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   15820篇
  免费   719篇
  国内免费   27篇
电工技术   153篇
综合类   9篇
化学工业   3166篇
金属工艺   273篇
机械仪表   329篇
建筑科学   999篇
矿业工程   34篇
能源动力   527篇
轻工业   1486篇
水利工程   213篇
石油天然气   71篇
无线电   1130篇
一般工业技术   3070篇
冶金工业   2277篇
原子能技术   82篇
自动化技术   2747篇
  2023年   97篇
  2022年   166篇
  2021年   311篇
  2020年   264篇
  2019年   301篇
  2018年   341篇
  2017年   355篇
  2016年   369篇
  2015年   357篇
  2014年   515篇
  2013年   1064篇
  2012年   880篇
  2011年   1189篇
  2010年   782篇
  2009年   798篇
  2008年   1016篇
  2007年   864篇
  2006年   722篇
  2005年   688篇
  2004年   573篇
  2003年   528篇
  2002年   486篇
  2001年   261篇
  2000年   243篇
  1999年   243篇
  1998年   252篇
  1997年   237篇
  1996年   244篇
  1995年   198篇
  1994年   173篇
  1993年   163篇
  1992年   142篇
  1991年   108篇
  1990年   133篇
  1989年   134篇
  1988年   77篇
  1987年   110篇
  1986年   99篇
  1985年   119篇
  1984年   112篇
  1983年   124篇
  1982年   92篇
  1981年   88篇
  1980年   66篇
  1979年   76篇
  1978年   61篇
  1977年   50篇
  1976年   45篇
  1975年   50篇
  1974年   34篇
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
81.
The use of computer models offers a general and flexible framework that can help to deal with some of the complexities and difficulties associated with the development of water management plans as prescribed by the Water Framework Directive. However, despite the advantages modelling presents, the integration of information derived from models into policy is far away from being trivial or the norm. Part of the difficulties of this integration is rooted in the lack of confidence policy makers have on the incorporation of modelling information into policy formulation. In this paper we examine the reasons for this apparent lack of confidence and explore how some tools, presently in use, address this problem. We conclude that public confidence in models is highly dependent on the way uncertainties are addressed and suggest possible directions of action to improve the current situation. Four real case studies illustrate how computer models have been used in The Netherlands for carrying out management plans at regional and national scale. We suggest that the solution to integrate modelling information into policy formulation lies on both the modelling and the policy-making communities.  相似文献   
82.
This paper presents long-term outcomes of the largest clinical trial of smokeless tobacco (SLT) cessation reported to date. SLT users in five northwestern states were recruited to call a toll-free number, and 1,069 users were randomized to one of two self-help conditions: either a manual-only condition or an assisted self-help condition, which included the manual, a targeted video, and two support phone calls. Significant between-group differences were not found for either the 12- or 18-month point-prevalence measure of abstinence from either SLT only or all tobacco products using outcomes based on either the responder or intention-to-treat outcomes. However, using a repeated point-prevalence measure across all three assessment points, we found that significantly more assisted self-help participants reported abstinence, compared with manual-only participants. Compared with manual-only participants, those in the assisted self-help condition were significantly more likely to use recommended cessation techniques. Results demonstrate that low-cost, minimal interventions delivered by mail and phone can help a sizable proportion of individuals quit using SLT.  相似文献   
83.
The associations between stressful life events and smoking have been established among adolescents in the United States. However, whether these relationships are similar in adolescents from other non-Western cultures is unknown. Understanding these relationships in adolescents may help to provide opportunities to reduce the smoking rates in those cultures by providing positive coping methods that do not include smoking. In this longitudinal study, the associations between nine stressful life events scales and smoking behaviors were examined in a sample of Chinese adolescents. Six of these scales, positive school-related, negative school-related, positive family-related, positive peer-related, negative peer-related, and negative health-related had significantly different means among females and males. Among males, positive school-related stress was a protective factor for smoking susceptibility. Among females, positive school-related stress was a protective factor and negative school-related stress was a risk factor for lifetime smoking, and negative family-related stress was a risk factor for smoking susceptibility. Findings indicate that smoking among male adolescents in China may not be the result of stress; however, in females stress may contribute to the decision to smoke. Future directions are discussed.  相似文献   
84.
85.
Rainwater collection as a possible water source in developing countries is introduced. The major parameters in calculating the size of the tank are defined. Six methods that have been used previously to relate demand, storage, reliability and the rainfall pattern are compared to the Ottawa Model over a wide range of demands.  相似文献   
86.
An introduction to parallel process interventions is provided by a comprehensive review of the theoretical constructs and empirical studies regarding the use of the parallel process in supervision. Although more direct investigations of the parallel process are needed, we conclude that parallel process interventions within the supervisory relationship can be extremely potent and impactful. Recommendations for the facilitative application of the parallel process in the supervision and training of professional psychologists, as well as case examples, are provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
87.
The rationale for developing a theoretical model of computer-mediated communication (CMC) competence is established through review of social trends in the use of new media technologies. Special attention is paid to the role new media play in the formation and development of personal relationships. A model of CMC competence is then developed along the lines of motivation, knowledge, skills, context, and outcomes as a metaphorical typology for organizing existing CMC research. This research is reviewed as it informs, and is organized by, the model of CMC competence. A sampling of formal propositions resulting from the model is elaborated, and the results of preliminary pilot studies of the model are reviewed. The model is offered as a first step in examining individual differences in the domain of CMC relationships and media choice.  相似文献   
88.
A specific radioimmunoassay for platelet-activating factor (PAF) sensitive in the range 10–1000 pg (0.02–2 pmoles) has been developed. Detailed quantitative hapten inhibition studies showed specificity for the acetyl group at C-2 of PAF, a requirement for the ether linkage at C-1 and some tolerance for substituents on the choline nitrogen. No significant cross-reactivity was found with phosphatidylcholine and lysophosphatidylcholine or with lysoPAF. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.  相似文献   
89.
90.
The group scanning model of feature integration theory suggests that Ss search visual displays serially by groups, but process items within each group in parallel. Group size is determined by the discriminability of the targets in the background of distractors. When the target is poorly discriminable, the size of the scanned group will be small, and search will be slow. The model predicts that group size will be smallest when targets of an intermediate value on a perceptual dimension are presented in a heterogeneous background of distractors that have higher and lower values on the same dimension. Experiment 1 (30 Ss) demonstrates this effect; Exp 2 (12 Ss) controls for a possible confound of decision complexity in Exp 1. For simple feature targets, the group scanning model provides a good account of the visual search process. (French abstract) (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