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   160793篇
  免费   4879篇
  国内免费   820篇
  2023年   526篇
  2022年   451篇
  2021年   984篇
  2020年   891篇
  2019年   890篇
  2018年   13423篇
  2017年   12133篇
  2016年   9761篇
  2015年   4027篇
  2014年   3740篇
  2013年   5041篇
  2012年   9561篇
  2011年   17291篇
  2010年   14593篇
  2009年   10277篇
  2008年   13129篇
  2007年   14455篇
  2006年   3605篇
  2005年   3341篇
  2004年   3759篇
  2003年   3491篇
  2002年   3020篇
  2001年   1822篇
  2000年   1703篇
  1999年   1254篇
  1998年   563篇
  1997年   452篇
  1996年   440篇
  1995年   402篇
  1994年   321篇
  1993年   330篇
  1992年   673篇
  1991年   604篇
  1990年   525篇
  1989年   513篇
  1988年   513篇
  1987年   458篇
  1986年   417篇
  1985年   452篇
  1984年   459篇
  1983年   341篇
  1982年   294篇
  1979年   320篇
  1978年   288篇
  1975年   286篇
  1974年   317篇
  1973年   332篇
  1972年   515篇
  1971年   492篇
  1969年   266篇
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
91.

Background  

Identifying essential genes in bacteria supports to identify potential drug targets and an understanding of minimal requirements for a synthetic cell. However, experimentally assaying the essentiality of their coding genes is resource intensive and not feasible for all bacterial organisms, in particular if they are infective.  相似文献   
92.

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   
93.
94.
Lateral membrane heterogeneity, in the form of lipid rafts and microdomains, is currently implicated in cell processes including signal transduction, endocytosis, and cholesterol trafficking. Various biophysical techniques have been used to detect and characterize lateral membrane domains. Among these, Förster resonance energy transfer (FRET) has the crucial advantage of being sensitive to domain sizes smaller than 50-100 nm, below the resolution of optical microscopy but, apparently, similar to those of rafts in cell membranes. In the last decade, several formalisms for the analysis of FRET in heterogeneous membrane systems have been derived and applied to the study of microdomains. They are critically described and illustrated here.  相似文献   
95.

Myrtaceae, Lauraceae and Fabaceae are regarded as essential floristic elements of Atlantic forests due to their outstanding species richness, endemism levels, and ecological functions. Nonetheless, Atlantic forests are being subjected to multiple human disturbances that compromise the conservation of their flora. This study, therefore, intended to address whether there exist potential areas for conservation with great richness of tree/shrub species of the aforementioned families in different forest types within the subtropical Atlantic Forest. For this, data collected systematically across?~?23% of the subtropical Brazilian Atlantic Forest were employed. The univariate Local Moran I statistic was used to search for clusters of sample plots with great richness of species of the studied families. Six clusters were found throughout the evergreen rainforest (ERF) and Araucaria forest (AF), and most of them contained more than half of all species of these families observed on the sample plots, besides many others belonging to different families. A cluster of Myrtaceae and a cluster of Lauraceae in the ERF were the only ones that overlapped protected areas. The clusters of Lauraceae in the AF, located in ecotone zones with the ERF, had?~?50% of native forest cover, whereas the clusters of Myrtaceae and Fabaceae had?~?10% of forest cover. Inasmuch as forests in the study area have been heavily exploited, the clusters have relevant conservation value. Protected areas could be expanded or converted into more restrictive conservation categories to enhance the conservation of populations of key elements of the Atlantic Forest. Yet, non-protected areas deserve attention regarding the management of forest resources and conservation-by-use strategies.

  相似文献   
96.
97.
98.
99.
100.
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