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   554180篇
  免费   58096篇
  国内免费   753篇
  2021年   5014篇
  2018年   7081篇
  2017年   6669篇
  2016年   9242篇
  2015年   12868篇
  2014年   14460篇
  2013年   19440篇
  2012年   22723篇
  2011年   22494篇
  2010年   14973篇
  2009年   13084篇
  2008年   19296篇
  2007年   19504篇
  2006年   18334篇
  2005年   17021篇
  2004年   17061篇
  2003年   15780篇
  2002年   15172篇
  2001年   21300篇
  2000年   21178篇
  1999年   16992篇
  1998年   6613篇
  1997年   6383篇
  1996年   6118篇
  1995年   5854篇
  1994年   5490篇
  1993年   5423篇
  1992年   13586篇
  1991年   13446篇
  1990年   13159篇
  1989年   12674篇
  1988年   11700篇
  1987年   11087篇
  1986年   10559篇
  1985年   10353篇
  1984年   8628篇
  1983年   7472篇
  1982年   5675篇
  1981年   5099篇
  1979年   8040篇
  1978年   6530篇
  1977年   5821篇
  1976年   5461篇
  1975年   6408篇
  1974年   7009篇
  1973年   6802篇
  1972年   6068篇
  1971年   5602篇
  1970年   4859篇
  1969年   4817篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
Astrocytes have long been considered as just providing trophic support for neurons in the central nervous system, but recently several studies have highlighted their importance in many functions such as neurotransmission, metabolite and electrolyte homeostasis, cell signaling, inflammation, and synapse modulation. Astrocytes are, in fact, part of a bidirectional crosstalk with neurons. Moreover, increasing evidence is stressing the emerging role of astrocyte dysfunction in the pathophysiology of neurological disorders, including neurodegenerative disease, stroke, epilepsy, migraine, and neuroinflammatory diseases.  相似文献   
972.
Results are presented from experimental investigations of the angular distributions and energy spectra of fast ions produced in deuterium polyethylene targets under irradiation by picosecond laser pulses with intensities of up to 2 × 1018 W/cm2 in the SOKOL-P facility. The parameters of ion fluxes were measured by time-of-flight spectrometers based on semiconductor detectors.  相似文献   
973.
974.
975.
976.
977.
The Devonian cemented brachiopod Schuchertellopsis durbutensis has proved difficult to classify and its possible taxonomic relationships are unknown. Morphologically Schuchertellopsis resembles more closely members of the Orthotetidina than the Davidsoniidina. Examination of the shell structure, a key diagnostic feature of the Orthotetidina, shows that Schuchertellopsis has the cross laminar secondary shell typical of all orthotetidines. However, the presence of both pseudopunctate and incipient an extropunctate fabric within the ventral valve is unique amongst orthotetidine brachiopods and is thought to represent a phase of shell fabric experimentation. Schuchertellopsis probably fits most comfortably within the Schuchertellidae, and is the earliest representative of that family.  相似文献   
978.
979.
Comparative mineral and hormonal analyses were made on tissue culture derived truncated leaf syndrome and wild type oil palm seedlings. Mineral analysis confirmed that Boron, Zinc and chlorophyll levels were significantly lower in truncated leaf syndrome leaves than those of wild type. Hormonal analysis also revealed various cytokinin derivatives such as trans-zeatin, trans-zeatin riboside, trans-zeatin O-glucoside and trans-zeatin riboside 5??mono phosphate were significantly higher in truncated leaf syndrome leaves compared to wild type leaves. Brassinolide level was also significantly higher in truncated leaf syndrome leaves than those of the wild type. These observations suggest that the truncated leaf syndrome abnormality could be associated to high cytokinin and brassinosteroid production which affects the uptake of Boron and Zinc.  相似文献   
980.
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