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   24434篇
  免费   150篇
  国内免费   119篇
系统科学   207篇
丛书文集   111篇
教育与普及   51篇
理论与方法论   96篇
现状及发展   10733篇
研究方法   988篇
综合类   12240篇
自然研究   277篇
  2013年   146篇
  2012年   482篇
  2011年   715篇
  2010年   148篇
  2008年   356篇
  2007年   441篇
  2006年   425篇
  2005年   600篇
  2004年   866篇
  2003年   838篇
  2002年   543篇
  2001年   762篇
  2000年   827篇
  1999年   541篇
  1992年   439篇
  1991年   347篇
  1990年   401篇
  1989年   369篇
  1988年   395篇
  1987年   389篇
  1986年   330篇
  1985年   489篇
  1984年   385篇
  1983年   309篇
  1982年   319篇
  1981年   302篇
  1980年   338篇
  1979年   778篇
  1978年   631篇
  1977年   530篇
  1976年   528篇
  1975年   533篇
  1974年   580篇
  1973年   512篇
  1972年   598篇
  1971年   675篇
  1970年   801篇
  1969年   635篇
  1968年   688篇
  1967年   645篇
  1966年   569篇
  1965年   396篇
  1964年   141篇
  1959年   188篇
  1958年   349篇
  1957年   228篇
  1956年   207篇
  1955年   183篇
  1954年   155篇
  1948年   141篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
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   
162.
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   
163.
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   
164.
Summary Prostaglandin (PG) release was measured from the isolated perfused rabbit heart. The effects of -adrenergic stimulation and blockade suggest that PG synthesis is regulated in part by adrenergic mechanisms.  相似文献   
165.
Summary Rats given aluminium hydroxide after cold-restraint stress but before the post-stress delay period, ulcerated significantly less severely and less frequently than rats given the drug before cold-restraint stress or those given water at either time period. Both aluminium hydroxide treated groups exhibited less ulceration than non-drug groups. These data suggest profound parasympathetic and hence, gastric acid, involvement in restraint delay-induced ulceration in rats.  相似文献   
166.
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   
167.
Summary The activity of (Na++K+)-ATPase and acetylcholine esterase were folloed in rat brain cerebral cortex, caudate, thalamus, hippocampus and medulla after i.v. administration of physostigmine. Both enzymes were found to be inhibited in a dose-dependent manner. The most pronounced inhibition of (Na++K+)-ATPase was found in caudate. where the highest activity of acetylcholine esterase is found.These studies were supported by a grant from the Union of Science of Republic Serbia, No. 40404-14.  相似文献   
168.
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   
169.
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   
170.
Summary In the sandal plant affected by spike disease, caused by mycoplasma-like organisms, the changes occurring in the 5-and 3-nucleotidase activities were studied and their possible significance discussed.  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