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   7741篇
  免费   510篇
各国政治   380篇
工人农民   269篇
世界政治   504篇
外交国际关系   261篇
法律   5350篇
中国政治   35篇
政治理论   1417篇
综合类   35篇
  2020年   171篇
  2019年   186篇
  2018年   223篇
  2017年   254篇
  2016年   244篇
  2015年   219篇
  2014年   206篇
  2013年   834篇
  2012年   179篇
  2011年   197篇
  2010年   233篇
  2009年   247篇
  2008年   187篇
  2007年   190篇
  2006年   188篇
  2005年   178篇
  2004年   197篇
  2003年   177篇
  2002年   146篇
  2001年   323篇
  2000年   266篇
  1999年   235篇
  1998年   102篇
  1997年   72篇
  1996年   70篇
  1995年   81篇
  1994年   90篇
  1993年   88篇
  1992年   153篇
  1991年   158篇
  1990年   147篇
  1989年   159篇
  1988年   125篇
  1987年   138篇
  1986年   125篇
  1985年   135篇
  1984年   105篇
  1983年   122篇
  1982年   82篇
  1981年   82篇
  1980年   56篇
  1979年   109篇
  1978年   69篇
  1977年   60篇
  1976年   51篇
  1975年   47篇
  1974年   55篇
  1973年   55篇
  1972年   44篇
  1968年   40篇
排序方式: 共有8251条查询结果,搜索用时 15 毫秒
951.
952.
Congress plays a central role in national environmental policy formation but appears ill equipped to set policy priorities and devise integrative legislation. Fragmentation of authority among a multiplicity of committees and subcommittees, especially in the House, contributes to these problems. This pattern is evident in the evolution of Superfund, the national program to clean up abandoned hazardous waste sites. The prolonged process of reauthorization in the 1980s contributed to serious program delay and failed to resolve a number of fundamental questions concerning the national cleanup effort. Institutional reforms could contribute to a more effective congressional role in future environmental policy deliberations.  相似文献   
953.
Book notes     
  相似文献   
954.
Supravital electrical excitability of muscles   总被引:1,自引:0,他引:1  
A new method of postmortem electrical stimulation of muscles, measuring the force of the reaction against time, is presented. Preliminary investigations have yielded the following results: The maximum force of reaction in response to a definitive stimulation, measured by a sensitive force transducer, decreases in proportion to the post mortem interval. Using this method, the mechanical reactions of muscles by electrical stimulation can be demonstrated over a much longer postmortem period as these movements are visible. The duration of postmortem reaction of different muscles seems to be much more uniform than was previously assumed. Occasionally, reactions of the M. orbicularis oculi can be seen for the longest time. The basal muscular tonus changes relative to time. The time course of a single force reaction also changes relative to the postmortal interval: the reaction becomes slower. It has been theoretically established that measurement of influencing factors such as temperature and pH in the tested muscle will enable the time of death to be more precisely estimated.  相似文献   
955.
956.
A current Supreme Court case concerning lawyer advertising, In re R.M.J., is analyzed in the context of a discussion of the diverse state regulations governing lawyer advertising and solicitation. The article considers the regulations in terms of their constitutionality, their tendency to impede effective advertising, and the effect they have on the legal profession's provision of information to potential clients about the nature, availability, and cost of legal services. Analysis of the major commercial speech cases, from Virginia State Board of Pharmacy to Central Hudson, indicates that many state rules infringe on attorneys' First Amendment rights.  相似文献   
957.
958.
A method is described for obtaining nondiffusing, nonfading fluorogenic zymograms for erythrocyte acid phosphatase variants separated by isoelectric focusing. The synthetic substrate 4-trifluoromethylcoumarin phosphate was impregnated into cellulose diacetate membranes and air-dried overnight. After isoelectric focusing, the substrate overlay membrane was rehydrated in 0.05M citrate buffer, pH 4.0, lightly blotted, and overlayed on the gel. A 5- to 10-min incubation at 37 degrees C produced intensely fluorescing, light-blue bands on the diacetate membrane. Interaction of the trifluoromethyl group on the substrate with hydrophobic regions of the diacetate membrane impeded diffusion, yielding a permanent zymogram. There were no discrepancies in phenotype determinations using this method when compared with the 4-methylumbelliferyl phosphate assay approach. Further, an increased number of conclusive calls were obtained (91.8 versus 79.5% and 54.1 versus 34.9%) with this new assay when compared with the 4-methylumbelliferyl phosphate substrate on known liquid bloods and questioned dried bloodstains, respectively.  相似文献   
959.
Principally new, simple and objective method for investigation of human hair density is suggested. Hair identity in relation to a concrete person can be confirmed or excluded by statistical processing of the results obtained.  相似文献   
960.
Flowers ofMelandrium album are frequently pollinated byCucullia umbratica L. This heavy moth always lands on the flowers. The process of insertion of the proboscis and the drinking thereafter is described. From experiments it is concluded that senses for perception of the relative humidity of the air are located on the antennae. The moth is able to locate flowers by smell only, but visual orientation seems to be more predominant. Legs and antennae possess contact chemoreceptors, sensitive to sucrose and to chemicals present on the surface ofM. album flowers. The moth responds after contact of the legs with petal lobes ofM. album by extension of the proboscis. Inserting behaviour follows only after contact of the proboscis tip with the ligula. The moth appears to be a specialised flower visitor.
Resume Les fleurs deMelandrium album sont polinisées parCucullia umbratica qui butine ces fleurs après s'y être posé. Les expériences rapportées ici témoignent que des organes sensoriels aptes à percevoir l'humidité de l'air sont localisés sur les antennes. Le papillon peut localiser les fleurs par simple odeur mais l'orientation visuelle semble prédominante. Les pattes et les antennes possèdent des chemorécepteurs de contact, sensibles au sucrose et aux composés chimiques associés aux fleurs deM. album. Le papillon, après contact de ses pattes avec les pétales de cette fleur manifeste une extension de son proboscis et ce n'est qu'après contact de ce dernier avec la ligula, que se réalise l'insertion dans la corolle. Ce papillon semble être spécialisé comme visiteur de fleurs.
  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