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   610361篇
  免费   69092篇
  国内免费   304篇
  2018年   5258篇
  2016年   7106篇
  2015年   9854篇
  2014年   11516篇
  2013年   16513篇
  2012年   18434篇
  2011年   18594篇
  2010年   12660篇
  2009年   11380篇
  2008年   16465篇
  2007年   17175篇
  2006年   15952篇
  2005年   15476篇
  2004年   15306篇
  2003年   14776篇
  2002年   14724篇
  2001年   29369篇
  2000年   29736篇
  1999年   23375篇
  1998年   7708篇
  1997年   8009篇
  1996年   7640篇
  1995年   7215篇
  1994年   7206篇
  1993年   6944篇
  1992年   19634篇
  1991年   18872篇
  1990年   18302篇
  1989年   17739篇
  1988年   16547篇
  1987年   15554篇
  1986年   14221篇
  1985年   14272篇
  1984年   11654篇
  1983年   10184篇
  1982年   7816篇
  1981年   6897篇
  1980年   6487篇
  1979年   11432篇
  1978年   8599篇
  1977年   7929篇
  1976年   7306篇
  1975年   8132篇
  1974年   8659篇
  1973年   8642篇
  1972年   7993篇
  1971年   7188篇
  1970年   6264篇
  1969年   6013篇
  1968年   5393篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
A patient with chronic anemia is presented who radiologically showed prominent rugae of the stomach. Angiography demonstrated an arteriovenous malformation with a large feeding artery and prominent draining veins.  相似文献   
5.
6.
7.
In a study of 2000 unselected pregnant women the development of a mature placental appearance (grade 3) on ultrasonography by 34-36 weeks'' gestation, observed in 15% of cases, was associated with maternal smoking, low parity, low maternal age, and being white. These women had an increased risk of problems during labour and their babies had an increased risk of low birth weight, poor condition at birth, and perinatal death. The women were randomly allocated to two groups: in one group the result of the placental grading was reported to the clinician responsible for care; in the second the result was noted but not reported. There was a significant decrease in the risk of perinatal death in the group where the grading was known. This reduction was responsible for a difference in the principal outcome index, a heterogeneous group of measures of mortality and morbidity, but this difference was not significant. This study alone does not justify routine late scanning, and further, larger trials are required. Nevertheless, the results do provide a basis for the reporting of placental grading when ultrasound examination is performed during the third trimester.  相似文献   
8.
Changes in the protein and steroid hormones of follicular fluid, aspirated from different follicles of sheep and human ovaries, have been measured and correlated with the size of the follicles. As the fluid contains a number of proteins, steroids have been measured directly and after ether extraction. The follicular fluid concentrations of progesterone and 17 beta-oestradiol measured directly in the fluid increased with the size of the follicles. The levels of free testosterone remained constant in all sizes of follicles, while those of bound hormone showed a 10- to 15-fold increase over the free testosterone concentrations in both the sheep and human follicular fluid. A decrease in the levels of bound testosterone in the fluid of large follicles (LFFL) coincided with the increase in bound 17 beta-oestradiol, suggesting the possible conversion of bound testosterone to oestrogen as the follicle attained maturity. The ratio of follicle-stimulating hormone (FSH) to luteinizing hormone (LH) varied in the fluid obtained from different size follicles, being 1:7 in small (SFFL), 1.3.5 in medium (MFFL) and 1:2.3 in large (LFFL) follicles of sheep ovaries. The LH content of follicular fluid of different size follicles appeared to be the same, with LFFL showing a minor increase over SFFL. In the human, the fluid from medium follicles contained very little LH compared to LFFL. These differences in the pattern of LH levels present in the fluid from different size follicles between human and sheep ovaries presumably reflect species variations in the entry of LH into the follicles.  相似文献   
9.
10.
In vivo EMG biofeedback was found to be an effective pedagogical tool for removing unwanted left-hand tension in nine violin and viola players. Improvement occurred rapidly and persisted throughout a 5-month follow-up period. Further studies will be necessary to assess the effect of biofeedback independent of placebo effects. The brevity of the method and the magnitude of improvement warrant further investigation.  相似文献   
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