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   40885篇
  免费   3682篇
  国内免费   19篇
  2023年   118篇
  2022年   95篇
  2021年   671篇
  2020年   408篇
  2019年   528篇
  2018年   666篇
  2017年   589篇
  2016年   1025篇
  2015年   1717篇
  2014年   1891篇
  2013年   2312篇
  2012年   3148篇
  2011年   3143篇
  2010年   1975篇
  2009年   1854篇
  2008年   2578篇
  2007年   2656篇
  2006年   2473篇
  2005年   2294篇
  2004年   2284篇
  2003年   2104篇
  2002年   2041篇
  2001年   583篇
  2000年   455篇
  1999年   563篇
  1998年   546篇
  1997年   408篇
  1996年   363篇
  1995年   332篇
  1994年   302篇
  1993年   298篇
  1992年   357篇
  1991年   274篇
  1990年   248篇
  1989年   267篇
  1988年   230篇
  1987年   213篇
  1986年   193篇
  1985年   201篇
  1984年   220篇
  1983年   166篇
  1982年   193篇
  1981年   165篇
  1980年   131篇
  1979年   120篇
  1978年   140篇
  1977年   111篇
  1976年   93篇
  1975年   91篇
  1974年   101篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
The Le Quesne test of character compatibility uses pairwise comparisons of characters to detect homoplasy in phylogenetic character data. If a pair of characters fails this test we can conclude that a minimum of a single extra step is required by the pair of characters. The rationale of the Le Quesne test is extended to comparisons of triplets of characters. The triplet homoplasy test can reveal that that there is a minimum of four extra steps across a triplet of characters and thus that there are at least two extra steps associated with one of the characters. The triplet homoplasy test can thus detect higher orders of homoplasy than can be detected by the pairwise Le Quesne test. The possibility of quartet and other higher-order homoplasy tests is discussed. The utility of higher-order homoplasy tests is discussed. It is suggested higher-order homoplasy tests have potential uses analogous to the uses of the Le Quesne test, particularly with respect to data exploration.  相似文献   
44.
45.
46.

Background  

NOL7 is a candidate tumor suppressor that localizes to a chromosomal region 6p23. This locus is frequently lost in a number of malignancies, and consistent loss of NOL7 through loss of heterozygosity and decreased mRNA and protein expression has been observed in tumors and cell lines. Reintroduction of NOL7 into cells resulted in significant suppression of in vivo tumor growth and modulation of the angiogenic phenotype. Further, NOL7 was observed to localize to the nucleus and nucleolus of cells. However, the mechanisms regulating its subcellular localization have not been elucidated.  相似文献   
47.
48.
49.
Comparative mapping studies of X-linked genes in mammals have provided insights into the evolution of the X chromosome. Many reptiles including the American alligator, Alligator mississippiensis, do not appear to possess heteromorphic sex chromosomes, and sex is determined by the incubation temperature of the egg during embryonic development. Mapping of homologues of mammalian X-linked genes in reptiles could lead to a greater understanding of the evolution of vertebrate sex chromosomes. One of the genes used in the mammalian mapping studies was ZFX, an X-linked copy of the human ZFY gene which was originally isolated as a candidate for the mammalian testis-determining factor (TDF). ZFX is X-linked in eutherians, but maps to two autosomal locations in marsupials and monotremes, close to other genes associated with the eutherian X. The alligator homologue of the ZFY/ZFX genes, Zfc, has been isolated and described previously. A detailed karyotype of A. mississippiensis is presented, together with chromosomal in situ hybridisation data localising the Zfc gene to chromosome 3. Further chromosomal mapping studies using eutherian X-linked genes may reveal conserved chromosomal regions in the alligator that have become part of the eutherian X chromosome during evolution.  相似文献   
50.
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