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   43191篇
  免费   4597篇
  国内免费   14篇
  2021年   566篇
  2020年   388篇
  2019年   473篇
  2018年   600篇
  2017年   572篇
  2016年   987篇
  2015年   1746篇
  2014年   1741篇
  2013年   2278篇
  2012年   2622篇
  2011年   2316篇
  2010年   1610篇
  2009年   1457篇
  2008年   1985篇
  2007年   1975篇
  2006年   1758篇
  2005年   1719篇
  2004年   1612篇
  2003年   1395篇
  2002年   1414篇
  2001年   1267篇
  2000年   1266篇
  1999年   1145篇
  1998年   645篇
  1997年   585篇
  1996年   587篇
  1995年   561篇
  1994年   509篇
  1993年   530篇
  1992年   1017篇
  1991年   771篇
  1990年   789篇
  1989年   774篇
  1988年   677篇
  1987年   605篇
  1986年   617篇
  1985年   721篇
  1984年   544篇
  1983年   423篇
  1982年   352篇
  1981年   326篇
  1980年   264篇
  1979年   391篇
  1978年   351篇
  1977年   249篇
  1976年   236篇
  1975年   203篇
  1974年   295篇
  1973年   262篇
  1972年   195篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
101.
102.
103.
104.
105.
Differential hybridization analysis revealed two cDNA clones, pBUS19 and pBUS30, to be overexpressed in progressionally advanced rat prostatic tumors. Northern blot analysis suggested the clones to be related although no homology in nucleotide sequence could be shown. Isolation and characterization of a pBUS19-related clone, pJG116, and computer-assisted database comparison showed that all three clones could be mapped within a rat-specific endogenous retrovirus. The importance of overexpression of retroviral sequences in advanced prostatic cancer remains unclear.  相似文献   
106.
The Lipomycetaceae (Endomycetales) are known from the generaDipodascopsis, Lipomyces andZygozyma with budding anamorphic states inMyxozyma. The family is easily recognized culturally and physiologically but is phenotypically and ecologically extremely diverse. This natural taxon is phylogenetically distinct from the Saccharomycetaceae, but probably related to the Dipodascaceae. The possible evolution of the lipomycetaceous anamorphs is discussed.  相似文献   
107.
Macrophages are essential for normal wound repair and many of their effects on healing wounds are likely to be mediated by the secretion of cytokines. This study examines the appearance of messenger RNA (mRNA) for cachectin/tumor necrosis factor (TNF), IL 1, and macrophage inflammatory proteins 1 and 2 (MIP-1 and MIP-2), as well as the mature peptides, in a model of wound healing using wound chambers. RNA for all four cytokines can be detected in wound inflammatory cells by polymerase chain reaction amplification throughout the first 7 days. Cachectin/TNF and IL 1 protein levels peaked on the first day after wound chamber implantation, and MIP-1 and MIP-2 were detected only on day 3. The data suggest that these cytokines participate in the early inflammatory response to wounding.  相似文献   
108.
109.
Phenology, morphology, life history and responses to different temperature and photoperiod conditions were studied in Japanese Stypocaulon durum (Ruprecht) Okamura. Erect thalli of the species were collected year-round, but the mature thalli forming either uniloc-ular sporangia or two different types of plurilocular structures (evidently gametangia) on separate thalli were found only in winter. ln culture, an isomorphic life history is suggested for the species, alternating between a sporophyte forming unilocular sporangia and gam-etophytes forming plurilocular macro- (female) and micro- (male) gametangia. Contents of unilocular sporangia were not released, but germinated in situ, developing into erect thalli forming plurilocular gametangia. Macrogametangia released aplanogametes (oospores), but male gametangia appeared to be non-functional, although flagellated cells were once formed in the loc-uli. This is the first report of plurilocular gametangia in the species. Although the species grew well and matured under considerably lower temperature conditions than European Stypocaulon scoparium (L.) Sauvageau, its temperature requirements showed similarity to northwestern Atlantic Stypocaulon species. This supports the notion that northwestern Atlantic Stypocaulon is conspecific with S. durum.  相似文献   
110.
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