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   43952篇
  免费   3604篇
  国内免费   5篇
  47561篇
  2023年   221篇
  2021年   325篇
  2020年   288篇
  2019年   275篇
  2018年   886篇
  2017年   911篇
  2016年   951篇
  2015年   778篇
  2014年   934篇
  2013年   1743篇
  2012年   3014篇
  2011年   3390篇
  2010年   1698篇
  2009年   1089篇
  2008年   2781篇
  2007年   2853篇
  2006年   2667篇
  2005年   2380篇
  2004年   2266篇
  2003年   2113篇
  2002年   2134篇
  2001年   1495篇
  2000年   1736篇
  1999年   901篇
  1998年   418篇
  1997年   339篇
  1996年   409篇
  1995年   355篇
  1994年   373篇
  1993年   343篇
  1992年   356篇
  1991年   295篇
  1990年   267篇
  1989年   256篇
  1988年   241篇
  1987年   246篇
  1986年   210篇
  1985年   308篇
  1984年   370篇
  1983年   335篇
  1982年   308篇
  1981年   294篇
  1980年   265篇
  1979年   258篇
  1978年   258篇
  1977年   242篇
  1976年   241篇
  1975年   287篇
  1974年   217篇
  1973年   206篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
In a section of the Liassic southwest of the village of Préjano (Prov. Logroño) Sinemurian Dasyclad algae were found for the first time in the “Bankkalk-Series” of the “Carniolas-Formation” which is not dated up to that time. Six species,Dissocladella lucasi (Cros & Lemoine),Dissocladella iberica nov. sp.,Dissocladella ebroensis nov. sp.,Sestrosphaera liasina Pia,Gyroporella retica (Zanin) andMacroporella nov. sp. aff. sturi Bystricky are described.  相似文献   
6.
7.
8.
9.
The mechanisms controlling early adenovirus gene expression in vivo have been studied using inhibitors of protein synthesis. When inhibitors were added shortly before or at the onset of infection, viral mRNA from all early regions was transcribed, spliced and accumulated over a 7 hr period. After longer pretreatment, accumulation of several early mRNAs were suppressed. Addition of inhibitors 1 hr after infection enhanced the accumulation of viral mRNA in the cytoplasm. Translation of early mRNA selected on adenovirus DNA in a cell-free system reflected the amount of viral mRNA present. A viral coded product may therefore control accumulation of viral mRNA.A different pattern emerged when inhibitors of protein synthesis were removed at 5 hr postinfection and cells were pulse-labeled in vivo. If inhibitors were introduced at or before infection, early viral proteins were synthesized only after a lag of 1–3 hr. However, if treatment was introduced 1 hr post-infection, reversion of the protein synthesis block was instantaneous. It appears that protein synthesis inhibitors reveal an in vivo translational block for viral mRNA. This block could be overcome by preinfection with a related virus. Furthermore, no block was observed in a virus-transformed human embryonic kidney cell line (293) which expresses early region 1 of the viral genome. Viral gene product(s) encoded in early region 1 may control translation of early adenovirus messenger RNA in vivo.  相似文献   
10.
A total dosage up to 1 mg PGF2a as i.v. infusions of 10–40 μg/min. was investigated on patients with arrhythmias of several kinds. We found therapeutic effects in 5 of 6 patients with constant extrasystoles and in one patient with digitalis - induced partial AV-block respectively. In 3 of 4 patients with acute tachyarrhythmias the results were not convincing, probably due to a dosage not high enough. An increase of the diastolic stimulation threshold usually seen with other antiarrhythmics was not to be observed in 3 patients. The mechanism of action of PGF2a has not yet been clarified.  相似文献   
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