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   32517篇
  免费   132篇
  国内免费   297篇
系统科学   432篇
丛书文集   538篇
教育与普及   130篇
理论与方法论   107篇
现状及发展   13075篇
研究方法   1190篇
综合类   16803篇
自然研究   671篇
  2013年   355篇
  2012年   619篇
  2011年   1289篇
  2010年   433篇
  2009年   421篇
  2008年   735篇
  2007年   836篇
  2006年   819篇
  2005年   755篇
  2004年   668篇
  2003年   553篇
  2002年   552篇
  2001年   867篇
  2000年   933篇
  1999年   640篇
  1994年   341篇
  1992年   504篇
  1991年   427篇
  1990年   481篇
  1989年   442篇
  1988年   434篇
  1987年   468篇
  1986年   454篇
  1985年   550篇
  1984年   437篇
  1983年   381篇
  1982年   354篇
  1981年   344篇
  1980年   405篇
  1979年   884篇
  1978年   724篇
  1977年   702篇
  1976年   536篇
  1975年   659篇
  1974年   846篇
  1973年   738篇
  1972年   737篇
  1971年   915篇
  1970年   1040篇
  1969年   891篇
  1968年   888篇
  1967年   855篇
  1966年   757篇
  1965年   558篇
  1959年   304篇
  1958年   524篇
  1957年   407篇
  1956年   321篇
  1955年   335篇
  1954年   313篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
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   
152.
The hyperthermic effect of a bacterial pyrogen has been studied in rabbits pretreated or not with p-chlorophenylalanine or 5, 6-dihydroxytryptamine. The results obtained indicate that a selective reduction of cerebral 5-hydroxytryptamine levels by these drugs do not significantly affect pyrogen hypertermia.  相似文献   
153.
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   
154.
Summary Tryptic treatment of muscle thick filaments reveals the underlying backbones of aggregatedl-meromyosin as a coli of 3 secondary filaments (helical repeat 130 nm) each in turn a coli of a 3 finer ones.  相似文献   
155.
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   
156.
Summary 4-isothiocyanato-4-nitrodiphenylamine was found to possess activity against intestinal nematodes in mice, against schistosomes in various hosts including primates and against two filarial species in the mongolian jird. Upon administration in a single oral dose it is equally effective againstS. haematobium, S. mansoni andS. japonicum.  相似文献   
157.
Summary The present results, using isolated rat aortic strips and portal vein segments, demonstrate that ethanol, depending upon concentration, can either enhance or attenuate the contractile actions of PGF2 on at least 2 different types of vascular smooth muscle. At the very least, the present findings question the use of ethanol as a solvent when investigating the contractile actions of PG molecules on smooth muscles.Supported by NIH grant No. HL-18015 and NIMH grant No. MH-26236. The authors are indebted to Dr.John E. Pike and Dr.John Babcock of the Upjohn Company for generously providing us with the PGF2 used in this study.  相似文献   
158.
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   
159.
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   
160.
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