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   512603篇
  免费   61047篇
  国内免费   317篇
  2018年   4581篇
  2017年   4224篇
  2016年   6643篇
  2015年   10121篇
  2014年   11383篇
  2013年   15965篇
  2012年   18462篇
  2011年   18731篇
  2010年   12400篇
  2009年   11401篇
  2008年   16468篇
  2007年   17024篇
  2006年   15601篇
  2005年   15391篇
  2004年   15249篇
  2003年   14338篇
  2002年   13867篇
  2001年   22382篇
  2000年   22278篇
  1999年   18129篇
  1998年   7214篇
  1997年   7199篇
  1996年   6971篇
  1995年   6335篇
  1994年   6363篇
  1993年   6143篇
  1992年   14177篇
  1991年   13471篇
  1990年   13108篇
  1989年   12994篇
  1988年   11619篇
  1987年   11245篇
  1986年   10278篇
  1985年   10171篇
  1984年   8841篇
  1983年   7629篇
  1982年   6185篇
  1981年   5693篇
  1980年   5271篇
  1979年   8117篇
  1978年   6388篇
  1977年   5886篇
  1976年   5536篇
  1975年   5703篇
  1974年   6243篇
  1973年   6051篇
  1972年   5347篇
  1971年   4959篇
  1970年   4177篇
  1969年   4097篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
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   
933.
934.
935.
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   
936.
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   
937.
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   
938.
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   
939.
940.
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