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   608155篇
  免费   68828篇
  国内免费   304篇
  2018年   5229篇
  2016年   7042篇
  2015年   9760篇
  2014年   11413篇
  2013年   16358篇
  2012年   18290篇
  2011年   18428篇
  2010年   12554篇
  2009年   11283篇
  2008年   16338篇
  2007年   17041篇
  2006年   15862篇
  2005年   15365篇
  2004年   15191篇
  2003年   14667篇
  2002年   14626篇
  2001年   29318篇
  2000年   29695篇
  1999年   23322篇
  1998年   7670篇
  1997年   7985篇
  1996年   7601篇
  1995年   7184篇
  1994年   7174篇
  1993年   6906篇
  1992年   19610篇
  1991年   18851篇
  1990年   18275篇
  1989年   17699篇
  1988年   16531篇
  1987年   15546篇
  1986年   14198篇
  1985年   14252篇
  1984年   11634篇
  1983年   10162篇
  1982年   7797篇
  1981年   6875篇
  1980年   6469篇
  1979年   11412篇
  1978年   8583篇
  1977年   7920篇
  1976年   7279篇
  1975年   8123篇
  1974年   8634篇
  1973年   8624篇
  1972年   7989篇
  1971年   7170篇
  1970年   6258篇
  1969年   5998篇
  1968年   5385篇
排序方式: 共有10000条查询结果,搜索用时 0 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.
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   
8.
9.
Human factor VIII procoagulant protein (factor VIII) was purified using a modification of our previously described method, in which Sephacryl S-400 elution, rather than QAE-cellulose chromatography, served as the final purification step. The protein had a specific activity of more than 2500 U/mg and consisted of a single polypeptide (Mr 100 000) when analyzed by SDS-polyacrylamide gel electrophoresis. Factor VIII was shown to be a glycoprotein by staining with periodic acid-Schiff's reagent following electrophoresis. Treatment of factor VIII with a mixture of exo- and endoglycosidases caused a reduction by about 50% in the intensity of periodic acid-Schiff staining, as determined by scanning densitometry, and an increase in electrophoretic mobility (equivalent to a new Mr 95 000). Removal of this portion of the total carbohydrate had no significant effect on factor VIII clotting activity or on thrombin potentiation of clotting activity. The in vivo survival curves of a native and sugar-depleted 125I-labeled factor VIII both showed similar patterns of initial rapid decay to 60 and 40% activity, respectively, followed by a one-half decay time of 4 h for both. These results suggest that the carbohydrate portion of human factor VIII does not contribute significantly to either clotting function in vitro or to biological turnover in vivo.  相似文献   
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