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   3418篇
  免费   75篇
  国内免费   19篇
电工技术   10篇
综合类   1篇
化学工业   302篇
金属工艺   70篇
机械仪表   25篇
建筑科学   23篇
矿业工程   1篇
能源动力   40篇
轻工业   46篇
水利工程   1篇
石油天然气   3篇
无线电   201篇
一般工业技术   337篇
冶金工业   2331篇
原子能技术   7篇
自动化技术   114篇
  2023年   9篇
  2022年   14篇
  2021年   30篇
  2020年   29篇
  2019年   40篇
  2018年   50篇
  2017年   44篇
  2016年   37篇
  2015年   28篇
  2014年   47篇
  2013年   76篇
  2012年   44篇
  2011年   79篇
  2010年   47篇
  2009年   56篇
  2008年   51篇
  2007年   36篇
  2006年   41篇
  2005年   26篇
  2004年   41篇
  2003年   19篇
  2002年   15篇
  2001年   23篇
  2000年   15篇
  1999年   82篇
  1998年   666篇
  1997年   385篇
  1996年   292篇
  1995年   177篇
  1994年   139篇
  1993年   145篇
  1992年   35篇
  1991年   66篇
  1990年   37篇
  1989年   55篇
  1988年   54篇
  1987年   52篇
  1986年   51篇
  1985年   54篇
  1984年   16篇
  1983年   18篇
  1982年   31篇
  1981年   40篇
  1980年   23篇
  1979年   9篇
  1978年   12篇
  1977年   45篇
  1976年   97篇
  1975年   10篇
  1971年   4篇
排序方式: 共有3512条查询结果,搜索用时 93 毫秒
41.
Polypropylene mesh, the routinely used material for mesh laparostomies is expensive. A economical and easily available substitute-nylon net was compared with polypropylene mesh with regard to efficacy and wound complications in a retrospective study. 51 patients, 25 in the polypropylene mesh group and 26 in the nylon net group were studied. The groups were matched with respect to age, sex, indication for surgery and mortality. The mean hospital stay (65 vs 54 days), fate of the wound, incidence of mesh extrusion (26% vs 20%), bowel perforation (1 vs none) and incisional hernia formation (21% vs 20%) in those with polypropylene mesh and nylon net respectively was similar. In conclusion, nylon net is an effective and inexpensive indigenous substitute for polypropylene mesh for mesh laparostomies.  相似文献   
42.
43.
In the present study, we have performed electrical characterization of oxides deposited via rapid thermal chemical vapor deposition using SiH4 and N2O. We have investigated the effect of temperature, pressure, and SiH4 to N2O ratio on the electrical and material properties of as-deposited films. We have found that as-deposited oxides deposited at low temperatures, low pressures, and with a low silane to nitrous oxide ratio of ~0.5% give good material and electrical properties. The as-deposited films are stoichiometric in nature and have high deposition rates. As-deposited films had very low Dit values, high breakdown fields, and excellent subthreshold swing. The leakage currents and metal oxide semiconductor field effect transistor current drive, although lower than thermal oxides, were found to be quite acceptable. We have also investigated the thickness dependence of the films and found that as the film thickness is reduced below 50Å, the reliability improves for all oxides including the silicon-rich deposited oxides.  相似文献   
44.
45.
Endocrine and exocrine pancreatic morphogenesis is known to occur from ductal epithelium, but the factors that regulate this process are unknown. Vascular endothelial growth factor (VEGF)/vascular permeability factor has recently been reported to affect fetal islet ontogenesis. VEGF is an angiogenic factor with a growth-promoting effect that is thought to be restricted to vascular endothelial cells. We demonstrated that VEGF is also a mitogen for adult rat pancreatic duct epithelial cells in primary culture. VEGF supplementation to a serum-free culture medium increased the 5-bromo-2'-deoxyuridine-pulse labeling index of ductal cells more than 2-fold. Immunohistochemical staining and protein blots revealed that pancreatic duct cells express fetal liver kinase-1 high-affinity receptors for VEGF. In pancreatic tissue, immunohistochemistry shows that VEGF peptide is expressed in normal pancreatic islet cells. In duct ligation-induced acute pancreatitis, numerous inflammatory leukocytes containing VEGF were seen to infiltrate between hyperplastic ducts. In the latter model, islet neogenesis has previously been observed. Our data indicate the possibility that VEGF plays a role in the paracrine regulation of ductal growth and differentiation in vivo, eg, in pancreatitis. In vitro, however, VEGF did not induce endocrine differentiation of ductal cells, indicating that it is not the only factor required for the activation of islet neogenesis.  相似文献   
46.
47.
48.
49.
This review reports the different genetic factors that have been identified either as risk factor for Alzheimer's disease (AD) or directly causing the disease. First are reviewed epidemiological data and biological mechanisms about the apoplipoprotein E gene allele epsilon 4 that is a major risk factor for Alzheimer's disease. The second part describes the mutations responsible for early-onset autosomal dominant AD found in three different genes. The gene located on chromosome 21 encodes the amyloid precusor protein (APP). The presenilin 1 and presenilin 2 genes, located on chromosome 14 and 1 respectively, encode not yet known membrane proteins.  相似文献   
50.
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