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   16674篇
  免费   1448篇
各国政治   787篇
工人农民   556篇
世界政治   1352篇
外交国际关系   698篇
法律   11101篇
中国共产党   1篇
中国政治   129篇
政治理论   3366篇
综合类   132篇
  2023年   70篇
  2021年   81篇
  2020年   413篇
  2019年   444篇
  2018年   574篇
  2017年   629篇
  2016年   689篇
  2015年   548篇
  2014年   554篇
  2013年   2023篇
  2012年   438篇
  2011年   519篇
  2010年   662篇
  2009年   623篇
  2008年   470篇
  2007年   470篇
  2006年   541篇
  2005年   416篇
  2004年   403篇
  2003年   369篇
  2002年   350篇
  2001年   539篇
  2000年   437篇
  1999年   395篇
  1998年   219篇
  1997年   211篇
  1996年   171篇
  1995年   192篇
  1994年   209篇
  1993年   191篇
  1992年   280篇
  1991年   294篇
  1990年   272篇
  1989年   275篇
  1988年   261篇
  1987年   214篇
  1986年   250篇
  1985年   258篇
  1984年   258篇
  1983年   218篇
  1982年   172篇
  1981年   160篇
  1980年   146篇
  1979年   169篇
  1978年   111篇
  1977年   95篇
  1976年   79篇
  1975年   84篇
  1974年   108篇
  1973年   74篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
981.
982.
983.
Empirical studies have found that policies aimed at reducing youth access to tobacco have been successful at increasing retail compliance, but their effects on actual tobacco use are mixed. This article presents a model of youth access policies that helps explain the apparently conflicting results in the extant literature, provides a framework for future empirical studies, and suggests implications for public policy. Our model highlights the interaction of components in a well-designed policy, including sufficient compliance checks, penalties, and community involvement. It also illustrates why it will be difficult to eliminate all of youth supply. Nonretail sources, such as borrowing or stealing from parents and siblings and purchasing from older peers through black markets, are an important component of youth supply and become more important as retail access is reduced. The analysis is limited to policies that affect the retail supply of cigarettes but suggests the need for other policies that affect the demand for cigarettes, such as taxes and cessation policies, in order to further reduce youth smoking rates.  相似文献   
984.
By means of the new method of Streifenlichttopometrie (SLT) it is possible to record the complete body surface of casualties in a practically photorealistic fashion, i.e. three-dimensionally and in colour. In comparison with the classic method of Photogrammetry Streifenlichttopometrie (SLT) is remarkably faster (10,000 points/s instead of 1 point/s) and in addition the colour of every point measured upon the corpse's surface is instantly recorded. Taking into consideration the resolution required and the qualities of the camera system the body surface is recorded in 'patches', i.e., areas of a defined extension (in the present case 500 mmx500 mmx200 mm) which are marked with a body fixed reference frame to grant the exact matching of the data after the recording process. Length, perimeter, square and volume of the body segments and injuries can be determined. Furthermore the natural colour of the wounds can be used for an immediate classification according to the intensity of the impact forces. In addition the 3-D coordinates of the body surface including the wounds can be transferred into an animated computer simulation for the reconstruction of the traumatic events.  相似文献   
985.
986.
The legal position in the UK on embryo research and preimplantation genetic diagnosis (PGD) is outlined and contrasted with the position in other EU countries. The "gradualist" position of the UK on the moral status of the embryo is defended on the basis of an argument that precaution must be applied in proportion to the degree to which the embryo has developed to display components of agency, on the assumption that mortality is categorically binding and requires agents to be granted rights and that it cannot be known with certainty that the embryo is not an agent. The extent to which this argument, when combined with vicarious protections that the embryo should receive in order to protect the rights of other agents, limits embryo research and PGD, is discussed. It is concluded that the complexities that attend deliberation about the moral problems attending embryo research and PGD are such that the proper response to these problems is via the procedures of political democracy to achieve accountable answers rather than "correct" answers. This allows for a variety of judgements.  相似文献   
987.
This paper describes a collaborative exercise organised under the auspices of the European Network of Forensic Science Institutes (ENFSI). The purpose of this EU (European Union) funded group is to carry out research to enable STR loci to be compared between European laboratories, ultimately leading to the formation of a pan-European database. Accordingly, an exercise was designed to evaluate a prototype STR multiplex system manufactured by Applied Biosystems (ABD). Each laboratory was sent 12 samples to analyse along with a multiplex kit. Of specific interest was the definition of parameters to define the efficiency of the system. Stutter, split allelic peaks (differing by one base), pull-up, heterozygous balance and between locus balance were all objectively measured. Once the important parameters are defined it is possible to directly compare performances of different multiplexes and the different laboratories carrying out the tests. Since the multiplex used was a prototype system, this exercise cannot be regarded as a proficiency test.  相似文献   
988.
The binding of charged substances from external aqueous media to hair has been investigated through the use of fluorescence microscopy. Eleven hair samples, reflecting various ethnic groups and cosmetic treatments, were tested. Rhodamine 6G, a cationic dye representative of drugs such as cocaine and opiates, showed incorporation throughout the hair of all samples except one. In contrast, fluorescein, an anionic dye representative of drugs such as THC carboxylic acid, was not readily incorporated. The incorporation of rhodamine 6G was faster for chemically 'straightened' and bleached African-American female hair than for untreated hair. Incorporation of rhodamine 6G followed a pH dependence, but an ionic strength dependence could not be established. These studies support three postulates: (1) electrostatic interactions explain the preferential binding of cationic drugs of abuse to hair; (2) the hair matrix, or the non-helical portion of hair, is accessible to external solutions and thus subject to contamination; and (3) cosmetic treatments may alter the helical portion of hair thereby increasing its accessibility to external contamination.  相似文献   
989.
990.
Household survey data on age at first use of alcohol, tobacco, marijuana,and hard drugs can be biased due to sample selection and inaccuraterecall. One potential concern is attrition, whereby individuals who getinvolved with substance use at an early age become increasingly less likelyto be surveyed in successive years. A comparison of data from the NationalHousehold Survey on Drug Abuse (NHSDA) with data from a longitudinal studysuggested that attrition might have caused substantially less bias thandid forward telescoping, the inflating of age at first useover time. The evidence of forward telescoping was particularly pronouncedwith respect to age at first use of alcohol. This paper presents a procedurefor correcting the distribution of age at first use for forward telescoping(but not attrition) by viewing a portion of the NHSDA data collected insuccessive years as constituting a cohort study. Results are presented fromapplying this procedure with NHSDA data collected from 1982 to 1995 forrespondents born 1968–1973. The findings suggest that preventionprograms need to be introduced at an earlier age than would be indicatedby uncorrected retrospective data. Other implications are alsohighlighted.  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