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   8769篇
  免费   44篇
  国内免费   2篇
电工技术   26篇
化学工业   240篇
金属工艺   29篇
机械仪表   40篇
建筑科学   51篇
矿业工程   7篇
能源动力   62篇
轻工业   144篇
水利工程   26篇
石油天然气   3篇
无线电   255篇
一般工业技术   278篇
冶金工业   7450篇
原子能技术   18篇
自动化技术   186篇
  2021年   10篇
  2020年   15篇
  2019年   17篇
  2018年   27篇
  2017年   21篇
  2016年   30篇
  2015年   19篇
  2014年   28篇
  2013年   72篇
  2012年   55篇
  2011年   60篇
  2010年   46篇
  2009年   56篇
  2008年   57篇
  2007年   79篇
  2006年   55篇
  2005年   51篇
  2004年   57篇
  2003年   42篇
  2002年   47篇
  2001年   53篇
  2000年   35篇
  1999年   261篇
  1998年   2502篇
  1997年   1399篇
  1996年   889篇
  1995年   472篇
  1994年   391篇
  1993年   477篇
  1992年   56篇
  1991年   74篇
  1990年   75篇
  1989年   78篇
  1988年   85篇
  1987年   69篇
  1986年   73篇
  1985年   64篇
  1984年   18篇
  1983年   41篇
  1982年   45篇
  1981年   43篇
  1980年   83篇
  1979年   25篇
  1978年   36篇
  1977年   165篇
  1976年   313篇
  1975年   24篇
  1974年   19篇
  1973年   15篇
  1972年   14篇
排序方式: 共有8815条查询结果,搜索用时 15 毫秒
11.
Great progress has been made in the last 10 years in the understanding of the various types of viral hepatitis, and new viruses, concepts, therapies, preventive measures, and control strategies have been recognized. Even more agents, vaccines, and drugs will be discovered or developed in the future, and pediatricians increasingly will be expected to provide guidance to patients and to the community on the importance and use of these new tools.  相似文献   
12.
Tumor necrosis factor alpha (TNF-alpha) may play a central role in the disease pathogenesis which occurs as a consequence of chlamydial infection. To investigate the importance of TNF-alpha gene promoter polymorphisms and TNF-alpha levels in tear fluid in scarring trachoma, a large matched-pair case-control study was performed in The Gambia. The -308A allele was present in a higher proportion of patients (28.4%) than controls (18.4%), with an increasing association for homozygotes (chi2 for trend, P = 0.032; allele frequency, 0.163 in patients and 0.099 in controls; chi2, P = 0.025). For the -238A allele, the association was similar but not significant. The disease association was highly significant when the number of either -308A or -238A sites in an individual was considered (P = 0.003). TNF-alpha promoter alleles are tightly linked to some HLA class I and II alleles, but multivariate analysis confirmed that the disease associations were independent of HLA, although a class I allele, A*6802, is also associated with disease. TNF-alpha was more frequently detected in tear samples from patients (27.6%) than from controls (15.9%), increasingly so for higher levels of detectable TNF-alpha (P = 0.015). Among patients, detectable TNF-alpha in tears was highly associated with the presence of ocular chlamydial infection (P < 0.001). The results indicate that TNF-alpha plays a major role in the tissue damage and scarring which occurs as a consequence of Chlamydia trachomatis infection.  相似文献   
13.
14.
15.
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program.  相似文献   
16.
17.
18.
19.
A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works.  相似文献   
20.
This article argues that an iconic event in the history of helping research--the story of the 38 witnesses who remained inactive during the murder of Kitty Genovese--is not supported by the available evidence. Using archive material, the authors show that there is no evidence for the presence of 38 witnesses, or that witnesses observed the murder, or that witnesses remained inactive. Drawing a distinction between the robust bystander research tradition and the story of the 38 witnesses, the authors explore the consequences of the story for the discipline of psychology. They argue that the story itself plays a key role in psychology textbooks. They also suggest that the story marks a new way of conceptualizing the dangers of immersion in social groups. Finally, they suggest that the story itself has become a modern parable, the telling of which has served to limit the scope of inquiry into emergency helping. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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