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   773篇
  免费   98篇
  国内免费   36篇
  2024年   1篇
  2023年   24篇
  2022年   19篇
  2021年   47篇
  2020年   40篇
  2019年   56篇
  2018年   54篇
  2017年   55篇
  2016年   56篇
  2015年   27篇
  2014年   30篇
  2013年   157篇
  2012年   23篇
  2011年   25篇
  2010年   18篇
  2009年   28篇
  2008年   43篇
  2007年   34篇
  2006年   21篇
  2005年   21篇
  2004年   25篇
  2003年   16篇
  2002年   14篇
  2001年   6篇
  2000年   11篇
  1999年   3篇
  1998年   14篇
  1997年   7篇
  1996年   8篇
  1995年   6篇
  1994年   1篇
  1993年   1篇
  1992年   4篇
  1991年   2篇
  1990年   3篇
  1989年   2篇
  1985年   2篇
  1980年   1篇
  1977年   1篇
  1976年   1篇
排序方式: 共有907条查询结果,搜索用时 15 毫秒
801.
Although the neighborhood microsystem is recognized as an important domain for adolescent development, relative to the family and peer contexts, neighborhood factors have been understudied in relation to adolescent substance abuse. In addition, recent research suggests that risk factors for adolescent substance use may differ for African Americans when compared to Caucasian youth. This study investigated the association between perceived neighborhood disorganization and later substance use, as well as possible mediators of that association, among a community sample of urban African American adolescents. Perceptions of neighborhood disorganization (i.e., violence/safety and drug activity) in grade 7 were associated with increased tobacco, alcohol, and marijuana use in grade 9. For females, this association was mediated by attitudes about drug use and perceptions of drug harmfulness. Findings highlight the importance of neighborhood contextual variables for African American substance use. Implications and directions for future research are presented.  相似文献   
802.
The Helsinki Declaration is the ‘gold standard’ — a directive, not a law, on how to conduct controlled studies in humans in conformity with ethical principles. In spite of many discussions about their unsuitability some articles have remained unchanged in the most recent (sixth) revision of the Declaration. The demand to use “the best treatment” excludes use of placebo in the control group and presents an obstacle to the scientific evaluation of a number of drugs and treatments in general. The use of placebo is justified whenever its use does not cause irreversible damage or considerable suffering to the well informed patient. It must be, is, and will be used in the controlled clinical trials of treatments of a great number of diseases especially those which have a tendency to spontaneous improvement, even healing, or have a pronounced psychological component An earlier version of this paper was presented at an international conference, “Placebo: Its Action and Place in Health Research Today,” held in Warsaw, Poland on 12–13 April, 2003.  相似文献   
803.
This research examined exchange and value attribution in tufted capuchin monkeys (Cebus apella). We presented subjects with opportunities to obtain various foods and a tool from an experimenter in exchange for the foods or tool in the subjects' possession. The times elapsed before the first chow biscuits were expelled and/or an exchange took place were recorded as the dependent measures. Laboratory chow biscuits, grapes, apples, and a metal bolt (a tool used to probe for syrup) were used as experimental stimuli. The subjects demonstrated the ability to recognize that exchanges could occur when an experimenter was present with a desirable food. Results indicate that subjects exhibited significant variation in their willingness to barter based upon the types of foods that were both in their possession and presented by the experimenter. Subjects more readily traded chow biscuits for fruit, and more readily traded apples for grapes than grapes for apples. During the exchange of tools and food, the subjects preferred the following in descending order when the probing apparatus was baited with sweet syrup: grapes, metal bolts, and chow biscuits. However when the apparatus was not baited, the values changed to the following in descending order: grapes, chow, and metal bolts. These results indicate that tufted capuchins recognize opportunities to exchange and engage in a simple barter system whereby low-valued foods are readily traded for more highly valued food. Furthermore, these capuchins demonstrate that their value for a tool changes depending upon its utility.  相似文献   
804.
The present investigation evaluated whether anxiety sensitivity interacted with marijuana use in relation to the prediction of panic-relevant variables among young adult tobacco smokers (n=265). Approximately 73% of the sample was composed of current marijuana smokers, with 78.5% of this sub-sample using marijuana more than once per week. As expected, after covarying cigarettes per day, alcohol use, and negative affectivity, the interaction between marijuana use and anxiety sensitivity predicted anxiety symptoms and agoraphobic cognitions. Partially consistent with prediction, the interaction between frequency of marijuana use and anxiety sensitivity predicted only anxiety symptoms. These results are discussed in relation to better understanding the potential role of regular marijuana use and anxiety sensitivity for panic-relevant emotional vulnerability among regular tobacco smokers.  相似文献   
805.
A review of the literature shows that explicit memory develops substantially from three years of age to adulthood, while implicit memory remains stable across this age range. Previously, this developmental dissociation has been attributed to different memory systems, or to confounds with perceptual vs. conceptual processing. Prompted by an alternative developmental framework, the experiments reported here provide evidence against both interpretations. Instead, it will be argued that (a) the implicit-explicit developmental dissociation reflects differences in strategic processing (strategy use and metamemory) across childhood and (b) that implicit memory can show development if a child's knowledge base in the tested domain is developing with age.  相似文献   
806.
Risk factors, such as emotional distress and peer substance involvement, are often tested as competing influences on adolescent substance use. However, the current study examined how affect (both positive and negative) and peers (both in terms of relationship quality and substance involvement) are interactive influences on adolescent substance use. A sample of 398 high school juniors and seniors completed surveys assessing each of these domains. Results of hierarchical regression analyses showed strong associations between an adolescent's and his or her best friend's substance use. Complex interactions supported the study hypothesis in that relations between affect and adolescent substance use were context dependent, with some peer contexts enhancing risk for substance use and others dampening this risk. Implications of these findings for interventions and preventions concerning adolescent substance use are discussed.  相似文献   
807.
This article explores the maternal role in the acquisition of tool-use behaviours by infant chimpanzees (Pan troglodytes). A honey-fishing task, simulating ant/termite fishing found in the wild, was introduced to three dyads of experienced mother and naïve infant chimpanzees. Four fishing sites and eight sets of 20 objects to be used as tools, not all appropriate, were available. Two of the mothers constantly performed the task, using primarily two kinds of tools; the three infants observed them. The infants, regardless of the amount of time spent observing, successfully performed the task around the age of 20–22 months, which is earlier than has been recorded in the wild. Two of the infants used the same types of tools that the adults predominantly used, suggesting that tool selectivity is transmitted. The results also show that adults are tolerant of infants, even if unrelated; infants were sometimes permitted to lick the tools, or were given the tools, usually without honey, as well as permitted to observe the adult performances closely.Electronic Supplementary Material Supplementary material is available in the online version of this article at  相似文献   
808.
Stereotypes and biological theories suggest that psychological gender differences found in predominantly heterosexual samples are smaller or reversed among gay men and lesbians. Computerized text analysis that compares peoples language style on a wide range of dimensions from pronoun use to body references offers a multivariate personality marker to test such assumptions. Analysis of over 1,500 internet personal advertisements placed by heterosexual men, heterosexual women, gay men, and lesbians found little evidence that orientation alters the impact of gender on linguistic behaviors. Previously reported gender differences were replicated in the gay as well as the heterosexual advertisements studied. Main effects of sexual orientation indicated that gay people of both sexes apparently felt less need to differentiate themselves from potential mates than did heterosexual people. Virtually no crossover sexual orientation by sex interactions emerged indicating that several popular models of sexual orientation are not supported on a linguistic level.  相似文献   
809.
The study utilized qualitative methods to study protective factors among middle school students who were at risk for substance use. Three focus groups (consisting of 6–7 parents each) were conducted to learn more about parent’s perceptions of protective factors within the neighborhood, school, family, and the individual. In terms of spirituality, parents stressed the importance of church involvement in preventing high-risk behaviors. These findings will be highlighted to provide information that may serve as a basis for further examining church involvement and spirituality as protective factors in adolescent substance use.  相似文献   
810.
An area where conflicts of interest can take place in Estonia is in the conduct of clinical trials. The paper lists the main areas where such conflicts of interest can occur. The author also briefly discusses Estonia’s current position with regard to regulating genetic information and the commencement of the Estonian Genome Project. An earlier version of this paper was presented at an International Conference on “Conflict of Interest and its Significance in Science and Medicine” held in Warsaw, Poland on 5–6 April, 2002.  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