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   25060篇
  免费   2273篇
  国内免费   4篇
  27337篇
  2023年   77篇
  2022年   183篇
  2021年   371篇
  2020年   209篇
  2019年   287篇
  2018年   439篇
  2017年   435篇
  2016年   774篇
  2015年   1205篇
  2014年   1265篇
  2013年   1576篇
  2012年   2002篇
  2011年   1868篇
  2010年   1173篇
  2009年   1089篇
  2008年   1463篇
  2007年   1474篇
  2006年   1379篇
  2005年   1371篇
  2004年   1252篇
  2003年   1205篇
  2002年   1138篇
  2001年   315篇
  2000年   270篇
  1999年   313篇
  1998年   266篇
  1997年   202篇
  1996年   172篇
  1995年   179篇
  1994年   157篇
  1993年   161篇
  1992年   211篇
  1991年   190篇
  1990年   155篇
  1989年   181篇
  1988年   157篇
  1987年   146篇
  1986年   141篇
  1985年   144篇
  1984年   145篇
  1983年   110篇
  1982年   123篇
  1981年   100篇
  1980年   96篇
  1979年   86篇
  1977年   69篇
  1976年   69篇
  1975年   66篇
  1974年   89篇
  1971年   65篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
Sydney Parkinson, aged 18, was Sir Joseph Banks' private assistant and artist on Captain Cook's first voyage around the world. Parkinson died on the voyage. Among his effects delivered to his brother Stanfield were drawings and notes which the latter published as a journal. Included in it is a chapter on the economic plants of Tahiti, and most of them are given scientific names, some of which were new. In 1941 Fosberg adopted two of them to form names which were new combinations under Artocarpus , and Inocarpus . The writer now indicates that Parkinson's names of 1773 were mononomials, hence invalid, but that in the German edition of 1774, edited by Herr "Z", the names are valid binomials. For the two plants mentioned, the authorship of the combinations is revised.  相似文献   
34.
Ted St. Godard 《CMAJ》2004,171(3):262-264
  相似文献   
35.
E. coli cells containing a temperature-sensitivednaE mutation, in the α-subunit of holoenzyme DNA polymerase III, do not survive at the restrictive temperature. Such cells may survive in the presence of thepcbA1 mutation, an allele of thegyrB gene. Such survival is dependent on an active DNA polymerase I. Evidence indicates that DNA polymerase I interacts directly in the replisome (REP·A). Despite normal survival for cells using thepcbA replication pathway after some type of DNA damage, we have noted a failure of damage-induced mutagenesis. Here we present evidence supporting a model of replisome pausing in cells dependent upon thepcbA replication pathway. The model argues that the (REP·A) complex pauses longer at the site of the lesion, allowing excision repair to occur completely. In the normal replication pathway (REP·E) bypass of the lesion occurs, fixing the mutation.  相似文献   
36.
37.
38.
Clastogenic effects of acrylamide in mouse bone marrow cells   总被引:5,自引:0,他引:5  
Acrylamide, known to induce dominant-lethal mutations (Shelby et al., 1986; Smith et al., 1986) and heritable translocations (Shelby et al., 1987) in rodent germ cells, was hitherto a questionable clastogen in rodent bone marrow (Shiraishi, 1978). Therefore, it was tested for chromosomal aberrations in mouse bone marrow cells, spermatogonia and by the micronucleus test. The intraperitoneally injected doses ranged from 50 to 150 mg/kg. In the chromosomal bone marrow test and the micronucleus assay positive results were obtained with acrylamide, and in the latter test the effect increased linearly with dose. Chromosomal aberrations were not induced in differentiating spermatogonia by the acute acrylamide treatment. Cisplatin was used as a positive control and gave the expected positive response in all 3 tests. The present results demonstrate that acrylamide is no exception among clastogens. It breaks chromosomes not only in mammalian germ cells but also in somatic cells.  相似文献   
39.
40.
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