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   70481篇
  免费   298篇
  国内免费   571篇
系统科学   1276篇
丛书文集   675篇
教育与普及   289篇
理论与方法论   541篇
现状及发展   35845篇
研究方法   1584篇
综合类   28953篇
自然研究   2187篇
  2013年   834篇
  2012年   865篇
  2011年   3004篇
  2009年   644篇
  2008年   1089篇
  2007年   1283篇
  2006年   1303篇
  2005年   1516篇
  2004年   2705篇
  2003年   2196篇
  2002年   1909篇
  2001年   1901篇
  2000年   1383篇
  1999年   1289篇
  1998年   654篇
  1997年   787篇
  1994年   703篇
  1993年   708篇
  1992年   1204篇
  1991年   976篇
  1990年   1086篇
  1989年   907篇
  1988年   857篇
  1987年   870篇
  1986年   931篇
  1985年   1155篇
  1984年   937篇
  1983年   813篇
  1982年   879篇
  1981年   911篇
  1980年   1023篇
  1979年   1797篇
  1978年   1560篇
  1977年   1533篇
  1976年   1321篇
  1975年   1332篇
  1974年   1440篇
  1973年   1537篇
  1972年   1634篇
  1971年   1731篇
  1970年   2072篇
  1969年   1771篇
  1968年   1676篇
  1967年   1579篇
  1966年   1392篇
  1965年   1066篇
  1959年   620篇
  1958年   967篇
  1957年   726篇
  1956年   621篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
651.
A thymic extract (TE) was prepared from supernatant of mice thymic epithelial cultures according to the purification of thymosin. TE and thymosin stimulated, in vitro, the immune response of mouse against deep red blood cells.  相似文献   
652.
Summary The effect of ethanol on thyroxine (T4) accumulation in the hypothalamus (H), pituitary gland (P) and cerebrospinal fluid (CSF) has been investigated in 1–15-day-old rabbits. It has been found that H or CSF serum ratios decreased with age by about 2 in the course of 13 postnatal days. Stable T4 resulted in an increase of125I-T4 in H, P and CSF. Ethanol per se caused an increase in transfer and accumulation of radiothyroxine or made the changes after loading animals with carrier T4 more pronounced.  相似文献   
653.
Summary A correlation between the postirradiation increase of the small intestine motility and the prostaglandin-like activity in this organ during gastrointestinal syndrome was observed. Indomethacin decreased the elevated motility of intestine and reduced the prostaglandin-like activity in this syndrome.Acknowledgments. The work was supported by the Polish Academy of Sciences.  相似文献   
654.
Summary The D-galactose specific lectin fromViscum album L. reacts with serum proteins that contain the corresponding D-galactopyranosyl residues. By affinity chromatography of human serum on lectin-sepharose IgM, 2-macroglobulin, haptoglobin and -lipoprotein were quantitatively retained. Only parts of IgA, IgG and transferrin were retarded. The other serum proteins are unbounded as albumin, 1A– and 1C.  相似文献   
655.
Summary Physostigmine in a dose of 0.1 mg/kg i.v. expressly stimulated the oxygen uptake in the rat cerebral cortex. This effect was blocked by propranolol and seems be mediated by catecholamines. Since atropine also antagonized the stimulant effect of physostigmine, it appears that the action of physostigmine is primarily cholinergic and that the adrenergic effect is a secondary phenomenon. The higher dose of physostigmine (0.4 mg/kg i.v.) caused a depression of rat brain oxygen uptake.This work was supported by a grant from Serbian Republic Scientific Fund (ZMNU SR Srbija), Belgrade (Yugoslavia).The authors wish to acknowledge the skilful technical assistance of Lj. Krsti.  相似文献   
656.
Summary A new enantiomeric sesquiterpene alcohol named (–)-maalian-5-ol was isolated from the liverwort, and the structure and absolute configuration was determined to be the stereostructureI by chemical and spectral evidence.The authors express their gratitude to Dr H. Inoue, National Science Museum, for identification of the liverwort, and Prof. T. Tokoroyama, Osaka City University, for sending of the data of (–)--maaliene and (+)-selina-5,11-diene. Thanks are also due to the Ministry of Education for financial support of this work.  相似文献   
657.
Three acidic polysaccharide (AP) fractions and the prostaglandin-like substances (PLS) isolated from P. acnes were investigated regarding their chemotactic activities on polymorphonuclear leukocytes. Both AP's and PLS induced a significant chemotatic response, which suggests their involvement in inflammatory acne vulgaris.  相似文献   
658.
It was shown that, in physiological concentrations, insulin enhances, in vitro, the immunological phagocytosis of sensitized sheep erythrocytes by cultured mouse peritoneal macrophages. Insulin seems to stimulate macrophage phagocytosis as a cholinomimetic agonist by increasing the intracellular levels of cyclic GMP.  相似文献   
659.
Summary 2 factors elaborated by distinct neurosecretory cells in the pars intercerebralis control moulting inPanstrongylus megistus. The 1st, originating probably in the A cells, activates the thoracic gland. The 2nd, produced by the A cells, acts at an earlier stage in a different way.Supported by CNPq., Brésil and DGRST (aide No. 76.7.0716).  相似文献   
660.
(3H)-Ouabain binding to liver and kidney preparations was utilized to estimate the number of Na+, K+-ATPase enzyme units in livers and kidneys from rats fed 2% corn oil supplemented or fat-free diets. The specific (3H)-ouabain binding in liver and kidney preparations from fatty acid deficient rats was increased approximately 40%, but the affinity of the binding sites for ouabain (Kd-value) remained unchanged. The increased concentration of Na+, K+-ATPase enzyme units observed in the essential fatty acid deficient rats may contribute to the reduced body fat accumulation and elevated heat production observed in these animals.  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