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   27708篇
  免费   141篇
  国内免费   292篇
系统科学   443篇
丛书文集   409篇
教育与普及   90篇
理论与方法论   91篇
现状及发展   11108篇
研究方法   1122篇
综合类   14242篇
自然研究   636篇
  2013年   307篇
  2012年   629篇
  2011年   1241篇
  2010年   424篇
  2009年   402篇
  2008年   685篇
  2007年   805篇
  2006年   803篇
  2005年   722篇
  2004年   551篇
  2003年   473篇
  2002年   517篇
  2001年   824篇
  2000年   851篇
  1999年   595篇
  1992年   471篇
  1991年   401篇
  1990年   422篇
  1989年   386篇
  1988年   374篇
  1987年   405篇
  1986年   372篇
  1985年   460篇
  1984年   430篇
  1983年   304篇
  1982年   321篇
  1981年   313篇
  1980年   344篇
  1979年   803篇
  1978年   647篇
  1977年   589篇
  1976年   521篇
  1975年   557篇
  1974年   682篇
  1973年   572篇
  1972年   570篇
  1971年   684篇
  1970年   813篇
  1969年   639篇
  1968年   682篇
  1967年   695篇
  1966年   614篇
  1965年   462篇
  1964年   200篇
  1959年   238篇
  1958年   387篇
  1957年   272篇
  1956年   220篇
  1955年   231篇
  1954年   204篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
181.
The spontaneous conversion of mammalian cyclic GMP-dependent protein kinase (G-PK) into modulator-dependent protein kinase (type II) (M-PKII) in the absence of cGMP or histone was observed in vitro. The findings, together with similarity in substrate protein specificity, suggest that M-PKII is the catalytic subunit of mammalian G-PK.  相似文献   
182.
M T Lin  A Chandra  Y F Chern  B L Tsay 《Experientia》1980,36(9):1077-1078
At ambient temperatures (Ta) of both 8 and 22 degrees C, intraventricular administration of TRH (10-80 microgram) produced a dose-dependent hypothermia in rats. The hypothermia was due to both decreased metabolic heat production and cutaneous vasodilatation. In contrast, at 30 degrees C Ta, TRH increased metabolic heat production (due to behavioral excitation) and led to hyperthermia.  相似文献   
183.
Summary Silver-staining has been used to identify the nucleolus organizer regions (NORs) in the bharal. These show homology with sheep, goat, cattle and aoudad. The association of the NORs on both telomeres of chromosome 3 results in a ring chromosome.  相似文献   
184.
Summary Amylase, - and -glucosidase, - and -galactosidase, -fructosidase, trypsin, aminotripeptidase, leucine-aminopeptidase, prolinase, prolidase glycyl-L-leucine dipeptidase and glycylglycine dipeptidase are present in the 3rd instar larvae ofChilo auricilius.Dr Kishan Singh, Indian Institute of Sugarcane Research, Lucknow, is gratefully acknowledged for providing necessary facilities.  相似文献   
185.
Summary The hemolymph volume ofHeliothis zea larvae was determined by the amaranth dye method and found to vary from 28 to 288 l. It averaged 30.6% of b.wt, a value comparable to that obtained with C14 inulin. Amaranth became evenly distributed in the hemocoele in 3–5 min.  相似文献   
186.
Summary A statistically significant decrease of prealbumin and statistically significant increases of alpha2-macroglobulin and IgA were found in blood plasma of patients with Down's syndrome using quantitative crossed immunoelectrophoresis.We are indebted to Prof. T.C. Bøg-Hansen, University of Copenhagen, for the helpful discussion of our results.  相似文献   
187.
Summary Contrary to the techniques of mere association, column chromatography has revealed a protoreceptor that accepts aldosterone agonists and antagonists only in the physiological target, the kidney, and is absent in non-targets, liver and serum; it is furthermore different from the aldosterone specific receptor in renal cytosol.Supported in part by grants from the CNRS AI 03 1917 and UER Broussais Hôtel Dieu.  相似文献   
188.
K R Dumbell  L C Archard 《Nature》1980,286(5768):29-32
Monkeypox mutants arising spontaneously or after serial, high multiplicity passage were characterized phenotypically and by restriction endonuclease mapping. Some resemble "whitepox" and variola viruses in several of the markers tested but all are distinguishable phenotypically from these. None resembles "whitepox" viruses in genome structure although near-terminal deletions or symmetrical, terminal rearrangements, relative to parental monkeypox, occurred. "Whitepox" viruses isolated from animals closely resemble variola in both phenotype and genome structure.  相似文献   
189.
Summary Furocaulerpin, an acetylenic sesquiterpenoid possessing a furan ring, has been isolated from the marine algaCaulerpa prolifera, and its stereostructure elucidated mainly on the basis of physico-chemical data.This work was carried out in the frame work of the Progetto Finalizzato per l'Oceanografia e i Fondi Marini, CNR, Rome. Thanks are due to the Centro di Metodologie Chimico-Fisiche of the University of Naples (Mr I. Giudicianni) for the determination of PMR-spectra.  相似文献   
190.
Summary Isonicotinic acid hydrazide (isoniazid) was shown to react readily with 17-ethinyl-17-hydroxyestr-4-en-3-one (norethindrone) to form the isonicotinyl hydrazone of the steroid under conditions likely to exist in the stomach. The hydrazone was detected in guinea-pig, but not rat, plasma following its oral administration. Rat liver tissue metabolized the compound more rapidly than guinea-pig liver in vitro which probably accounts for the failure to detect the hydrazone in rat plasma.  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