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   455429篇
  免费   161693篇
  国内免费   29888篇
  2018年   5888篇
  2017年   5486篇
  2016年   7292篇
  2015年   9824篇
  2014年   11164篇
  2013年   14368篇
  2012年   16330篇
  2011年   16635篇
  2010年   13661篇
  2009年   17447篇
  2008年   15691篇
  2007年   16178篇
  2006年   14350篇
  2005年   13781篇
  2004年   13518篇
  2003年   12763篇
  2002年   13280篇
  2001年   22639篇
  2000年   20572篇
  1999年   20707篇
  1998年   12878篇
  1997年   12759篇
  1996年   11919篇
  1995年   12035篇
  1994年   11392篇
  1993年   10885篇
  1992年   18518篇
  1991年   18138篇
  1990年   18321篇
  1989年   17268篇
  1988年   15972篇
  1987年   14561篇
  1986年   13505篇
  1985年   12948篇
  1984年   10502篇
  1983年   8955篇
  1982年   7860篇
  1981年   7145篇
  1980年   6811篇
  1979年   9455篇
  1978年   7706篇
  1977年   7179篇
  1976年   6579篇
  1975年   6744篇
  1974年   7097篇
  1973年   6962篇
  1972年   6783篇
  1971年   6014篇
  1970年   5460篇
  1969年   5344篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
1.
2.
3.
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   
4.
Plant Molecular Biology -  相似文献   
5.
6.
Essential genes were identified in the 1.5-map unit dpy-5 unc-13 region of chromosome I in the Caenorhabditis elegans genome by rescuing lethal mutations using the duplication sDp2. In this paper, we report the mapping and complementation testing of lethal mutations, 45 of which identify 18 new, essential genes. This analysis brings the number of essential genes defined by the sDp2 rescue of lethal mutants to 97; 64 of these map between dpy-5 and unc-13. 61% of these essential genes are identified by more than one allele. Positioning of the mutations was done using the breakpoints of six duplications. The mutant phenotypes of 14 loci essential for fertility were characterized by Nomarski microscopy and DAPI staining. None of the mutants were rescued by wild-type male sperm. The cytological data showed that four genes produced mutants with defects in gonadogenesis, let-395, let-603, let-605 and let-610. Mutations in seven genes, let-355, let-367, let-384, let-513, let-544, let-545 and let-606, affected germ cell proliferation or gametogenesis. Mutants for the remaining three genes, let-370, let-599 and let-604, produced eggs that failed to develop or hatch, thereby acting as maternal effect lethals. We observed a nonrandom distribution of arrest phenotypes with regard to map position. Received: 8 May 1996 / Accepted : 27 January 1997  相似文献   
7.
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