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   8622篇
  免费   818篇
  国内免费   585篇
电工技术   861篇
综合类   660篇
化学工业   1302篇
金属工艺   543篇
机械仪表   519篇
建筑科学   548篇
矿业工程   222篇
能源动力   245篇
轻工业   1170篇
水利工程   225篇
石油天然气   138篇
武器工业   80篇
无线电   733篇
一般工业技术   761篇
冶金工业   643篇
原子能技术   194篇
自动化技术   1181篇
  2024年   37篇
  2023年   95篇
  2022年   255篇
  2021年   354篇
  2020年   225篇
  2019年   224篇
  2018年   215篇
  2017年   247篇
  2016年   232篇
  2015年   319篇
  2014年   440篇
  2013年   555篇
  2012年   673篇
  2011年   669篇
  2010年   589篇
  2009年   613篇
  2008年   631篇
  2007年   534篇
  2006年   489篇
  2005年   433篇
  2004年   354篇
  2003年   299篇
  2002年   291篇
  2001年   250篇
  2000年   180篇
  1999年   97篇
  1998年   144篇
  1997年   103篇
  1996年   56篇
  1995年   40篇
  1994年   60篇
  1993年   52篇
  1992年   23篇
  1991年   15篇
  1990年   23篇
  1989年   20篇
  1988年   16篇
  1987年   9篇
  1986年   11篇
  1985年   15篇
  1984年   11篇
  1983年   11篇
  1982年   16篇
  1981年   8篇
  1980年   10篇
  1979年   6篇
  1977年   11篇
  1976年   19篇
  1975年   7篇
  1974年   7篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Compatibility equations for large deformations are developed on the sole basis of the div and curl concepts.  相似文献   
32.
冯向辉 《世界电信》2003,16(12):57-59
北电网络提供的Contivity解决方案不仅可以使用户建立各种类型的VPN,而且还可以把这些VPN集成到未来的融合话音和数据的网络中。该方案已实现了安全路由选择;可通过多种技术支持鉴权功能,从而实现安全接入;允许用户使用其各自的安全性配置文件设置;其设计中没有“后门”,重点介绍了Contivity 2700网关的主要特征及其优势。  相似文献   
33.
In order to maximize systems average availability during a given period of time, it has recently been developed a non-periodic surveillance test optimization methodology based on genetic algorithms (GA). The fact of allowing non-periodic tests turns the solution space much more flexible and schedules can be better adjusted, providing gains in the overall system average availability, when compared to those obtained by an optimized periodic test scheme. This approach, however, turns the optimization problem more complex. Hence, the use of a powerful optimization technique, such as GA, is required.Considering that some particular features of certain systems can turn it advisable to introduce other specific constraints in the optimization problem, this work investigates the application of seasonal constraints for the set of the Emergency Diesel Generation of a typical four-loop pressurized water reactor in order to planning and optimizing its surveillance test policy. In this analysis, the growth of the blackout accident probability during summer, due to electrical power demand increases, was considered. Here, the used model penalizes surveillance test interventions when the blackout probability is higher.Results demonstrate the ability of the method in adapting the surveillance test policy to seasonal constraints. The knowledge acquired by the GA during the searching process has lead to test schedules that drastically minimize test interventions at periods of high blackout probability. It is compensated by more frequent redistributed tests through the periods of low blackout probability in order to improve on the overall average availability at the system level.  相似文献   
34.
1. INTRODUCTION In the design of a discharge tunnel with high water head and large flow, it is important to study the cavitation and the energy dissipation, such as the prevention of cavitation for slots of various gates [1-4], the effects of entrained ai…  相似文献   
35.
The determination of the fundamental stress versus crack opening (σ-w) response of concrete under uniaxial tension is performed in this study through inverse analysis using data from notched beam tests. The procedure used for optimizing the parameters of the σ-w relation using the load versus crack mouth opening displacement response of the notched beam is described. Satisfactory comparisons have been obtained between the σ-w curves obtained through the inverse analysis and those directly measured in uniaxial tension tests. The use of weighting functions in the inverse analysis may be necessary when large crack widths are to be considered.  相似文献   
36.
This research focused on the syllable as a processing unit in handwriting. Participants wrote, in uppercase letters, words that had been visually presented. The interletter intervals provide information on the timing of motor production. In Experiment 1, French participants wrote words that shared the initial letters but had different syllable boundaries. In Experiment 2, French- and Spanish-speaking participants wrote cognates and pseudowords with a letter sequence that was always intrasyllabic in French and intersyllabic in Spanish. In Experiment 3, French-Spanish bilinguals wrote the cognates and pseudowords with the same type of sequences. In the 3 experiments, the critical interletter intervals were longer between syllables than within syllables, indicating that word syllable structure constrains motor production both in French and Spanish. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
37.
铅酸蓄电池的清洁生产   总被引:1,自引:0,他引:1  
就中国铅酸蓄电池工业的可持续性发展与清洁生产问题进行了初步探讨,并就蓄电池正负极板水洗的清洁生产实例进行了介绍。  相似文献   
38.
39.
A novel and efficient way of producing of aldonic acids is reported. The selective catalytic oxidation of monosaccharides (arabinose, ribose, xylose, lyxose, mannose, rhamnose, glucose, galactose, N-acetyl-glucosamine) and disaccharides (lactose, maltose, cellobiose, melibiose) on Au, Pd and Pt catalysts was investigated. By using the gold catalyst, a total selectivity with respect to aldonic acids and a high catalytic activity for all investigated sugars was found. The reaction conditions for the production of maltobionic and lactobionic acids via oxidation on gold catalysts were optimised. A high long-term stability of two different gold catalysts for the oxidation of maltose and lactose, respectively, was found.  相似文献   
40.
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