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   38100篇
  免费   66篇
  国内免费   100篇
系统科学   175篇
丛书文集   757篇
教育与普及   102篇
理论与方法论   221篇
现状及发展   16538篇
研究方法   1570篇
综合类   18393篇
自然研究   510篇
  2013年   200篇
  2012年   501篇
  2011年   1049篇
  2010年   211篇
  2008年   641篇
  2007年   668篇
  2006年   698篇
  2005年   707篇
  2004年   652篇
  2003年   680篇
  2002年   689篇
  2001年   1193篇
  2000年   1113篇
  1999年   755篇
  1994年   340篇
  1992年   720篇
  1991年   572篇
  1990年   624篇
  1989年   598篇
  1988年   583篇
  1987年   621篇
  1986年   629篇
  1985年   774篇
  1984年   620篇
  1983年   510篇
  1982年   445篇
  1981年   451篇
  1980年   551篇
  1979年   1223篇
  1978年   1044篇
  1977年   992篇
  1976年   720篇
  1975年   771篇
  1974年   1069篇
  1973年   914篇
  1972年   966篇
  1971年   1195篇
  1970年   1538篇
  1969年   1170篇
  1968年   1116篇
  1967年   1135篇
  1966年   982篇
  1965年   721篇
  1959年   417篇
  1958年   621篇
  1957年   500篇
  1956年   412篇
  1955年   355篇
  1954年   403篇
  1948年   236篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
361.
C J Hayes  J D Palmer 《Experientia》1976,32(4):469-470
The spontaneous locomotor activity of the laboratory mouse is significantly depressed by the ingestion of deuterium oxide. The response, which is reversible, is a retilinear one with up to 70% reduction in activity with the administration of 25% heavy water.  相似文献   
362.
Summary The C-11 proton of an aprophine possessing a C-1,2 methylenedioxy group falls relatively upfield between 7.47 and 7.86. Additionally, the i.c.s. for the two protons of the methylenedioxy group is large (4–12 Hz). The presence of a methylenedioxy at C-3,4 in a phenanthrene alkaloid also results in an upfield shift ( 8.95–9.00) of the C-5 proton.This project was supported by NIH research grant No. HL-12971, awarded by the National Heart and Lung Institute, PHS/DHEW.  相似文献   
363.
Summary The effect of dipyridamole on platelet phospholipids has been studied. After the platelet incubation with dipyridamole, a 38% reduction in the concentration of the sphingomyelin and a 21% increase in phosphatidyl choline were produced.  相似文献   
364.
T Dalton 《Experientia》1976,32(11):1421-1423
5-Hydroxytryptamine creatinine sulphate loses its biological activity when maintained at room temperature. The loss of 5-HT activity (in stimulating sodium transport across frog skin) is greater than the loss of creatinine sulphate activity (inhibition of sodium transport).  相似文献   
365.
Summary Adenylate kinase activity of intact mitochondria is strongly inhibited by Ap5A, i.e.p 1,p 5-Di (adenosine-5-) pentaphosphate, whereas oxidative phosphorylation is not affected. Therefore, Ap5A is a useful tool to distinguish between oxidative and non oxidative ATP generating reactions.Acknowledgment. The generous support of Prof. Dr.Walther Lamprecht is gratefully acknowledged. J. L. thanks the Stipendienfonds des Verbandes der Chemische Industrie for a scholarship.  相似文献   
366.
Summary Using Raman spectroscopy, we demonstrate that low levels of -carotene, lycopene, and xanthophyll give rise to resonance enhanced bands in blood plasma. These results explain the significance of previously unidentified spectral maxima which have been related to the state of health of the blood donor.  相似文献   
367.
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   
368.
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   
369.
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   
370.
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   
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