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   176692篇
  免费   11819篇
  国内免费   1349篇
耳鼻咽喉   2646篇
儿科学   3237篇
妇产科学   3975篇
基础医学   26562篇
口腔科学   3918篇
临床医学   16815篇
内科学   33660篇
皮肤病学   4930篇
神经病学   13274篇
特种医学   8971篇
外科学   23848篇
综合类   2262篇
现状与发展   6篇
一般理论   88篇
预防医学   10421篇
眼科学   4605篇
药学   14995篇
中国医学   1762篇
肿瘤学   13885篇
  2023年   1087篇
  2022年   3079篇
  2021年   5350篇
  2020年   2789篇
  2019年   4000篇
  2018年   4911篇
  2017年   3648篇
  2016年   4751篇
  2015年   6336篇
  2014年   7707篇
  2013年   9364篇
  2012年   14042篇
  2011年   13579篇
  2010年   8039篇
  2009年   6719篇
  2008年   10139篇
  2007年   9873篇
  2006年   9000篇
  2005年   8614篇
  2004年   7620篇
  2003年   6670篇
  2002年   5795篇
  2001年   4665篇
  2000年   4301篇
  1999年   3498篇
  1998年   1422篇
  1997年   1084篇
  1996年   1012篇
  1995年   917篇
  1994年   804篇
  1993年   703篇
  1992年   1677篇
  1991年   1692篇
  1990年   1460篇
  1989年   1329篇
  1988年   1240篇
  1987年   1106篇
  1986年   1087篇
  1985年   944篇
  1984年   685篇
  1983年   600篇
  1982年   427篇
  1981年   400篇
  1980年   359篇
  1979年   573篇
  1978年   444篇
  1977年   414篇
  1976年   362篇
  1975年   352篇
  1974年   387篇
排序方式: 共有10000条查询结果,搜索用时 15 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