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   14183篇
  免费   1651篇
  国内免费   724篇
电工技术   1590篇
技术理论   6篇
综合类   1783篇
化学工业   721篇
金属工艺   92篇
机械仪表   313篇
建筑科学   2845篇
矿业工程   630篇
能源动力   467篇
轻工业   1443篇
水利工程   1257篇
石油天然气   559篇
武器工业   85篇
无线电   484篇
一般工业技术   1053篇
冶金工业   1073篇
原子能技术   144篇
自动化技术   2013篇
  2024年   94篇
  2023年   232篇
  2022年   507篇
  2021年   632篇
  2020年   654篇
  2019年   504篇
  2018年   540篇
  2017年   496篇
  2016年   691篇
  2015年   605篇
  2014年   1123篇
  2013年   1182篇
  2012年   1171篇
  2011年   1112篇
  2010年   874篇
  2009年   884篇
  2008年   858篇
  2007年   927篇
  2006年   898篇
  2005年   603篇
  2004年   493篇
  2003年   394篇
  2002年   266篇
  2001年   195篇
  2000年   143篇
  1999年   96篇
  1998年   73篇
  1997年   47篇
  1996年   40篇
  1995年   25篇
  1994年   25篇
  1993年   20篇
  1992年   19篇
  1991年   13篇
  1990年   19篇
  1989年   17篇
  1988年   11篇
  1987年   5篇
  1986年   5篇
  1985年   7篇
  1984年   9篇
  1983年   7篇
  1982年   7篇
  1981年   5篇
  1979年   5篇
  1968年   2篇
  1965年   3篇
  1964年   3篇
  1963年   4篇
  1961年   3篇
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
51.
Children's perceived attachments with parents, and family cohesion and adaptability were examined as predictors, mediators, and moderators in the parental problem drinking-child outcomes link. A total of 216 6- to 12-year-olds (110 boys, 106 girls) participated. Data were obtained from children and their mothers, fathers, and teachers. A higher level of family cohesion and adaptability functioned as (a) a robust protective factor against adjustment and cognitive difficulties otherwise associated with problem drinking and (b) a mediator of adjustment problems. Children's perceptions of attachments to mothers and fathers were consistent predictors of behavioral, social, and cognitive problems and further moderated relations between problem drinking and child functioning. The results support that child-parent and family functioning variables act as either pathways and/or vulnerability and protective factors for children exposed to a high-risk environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
52.
Trust for Ubiquitous,Transparent Collaboration   总被引:1,自引:0,他引:1  
Shand  Brian  Dimmock  Nathan  Bacon  Jean 《Wireless Networks》2004,10(6):711-721
In this paper, trust-based recommendations control the exchange of personal information between handheld computers. Combined with explicit risk analysis, this enables unobtrusive information exchange, while limiting access to confidential information. The same model can be applied to a wide range of mobile computing tasks, such as managing personal address books and electronic diaries, to automatically provide an appropriate level of security. Recommendations add structure to the information, by associating categories with data and with each other, with degrees of trust belief and disbelief. Since categories also in turn confer privileges and restrict actions, they are analogous to rôles in a Rôle-Based Access Control system, while principals represent their trust policies in recommendations. Participants first compute their trust in information, by combining their own trust assumptions with others' policies. Recommendations are thus linked together to compute a considered, local trust assessment. Actions are then moderated by a risk assessment, which weighs up costs and benefits, including the cost of the user's time, before deciding whether to allow or forbid the information exchange, or ask for help. By unifying trust assessments and access control, participants can take calculated risks to automatically yet safely share their personal information.  相似文献   
53.
54.
Drug users are particularly at risk for contracting the human immunodeficiency virus and serve as a major mechanism for spreading the virus to other sectors of the population. As a result drug abuse treatment and potential behavioral change strategies are primary public health issues. The purpose of this article is to review the contributions included in this special edition, which represent an effort to describe the most current thinking in the field with a blend of theoretical, review, and empirical articles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
55.
The present study applied a semiparametric mixture model to a sample of 284 low-income boys to model developmental trajectories of overt conduct problems from ages 2 to 8. As in research on older children, 4 developmental trajectories were identified: a persistent problem trajectory, a high-level desister trajectory, a moderate-level desister trajectory, and a persistent low trajectory. Follow-up analyses indicated that initially high and low groups were differentiated in early childhood by high child fearlessness and elevated maternal depressive symptomatology. Persistent problem and high desister trajectories were differentiated by high child fearlessness and maternal rejecting parenting. The implications of the results for early intervention research are discussed, with an emphasis on the identification of at-risk parent-child dyads. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
The authors hypothesize that depressed states evolved to minimize risk in social interactions in which individuals perceive that the ratio of their social value to others, and their social burden on others, is at a critically low level. When this ratio reaches a point where social value and social burden are approaching equivalence, the individual is in danger of exclusion from social contexts that, over the course of evolution, have been critical to fitness. Many features of depressed states can be understood in relation to mechanisms that reduce social risk in such circumstances, including (a) hyper-sensitivity to signals of social threat from others, (b) sending signals to others that reduce social risks, and (c) inhibiting risk-seeking (e.g., confident, acquisitive) behaviors. These features are discussed in terms of psychosocial and neurobiological research on depressive phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
57.
针对目前大多数科研单位在内部会计控制中存在的问题,根据财政部颁布的《内部会计控制规范一基本规范》,探讨了科研单位在转制过程中应如何建立和完善内部会计控制制度,以达到防范经营风险,保护资产安全、完整,确保经营管理目标和政策有效实施.  相似文献   
58.
In this paper we introduce an empirical Bayes procedure for estimating an unknown parameter, say θ. This procedure gives the empirical Bayes estimator for θ and its associated minimum posterior risk in closed forms without estimating the unknown prior density function of θ. In such procedure the posterior probability density function of θ is not required. A sufficient statistic for θ with conditional probability density function in the one parameter exponential family is required. Instead of estimating the unknown prior density function, the marginal density function of the sufficient statistic must be estimated. As special cases the empirical Bayes estimators and their respective minimum posterior risks of the failure rate for the exponential distribution, the unknown scale parameters of Weibull and gamma distributions are obtained in simple forms as special cases. Numerical results and a simulation study are introduced to (i) investigate how the number of available past experiments and the sample size of each influence the accuracy of the empirical Bayes estimator, (ii) make a comparison between the presented procedure and the Bayes procedure when the prior probability density function of the parameter θ is gamma.  相似文献   
59.
周洁卿 《黄金》2006,27(2):3-6
近几年,我国外汇储备逐年增加,而美元汇率偏弱,使我国承担很大的外汇风险。为了规避外汇风险,应增加黄金储备。文中提出了我国增加黄金储备总量的理由以及增加黄金储备的途径。这些建议具有可操作性,可以提供给有关部门参考。  相似文献   
60.
Longitudinal neurobehavioral development was examined in 237 fetuses of low-risk pregnancies from 2 distinct populations-Baltimore, Maryland, and Lima. Peru-at 20. 24. 28. 32, 36. and 38 weeks gestation. Data were based on digitized Doppler-based fetal heart rate (FHR) and fetal movement (FM). In both groups. FHR declined while variability, episodic accelerations, and FM-FHR coupling increased, with discontinuities evident between 28 and 32 weeks gestation. Fetuses in Lima had higher FHR and lower variability, accelerations, and FM-FHR coupling. Declines in trajectories were typically observed 1 month sooner in Lima, which magnified these disparities. Motor activity differences were less consistent. No sex differences in fetal neurobehaviors were detected. It is concluded that population factors can influence the developmental niche of the fetus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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