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   701608篇
  免费   74452篇
  国内免费   368篇
  776428篇
  2018年   5884篇
  2016年   7814篇
  2015年   10537篇
  2014年   12460篇
  2013年   18206篇
  2012年   20078篇
  2011年   20464篇
  2010年   13941篇
  2009年   12752篇
  2008年   18245篇
  2007年   19280篇
  2006年   17999篇
  2005年   17298篇
  2004年   17063篇
  2003年   16616篇
  2002年   16386篇
  2001年   32240篇
  2000年   32450篇
  1999年   25588篇
  1998年   8532篇
  1997年   9043篇
  1996年   8600篇
  1995年   8071篇
  1994年   7941篇
  1993年   7775篇
  1992年   21809篇
  1991年   21312篇
  1990年   20892篇
  1989年   20333篇
  1988年   19023篇
  1987年   17860篇
  1986年   16611篇
  1985年   16871篇
  1984年   13838篇
  1983年   11957篇
  1982年   9055篇
  1981年   8074篇
  1980年   7549篇
  1979年   13261篇
  1978年   10232篇
  1977年   9424篇
  1976年   8821篇
  1975年   9801篇
  1974年   10534篇
  1973年   10360篇
  1972年   9581篇
  1971年   8537篇
  1970年   7516篇
  1969年   7339篇
  1968年   6763篇
排序方式: 共有10000条查询结果,搜索用时 0 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.
5.
6.
Random amplified polymorphic DNA (RAPD) analysis was used tostudy variation among and within selectedIxora (Rubiaceae) populationsand mutants. Six populations of I. congesta yielded identicalbanding patterns suggesting genetic uniformity of this species.However, six populations of I. coccinea varieties (three red-flowered,two yellow-flowered and one red-flowered wild-type) exhibitedinfraspecific differences in RAPD profiles. Small and largeleaves of an atavistic mutant cultivar of I. coccinea were alsosubjected to RAPD analysis. An extra band was amplified in thelarge leaves that was absent in small leaves, suggesting thatthe phenotypic alteration in this taxon is due to genetic mutationrather than epigenetic changes. Similarly, an extra band wasdetected in the white sectors of I. Variegated compared to thegreen sectors, suggesting that the shoot apical meristems ofthis cultivar exist as a genetic chimera. DNA gel blot hybridizationwas performed to confirm the specificities of selected bands.Our study indicates that differences among individuals of variouspopulations and mutants may be detected using RAPD markers.Copyright 1999 Annals of Botany Company Ixora L., variegated variety, RAPD fingerprinting, DNA gel blot, intraspecific genetic similarity, atavistic mutant.  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