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   6505篇
  免费   241篇
  国内免费   7篇
电工技术   61篇
综合类   5篇
化学工业   1285篇
金属工艺   135篇
机械仪表   143篇
建筑科学   393篇
矿业工程   13篇
能源动力   212篇
轻工业   662篇
水利工程   110篇
石油天然气   30篇
无线电   440篇
一般工业技术   1167篇
冶金工业   1055篇
原子能技术   47篇
自动化技术   995篇
  2023年   34篇
  2022年   64篇
  2021年   101篇
  2020年   91篇
  2019年   97篇
  2018年   112篇
  2017年   126篇
  2016年   120篇
  2015年   137篇
  2014年   185篇
  2013年   410篇
  2012年   338篇
  2011年   416篇
  2010年   289篇
  2009年   332篇
  2008年   438篇
  2007年   360篇
  2006年   301篇
  2005年   313篇
  2004年   252篇
  2003年   229篇
  2002年   213篇
  2001年   118篇
  2000年   90篇
  1999年   111篇
  1998年   118篇
  1997年   93篇
  1996年   114篇
  1995年   84篇
  1994年   88篇
  1993年   78篇
  1992年   66篇
  1991年   50篇
  1990年   58篇
  1989年   75篇
  1988年   39篇
  1987年   52篇
  1986年   45篇
  1985年   60篇
  1984年   61篇
  1983年   54篇
  1982年   44篇
  1981年   48篇
  1980年   28篇
  1979年   38篇
  1978年   33篇
  1977年   24篇
  1976年   22篇
  1975年   28篇
  1974年   20篇
排序方式: 共有6753条查询结果,搜索用时 78 毫秒
21.
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
22.
The current study investigated the impact of requiring respondents to elaborate on their answers to a biodata measure on mean scores, the validity of the biodata item composites, subgroup mean differences, and correlations with social desirability. Results of this study indicate that elaborated responses result in scores that are much lower than nonelaborated responses to the same items by an independent sample. Despite the lower mean score on elaborated items, it does not appear that elaboration affects the size of the correlation between social desirability and responses to biodata items or that it affects criterion-related validity or subgroup mean differences in a practically significant way. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
23.
24.
Imperative programs can be inverted directly from their forward-directed program code with the use of logical inference. The relational semantics of imperative computations treats programs as logical relations over the observable state of the environment, which is taken to be the state of the variables in memory. Program relations denote both forward and backward computations, and the direction of the computation depends upon the instantiation pattern of arguments in the relation. This view of inversion has practical applications when the relational semantics is treated as a logic program. Depending on the logic programming inference scheme used, execution of this relational program can compute the inverse of the imperative program. A number of nontrivial imperative computations can be inverted with minimal logic programming tools.  相似文献   
25.
26.
Dimensionless material balance equations describing an uninhibited enzyme hydrolysis process in a semi-batch reactor (i.e. fed-batch reactor) are formulated; numerical solution of these equations provided concentration profiles of the enzyme-substrate complex by using published kinetic parameters. The unrestricted values obtained are compared with estimates based separately on the reaction steady state and stationary state assumptions. Results are discussed in terms of the enzyme/substrate inventory used and it is found that the reaction steady state is a satisfactory approximation only when this ratio is sufficiently small. The stationary state may be a better approximation at other values, particularly when enzyme is added to substrate or when an empty tank is being filled. Reaction yields from semi-batch and batch operations are compared. Processing takes longer in the semi-batch operations and complete conversions are only practical in this mode when enzyme is added to substrate.  相似文献   
27.
28.
Air combat scenarios present unique problems where the solution is not obvious. An advanced networked simulation environment can be used to train high-level cognitive air combat skills such as problem solving. A problem in the development of principled and construct oriented assessment is related to determining the level of specificity of the assessment. We present a detailed discussion of the definition of critical competencies associated with combat mission problem solving performance, and we describe our approach to develop and implement an embedded performance assessment system that maps outcomes to these competencies. Finally, we discuss the implications for our approach for comprehensive assessment and discuss our goals for an evaluation of the competency-based approach to assessment.  相似文献   
29.
30.
A one–dimensional, transient thermal degradation heat transfer model for the response of composite materials when exposed to fire is presented. The model can handle layers of different materials. Material properties are functions of temperature. The reaction can be specified using Arrhenius‐type parameters or by inputting a density–temperature relationship determined by any experimental technique such as thermogravimetric analysis. The model is validated against the experimental data presented in Boyer's 1984 dissertation. Overall, the model provides excellent agreement with the experimental data. It is shown that very little difference is found between results arrived at by Arrhenius kinetics and results obtained by specifying the easier to measure density–temperature relationship. From this it is concluded that this technique is a viable alternative to Arrhenius‐type models. Copyright © 2006 John Wiley & Sons, Ltd.  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