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   40373篇
  免费   106篇
  国内免费   183篇
系统科学   203篇
丛书文集   722篇
教育与普及   66篇
理论与方法论   160篇
现状及发展   19278篇
研究方法   1553篇
综合类   18146篇
自然研究   534篇
  2013年   321篇
  2012年   508篇
  2011年   1039篇
  2010年   214篇
  2008年   651篇
  2007年   711篇
  2006年   733篇
  2005年   702篇
  2004年   805篇
  2003年   655篇
  2002年   648篇
  2001年   1169篇
  2000年   1087篇
  1999年   763篇
  1992年   748篇
  1991年   551篇
  1990年   618篇
  1989年   633篇
  1988年   578篇
  1987年   667篇
  1986年   636篇
  1985年   805篇
  1984年   615篇
  1983年   507篇
  1982年   472篇
  1981年   506篇
  1980年   604篇
  1979年   1291篇
  1978年   1084篇
  1977年   1031篇
  1976年   832篇
  1975年   932篇
  1974年   1259篇
  1973年   1085篇
  1972年   1100篇
  1971年   1272篇
  1970年   1598篇
  1969年   1223篇
  1968年   1242篇
  1967年   1212篇
  1966年   1020篇
  1965年   757篇
  1964年   249篇
  1959年   411篇
  1958年   727篇
  1957年   496篇
  1956年   411篇
  1955年   417篇
  1954年   405篇
  1948年   271篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
Summary Rats given aluminium hydroxide after cold-restraint stress but before the post-stress delay period, ulcerated significantly less severely and less frequently than rats given the drug before cold-restraint stress or those given water at either time period. Both aluminium hydroxide treated groups exhibited less ulceration than non-drug groups. These data suggest profound parasympathetic and hence, gastric acid, involvement in restraint delay-induced ulceration in rats.  相似文献   
222.
Summary The activity of (Na++K+)-ATPase and acetylcholine esterase were folloed in rat brain cerebral cortex, caudate, thalamus, hippocampus and medulla after i.v. administration of physostigmine. Both enzymes were found to be inhibited in a dose-dependent manner. The most pronounced inhibition of (Na++K+)-ATPase was found in caudate. where the highest activity of acetylcholine esterase is found.These studies were supported by a grant from the Union of Science of Republic Serbia, No. 40404-14.  相似文献   
223.
Summary Contrary to Srdi and Gloor's report, we find crystal cells (cc) in the lymph glands ofD. melanogaster larvae; the size and number of inclusions in the cc cannot be used to distinguish the 2 sibling species,D. melanogaster andD. simulans; cc in the hemocoel are not phagocytic cells; the surface properties of the lamellocytes are consistent with their derivation from plasmatocytes and not cc.Supported by grant No. CA16619 awarded by the National Cancer Institute, DHEW, USPHS.  相似文献   
224.
Summary The relaxant effects of isoprenaline on rabbit isolated renal artery and aorta were compared. The results suggest that although isoprenaline acts on -adrenoceptors in the aorta it stimulates dopamine receptors in the renal artery.  相似文献   
225.
Summary A novel sesquiterpene lactone, 9--hydroxyparthenolide (1) was isolated from a chloroform extract ofAnvillea garcini that was collected in Iran. The structure of1 was assigned on the basis of high field NMR decoupling experiments and other spectroscopic evidence. This -methylene lactone has shown significant activity in both the 9KB cell culture and P388 mouse leukemia test systems.The authors acknowledge the support of contract No. N01-CM-97296 from the National Cancer Institute and the use of the Purdue University Biochemical Magnetic Resonance Laboratory (NIH grant No. RR01077). This is paper 16 in the series Potential Antitumor Agents.  相似文献   
226.
Summary A needle type of colloid osmometer has been devised with special attachments which made it useable with 3-l samples. It has been used in oncometry of fresh water teleosts to give the following results: 5.1±1.0 mm Hg for goldfish, 5.2±0.71 mm Hg for carp, and 14.3±0.75 mm Hg for eel.This study was supported in part by Research Grant 387036 from the Ministry of Education of Japan.invited to National Institute of Physiological Sciences, Okazaki, Japan.  相似文献   
227.
228.
229.
Summary Autoradiographic, stereological and histological studies have been carried out to determine the origin of muscle fibre splitting which supposedly occurs during muscle hypertrophy. The results obtained clearly indicate that the supposedly split fibres are a transient response probably derived from satellite cells and are not derived from pre-existing fibres by true splitting. Similarly, increases in muscle fibre size are not achieved by recruitment of satellite structures as indicated by lack of myonuclear recruitment.Acknowledgment. This work was carried out with the aid of a grant from the Medical Research Council of Great Britain. The authors are grateful for the excellent technical assistance of Miss H. Caulton, M.J. Wild and M. Fenner.  相似文献   
230.
Summary Growth-promoting alpha-globulin (GPAG), a specific serum protein complex which induces mitotic activity in continually replicating metazoan cells in vitro, was shown in this study to support growth of astrocytes and mesenchymal cells as well as process formation of nerve cells isolated from cerebral hemispheres of chick embryos.  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