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   2494篇
  免费   2篇
化学工业   8篇
金属工艺   1篇
机械仪表   1篇
轻工业   5篇
石油天然气   1篇
一般工业技术   15篇
冶金工业   2458篇
自动化技术   7篇
  2016年   2篇
  2015年   1篇
  2014年   1篇
  2013年   2篇
  2012年   3篇
  2011年   2篇
  2008年   3篇
  2006年   3篇
  2005年   2篇
  2004年   5篇
  2003年   6篇
  2002年   1篇
  2000年   1篇
  1999年   76篇
  1998年   809篇
  1997年   408篇
  1996年   288篇
  1995年   161篇
  1994年   121篇
  1993年   175篇
  1992年   30篇
  1991年   24篇
  1990年   29篇
  1989年   20篇
  1988年   30篇
  1987年   29篇
  1986年   22篇
  1985年   25篇
  1983年   1篇
  1982年   12篇
  1981年   10篇
  1980年   26篇
  1978年   4篇
  1977年   52篇
  1976年   108篇
  1974年   1篇
  1955年   3篇
排序方式: 共有2496条查询结果,搜索用时 15 毫秒
31.
A drying method by desorption in a water activity meter was used to simulate the conditions of spray drying and to determine the water transfer inside dairy concentrates towards the surface and from the surface to the drying air. The concentrates were also spray dried and solubility index of powders were determined during reconstitution. Whey protein concentrates (WPC) and native phosphocaseinate suspensions (NPCS) were used to study the effect of NaCl (420 mM), CaCl2 (222 raM), sodium phosphate (173 mM) and sodium citrate (238 mM) on the water transfers. The decrease in water transfer during drying was explained by the high hygroscopicity of added mineral salts to WPC. NaCl addition to NPCS decreased the water transfer during drying, but increased the solubility index. Citrate and phosphate addition to NPCS increased the water transfer during drying and reconstitution. CaCl2 increased the water transfer during drying but the solubility index was always low. Results are discussed as a function of the aqueous environment, of the nature of mineral salts, of the structure of dairy proteins and of protein solvation.  相似文献   
32.
PURPOSE: The 4-defect repair of grade 4 cystocele corrects discrete and severe deficiencies of vesicourethral support. We describe this technique used during pelvic reconstruction in 130 women. MATERIALS AND METHODS: During a 3-year period 130 patients (age range 35 to 96 years) underwent repair of grade 4 cystocele using the 4-defect repair technique. Cystocele repair had been performed in 60 patients (46%) and hysterectomy had been performed in 85 (65%). A "goalpost incision" is used in the vaginal wall to facilitate separation of the wall from underlying perivesical fascia, entry into the retropubic space, and exposure of the urethropelvic ligament, cardinal ligament and perivesical fascia. The 4 polypropylene sutures are used to provide an anterior vaginal wall sling which is modified to incorporate perivesical fascia and cardinal ligaments. Central defect repair is achieved by approximation of the cardinal ligaments and midline plication of the perivesical fascia over absorbable mesh. RESULTS: A total of 112 patients were available for followup which ranged from 6 to 42 months (mean 21). Repair of grade 4 cystocele was accompanied by other transvaginal repairs in 94 patients (83%), including rectocele repair in 81, hysterectomy in 22 and enterocele repair in 31. Of the patients 92% had excellent objective and subjective results for anatomical cystocele repair. Of the patients with preoperative stress urinary incontinence 90% had excellent or good subjective results. De novo urge incontinence was seen in 7% of patients. CONCLUSIONS: The 4-defect repair technique relies on anatomical restoration of 4 distinct deficiencies of pelvic support and is highly effective for relief of symptoms of grade 4 cystocele.  相似文献   
33.
34.
Colonization of the nasopharynx by a middle ear pathogen is the first step in the development of otitis media in humans. The establishment of an animal model of nasopharyngeal colonization would therefore be of great utility in assessing the potential protective ability of candidate vaccine antigens (especially adhesins) against otitis media. A chinchilla nasopharyngeal colonization model for nontypeable Haemophilus influenzae (NTHI) was developed with antibiotic-resistant strains. This model does not require coinfection with a virus. There was no significant difference in the efficiency of NTHI colonization between adult (1- to 2-year-old) and young (2- to 3-month-old) animals. However, the incidence of middle ear infection following nasopharyngeal colonization was significantly higher in young animals (83 to 89%) than in adult chinchillas (10 to 30%). Chinchillas that had recovered either from a previous middle ear infection caused by NTHI or from an infection by intranasal inoculation with NTHI were completely protected against nasopharyngeal colonization with a homologous strain and were found to be the best positive controls in protection studies. Systemic immunization of chinchillas with inactivated whole-cell preparations significantly protected animals not only against homologous NTHI colonization but also partially against heterologous NTHI infection. In all protected animals, significant serum anti-P6 and anti-HMW antibody responses were observed. The outer membrane P6 and high-molecular-weight (HMW) proteins appear to be promising candidate vaccine antigens to prevent nasopharyngeal colonization and middle ear infection caused by NTHI.  相似文献   
35.
OBJECTIVE: To compare the composition and mechanical properties of the newly developed bladder acellular matrix graft (BAMG) with the normal urinary bladder in rat, pig and human. MATERIALS AND METHODS: Rat, pig and human urinary bladders were harvested and divided into control and experimental groups. For the latter, BAMGs were prepared, and light and transmission electron microscopic studies performed. Strips from the normal bladders and the BAMGs (10 in each group) were tested under tension, and the ultimate tensile strength, maximum strain, and elastic modulus were determined from stress/strain curves. RESULTS: Both types I and III collagen, as well as elastic fibres, were observed as major components of the matrix scaffold. There were more collagen type I fibres in the rat than in the pig and human BAMGs, whereas the pig, and particularly the human, both showed higher levels of type III collagen and elastic fibres. These different matrix scaffold patterns were confirmed by electron microscopy. Results from biomechanical testing showed no significant differences for strength, strain or elastic modulus between BAMG and control bladder strips, except in the rat where the maximum strain values were significantly lower. CONCLUSION: There are variations in the acellular matrix structure with similar biomechanical properties between the BAMG and the normal urinary bladder in three different species. These results may underscore the potential of the BAMG. Furthermore, this in vitro model provides a suitable method to study the mechanical properties of the urinary bladder and may serve as a diagnostic tool for various investigations.  相似文献   
36.
Although thoracoscopic sympathectomy or sympathicotomy is the best treatment for hyperhidrosis palmaris, a new approach of clipping only without transection of T2-sympathetic trunk is just as effective. Aside from the guaranteed cure of hyperhidrosis, this new method has fewer complications and has the advantage of recovery of the sympathetic tone in the hands if the procedure is reversed by the removal of the clips. Between March 18 and September 30 of 1996, 326 patients (190 female and 136 male with a mean age of 20.5 years) underwent thoracoscopic T2-sympathetic block by clipping to treat hyperhidrosis. Good results and few complications were noted during follow up six months to one year postoperatively. Five of the 326 patients, all female, had the operation reversed because of intolerable compensatory sweating. Three recovered from the compensatory sweating within two months and had less palmar sweating than before their sympathetic block; the fourth achieved relief of compensatory sweating after nine months, and the fifth reported no improvement.  相似文献   
37.
There has been increasing interest in the development of a hepatocyte bioreactor for the treatment of acute hepatic failure; however, little is known about the effect of hepatocyte byproducts on the viability of the cells in the bioreactor environment. We investigated the effects of increasing concentrations of bile on the growth and viability of the human hepatoma cell line Hep G2 and on the cytochrome P-450 content and dependent mixed function oxidase (MFO) activities, reduced glutathione (GSH) content, and glutathione S-transferase (GST) activity of primary cultures of rat hepatocytes. Our purpose was to determine whether or not it would be necessary to pretreat the plasma from patients with acute liver failure to remove elevated bile concentrations which might be toxic to the hepatocytes in an artificial liver device. Bile was found to inhibit Hep G2 cell growth at concentrations as low as 0.1% and to decrease viability at concentrations above 0.5%. The cytochrome P-450 and GSH contents and the activities of the MFO system and of GST were decreased in the primary cultures of hepatocytes following 24 h treatment with concentrations of bile at and above 0.5%. The MFO activities associated with different cytochrome P-450 isoenzymes decreased to different extents in the presence of bile with the O-dealkylation of pentoxyresorufin being more labile than that of ethoxyresorufin. Our data indicate that elevated bile concentrations are cytotoxic to liver cells, and it may be necessary to pretreat patient plasma to decrease its bile content to protect the cells during the clinical operation of a hepatocyte bioreactor device.  相似文献   
38.
BACKGROUND: Previous studies have suggested altered responses to repeat skin tests in the sites of IgE-mediated late-phase reactions (LPRs) induced within the previous 48 hours. To explore the possible modulation of LPRs in such rechallenge sites, we compared inflammatory responses in skin chambers induced over previous LPR and control sites. METHODS: Skin blisters were induced and unroofed in 12 human subjects over two sites of previous LPRs induced by intradermal injection of pollen antigens 24 hours or 48 hours earlier and two sites previously injected with buffer diluent (B). Skin chambers containing the same antigens were appended to one intradermal antigen site (called Ag/Ag) and one intradermal B site (B/Ag), and B-containing chambers were placed over antigen (Ag/B) and B (B/B) intradermal sites. Fluids were collected after the first and the second through fifth hours of challenge. RESULTS: In skin chamber challenges 24 hours after the intradermal injection, there was no significant difference after the first hours between the Ag/Ag or B/Ag sites in either histamine or tryptase levels; both were significantly higher than at Ag/B or B/B sites (p < 0.01). The same pattern of events was seen in fluids obtained from the second through fifth hours. The same pattern of findings was seen in examination of levels of the total leukocyte accumulation, total eosinophil accumulation, and frequency of activated (EG2+) eosinophils. Levels of lactoferrin, released from activated neutrophils, and eosinophil cationic protein, released from activated eosinophils, were also similar at Ag/Ag and B/Ag sites; both were significantly higher than at B/B sites, whereas levels at Ag/B sites were intermediate between those found at B/Ag and B/B sites. The pattern of events in skin chamber challenges 48 hours after intradermal injection was similar to that seen at 24 hours, except that levels of inflammatory mediators/cells in Ag/B sites were more intermediate between the B/Ag and B/B sites. CONCLUSION: There is no significant alteration of mediator or inflammatory cell responses after antigen rechallenge of previous LPR sites when compared with those found in antigen challenge of non-LPR sites.  相似文献   
39.
Six healthy male subjects aged 21-35 years participated in the present study. The subjects were exposed to dim light (150 lux) or bright light (3000 lux) at eye level, from 19.00 to 21.30 h for 5 days. Rectal temperature and wrist activity were monitored throughout the study period. Rectal temperature nadir was delayed significantly after the bright light exposure. Ease in sleep initiation and overall sleep quality, measured by questionnaire, were aggravated significantly by the evening bright light exposure. These results suggest that strong illumination at night may disturb nocturnal sleep.  相似文献   
40.
Recent reports have demonstrated fusion of the TEL gene on 12p13 to the JAK2 gene on 9p24 in human leukemias. Three variants have been identified that fuse the TEL pointed (PNT) domain to (i) the JAK2 JH1-kinase domain, (ii) part of and (iii) all of the JH2 pseudokinase domain. We report that all of the human TEL/JAK2 variants, and a human/mouse chimeric hTEL/mJAK2(JH1) fusion gene, transform the interleukin-3 (IL-3)-dependent murine hematopoietic cell line Ba/F3 to IL-3-independent growth. Transformation requires both the TEL PNT domain and JAK2 kinase activity. Furthermore, all TEL/JAK2 variants strongly activated STAT 5 by phosphotyrosine Western blots and by electrophoretic mobility shift assays (EMSA). Mice (n = 40) transplanted with bone marrow infected with the MSCV retrovirus containing either the hTEL/mJAK2(JH1) fusion or its human counterpart developed a fatal mixed myeloproliferative and T-cell lymphoproliferative disorder with a latency of 2-10 weeks. In contrast, mice transplanted with a TEL/JAK2 mutant lacking the TEL PNT domain (n = 10) or a kinase-inactive TEL/JAK2(JH1) mutant (n = 10) did not develop the disease. We conclude that all human TEL/JAK2 fusion variants are oncoproteins in vitro that strongly activate STAT 5, and cause lethal myelo- and lymphoproliferative syndromes in murine bone marrow transplant models of leukemia.  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