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   82891篇
  免费   8180篇
  国内免费   155篇
耳鼻咽喉   1181篇
儿科学   2488篇
妇产科学   1790篇
基础医学   11862篇
口腔科学   1999篇
临床医学   10173篇
内科学   14612篇
皮肤病学   1295篇
神经病学   6763篇
特种医学   2754篇
外国民族医学   10篇
外科学   11423篇
综合类   1659篇
一般理论   67篇
预防医学   9487篇
眼科学   1851篇
药学   6781篇
  1篇
中国医学   77篇
肿瘤学   4953篇
  2021年   1120篇
  2020年   745篇
  2019年   1126篇
  2018年   1399篇
  2017年   1006篇
  2016年   1096篇
  2015年   1252篇
  2014年   1638篇
  2013年   2583篇
  2012年   3485篇
  2011年   3761篇
  2010年   1996篇
  2009年   1917篇
  2008年   3234篇
  2007年   3553篇
  2006年   3425篇
  2005年   3488篇
  2004年   3263篇
  2003年   3029篇
  2002年   2963篇
  2001年   2713篇
  2000年   2828篇
  1999年   2503篇
  1998年   1062篇
  1997年   873篇
  1996年   860篇
  1995年   775篇
  1994年   802篇
  1993年   733篇
  1992年   2093篇
  1991年   2018篇
  1990年   1893篇
  1989年   1855篇
  1988年   1763篇
  1987年   1773篇
  1986年   1678篇
  1985年   1660篇
  1984年   1384篇
  1983年   1254篇
  1982年   836篇
  1981年   713篇
  1979年   1212篇
  1978年   871篇
  1977年   759篇
  1976年   714篇
  1975年   713篇
  1974年   859篇
  1973年   752篇
  1972年   733篇
  1971年   640篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
A combination of medial temporal lobe atrophy, shown by computed tomography, and reduced blood flow in the parietotemporal cortex, shown by single photon emission tomography, was found in 86% (44/51) of patients with a clinical diagnosis of senile dementia of the Alzheimer type (SDAT). The same combination of changes was found in four out of 10 patients with other clinical types of dementia and in two out of 18 with no evidence of cognitive deficit. Of the 12 patients who died, 10 fulfilled histopathological criteria for Alzheimer's disease, nine of them having a clinical diagnosis of SDAT, and one a clinical diagnosis of multi-infarct dementia. All 10 patients with histopathologically diagnosed Alzheimer's disease had shown a combination of hippocampal atrophy and reduced parietotemporal blood flow in life. In 10 patients (nine with SDAT) out of 12 in whom the hippocampal atrophy was more noticeable on one side of the brain than on the other the parietotemporal perfusion deficit was also asymmetrical, being greater on the side showing more hippocampal atrophy. These results suggest that the combination of atrophy of the hippocampal formation and reduced blood flow in the parietotemporal region is a feature of dementia of the Alzheimer type and that the functional change in the parietotemporal region might be related to the loss of the projection neurons in the parahippocampal gyrus that innervate this region of the neocortex.  相似文献   
105.
Sister chromatid exchange (SCE) and lymphocyte proliferation were studied in peripheral lymphocyte cultures derived from 5 patients with Alzheimer disease (AD), 5 control elderly subjects and 5 young donors. These parameters did not differ significantly between the AD group and the elderly control group, but higher SCE frequency and less intensive proliferation were observed in the AD group and in the elderly control group when compared to the young donors.  相似文献   
106.
107.
OBJECTIVES: The first democratic government elected in South Africa in 1994 inherited huge inequities in health status and health provision across all sections of the population. This study set out to assess the impact of the new government's commitment to address these inequities and implement policies to improve population health in general and address inequalities in health care in particular. DESIGN: A 1998 household survey assessed many aspects of health delivery, including their own perceived and actual access to health care among different segments of South African society. RESULTS: Race was the main predictor of perceived changes in access to health care, with black, coloured-and Indian respondents significantly more likely to feel that access had improved since 1994, compared with white respondents. Socio-economic status (SES) was the main predictor of actual access to health care, with low and middle SES classes significantly less likely to access care when ill. CONCLUSIONS: One-third of respondents perceived health care access to have improved between 1994 and 1998, and this response was partially determined along racial lines. About one-quarter reported an inability to access health care when they required it, and this response was partially determined along socio-economic lines. This set of contrasting responses suggests that at a political level perceptions are largely influenced by race, but at the operational level actual access is influenced by SES.  相似文献   
108.
Gene amplification is an important mechanism of increased gene expression in a number of human solid tumors. We have recently identified and cloned sequences from a novel DNA amplification unit in malignant fibrous histiocytoma. The amplified sequences are derived from chromosome 12q13-14 and encode a gene designated SAS (sarcoma amplified sequence). In the present study, a series of soft tissue sarcomas was studied to characterize further the phenomenon of SAS amplification. Seven of 22 (32%) malignant fibrous histiocytomas and three liposarcomas contained SAS amplification. Strikingly, all of the tumors with SAS amplification occurred in central sites (i.e., in the abdominal or inguinal regions) rather than in the extremities (i.e., in the arms of legs). These observations demonstrate that SAS amplification occurs with a significant frequency in mesenchymal tumors and is particularly associated with abdominal disease.  相似文献   
109.
BACKGROUND: Transplantation for patients with a high pulmonary vascular resistance (PVR) carries an increased risk of mortality and right heart failure following heart transplantation and continues to be a major problem. We evaluated the use of hearts from patients who underwent heart and lung transplantation for primary pulmonary hypertension (PPH) as part of a domino procedure because these hearts have hypertrophied right ventricles used to increased pulmonary pressures, but could have a compromised left ventricle or irreversible damage of the right ventricle. METHODS: We reviewed 12 patients with PVR >4 Wood units who underwent orthotopic heart transplantation between 1989 and 1998 using hearts from donors with PPH as part of a domino procedure. RESULTS: We studied 10 men and 2 women, mean age 42.9 years. Mean PVR was 5.3 (range, 4-9) Wood units. Mean ischemia time was 85.3 minutes, and mean donor age was 32 years. Actuarial survival was 75% at 1 year and 75% at 5 years. In the early post-operative period, 3 patients had temporary arrhythmias, 2 required permanent pacemaker implantation, 1 had atrial fibrillation, and 1 had ventricular tachycardia that required defibrillator implantation. At a mean follow-up of 7.8 years, 2 patients had developed asymptomatic transplant coronary disease (both at 8.5 years after transplantation), 1 moderate and 1 very mild; the rest had none. Mean left ventricular ejection fraction at latest follow-up was 70.1% (range, 63%-78%). Right ventricular function assessed clinically and by echocardiography was adequate in the short and long term. CONCLUSIONS: Our results suggest that heart and lung recipients with PPH can provide useful donor hearts to patients with increased PVR and that these hearts function well in the intermediate and long term.  相似文献   
110.
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