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   41307篇
  免费   4445篇
  国内免费   12篇
  2022年   227篇
  2021年   556篇
  2020年   365篇
  2019年   455篇
  2018年   570篇
  2017年   537篇
  2016年   937篇
  2015年   1677篇
  2014年   1634篇
  2013年   2154篇
  2012年   2464篇
  2011年   2186篇
  2010年   1503篇
  2009年   1366篇
  2008年   1887篇
  2007年   1853篇
  2006年   1665篇
  2005年   1611篇
  2004年   1512篇
  2003年   1320篇
  2002年   1293篇
  2001年   1249篇
  2000年   1236篇
  1999年   1111篇
  1998年   614篇
  1997年   570篇
  1996年   563篇
  1995年   537篇
  1994年   492篇
  1993年   522篇
  1992年   1008篇
  1991年   752篇
  1990年   773篇
  1989年   754篇
  1988年   656篇
  1987年   597篇
  1986年   616篇
  1985年   716篇
  1984年   537篇
  1983年   415篇
  1982年   341篇
  1981年   312篇
  1980年   255篇
  1979年   380篇
  1978年   346篇
  1977年   242篇
  1976年   225篇
  1975年   196篇
  1974年   289篇
  1973年   250篇
排序方式: 共有10000条查询结果,搜索用时 31 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