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   506060篇
  免费   56078篇
  国内免费   345篇
  2018年   9735篇
  2017年   9492篇
  2016年   9448篇
  2015年   8571篇
  2014年   9355篇
  2013年   13093篇
  2012年   17405篇
  2011年   22074篇
  2010年   15842篇
  2009年   14867篇
  2008年   18783篇
  2007年   20674篇
  2006年   12493篇
  2005年   13460篇
  2004年   12646篇
  2003年   12258篇
  2002年   11675篇
  2001年   21871篇
  2000年   22044篇
  1999年   17511篇
  1998年   6293篇
  1997年   6541篇
  1996年   6136篇
  1995年   5728篇
  1994年   5790篇
  1993年   5618篇
  1992年   13728篇
  1991年   13047篇
  1990年   12704篇
  1989年   12567篇
  1988年   11223篇
  1987年   10834篇
  1986年   9916篇
  1985年   9709篇
  1984年   8234篇
  1983年   7116篇
  1982年   5572篇
  1981年   5018篇
  1980年   4676篇
  1979年   7741篇
  1978年   5953篇
  1977年   5454篇
  1976年   5087篇
  1975年   5402篇
  1974年   5851篇
  1973年   5690篇
  1972年   5620篇
  1971年   5207篇
  1970年   3950篇
  1969年   3880篇
排序方式: 共有10000条查询结果,搜索用时 373 毫秒
991.
992.
The introduction of either PGF (10?7 M) or TPA (10?7 M) stimulated, ouabain-sensitive 86Rb+ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF at these concentrations stimulated the incorporation of 3H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na+/K+ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in 3H-TdR incorporation and ouabain-sensitive 86Rb+ influxes with 10?7 M TPA, whereas PGF stimulated a significant increase in 3H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive 86Rb+ influx in both. Therefore, although there appears to be a close correlation between Na+/K+ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF cannot be confirmed.  相似文献   
993.
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   
994.
995.
996.
C. P. W. Warren  K. S. Tse 《CMAJ》1974,110(4):425-427,429
Using a solid-phase radioimmunoassay, serum IgE level was determined in 46 normal subjects, 53 patients with bronchial asthma, 44 patients with chronic bronchitis and / or emphysema, and 19 patients with restrictive lung disease. Sputum IgE was measured simultaneously in 51 of the subjects. The range of serum IgE concentration in the normal subjects was wide. It varied between 15 and 750 ng/ml with a mean of 135 ng. Asthmatic patients had significantly higher levels of serum IgE with a mean of 579 ng/ml, but only 30% fell outside the normal 95% confidence limits. Patients with chronic bronchitis, emphysema and restrictive lung diseases had normal IgE levels. There was a significant correlation between serum and sputum IgE levels.  相似文献   
997.
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   
998.
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   
999.
C Gray 《CMAJ》1998,158(1):89-91
The disaster involving blood-borne pathogens and Canada''s blood system was in the spotlight in November with the release of the Krever inquiry report. Many physicians consider the report anticlimactic because action has already been taken on several fronts and the use of donated bloods has declined, but it will still have a far-reaching impact.  相似文献   
1000.
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