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   160869篇
  免费   5354篇
  国内免费   873篇
  2022年   409篇
  2021年   1101篇
  2020年   677篇
  2019年   853篇
  2018年   12712篇
  2017年   11485篇
  2016年   9164篇
  2015年   3767篇
  2014年   3470篇
  2013年   4793篇
  2012年   9082篇
  2011年   17217篇
  2010年   15106篇
  2009年   11029篇
  2008年   13537篇
  2007年   15042篇
  2006年   4109篇
  2005年   4245篇
  2004年   4444篇
  2003年   4224篇
  2002年   3938篇
  2001年   1042篇
  2000年   874篇
  1999年   836篇
  1998年   945篇
  1997年   679篇
  1996年   647篇
  1995年   621篇
  1994年   588篇
  1993年   635篇
  1992年   596篇
  1991年   544篇
  1990年   417篇
  1989年   430篇
  1988年   441篇
  1987年   384篇
  1986年   364篇
  1985年   420篇
  1984年   476篇
  1983年   404篇
  1982年   480篇
  1981年   424篇
  1980年   380篇
  1979年   262篇
  1978年   302篇
  1977年   293篇
  1976年   245篇
  1974年   248篇
  1972年   380篇
  1971年   404篇
排序方式: 共有10000条查询结果,搜索用时 4 毫秒
11.
12.
With DNA sequencing now getting cheaper more quickly than data storage or computation, the time may have come for genome informatics to migrate to the cloud.  相似文献   
13.
Rice fields are an alternative habitat for waterbirds and provide food and shelter for many avian species, but there is a lack of information about how the use of rice fields translates into population level effects. The aim of this study was to test the relationship between the use of rice fields by European waterbirds and trends in their populations. We tested this relationship during the autumn migration season and during the breeding season. Based on counts conducted over the last 23 years in natural marshes and areas of rice fields in Doñana (SW Spain), an index of rice field use was constructed for 76 bird species, which was then compared to these species’ European population trends obtained from the literature. A positive relationship was found between waterbird population trends and the use of rice fields during autumn migration season. Our study suggests that changes in the Common Agriculture Policy in Europe leading to reductions in areas of rice cultivation may have important effects on waterbirds. The restoration of former marsh areas and the maintenance of rice cultivation would seem to be more environmentally friendly approaches than the use of these areas to grow alternative crops or solar farms.  相似文献   
14.
15.
16.
With the use of a patch-clamp technique in the whole-cell configuration, we studied the effects of pinacidil and its fluorine derivatives on A-type potassium current (I A) through the membrane of pyramidal neurons of the rat hippocampus. Hydrogen peroxide (10 mM) exerted no influence on the rate of inactivation ofI A; therefore, this current is probably mediated by Shal Kv4.2 potassium channels. Pinacidil demonstrated the properties of a weakI A blocker: in the 500 μM concentration it blocked about 45% of the current, while 50 μM of pinacidil fluorine derivatives were capable of blocking up to 30% ofI A. The effects of pinacidil and its derivatives showed no dependence on the stimulating potential. A similar pattern of the effects of pinacidil fluorine derivatives, which are an order of magnitude stronger than those of pinacidil itself, allows us to suppose that the imine nitrogen of the tested compounds is significantly more involved in the molecular interaction with the site of an A-type potassium channel than the pyridine nitrogen.  相似文献   
17.

Background  

Recent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation.  相似文献   
18.
19.
20.
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