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   2359226篇
  免费   172448篇
  国内免费   3361篇
耳鼻咽喉   32225篇
儿科学   76184篇
妇产科学   62879篇
基础医学   349536篇
口腔科学   63896篇
临床医学   212139篇
内科学   459169篇
皮肤病学   51856篇
神经病学   186316篇
特种医学   88349篇
外国民族医学   489篇
外科学   355277篇
综合类   47721篇
现状与发展   12篇
一般理论   858篇
预防医学   183598篇
眼科学   54541篇
药学   175734篇
  11篇
中国医学   4581篇
肿瘤学   129664篇
  2021年   19104篇
  2019年   19659篇
  2018年   27185篇
  2017年   20449篇
  2016年   22839篇
  2015年   25760篇
  2014年   36285篇
  2013年   54308篇
  2012年   75079篇
  2011年   79850篇
  2010年   47340篇
  2009年   44780篇
  2008年   75103篇
  2007年   79980篇
  2006年   80804篇
  2005年   78293篇
  2004年   74913篇
  2003年   72229篇
  2002年   69881篇
  2001年   108862篇
  2000年   111558篇
  1999年   93636篇
  1998年   27126篇
  1997年   23765篇
  1996年   24162篇
  1995年   22828篇
  1994年   20999篇
  1993年   19810篇
  1992年   72130篇
  1991年   70201篇
  1990年   68503篇
  1989年   65784篇
  1988年   60438篇
  1987年   59222篇
  1986年   55358篇
  1985年   53148篇
  1984年   39450篇
  1983年   33526篇
  1982年   19998篇
  1979年   35949篇
  1978年   25772篇
  1977年   21314篇
  1976年   20422篇
  1975年   21911篇
  1974年   26227篇
  1973年   24893篇
  1972年   23260篇
  1971年   22081篇
  1970年   20289篇
  1969年   19343篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
55.
56.
57.
58.
OBJECTIVE: To establish reference intervals for the fetal right, left and total lung volumes and heart volume between 12 and 32 weeks of gestation. METHODS: Fetal lung and heart volumes were measured using three-dimensional (3D) ultrasound in 650 normal singleton pregnancies at 12-32 weeks. The VOCAL (Virtual Organ Computer-aided AnaLysis) technique was used to obtain a sequence of six sections of each lung and the heart around a fixed axis, each after a 30 degrees rotation from the previous one. The rotation axis for the lungs extended from the apex to the upper limit of the diaphragm dome, and the rotation axis for the heart extended from its apex to its connection to the great vessels. The contour of each of these organs was drawn manually in the six different rotation planes to obtain the 3D volume measurement. In 60 cases the fetal lungs and heart volumes were measured by the same sonographer twice and also by a second sonographer once in order to compare the measurements and calculate intra- and interobserver agreement. RESULTS: The total lung volume and heart volume increased with gestation, from respective mean values of 1.6 and 0.6 mL at 12 weeks to 10.9 and 4.3 mL at 20 weeks and 49.3 and 26.6 mL at 32 weeks. The right to left lung volume ratio did not change significantly with gestation (median, 0.7), whereas the heart to total lung volume ratio increased with gestation from about 0.3 at 12 weeks to 0.5 at 32 weeks. In the Bland-Altman plot, the difference between paired measurements by two sonographers was, in 95% of the cases, less than 0.05, 0.5 and 1.9 mL for each lung at 12-13, 19-22 and 29-32 weeks, respectively, and the corresponding values for the heart volumes were 0.04, 0.4 and 2.3 mL. CONCLUSIONS: In normal fetuses the lung and heart volumes increase between 12 and 32 weeks of gestation. The extent to which in pathological pregnancies possible deviations in these measurements from normal prove to be useful in the prediction of outcome remains to be determined.  相似文献   
59.
The increased number of lymphocytes in airways during an asthmatic response is believed to be the result of increased recruitment of these cells. However, it is possible that a decreased apoptotic rate could also contribute to the increased number. The aim of the present study was to investigate whether allergen airway provocation influences the apoptotic phenotype of lung and peripheral blood lymphocytes (PBL) in subjects with atopic asthma. Bronchoalveolar lavage (BAL) lymphocytes and PBL from 12 asthmatic subjects previously challenged with allergen (n = 7) or saline (n = 5) were exposed to the apoptotic stimulus tributyltin (TBT) in vitro and assayed for apoptosis. Airway allergen provocation resulted in decreased sensitivity of BAL lymphocytes to TBT-induced apoptosis, with 42.2% (range 33.9-62.5%) apoptotic cells before challenge versus 23.5% (range 15.3-42.4%) after challenge, while PBL were unaffected. The increased apoptosis resistance correlated with higher numbers of Bcl-2-expressing lymphocytes. Interestingly, baseline caspase-3-like activity was significantly elevated in viable BAL lymphocytes compared with viable PBL, and was unaltered by allergen exposure. In conclusion, allergen inhalation renders bronchoalveolar lavage lymphocytes more resistant to apoptosis while peripheral blood lymphocytes were not influenced at all, indicating that the apoptotic phenotype of airway lymphocytes may play a role in asthmatic inflammation.  相似文献   
60.
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