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   41881篇
  免费   15905篇
  国内免费   6篇
  57792篇
  2022年   178篇
  2021年   567篇
  2020年   2339篇
  2019年   3899篇
  2018年   4209篇
  2017年   4429篇
  2016年   4545篇
  2015年   4409篇
  2014年   4180篇
  2013年   4840篇
  2012年   2436篇
  2011年   2272篇
  2010年   3503篇
  2009年   2119篇
  2008年   1215篇
  2007年   880篇
  2006年   919篇
  2005年   867篇
  2004年   757篇
  2003年   800篇
  2002年   710篇
  2001年   645篇
  2000年   512篇
  1999年   374篇
  1998年   136篇
  1992年   243篇
  1991年   231篇
  1990年   188篇
  1989年   220篇
  1988年   237篇
  1987年   248篇
  1986年   222篇
  1985年   256篇
  1984年   207篇
  1983年   170篇
  1979年   245篇
  1978年   164篇
  1977年   145篇
  1976年   140篇
  1975年   171篇
  1974年   266篇
  1973年   265篇
  1972年   253篇
  1971年   242篇
  1970年   255篇
  1969年   246篇
  1968年   188篇
  1967年   186篇
  1966年   168篇
  1965年   123篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A fluorometric methods is described for determination of cardiac and urinary 3-methoxytyramine, a metabolite of dopamine. Methoxy metabolites were isolated on Amberlite CG-50 resin and oxidation to emitter form was performed with K3Fe(CN)6. Good specificity and sensitivity of determination, and a high recovery of 3-MT were obtained.  相似文献   
62.
63.
64.
65.
66.
For three types of self-sucking impellers (fourand six-pipe and disk impellers) mixing power, initial point, amount of gas leaving the impeller and mass transfer coefficient were determined experimentally. Investigations were performed for two systems: water and biomass solution.From the point of view of a minimum mixing power and maximum mass transfer coefficient the best impeller has been chosen. Fuzzy multiobjective optimization for determination of optimum operating conditions is proposed.List of Symbols c concentration of oxygen - D tank diameter - d impeller diameter - g acceleration of gravity - H height of liquid in the tank - H height of liquid above impeller, H=H-y - k consistency coefficient - k L a volumetric mass transfer coefficient - N rotational speed of impeller - n flow behaviour index - P mixing power for pure liquid - P G mixing power for aerated liquid - V G volumetric air flow rate - y distance of impeller from the tank bottom - v a apparent kinematic viscosity of liquid - density of liquid - time - gas hold-up - Eu=P/N 3 d 5 or EuG=P G /N 3 d 5 Euler Number for non-gassed or aerated liquid - Fr=N 2 d/g Froude Number - Fr*=N 2 d 2 /g(H -y) modified Froude Number - KG=V G /N d 3 gas flow number - Re=N d 2 /v a Reynolds Number - Sh=k K a/(g 2 /v a )1/3 Sherwood Number  相似文献   
67.
Summary Effect of LH, vinblastine and cytochalasin B on the cytoskeleton of cultured Leydig cells was investigated using monoclonal antibodies and fluorescence microscopy. After LH addition and treatment with cytoskeletal disrupting drugs, three main effects were observed: 1) increase of androgen level secreted by cultured mouse Leydig cells, 2) changes of cell-shape towards regular and rounded, 3) increase of 5,3-HSD activity. The results are discussed in respect to possible involvement of cytoskeleton in the regulation of steroidogenesis.  相似文献   
68.
The study involved 126 patients with cholelithiasis. Set of biochemical, radiological, endoscopic, and ultrasound examinations was carried out in these patients. Potential coincidence of clinical symptoms and causes of so-called postcholecystectomy syndrome was the purpose of a 1-year follow-up studies. The significance of the results are discussed.  相似文献   
69.
Monotherapy of hypertension with acebutolol in diabetics in daily dose of 200-400 mg for 6 weeks induced only non-significant and practically not acceptable hypotensive effect in groups of patients with hypertension and diabetes type I or type II without nephropathy. No therapeutical effect was observed in hypertension in diabetics type I with nephropathy. Administration of acebutolol to hypertensive diabetic patients with nephropathy resulted in tendency to increase in albuminuria. Values of creatinine clearance did not change at the same time. Also no effect of acebutolol on glycemic or lipid indices was observed. The lack of clear hypotensive effect under studied conditions of acebutolol in diabetic patients contrasted with its significant action in comparative group of hypertensive non-diabetic subjects.  相似文献   
70.
The tropharium of the common shorebug Saldula saltatoria consists of 2 zones: the apical mitotic region and the distal one comprising numerous mononucleate nurse cells. Each individual nurse cell is connected to the centrally located trophic core by a thin cytoplasmic projection referred to as a trophic process. The accumulations of a dense material interpreted as the remnants of intercellular bridge rim are observed associated with the trophic process membrane. In the light of these results the establishment of telotrophic ovarioles in hemipterans is 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