首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1943篇
  免费   0篇
化学工业   5篇
水利工程   1篇
无线电   9篇
一般工业技术   4篇
冶金工业   1924篇
  2010年   2篇
  2007年   1篇
  2006年   1篇
  2005年   4篇
  2004年   2篇
  2003年   3篇
  2002年   2篇
  2000年   1篇
  1999年   64篇
  1998年   567篇
  1997年   356篇
  1996年   238篇
  1995年   120篇
  1994年   94篇
  1993年   121篇
  1992年   12篇
  1991年   24篇
  1990年   13篇
  1989年   18篇
  1988年   20篇
  1987年   13篇
  1986年   18篇
  1985年   13篇
  1983年   3篇
  1982年   8篇
  1981年   10篇
  1980年   10篇
  1979年   2篇
  1978年   5篇
  1977年   62篇
  1976年   124篇
  1975年   6篇
  1972年   1篇
  1965年   1篇
  1963年   1篇
  1955年   2篇
  1954年   1篇
排序方式: 共有1943条查询结果,搜索用时 15 毫秒
51.
A strategy for DNA computing on surfaces using linked sets of 'DNA words' that are short oligonucleotides (16mers) is proposed. The 16mer words have the format 5'-FFFFvvvvvvvvFFFF-3' in which 4-8 bits of data are stored in 8 variable ('v') base locations, and the remaining fixed ('F') base locations are used as a word label. Using a template and map strategy, a set of 108 8mers each of which possesses at least a 4 base mismatch with the complements to all the other members of the set (4bm complements) are identified for use as a variable base sequence set. In addition, sets of 4 and 12 word labels of the form ABCD....DCBA that are respectively 8bm and 6bm complements with each other are identified. The 16mers are chosen to have a G/C content of 50% in order to make the thermodynamic stability of the perfectly matched hybridized DNA duplexes similar; a simple pairwise additive method is used to estimate the perfect match and mismatch hybridization thermodynamics. A series of preliminary experiments are presented that use small arrays of 16mers attached to chemically modified gold surfaces and fluorescently labeled complements to study the hybridization adsorption and enzymatic manipulation of the oligonucleotides.  相似文献   
52.
METHODS: In a randomized double-blind study, 134 patients were given 500 mg metronidazole as an intravenous infusion immediately before operation for abdominal total hysterectomy and again 8 hours later and 124 patients received placebo. RESULTS: There was more wound infection, postoperative hospitalization was longer and the sedimentation rate on the sixth postoperative day was significantly higher in the placebo group. There was no difference in postoperative temperature. Postoperative wound infections occurred in 12% in the placebo group and 6% in the metronidazole group. Eight percent in the total material had urinary tract infections, the diagnosis was based on urine cultures. CONCLUSIONS: Prophylaxis with intravenous infusion of metronidazole is recommended in total hysterectomies.  相似文献   
53.
This study was undertaken to evaluate the role of CD14 and complement receptors type 3 (CR3) and 4 (CR4) in mediating TNF release and NF-kappaB activation induced by LPS and cell wall preparations from group B streptococci type III (GBS). LPS and GBS caused TNF secretion from human monocytes in a CD14-dependent manner, and soluble CD14, LPS binding protein, or their combination potentiated both LPS- and GBS-induced activities. Blocking of either CD14 or CD18, the common beta-subunit of CR3 and CR4, decreased GBS-induced TNF release, while LPS-mediated TNF production was inhibited by anti-CD14 mAb only. Chinese hamster ovary cell transfectants (CHO) that express human CD14 (CHO/CD14) responded to both LPS and GBS with NF-kappaB translocation, which was inhibited by anti-CD14 mAb and enhanced by LPS binding protein. While LPS showed fast kinetics of NF-kappaB activation in CHO/CD14 cells, a slower NF-kappaB response was induced by GBS. LPS also activated NF-kappaB in CHO cells transfected with either human CR3 or CR4 cDNA, although responses were delayed and weaker than those of CHO/CD14 cells. In contrast to LPS, GBS failed to induce NF-kappaB in CHO/CR3 or CHO/CR4 cells. Both C3H/OuJ (Lps[n]) and C3H/HeJ (Lps[d]) mouse peritoneal macrophages responded to GBS with TNF production and NF-kappaB translocation, whereas LPS was active only in C3H/OuJ macrophages. Thus, LPS and GBS differentially involve CD14 and CR3 or CR4 for signaling NF-kappaB activation in CHO cells and TNF release in human monocytes, and engage a different set of receptors and/or intracellular signaling pathways in mouse macrophages.  相似文献   
54.
The dose of prophylactic cranial irradiation given to patients for acute lymphoblastic leukaemia has been decreased from 24 to 18 Gy, but the beneficial effect of this decrease on growth is controversial. This study compares the growth hormone (GH) secretion and growth of 35 patients (20 boys) given 18 Gy at 3.7+/-0.3 (SE) years, and routinely evaluated 5.4+/-0.4 years after irradiation to define the indications for GH treatment in these patients. Of these, 63% had a low GH peak (< 10 microg/l) after one (22 cases) or two (17 cases) stimulation tests. The plasma concentrations of insulin-like growth factor I and its GH-dependent binding protein were normal for age in all but two cases. The height changes between irradiation and evaluation were correlated with the GH peaks (P < 0.03) and were concordant, except in patients with early puberty. This occurred in 16 patients including all 12 girls irradiated before 4 years of age. A significant (P < 0.03) reduction in height (SD) between irradiation and adult height occurred in untreated GH-deficient patients (-1+/-0.3, n=6), but not in GH-deficient patients given GH (-0.6+/-0.3, n=8) or in those with normal GH peak (-0.4+/-0.3, n=7). CONCLUSION: In children irradiated for acute lymphoblastic leukaemia, GH deficiency is frequent after 18 Gy but its impact on adult height is smaller than after higher doses. We suggest that the indications for gonadotropin releasing hormone analogue therapy should be broad in patients with early or rapidly progressing puberty and those for GH therapy in those patients with a below average constitutional height before irradiation.  相似文献   
55.
Substantial evidence has accumulated to suggest that in the near future implementation of the veto-cell-suppressor concept in the treatment of kidney allograft recipients might lead to the establishment of life-long specific allograft tolerance in the absence of further immunosuppressive therapy. Veto suppression prevents the generation of antigen-specific T-helper and cytotoxic T lymphocytes in vitro provided that the T-lymphocyte precursors specifically recognize antigenic peptides associated with the major histocompatibility complex molecules class II and class I, respectively, expressed on the surface of the veto-active cell. Data from a large number of experimental and clinical studies strongly indicate that veto-active cells function in vivo and are capable of preventing allograft rejection. Thus, donor-cell-mediated veto activity is the most likely explanation for the well-known graft tolerizing effect of pretransplant donor blood transfusions in kidney graft recipients. A prerequisite for a veto-active environment in vivo is the establishment of lymphoid microchimerism, in which veto-active donor and recipient cells mutually downregulate potential alloaggression.  相似文献   
56.
PURPOSE: This study aimed to identify a dangerous new weapon capable of causing damage to the ocular and periocular regions. METHODS: The authors report two patients who had penetrating ocular injury in the past year because of homemade recreational potato guns. RESULTS: In one 14-year-old boy, projectiles from the firing of a potato gun resulted in orbital and cranial injuries that were life threatening with widespread fractures, marked disruption of facial structures, a cerebrospinal fluid fistula requiring bifrontal surgical repair, and loss of one eye. In a separate accident with a different potato gun, a 14-year-old boy who was wearing glasses at the time of injury had a sight-threatening perforating corneal laceration. CONCLUSION: Practitioners must be aware of the existence of these new, homemade unregulated devices. Information about the use and construction of these guns is widespread on the Internet, but no injuries resulting from these guns currently are documented in the medical literature.  相似文献   
57.
A randomized, open-label, comparative study was conducted in 30 male patients with moderately advanced human immunodeficiency virus (HIV) infection to examine the pharmacokinetics of an investigational intravenous preparation of itraconazole compared with pharmacokinetics after administration of itraconazole capsules. The study also assessed whether adequate plasma concentrations of itraconazole could be rapidly achieved with the intravenous formulation and then maintained after cessation of intravenous therapy with itraconazole capsules. All patients received 200 mg intravenous itraconazole as a 1-hour infusion in 40% hydroxypropyl-beta-cyclodextrin (HP-beta-CD) vehicle twice daily for 2 days, and then 200 mg intravenously once daily for 5 days. Patients then received itraconazole capsules, either 200 mg twice daily or 200 mg once daily for 28 days. Steady-state plasma concentrations of itraconazole were reached by day 3 with intravenous infusion, a much shorter time than observed with administration of itraconazole capsules. Steady-state concentrations of itraconazole and hydroxyitraconazole were effectively maintained during the rest of the intravenous infusions of itraconazole. Oral follow-up with administration of 200-mg capsules once daily could not maintain the plasma concentrations of itraconazole and hydroxyitraconazole obtained at the end of the intravenous treatment, whereas twice-daily oral administration maintained or increased these concentrations. Mean plasma concentrations of itraconazole and hydroxyitraconazole on day 7 were similar to those on day 36 in the twice-daily group. Mean renal clearance was comparable to mean total body clearance, and approximately 93% to 101% of the HP-beta-CD was excreted unchanged in urine within 12 hours of administration. The HP-beta-CD was essentially eliminated through the kidney, and little accumulation in the body was observed in this patient population. Adverse events during the intravenous phase were most commonly associated with intravenous administration. Intravenous infusion of itraconazole for 7 days followed by administration of itraconazole capsules twice daily for 28 days is an effective dose regimen in patients with advanced HIV infection.  相似文献   
58.
The permanent fibrocyte-like fish cell line RTG-2 from rainbow trout (Oncorhynchus mykiss) gonads was investigated by means of light and scanning electron microscopy with respect to alterations as a consequence of sublethal exposure to 0, 1, 10, 16, 25, and 50 mg/liter 3,5-dichlorophenol (3,5-DCP) for 24 h. Control RTG-2 cells were spindle-like in shape and almost three times longer than wide. In subconfluent cultures, they displayed widely spread, flat leading lamellae and formed small groups. Along the edges of the cell protrusions, numerous retraction fibrils could be identified. Except for shallow ridges and small folds, the surface of untreated cells was completely smooth. Following exposure to 3,5-DCP, distinct dose-dependent alterations in cell shape, the appearance of surface blebs and invaginations, as well as progressive retraction of cell extensions could be observed from the lowest test concentration. Morphological changes could be correlated to suppression of lactate dehydrogenase and reduced neutral red retention capacity.  相似文献   
59.
In Hirschsprung's disease (HD), certain intestinal nervous plexuses are absent. Sprouting nerve endings contain different amounts of synaptophysin (SY), a protein and main constituent of acetylcholinesterase (AChE) storage compartments. Due to the lack of specific markers for synapses, a qualitative analysis of nerve endings of intestinal segments affected by HD has not yet been undertaken. For this study, resected colorectal specimens from patients with HD (n = 8, mean age 2.1 years) were investigated in parallel for AChE, SY, and content of small synaptic vesicles by biochemical, immunohistochemical, and electronmicroscopic means. In the microdissected muscular layer, reduced SY (1.4 microgram/mg total protein, normal 24 +/- 0.3) was observed. Immunohistochemistry showed in affected tissues reduced numbers of SY-positive nerve fibers and nerve endings, which in turn were thickened and distorted, in both the muscle proper and the muscularis mucosae. Combining both morphologic and biochemical findings, in HD the number of cholinergic vesicles in the remaining nerve endings seems to be increased as measured by SY, a marker molecule specific for synaptic vesicles. Our data also suggest that nerve endings in HD may contain high concentrations of cholinergic vesicles, paralleling the known high amounts of acetylcholine and AChE found in intestinal segments of patients with HD.  相似文献   
60.
BACKGROUND: The use of fine-needle aspiration cytology (FNAC) in the diagnosis of colonic lesions was investigated. METHODS: Some 22 patients (median age 71 years) with a colonic lesion identified on abdominal ultrasonography underwent ultrasonographically-guided FNAC using a 21-G needle. The sample was checked immediately by a cytopathologist for adequacy. RESULTS: Eighteen patients had colonic carcinoma; aspiration cytology detected malignant epithelial cells consistent with colonic carcinoma in 17 patients and severely dysplastic cells in one patient. The sensitivity and specificity of ultrasonographically-guided FNAC in the diagnosis of colonic carcinoma was 94 and 100 per cent respectively. The remaining four patients had a diagnosis of ileocaecal tuberculosis, ileocaecal Crohn's disease, and metastatic adenocarcinoma in the liver with no identifiable primary (two patients). One demonstrated granulomata, grew acid-fast bacilli and the patient was treated for tuberculosis. One had inflammatory cells and the patient was found to have Crohn's disease on histology. The remaining two patients had confirmed metastatic adenocarcinoma in the liver on aspiration cytology but suspected colonic lesions were found to be benign on cytological examination and no primary lesion was subsequently demonstrated. There were no complications of FNAC and patients complained of minimal discomfort. There has been no evidence of tumour recurrence with a median follow-up of 12 (range 1-25) months. CONCLUSION: Ultrasonographically-guided FNAC is a valid method for the diagnosis of colonic tumours.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号