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   38542篇
  免费   129篇
  国内免费   149篇
系统科学   180篇
丛书文集   537篇
教育与普及   63篇
理论与方法论   132篇
现状及发展   16447篇
研究方法   1566篇
综合类   19166篇
自然研究   729篇
  2013年   345篇
  2012年   549篇
  2011年   1270篇
  2010年   241篇
  2008年   634篇
  2007年   797篇
  2006年   740篇
  2005年   764篇
  2004年   794篇
  2003年   674篇
  2002年   705篇
  2001年   1283篇
  2000年   1228篇
  1999年   768篇
  1992年   727篇
  1991年   557篇
  1990年   618篇
  1989年   607篇
  1988年   569篇
  1987年   571篇
  1986年   630篇
  1985年   778篇
  1984年   569篇
  1983年   502篇
  1982年   432篇
  1981年   440篇
  1980年   513篇
  1979年   1243篇
  1978年   953篇
  1977年   922篇
  1976年   753篇
  1975年   770篇
  1974年   1147篇
  1973年   928篇
  1972年   1002篇
  1971年   1125篇
  1970年   1522篇
  1969年   1149篇
  1968年   1069篇
  1967年   1024篇
  1966年   993篇
  1965年   709篇
  1964年   212篇
  1959年   370篇
  1958年   689篇
  1957年   474篇
  1956年   372篇
  1955年   352篇
  1954年   376篇
  1948年   258篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
311.
R Foa  M T Kramers  D Catovsky 《Experientia》1979,35(2):269-270
The levels of membrane alkaline phosphatase have been measured on different lymphocyte fractions from human peripheral blood separated on bovine serum albumin discontinuous gradients. The peak in enzyme activity was observed in a non-T-, non-B-cell fraction, rich in "null" lymphocytes; the lowest values were found in the fraction with the highest proportion of T-cells.  相似文献   
312.
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   
313.
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   
314.
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   
315.
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   
316.
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   
317.
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   
318.
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   
319.
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   
320.
G Kaiser  J Dietz  G Wiemer  D Palm 《Experientia》1979,35(4):453-455
During the maturation of red blood cells from rats after stress erythropoiesis, adenyl cyclase activity and beta-adrenoceptor density (pmoles/mg protein) decrease at distinctly different rates suggesting a different turnover of these membrane units.  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