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   181149篇
  免费   12178篇
  国内免费   1444篇
耳鼻咽喉   2667篇
儿科学   3322篇
妇产科学   4029篇
基础医学   27133篇
口腔科学   4050篇
临床医学   17263篇
内科学   34744篇
皮肤病学   4959篇
神经病学   13594篇
特种医学   9239篇
外国民族医学   2篇
外科学   24432篇
综合类   2394篇
现状与发展   6篇
一般理论   88篇
预防医学   10811篇
眼科学   4755篇
药学   15314篇
  1篇
中国医学   1826篇
肿瘤学   14142篇
  2023年   1130篇
  2022年   3196篇
  2021年   5523篇
  2020年   2885篇
  2019年   4118篇
  2018年   5059篇
  2017年   3730篇
  2016年   4897篇
  2015年   6490篇
  2014年   7913篇
  2013年   9611篇
  2012年   14444篇
  2011年   13902篇
  2010年   8174篇
  2009年   6876篇
  2008年   10383篇
  2007年   10072篇
  2006年   9203篇
  2005年   8827篇
  2004年   7812篇
  2003年   6851篇
  2002年   5959篇
  2001年   4789篇
  2000年   4426篇
  1999年   3609篇
  1998年   1476篇
  1997年   1122篇
  1996年   1050篇
  1995年   945篇
  1994年   827篇
  1993年   722篇
  1992年   1703篇
  1991年   1729篇
  1990年   1484篇
  1989年   1355篇
  1988年   1269篇
  1987年   1125篇
  1986年   1113篇
  1985年   964篇
  1984年   701篇
  1983年   619篇
  1982年   440篇
  1981年   412篇
  1980年   370篇
  1979年   588篇
  1978年   454篇
  1977年   418篇
  1976年   371篇
  1975年   360篇
  1974年   396篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
1.
2.

Physical activity brings significant health benefits to middle-aged adults, although the research to date has been focused on late adulthood. This study aims to examine how ageing affects the self-reported and accelerometer-derived measures of physical activity levels in middle-aged adults. We employed the data recorded in the UK Biobank and analysed the physical activity levels of 2,998 participants (1381 men and 1617 women), based on self-completion questionnaire and accelerometry measurement of physical activity. We also assessed the musculoskeletal health of the participants using the dual-energy X-ray absorptiometry (DXA) measurements provided by the UK Biobank. Participants were categorised into three groups according to their age: group I younger middle-aged (40 to 49 years), group II older middle-aged (50 to 59 years), and group III oldest middle-aged (60 to 69 years). Self-reported physical activity level increased with age and was the highest in group III, followed by group II and I (P?<?0.05). On the contrary, physical activity measured by accelerometry decreased significantly with age from group I to III (P?<?0.05), and the same pertained to the measurements of musculoskeletal health (P?<?0.05). It was also shown that middle-aged adults mostly engaged in low and moderate intensity activities. The opposing trends of the self-reported and measured physical activity levels may suggest that middle-aged adults over-report their activity level as they age. They should be aware of the difference between their perceived and actual physical activity levels, and objective measures would be useful to prevent the decline in musculoskeletal health.

  相似文献   
3.
4.
5.
6.
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   
7.
8.
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