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   37355篇
  免费   706篇
  国内免费   1327篇
系统科学   1015篇
丛书文集   964篇
教育与普及   337篇
理论与方法论   151篇
现状及发展   8151篇
研究方法   758篇
综合类   27845篇
自然研究   167篇
  2022年   414篇
  2021年   521篇
  2020年   380篇
  2017年   352篇
  2016年   373篇
  2015年   677篇
  2014年   881篇
  2013年   873篇
  2012年   1083篇
  2011年   1371篇
  2010年   987篇
  2009年   1048篇
  2008年   1395篇
  2007年   1351篇
  2006年   1218篇
  2005年   1181篇
  2004年   1023篇
  2003年   937篇
  2002年   1262篇
  2001年   1488篇
  2000年   1176篇
  1999年   1198篇
  1998年   660篇
  1997年   589篇
  1996年   579篇
  1995年   553篇
  1994年   486篇
  1993年   415篇
  1992年   595篇
  1991年   540篇
  1990年   524篇
  1989年   469篇
  1988年   398篇
  1987年   380篇
  1986年   358篇
  1985年   359篇
  1979年   566篇
  1978年   475篇
  1977年   437篇
  1975年   405篇
  1974年   565篇
  1973年   452篇
  1972年   477篇
  1971年   555篇
  1970年   699篇
  1969年   541篇
  1968年   540篇
  1967年   538篇
  1966年   430篇
  1965年   373篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Summary An intermediate stage between the elementary and the initial bodies of theRickettsiella genus is defined as the beginning of an intracellular cycle. It is characterized by several structural changes in the dense elementary body: the cytoplasm becomes less electron-dense; thus, the nucleoid and the ribosomes are visible. The inner layer of the cell-wall becomes progressively clearer and the trilamellar structure of the inner and outer membranes appears distinctly. Preinitial body is proposed as name of this stage of development.  相似文献   
92.
Summary Viable cerebellar perikarya of mixed cell type obtained from 7–9-day-old rats were maintained in monolayer culture for up to 12 days. During this time extensive neurite formation and outgrowth occurred. The large majority of the cells developing in culture were tentatively identified as granule neurons. This identification was based on the large number isolated from the starting tissue, and the cells general morphological features in culture such as perikaryal and nuclear size, the bipolar nature of neurite extension, and their migratory behaviour.D.N. Currie was supported by a grant from Hoechst Pharmaceuticals, Ld, U.K.J.C. was supported by an S.R.C. Grant to S.P.R. RoseThe authors would like to thank Kathleen Tear for excellent technical assistance and members of the Brain Research Group for helpful discussions.  相似文献   
93.
Summary The insulinemic response to 1 g of tolbutamide i.v. is greatly enhanced (+145%) after a 60-min infusion of the -lytic dihydrogenated ergot alkaloid, dihydroergocristine (83.3 m/min, corresponding to a total dose of 5 mg) in 7 healthy subjects. No differences are observed in the glycemic responses.Acknowledgment. The authors are grateful to Mr Franco Della Sala, M.D., for his skillful technical assistance.  相似文献   
94.
Summary In 10 human subjects plasma dopamine--hydroxylase activity was found in the adrenal vein blood to be as high as in the periphery of the circulation. Adrenaline concentration in the adrenal vein blood was in the mean 170 times, noradrenaline concentration 11 times and dopamine concentration little higher than levels in the periphery.This study was supported by the Deutsche Forschungsgemeinschaft.  相似文献   
95.
G A Hashim 《Nature》1975,256(5518):953-955
  相似文献   
96.
Isolation of immunogenic tumor cells by cell-affinity chromatography.   总被引:2,自引:0,他引:2  
J J Killion  G M Kollmorgen 《Nature》1976,259(5545):674-676
  相似文献   
97.
Summary The three enzymes of ethanol metabolism alcohol dehydrogenase, aldehyde dehydrogenase and acetyl-CoA synthetase in the obligate aerobic yeastRhodotorula gracilis are repressed by glucose and induced by C2 metabolic fuels with a regulatory pattern indicating a correlation in the control mechanisms. To try an identification of the molecular signals involved in the transmission of the inducing stimulus, experiments were carried out by blocking with 2 mM pyrazole the ethanol acetaldehyde metabolic step. Results indicate that ethanol is not specifically required as a molecular signal for induction.This work was supported by a grant from the Italian Consiglio Nazionale delle Ricerche.  相似文献   
98.
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   
99.
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   
100.
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   
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