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   76764篇
  免费   1304篇
  国内免费   2001篇
系统科学   2324篇
丛书文集   1373篇
教育与普及   1613篇
理论与方法论   643篇
现状及发展   29237篇
研究方法   204篇
综合类   42482篇
自然研究   2193篇
  2022年   653篇
  2021年   817篇
  2016年   712篇
  2015年   1051篇
  2014年   1438篇
  2013年   1752篇
  2012年   1580篇
  2011年   3669篇
  2010年   1605篇
  2009年   2002篇
  2008年   2101篇
  2007年   2209篇
  2006年   1992篇
  2005年   2185篇
  2004年   2799篇
  2003年   2302篇
  2002年   1937篇
  2001年   1759篇
  2000年   1437篇
  1999年   2587篇
  1998年   2196篇
  1997年   2403篇
  1996年   2083篇
  1995年   1745篇
  1994年   1837篇
  1993年   1718篇
  1992年   1525篇
  1991年   1378篇
  1990年   1336篇
  1989年   1091篇
  1988年   955篇
  1987年   754篇
  1986年   707篇
  1985年   701篇
  1984年   618篇
  1982年   706篇
  1981年   755篇
  1980年   816篇
  1979年   1045篇
  1978年   999篇
  1977年   1009篇
  1976年   910篇
  1975年   871篇
  1973年   941篇
  1972年   1014篇
  1971年   947篇
  1970年   914篇
  1969年   905篇
  1968年   867篇
  1967年   726篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
D-6-Methyl-8-[-isopropylaminoethyl] ergoline-I [VÚFB-10726], beginning from the dose of 0.05 mg/kg p.o., suppresses lactation through the inhibition of prolactin secretion in nursing rats.  相似文献   
992.
Summary Rat brain mitochondria contain a significant proportion of poly(A) associated RNA which is higher than that found in microsomes from the same source. When steady state poly(A) RNA of brain mitochondria was analyzed by microelectrophoresis, it displayed a characteristic separation pattern with a large amount of free poly(A).  相似文献   
993.
Summary In normal rats, prostaglandin F2 is a potent vasoconstrictor. The corresponding systemic hypertension is progressively attenuated by tachyphylaxis, revealing a longlasting fall of blood pressure. Tachyphylaxis is accelerated by previous injection of arachidonic acid and bradykinin. The vasodepressive activity of PGF2 is inhibited by indomethacin.

Nous remercions vivement le docteurPike (Upjohn, Kalamazoo) qui nous a fourni gracieusement ces prostaglandines.  相似文献   
994.
Summary The incorporation of leucice-14C into protein in bovine mesenteric arteries was augmented by cyclic GMP (10–3 M) and decreased by cyclic AMP (10–3 M). There was no effect of 5 AMP (10–3 M). The phosphodiesterase inhibiting drugs theophylline (10–3 M) and papaverine (5×10–5 g/ml) both decreased the leucine-14C incorporation.We are indebted to Mrs.Lena Burlin for hear assistance. Finacial support has been provided by the Swedish State Medical Research Council (No. 04X-101X-4498).  相似文献   
995.
Summary An ecdysone 20-hydroxylase enzyme system that converts -ecdysone to 20-hydroxyecdysone was prepared from the midgut of the tobacco hornworm prepupa. This partially purified enzyme is NADPH dependent and is localized in the mitochondrial fraction of the midgut tissue.  相似文献   
996.
Summary The effect of negative and positive air ionisation on siliconized blood serotonin was studied in vitro. The experiments showed that within 10 min positive ionisation increased serotonin levels in total blood (+40%), plasma (+90%), erythrocytes (+50%) and thrombocytes (+200%). On the other hand, negative ionization (10 min) lowered the serotonin content of total blood (–30%), plasma (–42.5%), erythrocytes (–41.7%) and thrombocytes (–72.3%), thus confirming the Krueger Effect in vitro.This research was generously supported by a grant from the Joint Research Fund of the Hebrew University and Hadassah, and Dr. and Mrs.Leonard Appleby of Palmbeach, Florida.Acknowledgment: Our thanks are due to Mr.B. Shalita, Mrs.Zippora Adar and Mrs.Olga Fradkin for devoted technical assistance.  相似文献   
997.
Summary 9 (10 mg/kg, i.p.) administered to mice immediately after withdrawal from a 3-day exposure to ethanol vapor was found to intensify withdrawal reactions. No effect was seen when 9 was administered chronically during the exposure to ethanol.  相似文献   
998.
Summary The octopamine, dopamine and noradrenaline content of the brain of the locust,Schistocerca gregaria has been determined using sensitive radiochemical-enzymatic assays. Octopamine and dopamine are present in high concentration but the noradrenaline content is only 1/25 that of octopamine. Both reserpine and fusaric acid (a dopamine--hydroxylase inhibitor) produce a significant depletion of the octopamine stores.The author is a M.R.C. of Canada Fellow. Thanks are due to Drs.A. A. Boulton, A. V. Juorio, andP. H. Wu for helpful discussion.  相似文献   
999.
Summary - and -ecdysone were synthesized from labelled cholesterol by premolt crayfish in vivo and by their Y-organs in vitro.  相似文献   
1000.
Summary The treatment with cycloheximide of rats previously poisoned with -amanitin hinders the recovery of RNA synthesis observed in the liver of rats treated with -amanitin alone. The recovery of RNA synthesis can be ascribed to the capability of poisoned rats to synthesize new RNA-polymerase II.Acknowledgments: We thank ProfessorT. Wieland for the generous gift of -amanitin. This work was supported by grants from C.N.R., Rome, and by Pallotti's legacy for Cancer Research.  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