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   41239篇
  免费   3971篇
  国内免费   18篇
  45228篇
  2022年   255篇
  2021年   579篇
  2020年   315篇
  2019年   460篇
  2018年   532篇
  2017年   490篇
  2016年   826篇
  2015年   1268篇
  2014年   1471篇
  2013年   1909篇
  2012年   2277篇
  2011年   2375篇
  2010年   1472篇
  2009年   1400篇
  2008年   2102篇
  2007年   2161篇
  2006年   2041篇
  2005年   2133篇
  2004年   2021篇
  2003年   2023篇
  2002年   1911篇
  2001年   565篇
  2000年   390篇
  1999年   508篇
  1998年   556篇
  1997年   422篇
  1996年   408篇
  1995年   343篇
  1994年   377篇
  1993年   377篇
  1992年   412篇
  1991年   386篇
  1990年   393篇
  1989年   345篇
  1988年   365篇
  1987年   324篇
  1986年   311篇
  1985年   409篇
  1984年   473篇
  1983年   393篇
  1982年   440篇
  1981年   490篇
  1980年   471篇
  1979年   336篇
  1978年   320篇
  1977年   341篇
  1976年   321篇
  1975年   242篇
  1974年   282篇
  1973年   255篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.

Background  

Phylogenies capture the evolutionary ancestry linking extant species. Correlations and similarities among a set of species are mediated by and need to be understood in terms of the phylogenic tree. In a similar way it has been argued that biological networks also induce correlations among sets of interacting genes or their protein products.  相似文献   
22.
An I125 radioimmunoassay (RIA) has been developed for the measurement of plasma and tissue epinephrine (E) and norepinephrine (NE). The assay utilizes an antibody which specifically binds metanephrine. E and NE are detected by conversion to metanephrine with the enzymes catechol-0-methyltransferase and phenylethanol-amine-N-methyltransferase. The assay is very specific and will allow the measurement of E and NE in less than 500 μl of normal human plasma. E and NE concentrations were determined by both the RIA and a radioenzymatic assay in canine, human and rat biologic samples. The correlation coefficients between the two assays were .962 for E and .956 for NE. The RIA is sensitive, specific, precise and significantly less costly and time consuming than present radioenzymatic methods.  相似文献   
23.
24.
Hepatic alcohol dehydrogenase activity and mass content change coordinately during development in male rats. Enzyme activity and mass content increase continuously after birth to 100 and 80% of maximal values within 6 weeks (2.6 ± 0.4 μmole/min/g liver and 92 ± 20 μg/g liver), respectively. When expressed per milligram of soluble proteins, both parameters peak at 3 weeks (0.052 ± 0.002 μmole/min/mg protein and 2.0 ± 0.4 μg/mg protein) and then decrease gradually to plateau levels. These decreases probably arise from a “surge” in soluble liver protein levels that occurs after weaning. Similar developmental patterns also occur in female rats. These findings are the first quantitative measurements of this enzyme in developing animals.  相似文献   
25.
26.
27.
28.
29.
30.
A survey was done of Canadians who had been interned by the Japanese during World War II to assess the prevalence of latent infection with Strongyloides stercoralis in this group. Packages containing three mail-in kits and a questionnaire were sent to 992 men, 694 (70%) of whom responded. Larvae were found in the stool specimens of four of the respondents. Examination of stool specimens after formalin-ether concentration was the most successful method of detecting Strongyloides larvae. The Baermann concentration technique yielded negative results in all four men. Three of the four cases of strongyloidiasis were detected after sampling of three fecal specimens. In the fourth case additional specimens were requested on the basis of data derived from the questionnaire. The most frequently cited clinical manifestations were abdominal pain, weight loss, diarrhea and rashes.  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