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   14090篇
  免费   495篇
各国政治   515篇
工人农民   582篇
世界政治   1027篇
外交国际关系   535篇
法律   8248篇
中国共产党   34篇
中国政治   146篇
政治理论   3327篇
综合类   171篇
  2021年   82篇
  2020年   191篇
  2019年   183篇
  2018年   300篇
  2017年   350篇
  2016年   412篇
  2015年   312篇
  2014年   299篇
  2013年   1446篇
  2012年   351篇
  2011年   373篇
  2010年   318篇
  2009年   399篇
  2008年   439篇
  2007年   479篇
  2006年   453篇
  2005年   418篇
  2004年   402篇
  2003年   353篇
  2002年   343篇
  2001年   421篇
  2000年   408篇
  1999年   326篇
  1998年   248篇
  1997年   185篇
  1996年   181篇
  1995年   180篇
  1994年   185篇
  1993年   187篇
  1992年   265篇
  1991年   300篇
  1990年   260篇
  1989年   256篇
  1988年   281篇
  1987年   269篇
  1986年   275篇
  1985年   254篇
  1984年   223篇
  1983年   202篇
  1982年   152篇
  1981年   170篇
  1980年   140篇
  1979年   139篇
  1978年   124篇
  1977年   107篇
  1976年   89篇
  1975年   86篇
  1974年   88篇
  1973年   97篇
  1969年   65篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
954.
955.
956.
The purpose of this study was to increase the knowledge base of adolescent substance use by examining the influences of risk and protective factors for specific substance use, namely alcohol, cigarettes, and marijuana. Participants included 271 adolescents and their primary caregivers referred for mental health services across North Carolina. A series of hierarchical multiple regressions showed that the relative influences of risk and protective factors differed depending on the target substance in some cases. History of parental felony predicted use of all 3 substances, although the direction of association was substance specific. Parental behavioral control (how families express and maintain standards of behavior) was predictive only of cigarette and marijuana use, not alcohol use. The different links among risk factors, protective factors, and specific substance use are discussed, and recommendations for both mental health and substance use professionals are offered.She received her M.A. in Psychology from Wake Forest University and is currently a doctoral student in Clinical Psychology at the University of North Carolina at Greensboro. Her major research interests include developmental pathways to aggressive behavior among females.An evaluator for the North Carolina Department of Health and Human Services, her major research interests include system of care intervention programming.She received her PhD in Clinical Psychology from Purdue University. Her major research interests include developmental psychopathology and early intervention.His research interests focus on youth violence and youth involved with the juvenile justice system.She received her PhD in Clinical Psychology from the University of North Carolina at Greensboro. Her research interests focus on early intervention with young children.  相似文献   
957.
958.
959.
In a second test of an arthropod saturation hypothesis, we analyzed if the on-campus Anthropology Research Facility (ARF) at the University of Tennessee, Knoxville, with its 20+ yr history of carcass enrichment, is comparable to non-enriched sites in community structure of predatory and parasitic arthropods that prey upon the sarcosaprophagous fauna. Over a 12-day period in June 1998, using pitfall traps and sweep nets, 10,065 predaceous, parasitic, and hematophagous (blood-feeding) arthropods were collected from freshly euthanized pigs (Sus scrofa L.) placed at ARF and at three surrounding sites various distances away (S2-S4). The community structure of these organisms was comparable in most paired-site tests with respect to species composition, colonization rates, and evenness of pitfall-trap abundances on a per carcass basis. Site differences were found in rarefaction tests of both sweep-net and pitfall-trap taxa and in tests of taxonomic evenness and ranked abundances of sweep-net samples. Despite these differences, no evidence was found that the predatory/parasitic fauna at ARF was impoverished with fewer but larger populations as a result of carcass enrichment. Comparison of the sarcosaprophagous and predatory/parasitic faunas revealed a tighter (and more predictable) linkage between carrion feeders (sarcosaprovores) and their carrion than between carrion feeders and their natural enemies (predators and parasitoids), leading us to conclude that ARF is more representative of surrounding sites with respect to the sarcosaprovore component than to the predatory/parasitic component within the larger carrion-arthropod community.  相似文献   
960.
Specimens from fatal aviation accident victims are submitted to the FAA Civil Aerospace Medical Institute for toxicological analysis. During toxicological evaluations, ethanol analysis is performed on all cases. Care must be taken when interpreting a positive ethanol result due to the potential for postmortem ethanol formation. Several indicators of postmortem ethanol formation exist; however, none are completely reliable. The consumption of ethanol has been shown to alter the concentration of two major serotonin metabolites, 5-hydroxytryptophol (5-HTOL) and 5-hydroxyindole-3-acetic acid (5-HIAA). While the 5-HTOL/5-HIAA ratio is normally very low, previous studies using living subjects have demonstrated that the urinary 5-HTOL/5-HIAA ratio is significantly elevated for 11-19 h after acute ethanol ingestion. Recently, our laboratory developed and validated an analytical method for the simultaneous determination of both 5-HTOL and 5-HIAA in forensic urine samples using a simple liquid/liquid extraction and LC/MS/MS and LC/MS/MS/MS. In this previous work a 15 pmol/nmol serotonin metabolite ratio cutoff was established in postmortem urine, below which it could be conclusively determined that no recent antemortem ethanol consumption had occurred. In the current study this newly validated analytical method was applied to five ethanol-positive aviation fatalities where the origin of the ethanol present could not previously be conclusively determined. In four of the five cases examined the detected ethanol was demonstrated to be present due to postmortem microbial formation, and not consumption, even though some indication of ethanol consumption may have been present.  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