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   46367篇
  免费   3418篇
  国内免费   161篇
耳鼻咽喉   664篇
儿科学   1239篇
妇产科学   797篇
基础医学   6263篇
口腔科学   584篇
临床医学   4740篇
内科学   9780篇
皮肤病学   500篇
神经病学   4437篇
特种医学   1676篇
外科学   7717篇
综合类   846篇
现状与发展   1篇
一般理论   41篇
预防医学   3676篇
眼科学   599篇
药学   3159篇
中国医学   59篇
肿瘤学   3168篇
  2023年   269篇
  2022年   516篇
  2021年   1187篇
  2020年   666篇
  2019年   1095篇
  2018年   1307篇
  2017年   878篇
  2016年   1030篇
  2015年   1248篇
  2014年   1643篇
  2013年   2181篇
  2012年   3630篇
  2011年   3690篇
  2010年   2052篇
  2009年   1836篇
  2008年   3077篇
  2007年   3167篇
  2006年   3076篇
  2005年   3113篇
  2004年   2777篇
  2003年   2640篇
  2002年   2390篇
  2001年   431篇
  2000年   305篇
  1999年   400篇
  1998年   496篇
  1997年   432篇
  1996年   357篇
  1995年   341篇
  1994年   293篇
  1993年   267篇
  1992年   241篇
  1991年   214篇
  1990年   187篇
  1989年   178篇
  1988年   165篇
  1987年   148篇
  1986年   138篇
  1985年   127篇
  1984年   141篇
  1983年   113篇
  1982年   150篇
  1981年   154篇
  1980年   112篇
  1979年   81篇
  1978年   74篇
  1977年   82篇
  1976年   63篇
  1975年   61篇
  1973年   63篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
25.
26.
BACKGROUND: Physical activity is a healthful behavior that has promise for combating feelings of low energy and fatigue. Despite evidence suggesting that fatigue is a prodromal symptom of major cardiac events, improvements in feelings of energy and fatigue have largely been ignored by reviewers of cardiac rehabilitation literature who have focused on anxiety, depression and general measures of quality of life. DESIGN: A meta-analytical review. METHODS AND RESULTS: Computer databases were searched from January 1945 to May 2005 to identify relevant literature. A total of 36 studies consisting of 4765 subjects were included. Cardiac rehabilitation exercise programs were consistently associated with increases in energy and decreases in fatigue. The magnitude of the effect was moderately large (mean delta 0.51; 95% confidence interval 0.42-0.61) but was heterogeneous and modified by features of the research design. Comparison of effect sizes in cardiac rehabilitation studies concurrently measuring energy/fatigue, anxiety and depression suggest that exercise-based cardiac rehabilitation programs have larger effects on feelings of energy and fatigue compared with anxiety and depression. CONCLUSION: This review quantifies the potential benefit of cardiac rehabilitation exercise programs on feelings of energy and fatigue, and suggests that cardiac rehabilitation researchers and practitioners may benefit from examining, and perhaps even focusing on, feelings of energy and fatigue as an important outcome variable. A greater understanding of the effect of cardiac rehabilitation exercise programs on feelings of energy and fatigue will be reached when more true experiments are conducted thereby avoiding the primary limitation of the literature reviewed; that is, the frequent use of non-experimental research designs.  相似文献   
27.
Retinal fundus photographs are employed as standard diagnostic tools in ophthalmology. Serial photographs of the flow of fluorescein and indocyanine green (ICG) dye are used to determine the areas of the retinal lesions. For objective measurements of features, the registration of the images is a necessity. In this paper, we employ optimization techniques for registration with the help of 2-parameter translational motion model of retinal angiograms, based on non-linear pre-processing (Wiener filtering and morphological gradient) and computation of the similarity criteria for the alignment of the two gradient images for any given rigid transformation. The optimization methods are effectively employed to minimize the similarity criterion.

The presence of noise, the variations in the background and the temporal variation of the fluorescence level pose serious problems in obtaining a robust registration of the retinal images. Moreover, local search strategies are not robust in the case of ICG angiograms, even if one uses a multiresolution approach.

The present work makes a systematic comparison of different optimization techniques, namely the minimization method derived from the optical flow formulation, the Nelder-Mead local search and the HCIAC ant colony metaheuristic, each optimizing a similarity criterion for the gradient images. The impact of the resolution and median filtering of gradient image is studied and the robustness of the approaches is tested through experimental studies, performed on macular fluorescein and ICG angiographies.

Our proposed optimization techniques have shown interesting results especially for high resolution difficult registration problems. Moreover, this approach seems promising for affine (6-parameter motion model) or elastical registrations.  相似文献   

28.
29.
30.
We have noted that colons of patients prepared for colonoscopy with Golytely, a nonabsorbable electrolyte lavage solution, frequently contain foam which may obscure small mucosal lesions. Therefore, a randomized, blinded controlled trial was performed to determine the prevalence of Golytely-induced foam and the effect of supplemental simethicone in decreasing the prevalence of foam. Foam was present in 32% of colons prepared with Golytely alone but in none of the colons prepared with Golytely supplemented with simethicone. In addition, only 5% of colons prepared with supplemental simethicone had residual stool noted at the time of colonoscopy, a significant improvement over the 39% prevalence of residual stool in colons prepared with Golytely alone. Addition of simethicone to Golytely lavage decreases the prevalence of colonic foam and residual stool.  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