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   1515950篇
  免费   123127篇
  国内免费   3738篇
耳鼻咽喉   19787篇
儿科学   49356篇
妇产科学   42891篇
基础医学   214668篇
口腔科学   40234篇
临床医学   136878篇
内科学   306081篇
皮肤病学   35025篇
神经病学   127230篇
特种医学   57432篇
外国民族医学   468篇
外科学   226209篇
综合类   34549篇
现状与发展   4篇
一般理论   662篇
预防医学   120024篇
眼科学   34019篇
药学   106139篇
  3篇
中国医学   3505篇
肿瘤学   87651篇
  2021年   12567篇
  2019年   13383篇
  2018年   18531篇
  2017年   14204篇
  2016年   15944篇
  2015年   18053篇
  2014年   25532篇
  2013年   38011篇
  2012年   51956篇
  2011年   55083篇
  2010年   32220篇
  2009年   30977篇
  2008年   51228篇
  2007年   54202篇
  2006年   54724篇
  2005年   53331篇
  2004年   50910篇
  2003年   48706篇
  2002年   46810篇
  2001年   74060篇
  2000年   75376篇
  1999年   62651篇
  1998年   18496篇
  1997年   16665篇
  1996年   16574篇
  1995年   15764篇
  1994年   14199篇
  1993年   13402篇
  1992年   46517篇
  1991年   44079篇
  1990年   42084篇
  1989年   40118篇
  1988年   36696篇
  1987年   35850篇
  1986年   33376篇
  1985年   31892篇
  1984年   24557篇
  1983年   20778篇
  1982年   13210篇
  1981年   11697篇
  1979年   21123篇
  1978年   15108篇
  1977年   12588篇
  1976年   11773篇
  1975年   11996篇
  1974年   14316篇
  1973年   13830篇
  1972年   12858篇
  1971年   11616篇
  1970年   11053篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
Using data on waterfowl band recoveries, we identified spatially explicit hotspots of concentrated waterfowl movement to predict occurrence and spatial spread of a novel influenza A virus (clade 2.3.4.4) introduced from Asia by waterfowl from an initial outbreak in North America in November 2014. In response to the outbreak, the hotspots of waterfowl movement were used to help guide sampling for clade 2.3.4.4 viruses in waterfowl as an early warning for the US poultry industry during the outbreak . After surveillance sampling of waterfowl, we tested whether there was greater detection of clade 2.3.4.4 viruses inside hotspots. We found that hotspots defined using kernel density estimates of waterfowl band recoveries worked well in predicting areas with higher prevalence of the viruses in waterfowl. This approach exemplifies the value of ecological knowledge in predicting risk to agricultural security.  相似文献   
182.
183.
184.
185.
186.
187.
Pulse oximetry is used widely to titrate oxygen therapy and for triage in patients who are critically ill. However, there are concerns regarding the accuracy of pulse oximetry in patients with COVID-19 pneumonitis and in patients who have a greater degree of skin pigmentation. We aimed to determine the impact of patient ethnicity on the accuracy of peripheral pulse oximetry in patients who were critically ill with COVID-19 pneumonitis by conducting a retrospective observational study comparing paired measurements of arterial oxygen saturation measured by co-oximetry on arterial blood gas analysis (SaO2) and the corresponding peripheral oxygenation saturation measured by pulse oximetry (SpO2). Bias was calculated as the mean difference between SaO2 and SpO2 measurements and limits of agreement were calculated as bias ±1.96 SD. Data from 194 patients (135 White ethnic origin, 34 Asian ethnic origin, 19 Black ethnic origin and 6 other ethnic origin) were analysed consisting of 6216 paired SaO2 and SpO2 measurements. Bias (limits of agreement) between SaO2 and SpO2 measurements was 0.05% (−2.21–2.30). Patient ethnicity did not alter this to a clinically significant degree: 0.28% (1.79–2.35), −0.33% (−2.47–2.35) and −0.75% (−3.47–1.97) for patients of White, Asian and Black ethnic origin, respectively. In patients with COVID-19 pneumonitis, SpO2 measurements showed a level of agreement with SaO2 values that was in line with previous work, and this was not affected by patient ethnicity.  相似文献   
188.
189.

Background

Pump speed optimization in patients implanted with a ventricular assist device represents a major challenge during the follow-up period. We present our findings on whether combined invasive hemodynamic ramp tests and cardiopulmonary exercise testing (CPX) can help optimize patient management.

Methods

Eighteen patients implanted with a HeartMate 3 (HM3) device underwent ramp tests with right heart catheterization (including central venous pressure [CVP], pulmonary artery pressure, pulmonary capillary wedge pressure [PCWP], and blood pressure) and echocardiography. Data were recorded at up to 4 speed settings. Speed changes were in steps of 200 revolutions/min (rpm). Evaluation of functional capacity by CPX was conducted according to the modified Bruce protocol.

Results

Only 30% of patients had normal PCWPs at their original rpm settings. In going from lowest to highest speeds, cardiac output improved by 0.25 ± 0.35 L/min/step (total change, 1.28 ± 0.3 L/min), and PCWP decreased by 1.9 ± 0.73 mm Hg/step (total change, 6 ± 1.6 mm Hg). CVP and systolic blood pressure did not change significantly with rpm. The rpm assessment was adjusted based on test results to achieve CVPs and PCWPs as close to normal limits as possible, which was feasible in all patients. On CPX, all patients demonstrated good performance (peak VO2, 16.8 ± 3.5 mL/kg/min).

Conclusion

Hemodynamic ramp testing provides an objective means of optimizing rpm, and has the potential to provide good exercise tolerance.  相似文献   
190.
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