首页 | 官方网站   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   46471篇
  免费   3347篇
  国内免费   161篇
医药卫生   49979篇
  2023年   277篇
  2022年   517篇
  2021年   1177篇
  2020年   670篇
  2019年   1089篇
  2018年   1313篇
  2017年   891篇
  2016年   1036篇
  2015年   1250篇
  2014年   1656篇
  2013年   2193篇
  2012年   3642篇
  2011年   3718篇
  2010年   2068篇
  2009年   1852篇
  2008年   3091篇
  2007年   3182篇
  2006年   3103篇
  2005年   3133篇
  2004年   2798篇
  2003年   2640篇
  2002年   2389篇
  2001年   428篇
  2000年   311篇
  1999年   406篇
  1998年   495篇
  1997年   430篇
  1996年   352篇
  1995年   348篇
  1994年   298篇
  1993年   268篇
  1992年   248篇
  1991年   217篇
  1990年   194篇
  1989年   184篇
  1988年   180篇
  1987年   158篇
  1986年   138篇
  1985年   136篇
  1984年   143篇
  1983年   117篇
  1982年   150篇
  1981年   156篇
  1980年   108篇
  1979年   79篇
  1978年   74篇
  1977年   73篇
  1976年   66篇
  1975年   59篇
  1973年   62篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
6.
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   
7.
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   

8.
Abstract  The discipline of nursing is still struggling with the differences that need to be clearly defined between the notions of care and nursing care. To be able to clarify this distinction, agreement must first be reached on the meaning of care itself. The present article proposes a conception of care in light of the philosophy of Emmanuel Levinas (1906–1995). This philosopher's thought throws considerable light on the ontology of care, thanks especially to his focus on the deeper implications of human encounter. A profound sense of responsibility towards the other enables Levinas to bring out such dimensions of the concept of care as the relation involved, the feeling of affection, and the interventions. We examine here what these entail regarding nursing care.  相似文献   
9.
10.
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-23

京公网安备 11010802026262号