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   4836939篇
  免费   379990篇
  国内免费   16921篇
耳鼻咽喉   67804篇
儿科学   156285篇
妇产科学   129745篇
基础医学   731088篇
口腔科学   134039篇
临床医学   447982篇
内科学   873601篇
皮肤病学   116639篇
神经病学   400352篇
特种医学   186574篇
外国民族医学   826篇
外科学   729517篇
综合类   138426篇
现状与发展   23篇
一般理论   2810篇
预防医学   409862篇
眼科学   114582篇
药学   342033篇
  25篇
中国医学   13301篇
肿瘤学   238336篇
  2021年   56809篇
  2019年   59298篇
  2018年   76130篇
  2017年   57992篇
  2016年   64241篇
  2015年   76707篇
  2014年   111404篇
  2013年   177220篇
  2012年   142880篇
  2011年   152085篇
  2010年   132503篇
  2009年   131389篇
  2008年   136840篇
  2007年   146907篇
  2006年   154355篇
  2005年   148885篇
  2004年   148336篇
  2003年   137771篇
  2002年   126490篇
  2001年   180020篇
  2000年   176546篇
  1999年   160100篇
  1998年   74178篇
  1997年   69228篇
  1996年   67307篇
  1995年   62654篇
  1994年   56755篇
  1993年   52664篇
  1992年   117743篇
  1991年   114412篇
  1990年   110275篇
  1989年   106892篇
  1988年   98788篇
  1987年   96949篇
  1986年   91839篇
  1985年   89901篇
  1984年   73600篇
  1983年   65288篇
  1982年   50254篇
  1981年   46318篇
  1980年   43381篇
  1979年   64807篇
  1978年   51416篇
  1977年   44582篇
  1976年   42153篇
  1975年   42678篇
  1974年   48058篇
  1973年   46320篇
  1972年   43528篇
  1971年   40621篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
21.
22.
Journal of Behavioral Medicine - Evidence supports the use of graphic warnings to educate the public about the health harms of smoking and suggests warnings eliciting negative emotional responses...  相似文献   
23.
Noninvasive imaging of cardiac fibrosis is important for early diagnosis and intervention in chronic heart diseases. Here, we investigated whether noninvasive, contrast agent-free MRI T2-mapping can quantify myocardial fibrosis in preclinical models of aging and pressure overload. Myocardial fibrosis and remodeling were analyzed in two animal models: (i) aging (15-month-old male CF-1 mice vs. young 6- to 8-week-old mice), and (ii) pressure overload (PO; by transverse aortic constriction in 4- to 5-month-old male C57BL/6 mice vs. sham-operated for 14 days). In vivo T2-mapping was performed by acquiring data during the isovolumic and early diastolic phases, with a modified respiratory and ECG-triggered multiecho TurboRARE sequence on a 7-T MRI. Cine MRI provided cardiac morphology and function. A quantitative segmentation method was developed to analyze the in vivo T2-maps of hearts at midventricle, apex, and basal regions. The cardiac fibrosis area was analyzed ex vivo by picro sirius red (PSR) staining. Both aged and pressure-overloaded hearts developed significant myocardial contractile dysfunction, cardiac hypertrophy, and interstitial fibrosis. The aged mice had two phenotypes, fibrotic and mild-fibrotic. Notably, the aged fibrotic subgroup and the PO mice showed a marked decrease in T2 relaxation times (25.3 ± 0.6 in aged vs. 29.9 ± 0.7 ms in young mice, p = 0.002; and 24.3 ± 1.7 in PO vs. 28.7 ± 0.7 ms in shams, p = 0.05). However, no significant difference in T2 was detected between the aged mild-fibrotic subgroup and the young mice. Accordingly, an inverse correlation between myocardial fibrosis percentage (FP) and T2 relaxation time was derived (R2 = 0.98): T2 (ms) = 30.45 – 1.05 × FP. Thus, these results demonstrate a statistical agreement between T2-map–quantified fibrosis and PSR staining in two different clinically relevant animal models. In conclusion, T2-mapping MRI is a promising noninvasive contrast agent-free quantitative technique to characterize myocardial fibrosis.  相似文献   
24.
25.
Collagens are the most abundant proteins in the extracellular matrix. They provide a framework to build organs and tissues and give structural support to make them resistant to mechanical load and forces. Several intra‐ and extracellular modifications are needed to make functional collagen molecules, intracellular post‐translational modifications of proline and lysine residues having key roles in this. In this article, we provide a review on the enzymes responsible for the proline and lysine modifications, that is collagen prolyl 4‐hydroxylases, 3‐hydroxylases and lysyl hydroxylases, and discuss their biological functions and involvement in diseases.  相似文献   
26.
27.
28.
29.
Coronavirus disease-19 (COVID-19) caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is now a pandemic threat. This virus is supposed to be spread by human to human transmission. Cellular angiotensin-converting enzyme 2 (ACE2) is the receptor of SARS-CoV-2 which is identical or similar in different species of animals such as pigs, ferrets, cats, orangutans, monkeys, and humans. Moreover, a recent study predicted that dogs might be secondary hosts during the evolution of SARS-CoV-2 from bat to human. Therefore, there is a possibility of spreading SARS-CoV-2 through domestic pets. There are now many reports of SARS-CoV-2 positive cases in dogs, cats, tigers, lion, and minks. Experimental data showed ferrets and cats are highly susceptible to SARS-CoV-2 as infected by virus inoculation and can transmit the virus directly or indirectly by droplets or airborne routes. Based on these natural infection reports and experimental data, whether the pets are responsible for SARS-CoV-2 spread to humans; needs to be deeply investigated. Humans showing clinical symptoms of respiratory infections have been undergoing for the COVID-19 diagnostic test but many infected people and few pets confirmed with SARS-CoV-2 remained asymptomatic. In this review, we summarize the natural cases of SARS-CoV-2 in animals with the latest researches conducted in this field. This review will be helpful to think insights of SARS-CoV-2 transmissions, spread, and demand for seroprevalence studies, especially in companion animals.  相似文献   
30.
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