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   65685篇
  免费   18995篇
  国内免费   9300篇
  2024年   118篇
  2023年   738篇
  2022年   1230篇
  2021年   2712篇
  2020年   3975篇
  2019年   5708篇
  2018年   5420篇
  2017年   5487篇
  2016年   5849篇
  2015年   6491篇
  2014年   6820篇
  2013年   7323篇
  2012年   5688篇
  2011年   5084篇
  2010年   5452篇
  2009年   4118篇
  2008年   3335篇
  2007年   2649篇
  2006年   2417篇
  2005年   2172篇
  2004年   1823篇
  2003年   1589篇
  2002年   1416篇
  2001年   1237篇
  2000年   1091篇
  1999年   816篇
  1998年   428篇
  1997年   368篇
  1996年   337篇
  1995年   322篇
  1994年   268篇
  1993年   206篇
  1992年   247篇
  1991年   196篇
  1990年   182篇
  1989年   145篇
  1988年   106篇
  1987年   83篇
  1986年   72篇
  1985年   73篇
  1984年   49篇
  1983年   41篇
  1982年   48篇
  1981年   21篇
  1980年   6篇
  1979年   2篇
  1977年   2篇
  1975年   3篇
  1950年   8篇
  1873年   1篇
排序方式: 共有10000条查询结果,搜索用时 875 毫秒
111.
A cDNA clone encoding the N-terminal sequence of the murine integrin beta 7 subunit, a novel member of the leukocyte cell adhesion molecule subset (Leu-CAM), has been isolated. An N-terminal region of 13 contiguous amino acids deduced from the cDNA shows complete identity with the N-terminus of the 120 kDa subunit of the M290 antigen, a surface molecule found highly expressed on mouse intestinal intraepithelial lymphocytes (IEL). This unexpected result focuses two previously unconnected areas of research and suggests that integrins may have a special role to play in the defence of the gut mucosa.  相似文献   
112.
After observing specimens of Calligonum pumilum Losinsk. and C. juochiangense Y. X. Liou in both the field and in herbarium collections, it was found that the morphological characters of these two species are quite different, especially with respect of the twisted direction of fruit ribs, number of bristle rows along each rib, rigidity and degree of interweaving of bristles, as well as their geographic distribution. Therefore, it is concluded that C. pumilum and C. juochiangense should be accepted as two independent species.  相似文献   
113.
114.
Small molecule cholinesterases inhibitor (ChEI) provides an effective therapeutic strategy to treat Alzheimer’s disease (AD). Currently, the discovery of new ChEI with multi-target effect is still of great importance. Herein, we report the synthesis, structure–activity relationship study and biological evaluation of a series of tacrine-cinnamic acid hybrids as new ChEIs. All target compounds are evaluated for their in vitro cholinesterase inhibitory activities. The representatives which show potent activity on cholinesterase, are evaluated for the amyloid β-protein self-aggregation inhibition and in vivo assays. The optimal compound 19, 27, and 30 (human AChE IC50?=?10.2?±?1.2, 16.5?±?1.7, and 15.3?±?1.8?nM, respectively) show good performance in ameliorating the scopolamine-induced cognition impairment and preliminary safety in hepatotoxicity evaluation. These compounds deserve further evaluation for the development of new therapeutic agents against AD.  相似文献   
115.
116.
The spatial epidemiology of Bluetongue virus (BTV) at the landscape level relates to the fine‐scale distribution and dispersal capacities of its vectors, midges belonging to the genus Culicoides Latreille (Diptera: Ceratopogonidae). Although many previous researches have carried out Culicoides sampling on farms, little is known of the fine‐scale distribution of Culicoides in the landscape immediately surrounding farms. The aim of this study was to gain a better understanding of Culicoides populations at increasing distances from typical dairy farms in north‐west Europe, through the use of eight Onderstepoort‐type black‐light traps positioned along linear transects departing from farms, going through pastures and entering woodlands. A total of 16 902 Culicoides were collected in autumn 2008 and spring 2009. The majority were females, of which more than 97% were recognized as potential vectors. In pastures, we found decreasing numbers of female Culicoides as a function of the distance to the farm. This pattern was modelled by leptokurtic models, with parameters depending on season and species. By contrast, the low number of male Culicoides caught were homogeneously distributed along the transects. When transects entered woodlands, we found a higher abundance of Culicoides than expected considering the distance of the sampling sites to the farm, although this varied according to species.  相似文献   
117.
118.
119.
120.
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