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   50406篇
  免费   4848篇
  国内免费   2461篇
电工技术   3402篇
技术理论   1篇
综合类   3990篇
化学工业   6709篇
金属工艺   1987篇
机械仪表   3404篇
建筑科学   7492篇
矿业工程   1030篇
能源动力   3406篇
轻工业   5494篇
水利工程   678篇
石油天然气   2364篇
武器工业   693篇
无线电   3133篇
一般工业技术   5011篇
冶金工业   2337篇
原子能技术   329篇
自动化技术   6255篇
  2024年   347篇
  2023年   987篇
  2022年   1815篇
  2021年   2145篇
  2020年   2255篇
  2019年   1884篇
  2018年   1822篇
  2017年   2067篇
  2016年   2169篇
  2015年   2185篇
  2014年   3340篇
  2013年   3213篇
  2012年   3776篇
  2011年   3814篇
  2010年   2844篇
  2009年   2865篇
  2008年   2501篇
  2007年   3207篇
  2006年   2677篇
  2005年   2280篇
  2004年   1831篇
  2003年   1520篇
  2002年   1225篇
  2001年   1021篇
  2000年   765篇
  1999年   603篇
  1998年   412篇
  1997年   348篇
  1996年   336篇
  1995年   227篇
  1994年   179篇
  1993年   134篇
  1992年   107篇
  1991年   97篇
  1990年   76篇
  1989年   59篇
  1988年   44篇
  1987年   37篇
  1986年   20篇
  1985年   32篇
  1984年   43篇
  1983年   28篇
  1982年   26篇
  1980年   47篇
  1965年   19篇
  1964年   28篇
  1963年   26篇
  1961年   22篇
  1956年   18篇
  1955年   25篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
The relationship between teachers' judgments versus actual performance on curriculum-based measures in reading was examined. A total of 30 regular education teachers were asked to predict the oral reading fluency score of students along with a rating scale of reading subskills. Correlations between teacher judgment measures and student performance found that teachers were accurate reporters of student performance levels in reading. However, some questions were raised whether teachers were accurate at predicting the actual level of student oral reading fluency when effect sizes were used to compare teacher judgment and actual student performance. Recommendations for continued research in understanding the parameters of the accuracy of teacher judgment are made. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
22.
This study investigated the relationship between self-appraisals of performance, symptom severity and post-event rumination in social phobia, and evaluated the effect of treatment on these variables. A socially phobic group and a nonanxious control group performed an impromptu speech and were told that their performance would be evaluated. Participants appraised their performance immediately after the speech and 1 week later, and the frequency of post-event rumination during the week following the speech was assessed. The socially phobic group maintained the negative appraisals of their speech over the week, whereas the nonclinical group showed increased positivity about their performance The socially phobic group also engaged in more negative rumination than controls. Treatment improved perceptions of performance and reduced negative rumination. These results are discussed in the light of cognitive models of social phobia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
23.
Evaluating the design of flexible manufacturing systems is complex. Developing a measure of performance useful for evaluating alternate designs continues to be interesting. Here, total productivity of the system is proposed as an appropriate measure. Specification of parameters based upon strategic considerations for this measure are discussed. Finally, the usefulness of the measure is demonstrated through an example.  相似文献   
24.
Large technical systems need to be designed both reliable and efficient. Specialized design tools offer therefore a simplified, abstract design and extend details autonomously in the background. Analytic and simulation based models could improve the quality by testing and dimensioning the design before implementation, but setting up the necessary models is time-consuming and expensive. Therefore many developers ask for analysis tools which are able to create their models from the available information in the design tools. This paper presents such an automated modeling approach basing on an existing design database at the example of a network analysis for building automation fieldbuses. The process of automated modeling is unfolded, and the potentials and limitations are discussed.  相似文献   
25.
王日清 《核动力工程》1989,10(4):23-27,42
本文着重介绍了 IAEA 所制定的核电厂运行安全指标,同时也介绍了美国所制定的类似指标。这些指标为定量地评估和比较各国核电厂运行安全提供了可靠的依据。  相似文献   
26.
Although computer speed has steadily increased and memory is getting cheaper, the need for storage managers to deal efficiently with applications that cannot be held into main memory is vital. Dealing with large quantities of clauses implies the use of persistent knowledge and thus, indexing methods are essential to access efficiently the subset of clauses relevant to answering a query. We introduce PerKMan, a storage manager that uses G-trees, and aims at efficient manipulation of large amounts of persistent knowledge. PerKMan may be connected to Prolog systems that offer an external C language interface. As well as the fact that the storage manager allows different arguments of a predicate to share a common index dimension in a novel manner, it indexes rules and facts in the same manner. PerKMan handles compound terms efficiently and its data structures adapt their shape to large dynamic volumes of clauses, no matter what the distribution. The storage manager achieves fast clause retrieval and reasonable use of disk space.  相似文献   
27.
本文综述了DCS(集散控制系统)三代产品的总体水平评价,介绍了DCS的总体性能、评价指标和它的选择准则。  相似文献   
28.
Computer based discrete event simulation (DES) is one of the most commonly used aids for the design of automotive manufacturing systems. However, DES tools represent machines in extensive detail, while only representing workers as simple resources. This presents a problem when modelling systems with a highly manual work content, such as an assembly line. This paper describes research at Cranfield University, in collaboration with the Ford Motor Company, founded on the assumption that human variation is the cause of a large percentage of the disparity between simulation predictions and real world performance. The research aims to improve the accuracy and reliability of simulation prediction by including models of human factors.  相似文献   
29.
本文以渤中28-1(BZ28-1)油田N6H水平井为例,从多方面对该井的动态和产能变化进行了系统分析,所用的方法对水平井动态分析有一定的指导意义。  相似文献   
30.
This paper concerns the following problem: given a set of multi-attribute records, a fixed number of buckets and a two-disk system, arrange the records into the buckets and then store the buckets between the disks in such a way that, over all possible orthogonal range queries (ORQs), the disk access concurrency is maximized. We shall adopt the multiple key hashing (MKH) method for arranging records into buckets and use the disk modulo (DM) allocation method for storing buckets onto disks. Since the DM allocation method has been shown to be superior to any other allocation methods for allocating an MKH file onto a two-disk system for answering ORQs, the real issue is knowing how to determine an optimal way for organizing the records into buckets based upon the MKH concept.

A performance formula that can be used to evaluate the average response time, over all possible ORQs, of an MKH file in a two-disk system using the DM allocation method is first presented. Based upon this formula, it is shown that our design problem is related to a notoriously difficult problem, namely the Prime Number Problem. Then a performance lower bound and an efficient algorithm for designing optimal MKH files in certain cases are presented. It is pointed out that in some cases the optimal MKH file for ORQs in a two-disk system using the DM allocation method is identical to the optimal MKH file for ORQs in a single-disk system and the optimal average response time in a two-disk system is slightly greater than one half of that in a single-disk system.  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