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   2648835篇
  免费   197584篇
  国内免费   26918篇
耳鼻咽喉   34452篇
儿科学   76325篇
妇产科学   67420篇
基础医学   370038篇
口腔科学   75013篇
临床医学   253530篇
内科学   501426篇
皮肤病学   54780篇
神经病学   199322篇
特种医学   100448篇
外国民族医学   532篇
外科学   391747篇
综合类   101499篇
现状与发展   80篇
一般理论   750篇
预防医学   188916篇
眼科学   65210篇
药学   205929篇
  352篇
中国医学   23491篇
肿瘤学   162077篇
  2021年   32679篇
  2020年   22738篇
  2019年   28191篇
  2018年   36747篇
  2017年   29391篇
  2016年   30795篇
  2015年   38677篇
  2014年   51274篇
  2013年   64684篇
  2012年   90795篇
  2011年   97327篇
  2010年   58326篇
  2009年   52274篇
  2008年   84593篇
  2007年   88622篇
  2006年   89669篇
  2005年   86279篇
  2004年   78025篇
  2003年   73936篇
  2002年   70652篇
  2001年   130942篇
  2000年   134967篇
  1999年   113982篇
  1998年   32268篇
  1997年   28997篇
  1996年   28057篇
  1995年   26603篇
  1994年   24028篇
  1993年   21365篇
  1992年   83010篇
  1991年   79684篇
  1990年   76663篇
  1989年   73822篇
  1988年   67069篇
  1987年   65264篇
  1986年   61310篇
  1985年   58136篇
  1984年   42340篇
  1983年   35977篇
  1982年   19828篇
  1979年   37399篇
  1978年   25617篇
  1977年   21838篇
  1976年   19992篇
  1975年   21323篇
  1974年   25872篇
  1973年   24778篇
  1972年   23149篇
  1971年   21580篇
  1970年   20260篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.

Background

Whether prolonged operative time is an independent risk factor for subsequent surgical site infection (SSI) and periprosthetic joint infection (PJI) following total joint arthroplasty (TJA) remains a clinically significant and underexplored issue. The aim of this study is to investigate the association between operative time and the risk of subsequent SSI and PJI in patients undergoing primary TJA.

Methods

We retrospectively reviewed 17,342 primary unilateral total knee arthroplasty and total hip arthroplasty performed at a single institution between 2005 and 2016, with a minimum follow-up of 1 year. A multivariate logistic regression model was conducted to identify the association between operative time and the development of SSI within 90 days and PJI within 1 year.

Results

Overall, the incidence of 90-day SSI and 1-year PJI was 1.2% and 0.8%, respectively. Patients with an operative time of >90 minutes had a significantly higher incidence of SSI and PJI (2.1% and 1.4%, respectively) compared to cases lasting between 60 and 90 minutes (1.1% and 0.7%), and those lasting ≤60 minutes (0.9% and 0.7%, P < .01). In the multivariate model, the risk for infection increased by an odds ratio of 1.346 (95% confidential interval 1.114-1.627) for 90-day SSI and 1.253 (95% confidential interval 1.060-1.481) for 1-year PJI for each 20-minute increase in operative time.

Conclusion

In patients undergoing primary TJA, each 20-minute increase in operative time was associated with nearly a 25% increased risk of subsequent PJI. We advocate that surgeons pay close attention to this underappreciated risk factor while maintaining safe operative practices, which minimize unnecessary steps and wasted time in the operating room.  相似文献   
32.
33.
Objective: Associations between social networks and loneliness or social isolation are well established among older adults. Yet, limited research examines personal networks and participation on perceived loneliness and social isolation as distinct experiences among younger adults. Accordingly, we explore relationships among objective and subjective measures of personal networks with loneliness and isolation, comparing a younger and older cohort.

Methods: The UC Berkeley Social Networks Study offers unique cohort data on young (21–30 years old, n = 472) and late middle-age adults’ (50–70 years old, n = 637) personal network characteristics, social participation, network satisfaction, relationship status, and days lonely and isolated via online survey or in-person interview. Negative binomial regression models were used to examine associations between social network characteristics, loneliness, and isolation by age group.

Results: Young adults reported twice as many days lonely and isolated than late middle-age adults, despite, paradoxically, having larger networks. For young adults, informal social participation and weekly religious attendance were associated with fewer days isolated. Among late middle-age adults, number of close kin and relationship status were associated with loneliness. Network satisfaction was associated with fewer days lonely or isolated among both age groups.

Conclusion: Distinct network characteristics were associated with either loneliness or isolation for each cohort, suggesting network factors are independently associated with each outcome, and may fluctuate over time. Network satisfaction was associated with either loneliness or isolation among both cohorts, suggesting perceptions of social networks may be equally important as objective measures, and remain salient for loneliness and isolation throughout the life course.  相似文献   

34.
35.
Introduction: Significance testing for comparison of the baseline differences between the intervention arms has received a strong condemnation. The goal of this study was to assess the prevalence of randomized controlled trials (RCTs) comparing the baseline characteristics between intervention groups using significance tests in top ten impact factor dental journals.

Materials and methods: RCTs published in 10 high impact factor dental journals were searched in PubMed database. Literature search was limited to time duration of 5 years from September 2012 to August 2017.

Results: We analysed 521 RCTs after excluding 47 non-RCT articles from the total of 568 articles. Baseline demographic characteristics table was not reported in 45.9% of the RCTs and 26.2% of the RCTs did not report table of baseline clinical characteristics. In 38.9% of the studies, significance testing was employed to compare baseline differences between the intervention arms.

Conclusions: Many trials published in the reputed dental journals failed to follow the recommendations of CONSORT statement regarding reporting of baseline tables and avoiding comparison of baseline differences with significance test.  相似文献   
36.
37.

Background and aims

There is controversy on the potentially benign nature of metabolically healthy obesity (MHO), i.e., obese persons with few or no metabolic abnormalities. So far, associations between MHO and coronary artery calcification (CAC), a measure of subclinical atherosclerosis, have mainly been studied cross-sectionally in Asian populations. We assessed cross-sectional and longitudinal MHO CAC associations in a Caucasian population.

Methods and results

In the Heinz Nixdorf Recall Study, a population-based cohort study in Germany, CAC was assessed by electron-beam tomography at baseline and at 5-year follow-up. For cross-sectional and longitudinal analyses, we included 1585 participants free of coronary heart disease at baseline, with CAC measurements at baseline and at follow-up, and with either normal weight (BMI 18.5–24.9 kg/m2) or obesity (BMI ≥30.0 kg/m2) at baseline. We used four definitions of MHO. In our main analysis, we defined obese persons as metabolically healthy if they met ≤1 of the NCEP ATP III criteria for the definition of the metabolic syndrome – waist circumference was not taken into account because of collinearity with BMI.Persons with MHO had a higher prevalence of CAC than metabolically healthy normal weight (MHNW) persons (prevalence ratio = 1.59 (95% confidence interval 1.38–1.84) for the main analysis). Persons with MHO had slightly larger odds of CAC progression than persons with MHNW (odds ratios ranged from 1.17 (0.69–1.99) to 1.48 (1.02–2.13) depending on MHO definition and statistical approach).

Conclusion

Our analyses on MHO CAC associations add to the evidence that MHO is not a purely benign health condition.  相似文献   
38.
39.

Objectives

Post-thoracotomy pain leads to patient discomfort, pulmonary complications, and increased analgesic use. Intercostal nerve injury during thoracotomy or its entrapment during closure can contribute to post-thoracotomy pain. We hypothesized that a modified technique of posterolateral thoracotomy and closure, preserving the intercostal neurovascular bundle, would reduce acute and chronic post-thoracotomy pain.

Methods

We randomized 90 patients undergoing posterolateral thoracotomy for pulmonary resection at a tertiary level oncology center to standard posterolateral (control arm) or modified nerve-sparing thoracotomy. All patients received morphine via patient-controlled analgesia pumps. The primary outcome was the worst postoperative pain score in the first 3 postoperative days. Secondary outcomes included the average pain score and analgesic requirements in the first 3 postoperative days and the incidence of post-thoracotomy pain 6 months after surgery.

Results

No significant differences were seen between the groups in acute or chronic post-thoracotomy measured by the numeric rating scale. There was no difference seen in the worst (mean) postoperative pain scores (3.71 vs 3.83, difference 0.12; 99% confidence interval [CI], ?0.7 to +0.9; P = .7), average (mean) pain scores in the first 3 postoperative days (1.77 vs 1.85, difference 0.08; 99% CI, ?0.4 to +0.6; P = .69), mean consumption of morphine (mg/kg) (1.45 vs 1.40, difference ?0.05; 99% CI, ?0.4 to +0.3; P = .73), or incidence of chronic postoperative pain (37.8% vs 40%, difference 4.9%; 99% CI, ?22.8 to +30.7%; P = .73).

Conclusions

The modified nerve-sparing thoracotomy technique does not reduce post-thoracotomy pain compared with standard posterolateral thoracotomy.  相似文献   
40.
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