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   1361948篇
  免费   96365篇
  国内免费   2974篇
耳鼻咽喉   20186篇
儿科学   41288篇
妇产科学   39535篇
基础医学   190801篇
口腔科学   40562篇
临床医学   114892篇
内科学   268238篇
皮肤病学   30848篇
神经病学   109051篇
特种医学   54490篇
外国民族医学   438篇
外科学   211458篇
综合类   31492篇
现状与发展   6篇
一般理论   476篇
预防医学   93983篇
眼科学   31897篇
药学   101540篇
  4篇
中国医学   2994篇
肿瘤学   77108篇
  2018年   12176篇
  2015年   12272篇
  2014年   17243篇
  2013年   26088篇
  2012年   34084篇
  2011年   36029篇
  2010年   21415篇
  2009年   20833篇
  2008年   34617篇
  2007年   37801篇
  2006年   38372篇
  2005年   37071篇
  2004年   36157篇
  2003年   35041篇
  2002年   34628篇
  2001年   64484篇
  2000年   66238篇
  1999年   56170篇
  1998年   14963篇
  1997年   13720篇
  1996年   13211篇
  1995年   12455篇
  1994年   11701篇
  1992年   43439篇
  1991年   41905篇
  1990年   41097篇
  1989年   40111篇
  1988年   37474篇
  1987年   36948篇
  1986年   35351篇
  1985年   33611篇
  1984年   25266篇
  1983年   21413篇
  1982年   12910篇
  1981年   11747篇
  1980年   10982篇
  1979年   24265篇
  1978年   17297篇
  1977年   15037篇
  1976年   13599篇
  1975年   15474篇
  1974年   18312篇
  1973年   17790篇
  1972年   17011篇
  1971年   15924篇
  1970年   15092篇
  1969年   14504篇
  1968年   13600篇
  1967年   12153篇
  1966年   11397篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Setting goals to maintain hope.   总被引:3,自引:0,他引:3  
  相似文献   
43.
44.
45.
46.
47.
BACKGROUND: The aim of this study was to estimate the cost effectiveness of screening for abdominal aortic aneurysm (AAA). MATERIAL AND METHODS: All 12,639 men born in the years 1921-1933 (aged 64-73) living in Viborg County, Denmark, were randomly allocated either to receive an invitation to abdominal ultrasound scanning for AAA or to be controls. Costs for screening and surveillance were assessed prospectively. Diagnosis Related Group (DRG) costs from 1999 were used concerning admissions with uncomplicated and complicated operations. Admissions for AAA surgery were retrospectively classified according to complications in patient records. RESULTS: Mean follow-up time was 52 months. 76.6% of invited men attended screening, and 191 (4.0%) had an AAA. As previously reported, the cumulative 5-year AAA-specific mortality in the invited group was significantly reduced by 67% compared to the control group (P = 0.003). The costs were estimated to be Euro 11.23 per scan. The costs per life-year saved were Euro 9057 (Euro 5872-20,063) after 5 years, and were expected to decrease to Euro 2708 (Euro 1758-6031) after 10 years and to Euro 1825 (Euro 1185-4063) after 15 years. CONCLUSION: Screening of 64-73 years old males in Denmark seems cost effective.  相似文献   
48.
49.
BACKGROUND: Three dimensional skin equivalents are widely used in dermatopharmacological and toxicological studies and as autologous transplants in wound healing. In pharmacology, there is tremendous need for monitoring the response of engineered skin equivalents to external treatment. Transplantation of skin equivalents for wound healing requires careful verification of their quality prior to transplantation. Optical coherence tomography (OCT) is a non-contact, non-destructive imaging technique for living tissues offering the potential to fulfill these needs. This work presents an analysis of OCT for high-resolution monitoring of skin equivalents at different stages during the culture process. METHODS: We developed a high-resolution OCT imaging setup based on a commercially available OCT system. A broadband femtosecond laser light source replaces the original superluminescence diode. Tomograms of living skin equivalents were recorded with an axial resolution of 3 mum and correlated with histology and immunofluorescence images. Comparison with standard low-resolution OCT is presented to emphasize the advantages of high-resolution OCT for this application. RESULTS: OCT is particularly able to distinguish between different layers of skin equivalents including stratum corneum, epidermal and dermal layer as well as the basement membrane zone. The high-resolution OCT scans correlate closely with two key benchmarks, histology and immunofluorescence imaging. CONCLUSIONS: This study clearly demonstrates the benefits of high-resolution OCT for identifying living tissue structure and morphology. Compared with the current gold standard histology, OCT offers non-destructive tissue imaging, enabling high-resolution evaluation of living tissue morphology and structure as it evolves.  相似文献   
50.
OBJECTIVE: To establish reference intervals for the fetal right, left and total lung volumes and heart volume between 12 and 32 weeks of gestation. METHODS: Fetal lung and heart volumes were measured using three-dimensional (3D) ultrasound in 650 normal singleton pregnancies at 12-32 weeks. The VOCAL (Virtual Organ Computer-aided AnaLysis) technique was used to obtain a sequence of six sections of each lung and the heart around a fixed axis, each after a 30 degrees rotation from the previous one. The rotation axis for the lungs extended from the apex to the upper limit of the diaphragm dome, and the rotation axis for the heart extended from its apex to its connection to the great vessels. The contour of each of these organs was drawn manually in the six different rotation planes to obtain the 3D volume measurement. In 60 cases the fetal lungs and heart volumes were measured by the same sonographer twice and also by a second sonographer once in order to compare the measurements and calculate intra- and interobserver agreement. RESULTS: The total lung volume and heart volume increased with gestation, from respective mean values of 1.6 and 0.6 mL at 12 weeks to 10.9 and 4.3 mL at 20 weeks and 49.3 and 26.6 mL at 32 weeks. The right to left lung volume ratio did not change significantly with gestation (median, 0.7), whereas the heart to total lung volume ratio increased with gestation from about 0.3 at 12 weeks to 0.5 at 32 weeks. In the Bland-Altman plot, the difference between paired measurements by two sonographers was, in 95% of the cases, less than 0.05, 0.5 and 1.9 mL for each lung at 12-13, 19-22 and 29-32 weeks, respectively, and the corresponding values for the heart volumes were 0.04, 0.4 and 2.3 mL. CONCLUSIONS: In normal fetuses the lung and heart volumes increase between 12 and 32 weeks of gestation. The extent to which in pathological pregnancies possible deviations in these measurements from normal prove to be useful in the prediction of outcome remains to be determined.  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