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   190301篇
  免费   9280篇
  国内免费   851篇
  2022年   738篇
  2021年   1728篇
  2020年   972篇
  2019年   1295篇
  2018年   13101篇
  2017年   11800篇
  2016年   9582篇
  2015年   4628篇
  2014年   4857篇
  2013年   5741篇
  2012年   11417篇
  2011年   19494篇
  2010年   16114篇
  2009年   12229篇
  2008年   15447篇
  2007年   16992篇
  2006年   5928篇
  2005年   5991篇
  2004年   6235篇
  2003年   6101篇
  2002年   5561篇
  2001年   1375篇
  2000年   1039篇
  1999年   1177篇
  1998年   1396篇
  1997年   977篇
  1996年   881篇
  1995年   819篇
  1994年   710篇
  1993年   804篇
  1992年   781篇
  1991年   683篇
  1990年   670篇
  1989年   628篇
  1988年   603篇
  1987年   543篇
  1986年   504篇
  1985年   688篇
  1984年   746篇
  1983年   676篇
  1982年   771篇
  1981年   690篇
  1980年   698篇
  1979年   455篇
  1978年   515篇
  1977年   434篇
  1976年   430篇
  1974年   405篇
  1972年   493篇
  1971年   494篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
91.
Summary An improved method for separating analogues of coenzyme F420 by isocratic reversed-phase high performance liquid chromatography is described. The method offers improved resolution, shorter chromatography runs and requires less complex apparatus.  相似文献   
92.

Background  

Radial chromosome positioning in interphase nuclei is nonrandom and can alter according to developmental, differentiation, proliferation, or disease status. However, it is not yet clear when and how chromosome repositioning is elicited.  相似文献   
93.
94.

Background  

In heterogeneous environments, sex-biased dispersal could lead to environmental adaptive parental effects, with offspring selected to perform in the same way as the parent dispersing least, because this parent is more likely to be locally adapted. We investigate this hypothesis by simulating varying levels of sex-biased dispersal in a patchy environment. The relative advantage of a strategy involving pure maternal (or paternal) inheritance is then compared with a strategy involving classical biparental inheritance in plants and in animals.  相似文献   
95.
Voronoi polyhedra as structure probes in large molecular systems   总被引:2,自引:0,他引:2  
C W David 《Biopolymers》1988,27(2):339-344
  相似文献   
96.
TNF inhibitors are currently considered both effective and cost-effective in patients with active rheumatoid arthritis (RA), particularly in patients who have not responded fully to methotrexate. There is substantial doubt about the cost-effectiveness of TNF inhibitors as initial treatment for active RA. New data from the National Data Bank for Rheumatic Diseases now question the current consensus in methotrexate failures. The data suggest that in routine clinical practice TNF inhibitors provide only modest incremental benefits over best conventional therapy. If confirmed, these observational studies suggest that the economic argument underpinning the widespread use of TNF inhibitors in established RA is unsustainable.  相似文献   
97.

Background  

DNA Microarrays have become the standard method for large scale analyses of gene expression and epigenomics. The increasing complexity and inherent noisiness of the generated data makes visual data exploration ever more important. Fast deployment of new methods as well as a combination of predefined, easy to apply methods with programmer's access to the data are important requirements for any analysis framework. Mayday is an open source platform with emphasis on visual data exploration and analysis. Many built-in methods for clustering, machine learning and classification are provided for dissecting complex datasets. Plugins can easily be written to extend Mayday's functionality in a large number of ways. As Java program, Mayday is platform-independent and can be used as Java WebStart application without any installation. Mayday can import data from several file formats, database connectivity is included for efficient data organization. Numerous interactive visualization tools, including box plots, profile plots, principal component plots and a heatmap are available, can be enhanced with metadata and exported as publication quality vector files.  相似文献   
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