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   1431125篇
  免费   105430篇
  国内免费   3307篇
耳鼻咽喉   18672篇
儿科学   46818篇
妇产科学   41269篇
基础医学   202045篇
口腔科学   38010篇
临床医学   127422篇
内科学   286725篇
皮肤病学   33539篇
神经病学   117927篇
特种医学   54163篇
外国民族医学   464篇
外科学   211936篇
综合类   32999篇
现状与发展   3篇
一般理论   494篇
预防医学   111164篇
眼科学   31730篇
药学   99257篇
  38篇
中国医学   3354篇
肿瘤学   81833篇
  2021年   11198篇
  2019年   12262篇
  2018年   16777篇
  2017年   12846篇
  2016年   14425篇
  2015年   16188篇
  2014年   22771篇
  2013年   33698篇
  2012年   45786篇
  2011年   48332篇
  2010年   28385篇
  2009年   27243篇
  2008年   44682篇
  2007年   47208篇
  2006年   47774篇
  2005年   46240篇
  2004年   44124篇
  2003年   42073篇
  2002年   40540篇
  2001年   73254篇
  2000年   74838篇
  1999年   61805篇
  1998年   17107篇
  1997年   15521篇
  1996年   15678篇
  1995年   14874篇
  1994年   13483篇
  1993年   12648篇
  1992年   46032篇
  1991年   43666篇
  1990年   41668篇
  1989年   39722篇
  1988年   36319篇
  1987年   35509篇
  1986年   33028篇
  1985年   31430篇
  1984年   23946篇
  1983年   20129篇
  1982年   12295篇
  1981年   10845篇
  1979年   20840篇
  1978年   14647篇
  1977年   12165篇
  1976年   11430篇
  1975年   11684篇
  1974年   14074篇
  1973年   13618篇
  1972年   12717篇
  1971年   11558篇
  1970年   10989篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Vinylogous (Groups III and V ) and acetylenologous (Group IV ) analogs of the classical β-adrenergic agents — stimulants and blockers — were prepared in order to evaluate the effect of degree of saturation, position of unsaturation and rigidity of the chain linking the aromatic ring and the amino containing functional group on biological activity. Derivatives from Group III , which represent 4-aryl-3-butenyl-2-ol-amine analogs of Group II , retained β1-adrenoceptor antagonist activity albeit substantially less potent (50–200-fold) than that possessed by their aryloxy counterparts. Consistent with the SAR for Group II compounds, substitution at position 2 of the aromatic ring yielded the most potent antagonists ( 5a, 5d, 5g ), with KB's ranging from 73–93 nM while 3,4-dichloro substitution ( 5e ) markedly reduced antagonist potency (KB = 2,400 nM). Agonist activity was also noted for 5b and 5d , suggesting that these compounds may be best classified as partial agonists. Representatives from Groups IV and V were inactive as antagonists at the β1-adrenoceptor confirming the importance of the spatial relationship between the hydroxyl and the amino nitrogen.  相似文献   
112.
The adult mammalian central nervous system (CNS) lacks the capacity to support axonal regeneration. There is increasing evidence to suggest that astrocytes, the major glial population in the CNS, may possess both axon-growth promoting and axon-growth inhibitory properties and the latter may contribute to the poor regenerative capacity of the CNS. In order to examine the molecular differences between axon-growth permissive and axon-growth inhibitory astrocytes, a panel of astrocyte cell lines exhibiting a range of axon-growth promoting properties was generated and analysed. No clear correlation was found between the axon-growth promoting properties of these astrocyte cell lines with: (i) the expression of known neurite-outgrowth promoting molecules such as laminin, fibronectin andN-cadherin; (ii) the expression of known inhibitory molecules such tenascin and chondroitin sulphate proteoglycan; (iii) plasminogen activator and plasminogen activator inhibitor activity; and (iv) growth cone collapsing activity. EM studies on aggregates formed from astrocyte cell lines, however, revealed the presence of an abundance of extracellular matrix material associated with the more inhibitory astrocyte cell lines. When matrix deposited by astrocyte cell lines was assessed for axon-growth promoting activity, matrix from permissive lines was found to be a good substrate, whereas matrix from the inhibitory astrocyte lines was a poor substrate for neuritic growth. Our findings, taken together, suggest that the functional differences between the permissive and the inhibitory astrocyte cell lines reside largely with the ECM.  相似文献   
113.
We describe a mild form of drug-induced pemphigus in a woman with essential arterial hypertension treated with captopril. Complete recovery was observed three weeks after the therapy had been discontinued.  相似文献   
114.
. Neutrophil-mediated tissue damage has been implicated in the pathogenesis of diarrhoea-associated haemolytic uraemic syndrome (D+ HUS). This study evaluates priming and activation of the neutrophil oxidative burst in D+ HUS using chemiluminescent techniques. Peripheral blood neutrophils from 11 children with acute D+ HUS were examined. No difference was found in the oxidative burst of neutrophils from patients and controls. Serum elastase levels were measured in 8 patients and found to be significantly elevated. Although elastase results suggest neutrophil activation, chemiluminescence studies do not confirm this in the peripheral blood neutrophil. This does not support a significant role for circulating agents in priming and activating the peripheral blood neutrophil. Received August 17, 1995; received in revised form and accepted November 27, 1995  相似文献   
115.
116.
The introduction of new diagnostic tools for neuroimaging has resulted in the early recognition of congenital brain tumors. In the present report we describe a personal series of 39 children and an International Multicenter Series of 876 children with brain tumors, in whom the diagnosis was obtained during the first 12 months of life. Most of the tumors were located within the supratentorial compartment. In spite of a relatively high operative mortality, surgery still appears to be the more effective therapy. Radiotherapy in this age group is of a scarce value, due to the vulnerability of the infantile brain. At the present time, chemotherapy still plays a controversial role.  相似文献   
117.
The role of caffeine or coffee in causing or promoting the incidence of serious disease is equivocal. Two design factors may account for the discrepancies in reported findings on the effects of coffee drinking: (a) imprecision of measurement and (b) confounding variables. A study of 2,714 white U.S. adults disclosed that, of 32 risk factors analyzed by linear and logistic regression, only sex and cigarette smoking were found to be important potential confounders of caffeine and coffee intake. Partial R2 values of the other 30 risk factors were relatively small and were inconsistent for each sex. It is unlikely that any of these factors could explain any of the reported associations between caffeine or coffee consumption and certain diseases. However, certain weak associations with caffeine or coffee intake should be included in the study design when they are known to be risk factors of a disease under investigation. These factors for men are dietary fat intake, vitamin C intake, and body mass index; and for women are vitamin use, alcohol intake, stress, and perceived health status.  相似文献   
118.
119.
120.
During recent decades there has been a controversial discussion if comparable plasma level profiles which are rather constant or those which show a high peak are more efficient for the cure of gonorrhoea. So far, investigations in this field were not based on the Grasso apparatus. Although the findings with cefotiam and ceftizoxime do not allow to formulate a general hypothesis without any restriction, it can be stated that on the basis of an identical area under the antibiotic level time curve, 'peak concentration' profiles are more favourable.  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