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   29128篇
  免费   2128篇
  国内免费   1608篇
  32864篇
  2024年   64篇
  2023年   345篇
  2022年   830篇
  2021年   1405篇
  2020年   961篇
  2019年   1190篇
  2018年   1166篇
  2017年   828篇
  2016年   1228篇
  2015年   1895篇
  2014年   2124篇
  2013年   2284篇
  2012年   2610篇
  2011年   2286篇
  2010年   1452篇
  2009年   1234篇
  2008年   1511篇
  2007年   1328篇
  2006年   1165篇
  2005年   983篇
  2004年   790篇
  2003年   695篇
  2002年   533篇
  2001年   479篇
  2000年   379篇
  1999年   411篇
  1998年   243篇
  1997年   265篇
  1996年   252篇
  1995年   214篇
  1994年   217篇
  1993年   150篇
  1992年   216篇
  1991年   184篇
  1990年   130篇
  1989年   106篇
  1988年   79篇
  1987年   108篇
  1986年   82篇
  1985年   69篇
  1984年   52篇
  1983年   36篇
  1982年   36篇
  1981年   26篇
  1980年   21篇
  1979年   25篇
  1978年   17篇
  1975年   21篇
  1974年   18篇
  1972年   17篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The transformation of 6-keto-PGF to two prostacyclin metabolites, 2,3-dinor-6-keto-PGF (I) and 2,3-dinor-6,15-diketo-13,14-dihydro-PGF (II) by Mycobacterium rhodochrous UC-6176 is described. The finding that the bacterium oxidized 6-keto-PGF to the 6,15-diketo metabolite II shows that it contains 15-hydroxy prostaglandin dehydrogenase and Δ13 reductase enzyme systems.  相似文献   
32.
33.
34.
35.
36.
Thoracic ossification of the ligamentum flavum (TOLF) is ectopic ossification of the spinal ligaments. Histologically, the development of TOLF can be described as the process of endochondral ossification. However, the underlying aetiology has not been completely clarified. In this investigation, the gene expression profile associated with leucine‐rich repeat‐containing G‐protein‐coupled receptors (LGR) and Wnt signalling pathway in the thoracic ligamentum flavum cells (TLFCs) of different ossification stages was analysed via RNA sequencing. We further confirmed the significant differences in the related gene expression profile by Gene Ontology (GO) enrichment analysis. LGR5 was first identified in primary human TLFCs during osteogenic differentiation. To evaluate the effect of LGR5 on osteogenic differentiation, LGR5 has been knocked down and overexpressed in human TLFCs. We observed that the knockdown of LGR5 inhibited the activity of Wnt signalling and attenuated the potential osteogenic differentiation of TLFCs, while overexpression of LGR5 activated the Wnt signalling pathway and increased osteogenic differentiation. Our results provide important evidence for the potent positive mediatory effects of LGR5 on osteogenesis by enhancing the Wnt signalling pathway in TOLF.  相似文献   
37.
38.
为了科学、定量地评价污水土地处理生态工程的综合效益,运用层次分析法(AHP),提出了评价指标体系、指标权重和综合效益计算方法.应用此方法对霍林河森林型慢速渗滤土地处理工程的综合效益进行了分析与评价.结果表明,霍林河森林型慢速渗滤土地处理工程的综合效益值CE=0.64,属于中级生态经济系统,而且具有良好的环境效益和社会效益  相似文献   
39.
40.
The effects on the fecundity and fertility of redbanded leafroller, Argyrotaenia velutinana (Walker), and obliquebanded leafroller,Choristoneura rosaceana (Harris), exposed as adults to surfaces treated with the ecdysone agonists tebufenozide (RH-5992) and methoxyfenozide (RH-2485) were examined. The first part of the study consisted of recently emerged moths being exposed to treated surfaces continuously throughout their lives (including mating and oviposition). Continuous exposure to tebufenozide- or methoxyfenozide-treated surfaces significantly reduced the mean number of eggs laid and the percent of eggs that hatched in both species. The second part of the study involved exposure of recently emerged virgin moths (by sex) to treated surfaces for 24 h, after which, the exposed moths were paired with a nontreated partner to mate and oviposit on nontreated surfaces. In this experiment, for A. velutinana, significant reductions in fecundity occurred only when the female was exposed to methoxyfenozide-treated surfaces. Significant reductions in A. velutinana egg fertility occurred with both male and female exposure in the methoxyfenozide treatments and only female exposure in the tebufenozide treatments. For C. rosaceana, significant reductions in fecundity occurred with both male and female exposure in the tebufenozide and methoxyfenozide treatments. Significant reductions in C. rosaceana egg fertility occurred with both male and female exposure in the tebufenozide treatments and only with female exposure in the methoxyfenozide treatments.  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