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   82499篇
  免费   4691篇
  国内免费   9篇
  2021年   1002篇
  2020年   902篇
  2019年   913篇
  2018年   2221篇
  2017年   1946篇
  2016年   2633篇
  2015年   3498篇
  2014年   3605篇
  2013年   4733篇
  2012年   5558篇
  2011年   4870篇
  2010年   3197篇
  2009年   2408篇
  2008年   3911篇
  2007年   3721篇
  2006年   3676篇
  2005年   3082篇
  2004年   3084篇
  2003年   2745篇
  2002年   2517篇
  2001年   2049篇
  2000年   1901篇
  1999年   1485篇
  1998年   669篇
  1997年   479篇
  1996年   531篇
  1995年   475篇
  1992年   921篇
  1991年   843篇
  1990年   825篇
  1989年   895篇
  1988年   737篇
  1987年   753篇
  1986年   690篇
  1985年   760篇
  1984年   622篇
  1983年   548篇
  1979年   670篇
  1978年   490篇
  1977年   492篇
  1975年   587篇
  1974年   626篇
  1973年   597篇
  1972年   548篇
  1971年   492篇
  1970年   537篇
  1969年   610篇
  1968年   574篇
  1967年   479篇
  1966年   466篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Analogs of deamino-oxytocin and deamino-oxypressin containing a CH2-NH group instead of an amide bond between positions 8 and 9 were synthesized. All tested compounds exhibit significantly lowered biological activities.  相似文献   
52.
53.
54.
The in vitro determination of the effects of some pharmacological agents on the outer diameter and axial tension of human Fallopian tube ampullar segments showed that some drugs may act on the circular and longitudinal smooth muscle layers relatively separately. PGF2 alpha elicited an excitatory response in both muscle layers while norepinephrine and isoproterenol decreased the activity. Oxytocin and indomethacin had relatively limited effects on the spontaneous motility of the ampullar segments. The calcium antagonist verapamil inhibited the spontaneous periodic activity.  相似文献   
55.
56.
A strain of 1,507 typised donors enables 15.97 average donors to be selected for a thrombocyte transfusion in one of 75 patients selected at random with HLA antibodies being previously determined (1 to 66 donors per patient). HLA compatible donors were found for 72 patients (97.33 per cent). More than 5 HLA compatible donors could be found for 58 patients. The high number of compatible donors is based on the fact that among 1,507 donors there were 156 HLA homozygotes and 556 donors with 3 HLA-A or B-antigens respectively. Compatibility in the ABO-system was not taken into account.  相似文献   
57.
Lateral membrane heterogeneity, in the form of lipid rafts and microdomains, is currently implicated in cell processes including signal transduction, endocytosis, and cholesterol trafficking. Various biophysical techniques have been used to detect and characterize lateral membrane domains. Among these, Förster resonance energy transfer (FRET) has the crucial advantage of being sensitive to domain sizes smaller than 50-100 nm, below the resolution of optical microscopy but, apparently, similar to those of rafts in cell membranes. In the last decade, several formalisms for the analysis of FRET in heterogeneous membrane systems have been derived and applied to the study of microdomains. They are critically described and illustrated here.  相似文献   
58.
59.
60.
Kitner  Miloslav  Poulícková  Aloisie 《Hydrobiologia》2003,506(1-3):519-524

The littoral zone of shallow water bodies in the Czech Republic has been studied quite consistently at several fishponds. The use of algae, especially diatoms, for the monitoring of the state of lotic freshwater also has a long tradition. The main objective of the presented paper is to validate the feasibility of the use of littoral periphyton comunities for the biomonitoring of standing waters. At the investigated sites, littoral periphytic diatoms were studied together with selected enviromental variables (pH, conductivity, nutrients – especially total phosphorus) on three types of natural substrates (epilithon, epiphyton, epipelon). The evaluation of the diatom community was performed on the basis of the checklists of algal indicator species published by authors from the Czech Republic, Austria and the Netherlands. The data were subjected to statistical software NCCS 2000 (GLM Anova and ``Ward's minimum'' variance cluster analysis). Littoral periphytic diatoms appear to be good indicators of the fishpond water quality. The selected substrates show non-significant differences therefore the average values from all substrates were used. The best indicatory system for evaluation of Czech fishponds was van Dam's index.

  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