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   264782篇
  免费   54803篇
  国内免费   3400篇
耳鼻咽喉   3839篇
儿科学   7591篇
妇产科学   4612篇
基础医学   42195篇
口腔科学   8644篇
临床医学   31309篇
内科学   55974篇
皮肤病学   11795篇
神经病学   25841篇
特种医学   11610篇
外国民族医学   7篇
外科学   37529篇
综合类   9380篇
现状与发展   16篇
一般理论   102篇
预防医学   17023篇
眼科学   6187篇
药学   23048篇
  34篇
中国医学   5019篇
肿瘤学   21230篇
  2023年   1201篇
  2022年   3912篇
  2021年   7628篇
  2020年   8373篇
  2019年   14466篇
  2018年   14760篇
  2017年   14841篇
  2016年   16325篇
  2015年   18224篇
  2014年   19880篇
  2013年   22042篇
  2012年   19699篇
  2011年   19447篇
  2010年   17982篇
  2009年   13023篇
  2008年   13559篇
  2007年   12261篇
  2006年   11296篇
  2005年   10448篇
  2004年   9107篇
  2003年   8182篇
  2002年   7222篇
  2001年   5971篇
  2000年   5327篇
  1999年   3914篇
  1998年   1566篇
  1997年   1218篇
  1996年   1126篇
  1995年   1015篇
  1994年   885篇
  1993年   732篇
  1992年   1669篇
  1991年   1646篇
  1990年   1403篇
  1989年   1291篇
  1988年   1187篇
  1987年   1055篇
  1986年   1035篇
  1985年   902篇
  1984年   656篇
  1983年   574篇
  1982年   402篇
  1981年   385篇
  1980年   343篇
  1979年   544篇
  1978年   413篇
  1977年   390篇
  1976年   346篇
  1974年   360篇
  1973年   328篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.

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   
2.
3.
4.
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   
5.
ObjectiveSpinal cord stimulation (SCS) is an effective treatment in failed back surgery syndrome (FBSS). We studied the effect of preimplantation opioid use on SCS outcome and the effect of SCS on opioid use during a two-year follow-up period.Materials and methodsThe study cohort included 211 consecutive FBSS patients who underwent an SCS trial from January 1997 to March 2014. Participants were divided into groups, which were as follows: 1) SCS trial only (n = 47), 2) successful SCS (implanted and in use throughout the two-year follow-up period, n = 131), and 3) unsuccessful SCS (implanted but later explanted or revised due to inadequate pain relief, n = 29). Patients who underwent explantation for other reasons (n = 4) were excluded. Opioid purchase data from January 1995 to March 2016 were retrieved from national registries.ResultsHigher preimplantation opioid doses associated with unsuccessful SCS (ROC: AUC = 0.66, p = 0.009), with 35 morphine milligram equivalents (MME)/day as the optimal cutoff value. All opioids were discontinued in 23% of patients with successful SCS, but in none of the patients with unsuccessful SCS (p = 0.004). Strong opioids were discontinued in 39% of patients with successful SCS, but in none of the patients with unsuccessful SCS (p = 0.04). Mean opioid dose escalated from 18 ± 4 MME/day to 36 ± 6 MME/day with successful SCS and from 22 ± 8 MME/day to 82 ± 21 MME/day with unsuccessful SCS (p < 0.001).ConclusionsHigher preimplantation opioid doses were associated with SCS failure, suggesting the need for opioid tapering before implantation. With continuous SCS therapy and no explantation or revision due to inadequate pain relief, 39% of FBSS patients discontinued strong opioids, and 23% discontinued all opioids. This indicates that SCS should be considered before detrimental dose escalation.  相似文献   
6.
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