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   1027307篇
  免费   66594篇
  国内免费   1342篇
耳鼻咽喉   13648篇
儿科学   27655篇
妇产科学   24720篇
基础医学   144305篇
口腔科学   28781篇
临床医学   86468篇
内科学   202519篇
皮肤病学   19665篇
神经病学   81862篇
特种医学   41059篇
外国民族医学   79篇
外科学   168501篇
综合类   18844篇
现状与发展   1篇
一般理论   234篇
预防医学   70361篇
眼科学   22279篇
药学   77548篇
  3篇
中国医学   2167篇
肿瘤学   64544篇
  2018年   19943篇
  2017年   15957篇
  2016年   18449篇
  2015年   9240篇
  2014年   12281篇
  2013年   17758篇
  2012年   27117篇
  2011年   34804篇
  2010年   22588篇
  2009年   20099篇
  2008年   34750篇
  2007年   38257篇
  2006年   26721篇
  2005年   27436篇
  2004年   27049篇
  2003年   27288篇
  2002年   25602篇
  2001年   55025篇
  2000年   57059篇
  1999年   47151篇
  1998年   10920篇
  1997年   9721篇
  1996年   9748篇
  1995年   9091篇
  1994年   8445篇
  1993年   7728篇
  1992年   35626篇
  1991年   34057篇
  1990年   32875篇
  1989年   31994篇
  1988年   29098篇
  1987年   28369篇
  1986年   26396篇
  1985年   25250篇
  1984年   17907篇
  1983年   15215篇
  1982年   7884篇
  1981年   6786篇
  1979年   15881篇
  1978年   10664篇
  1977年   9071篇
  1976年   7944篇
  1975年   8630篇
  1974年   10499篇
  1973年   9869篇
  1972年   9357篇
  1971年   8852篇
  1970年   8453篇
  1969年   7959篇
  1968年   7224篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Pharmaceutical Chemistry Journal - An HPLC-MS method for simultaneous quantitative determination of a novel gestagenic pharmaceutical and two of its metabolites in rat and rabbit blood sera was...  相似文献   
3.

Objectives

Expedient extubation after cardiac surgery has been associated with improved outcomes, leading to postoperative extubation frequently during overnight hours. However, recent evidence in a mixed medical-surgical intensive care unit population demonstrated worse outcomes with overnight extubation. This study investigated the impact of overnight extubation in a statewide, multicenter Society of Thoracic Surgeons database.

Methods

Records from 39,812 patients undergoing coronary artery bypass grafting or valve operations (2008-2016) and extubated within 24 hours were stratified according to extubation time between 06:00 and 18:00 (day) or between 18:00 and 6:00 (overnight). Outcomes including reintubation, mortality, and composite morbidity-mortality were evaluated using hierarchical regression models adjusted for Society of Thoracic Surgeons predictive risk scores. To further analyze extubation during the night, a subanalysis stratified patients into 3 groups: 06:00 to 18:00, 18:00 to 24:00, and 24:00 to 06:00.

Results

A total of 20,758 patients were extubated overnight (52.1%) and were slightly older (median age 66 vs 65 years, P < .001) with a longer duration of ventilation (4 vs 7 hours, P < .001). Day and overnight extubation were associated with equivalent operative mortality (1.7% vs 1.7%, P = .880), reintubation (3.7% vs 3.4%, P = .141), and composite morbidity-mortality (8.2% vs 8.0%, P = .314). After risk adjustment, overnight extubation was not associated with any difference in reintubation, mortality, or composite morbidity-mortality. On subanalysis, those extubated between 24:00 and 06:00 exhibited increased composite morbidity-mortality (odds ratio, 1.18; P = .001) but no difference in reintubation or mortality.

Conclusions

Extubation overnight was not associated with increased mortality or reintubation. These results suggest that in the appropriate clinical setting, it is safe to routinely extubate cardiac surgery patients overnight.  相似文献   
4.
5.
6.
7.
Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.  相似文献   
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