms) oral dose of CT. Secretion of the same anti-CTB IgA antibodies into the intestines of mice bearing IgA hybridoma backpack tumors, however, failed to protect against lethal oral doses of either CT (5 micrograms) or V. cholerae (10(7) cells). Furthermore, monoclonal anti-CTB IgA, either delivered orally or secreted onto mucosal surfaces in mice bearing hybridoma tumors, did not significantly enhance protection over that provided by oral anti-LPS IgA alone. These results demonstrate that anti-LPS sIgA is much more effective than anti-CT IgA in prevention of V. cholerae-induced diarrheal disease. 相似文献
12.
CF Lange 《Canadian Metallurgical Quarterly》1995,89(2):241-255
Placement of ten different anti-streptococcal monoclonal antibody (mAb) secreting hybridoma cells, as well as positive and negative controls into animals and sacrificing on a daily basis showed a difference in the tissue sites of accumulating mAb as noted by fluorescent antibody testing. Initial binding of the mAb was noted by day two on the kidney GBM in all the animals. Striated muscle tissues tested positive starting at day nine with only four of the mAbs, by which time the GBM was strongly positive. Fluorescent antibody testing of heart and skeletal muscle from animals in which one of the polyreactive IgM mAb secreting hybridoma cell lines was placed showed a distinctive staining of the Z-lines. Indirect fluorescent and immunoperoxidase testing as well as competitive blocking experiments confirmed the reactivity of this mAb for the Z-line of heart and skeletal muscle. Immunodots and Western blots along with direct and blocking assays confirmed that the critical cross-reactive Z-line antigen was alpha-actinin, supporting the concept that this anti-SCM mAb was reactive both in vivo and in vitro. These results confirm the cross-reactive nature of anti-SCM antibodies for mammalian tissue and bear important implications on the etiology of post-streptococcal glomerulonephritis and rheumatic heart disease. 相似文献
13.
C Pinilla J Buencamino JR Appel RA Houghten JA Brassard ZM Ruggeri 《Canadian Metallurgical Quarterly》1995,1(3):199-204
Fulminant hepatic failure is infrequently seen as a consequence of acute congestive heart failure. Recognition of this entity is important as treatment directed towards heart failure should help resolve the liver failure. A case of fulminant hepatic failure due to previously unrecognized cardiomyopathy is presented. A liver transplantation was being considered for fulminant hepatic failure until hemodynamic monitoring studies demonstrated that, in fact, the patient had severe cardiomyopathy. Treatment directed at his cardiomyopathy resolved the liver failure. Therefore, prompt recognition of such a phenomenon would enable early institution of appropriate therapeutic measures with the hope of clinical benefit to the patient. 相似文献
14.
In skeletal muscle, acetylcholinesterase (AChE) exists in homomeric globular forms of type T catalytic subunits (ACHET) and heteromeric asymmetric forms composed of 1, 2, or 3 tetrameric ACHET attached to a collagenic tail (ColQ). Asymmetric AChE is concentrated at the endplate (EP), where its collagenic tail anchors it into the basal lamina. The ACHET gene has been cloned in humans; COLQ cDNA has been cloned in Torpedo and rodents but not in humans. In a disabling congenital myasthenic syndrome, EP AChE deficiency (EAD), the normal asymmetric species of AChE are absent from muscle. EAD could stem from a defect that prevents binding of ColQ to ACHET or the insertion of ColQ into the basal lamina. In six EAD patients, we found no mutations in ACHET. We therefore cloned human COLQ cDNA, determined the genomic structure and chromosomal localization of COLQ, and then searched for mutations in this gene. We identified six recessive truncation mutations of COLQ in six patients. Coexpression of each COLQ mutant with wild-type ACHET in SV40-transformed monkey kidney fibroblast (COS) cells reveals that a mutation proximal to the ColQ attachment domain for ACHET prevents association of ColQ with ACHET; mutations distal to the attachment domain generate a mutant approximately 10.5S species of AChE composed of one ACHET tetramer and a truncated ColQ strand. The approximately 10.5S species lack part of the collagen domain and the entire C-terminal domain of ColQ, or they lack only the C-terminal domain, which is required for formation of the triple collagen helix, and this likely prevents their insertion into the basal lamina. 相似文献
15.
p53 antibodies in patients with various types of cancer: assay, identification, and characterization 总被引:2,自引:0,他引:2
R Lubin B Schlichtholz JL Teillaud E Garay A Bussel CP Wild 《Canadian Metallurgical Quarterly》1995,1(12):1463-1469
Alteration of the p53 gene is the most frequent genetic alteration in human cancer and leads to the accumulation of mutant p53 in the nucleus of tumor cells. In addition, it has been shown that patients with various types of neoplasia have p53 antibodies in their sera which could be used as an indirect diagnostic procedure for p53 alteration. Using a new ELISA, we have analyzed the sera from more than 1000 patients with various types of cancer and from healthy blood donors. We demonstrate that p53 antibodies are detected mainly in cancer patients and are strictly proportional to the occurrence of p53 mutations. Using various immunological approaches, these antibodies were unambiguously demonstrated to be directed toward the human p53 protein. Isotyping analysis of these antibodies strongly suggested that they correspond to a humoral response to the p53 protein which accumulates in the tumor cell. This finding suggests that serological analysis, combined with histochemistry, is suitable for assessing the integrity of the p53 gene in cancer patients. 相似文献
16.
Infection of BALB/c mice with a standard and substantial number of Leishmania major parasites results in progressive disease, following the induction of a parasite-specific Th2 response. These mice have been designated as "susceptible" on this basis. We show that distinct types of immune response can be generated in "susceptible" BALB/c mice depending upon the number of parasites employed for infection, and that the pathophysiological consequences of such distinct responses are dramatically different. Infection with very low numbers of parasites results in the exclusive induction of a cell-mediated, Th1 response, and the generation of resistance to the standard and substantial challenge. Spleen cells from such resistant mice can confer resistance upon normal mice when transferred to them, but these spleen cells do not contain T cells expressing DTH or Th1 effector cells that produce IFN gamma on short term culture (48 hrs) with parasite antigen. The immune response in this case appears to result in the virtual elimination of parasites from the lymph node draining the site of infection and, by implication, from the infected mouse. We suggest that such elimination results in the absence of antigen stimulation and hence of effector T cells, and that "memory Th1 cells" are responsible for the capacity of spleen cells to confer resistance on normal mice. We predict such mice will not suffer parasitemia upon immune suppression, i.e. are not susceptible to reactivation disease. This is the "beneficial state". In contrast to this infection with a very low number of parasites infection with a low number usually results in one of two states: (i) The generation of a response with a very small Th2 component, production of a small amount of antibody, chronic parasitemia and hence chronic generation of parasite-specific effector Th1/Th2 cells, or (ii) The generation of a response with a greater Th2 component, the production of more antibody, the formation of a frank lesion, and the long term generation of a stable, mixed Th1/Th2 response. We refer to the latter state as borderline leishmaniasis in analogy with borderline leprosy. Parasites can be recovered from the draining lymph node in both these cases many months after infection. We therefore believe that mice infected with a low number of parasites, that harbour a chronic subclinical infection, will suffer reactivation disease upon immune suppression, and we consequently designate the state generated as potentially harmful. We consider mice with borderline disease to be in a harmful state. Mice immunised with high doses of parasite antigen produce in the long term Th2 responses, whereas those immunised with lower doses produce Th1 responses. Mice immunised to produce a Th2 response were subsequently infected with a very low number of parasites that is normally contained. The generation of a Th2 response results in the generation of a Th2 imprint, such that the response to the low dose infection is modulated from a Th1 to a Th2 mode, resulting in progressive disease. We argue that immunisation/vaccination, resulting in a state that deviates the protective response to a non-protective mode, may result in epidemics. Such a state has the potential for being extremely harmful. 相似文献
17.
M Jeyakumar HN Krishnamurthy RR Dighe NR Moudgal 《Canadian Metallurgical Quarterly》1997,7(4):299-310
The concurrent influence of multiple neurotransmitter systems in mediating cocaine-induced convulsions is predicted by the results of previous receptor binding studies. The present results demonstrate that pharmacological manipulations of these predicted neurotransmitter systems alters the occurrence of cocaine-induced convulsions. The 5-HT reuptake inhibitor fluoxetine enhanced the occurrence and severity of convulsions produced by 100 mg/kg (-) cocaine, while the 5-HT2 receptor antagonists cinanserin, ketanserin and pirenperone antagonized cocaine-induced convulsions in a dose-dependent manner. Further, the M1 receptor antagonist pirenzepine antagonized cocaine-induced convulsions, but atropine did not. In addition, both the (+) and (-) stereoisomers of the sigma ligand SKF 10047 significantly attenuated cocaine-induced convulsions. (+)SKF 10047 was more potent than (-)SKF 10047 in this effect, suggesting a stereoselective effect at sigma receptor sites. In constrast, DA and NE neurotransmission do not appear to modulate the proconvulsant effects of cocaine in a specific, dose-dependent manner. Thus, of the CNS binding sites with which cocaine is known to interact, the results are consistent with the conclusion that 5-HT transporters and 5-HT2 receptor sites appear to be direct and primary sites related to cocaine-induced convulsions, while M1 and sigma binding sites appear to play important but secondary and modulatory roles in this response. 相似文献
18.
MP Oliveira-Neto A Schubach M Mattos SC Gon?alves-Costa C Pirmez 《Canadian Metallurgical Quarterly》1997,45(6):496-499
There is debate about the margin of normal tissue that should be included with excisions of melanocytic lesions of the skin, and about which lesions should be referred for specialist care. We describe the determinants of the margins of excised melanocytic skin lesions and of referral patterns from primary care. Copies of the pathology reports of melanocytic skin lesions excised from two cities in tropical Queensland were obtained; questionnaires about each lesion were administered to the excising doctor. Data about 3275 lesions (2914 naevi, 130 lentigos, 151 melanomas, 51 dysplastic naevi, 21 Hutchinson's melanotic freckles and eight other melanocytic lesions) were analysed. Twenty-one per cent of the treatment sessions involved the excision of more than one lesion; 5% involved three lesions or more. Most lesions were managed by one doctor. The overall mean margin of excision was 2.8 mm. It was greater for longer qualified doctors, surgeons and college-affiliated general practitioners, for lesions excised to address malignancy (3.0 mm) rather than cosmetic appearance (2.4 mm), for Hutchinson's melanotic freckles (5.9 mm) and melanomas (5.1 mm) compared with benign lesions (2.7 mm) (P < 0.001) and for older patients (2.6 mm for those < or = 15, 3.5 mm for those > 40 years) (P = 0.001). Wider excisions of skin melanocytic lesions are performed by older and more experienced doctors, on older patients, and for lesions in which malignancy is being addressed. 相似文献
19.
F Cardillo E de Paula GR Oliveira S Marangoni B Oliveira NC Meirelles 《Canadian Metallurgical Quarterly》1997,41(3):497-509
1) The Soret region absorption spectrum of erythrocruorin (ERC) obtained from Glossoscolex paulistus, shows that oxy-ERC has a maximum absorption peak at 416 nm while the deoxy-ERC from has a maximum at 427 nm. 2) In the presence of a specific antiserum (anti-ERC) and of anti-ERC immunoglobulin G raised in rabbits, there is a deviation to low wavelengths in the maximum absorption peak of deoxy-ERC while for the oxy form a red-shift is noticed. These shifts accompanied an increased affinity of the hemeprotein for oxygen, possibly because of changes in the overall macromolecular conformation. 3) A decrease in the oxygen affinity of erythrocruorin is observed when large amounts of non-specific serum are used. The same effect is observed in the presence of serum albumin, probably as a result of non-specific binding between the albumin and erythrocruorin. 4) The fluorimetric titration of erythrocruorin with anti-ERC Fab fragments results in a decrease in the intrinsic tryptophan fluorescence of the hemeprotein, a response indicative of a modification in the ERC's quaternary structure. 相似文献
20.
F Vely N Gruel J Moncuit O Cochet H Rouard S Dare J Galon C Sautes WH Fridman JL Teillaud 《Canadian Metallurgical Quarterly》1997,16(6):519-528
Four mouse anti-human Fc gamma RII (CD32) (6C4, 2B2, 3D3, 93.4) (IgG1, kappa) and one anti-human Fc gamma RIII (CD16) (7.5.4) IgG1, kappa) MAbs were raised. An in vitro switch variant, 7.5.4Sw50 (IgG2b, kappa), was also derived from the 7.5.4 MAb. 6C4, 2B2, and 3D3 MAbs bind both Fc gamma RIIa and Fc gamma RIIb isoforms. Two of them (6C4 and 2B2 MAbs) allow a complete blockade of the binding of immune complexes to Fc gamma RII. All three MAbs immunoprecipitate the receptor and bind both its glycosylated and nonglycosylated forms. The fourth anti Fc gamma RII MAb, 93.4, directed against the intracellular region of Fc gamma RIIa1/2, allows its detection by Western blotting only when it is not phosphorylated. The 7.5.4 MAb binds both Fc gamma RIIIa and Fc gamma RIIIb, can be used in Western blotting and does not inhibit aggregated IgG binding. ELISA using IV.3 (anti-Fc gamma RIIa1/2)/6C4 and 3G8 (anti-Fc gamma RIIIa/b)/7.5.4Sw50 MAb pairs make it possible to detect soluble Fc gamma RIIa1/2 and Fc gamma RIII, with a sensitivity of 200 pg/mL and 1 ng/mL, respectively. Surface plasmon resonance analyses indicated that the KD of two of the three anti-Fc gamma RII and of the anti-Fc gamma RIII are in the same order of magnitude (6C4: 0.78 nM, 2B2: 0.28 nM, 7.5.4: 0.47 nM). The anti-Fc gamma RII 3D3 MAb exhibits an off-rate constant higher than the 6C4 and 2B2 MAbs and a KD of 2.19 nM. 相似文献