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   292679篇
  免费   30125篇
  国内免费   21734篇
电工技术   41807篇
技术理论   23篇
综合类   33276篇
化学工业   13005篇
金属工艺   9207篇
机械仪表   24830篇
建筑科学   20262篇
矿业工程   10117篇
能源动力   10210篇
轻工业   5818篇
水利工程   7558篇
石油天然气   7620篇
武器工业   4957篇
无线电   34016篇
一般工业技术   16300篇
冶金工业   7858篇
原子能技术   2654篇
自动化技术   95020篇
  2024年   1248篇
  2023年   3193篇
  2022年   6247篇
  2021年   7560篇
  2020年   8188篇
  2019年   6252篇
  2018年   5997篇
  2017年   7904篇
  2016年   9299篇
  2015年   11064篇
  2014年   18899篇
  2013年   16840篇
  2012年   22227篇
  2011年   23781篇
  2010年   18243篇
  2009年   18518篇
  2008年   19107篇
  2007年   23286篇
  2006年   20366篇
  2005年   17841篇
  2004年   14558篇
  2003年   12899篇
  2002年   9765篇
  2001年   8050篇
  2000年   6698篇
  1999年   5431篇
  1998年   4128篇
  1997年   3341篇
  1996年   2879篇
  1995年   2372篇
  1994年   1998篇
  1993年   1368篇
  1992年   1170篇
  1991年   803篇
  1990年   697篇
  1989年   563篇
  1988年   408篇
  1987年   211篇
  1986年   153篇
  1985年   164篇
  1984年   130篇
  1983年   118篇
  1982年   98篇
  1981年   84篇
  1980年   70篇
  1979年   57篇
  1978年   47篇
  1977年   37篇
  1976年   26篇
  1959年   27篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
凤滩水电厂自动发电控制策略   总被引:1,自引:0,他引:1  
介绍了凤滩水电厂自动发电控制(AGC)策略的实现方法,重点介绍了修正等容量比例有功分配方法及相应措施.程序设计的原则是,机组紧跟目标负荷的情况下,在最佳效率下运行,同时减少机组开/停机次数、有功调节频率和跨越振动区次数,从而减少机组磨损,兼顾运行效率和机组运行安全.  相似文献   
82.
This paper addresses the application of Genetic Programming (GP) to the synthesis of multicomponent product nonsharp distillation sequences. Combined with the domain knowledge of chemical engineering, some evolutionary factors are improved, and a set of special encoding method and solving strategy is proposed to deal with this kind of problem. The system structural variable is optimized by GP and the continuous variable is optimized by the simulated annealing algorithm simultaneously. Because GP has an automatic searching function, the optimal solution can be found including distillation, splitting, blending and bypassing operations automatically without any superstructures of nonsharp distillation sequences. Three illustrative examples are presented to demonstrate the effective computational strategies.  相似文献   
83.
In this paper, genetic algorithm is used to help improve the tolerance of feedforward neural networks against an open fault. The proposed method does not explicitly add any redundancy to the network, nor does it modify the training algorithm. Experiments show that it may profit the fault tolerance as well as the generalisation ability of neural networks.  相似文献   
84.
In today's competitive business environment, it is important that customers are able to obtain their preferred items in the shops they visit, particularly for convenience store chains such as 7–Eleven where popular items are expected to be readily available on the shelves of the stores for buyers. To minimize the cost of running such store chains, it is essential that stocks be kept to a minimum and at the same time large varieties of popular items are available for customers. In this respect, the replenishment system needs to be able to cope with the taxing demands of minimal inventory but at the same time keeping large varieties of needed items. This paper proposes a replenishment system which is able to respond to the fluctuating demands of customers and provide a timely supply of needed items in a cost–effective way. The proposed system embraces the principle of fuzzy logic which is able to deal with uncertainties by virtue of its fuzzy rules reasoning mechanism, thereby leveraging the responsiveness of the entire replenishment system for the chain stores. To validate the feasibility of the approach, a case study has been conducted in an emulated environment with promising results.  相似文献   
85.
Hyun Kyu Suh 《Fuel》2008,87(6):925-932
This paper investigates the effect of injection parameters on the characteristics of dimethyl ether (DME) as an alternative fuel in a diesel engine with experimental and analytical models based on empirical equations. In order to study macroscopic and microscopic characteristics of DME fuel, this work focuses on the atomization characteristics of DME and compares experimental and predicted results for spray development obtained by empirical models for diesel and DME fuel. Detailed comparisons of spray tip penetration from three different empirical correlations and from visualization experiments of diesel and DME fuels were conducted under various fuel injection conditions. In comparison with the results of different empirical equations for measured spray tip penetration, the experimental results of this study provide good agreement with the calculation results based on empirical equations, except during the earliest stage of the injected spray sequence. The results of atomization characteristics indicate that DME showed better spray characteristics than conventional diesel fuel. Also, the fuel injection delay and maximum injection rate of DME fuel are shorter and lower than those of diesel fuel at the same injection conditions, respectively.  相似文献   
86.
The chemical oxidation of aniline to form polyaniline (PANI) films and powder samples was made using Fenton reagent as an oxidizing agent in aqueous sulfuric acid medium. The PANI films were monitored by using the quartz crystal microbalance and the electronic absorption techniques. The optimum concentration was determined and the results were justified by measuring the UV–vis absorption spectra for the in situ PANI films. The conductivity for the PANI films and powder samples, prepared in different conditions, was measured. Also, the IR spectra, X‐ray and the thermogravimetric analysis for the PANI powder formed in the bulk were measured and compared with the polymer prepared using ammonium peroxydisulfate. A preliminary investigation to the dielectric properties of the polymer powder was measured and discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   
87.
苗青云 《山西建筑》2003,29(15):69-70
介绍了热水采暖系统运行及调整的注意事项,分析了立支管阀门、集气罐的作用,提出了使热水采暖系统的调节和集排气操作达到理想程度的有效措施,以实现良好的供暖效果。  相似文献   
88.
现场总线控制系统浅谈   总被引:1,自引:0,他引:1  
简述了现场总线控制系统的结构及其显优点。现场总线控制系统的结构包括:主控器、总线接口、电源、输入/输出接点、总线电揽和终端电阻。另外对其显优点做了逐一介绍。现场总线控制系统可在工业自动化控制系统中推广应用。  相似文献   
89.
GSM技术在配电网故障自动隔离及恢复系统的应用   总被引:1,自引:0,他引:1  
为了使配电网故障的隔离和恢复的通讯更加可靠、迅速、经济,设计了一种基于GSM通讯技术,借助移动通讯系统短信业务和数据业务,实现配电网故障的自动隔离与恢复的系统。该系统通过MCU采集数据,判断故障位置与故障类型,经GSM通讯模块上传主站,主站统筹全局,实现故障段的切除,非故障区的供电。阐述了系统的工作原理、硬件结构、通讯协议和软件流程。现场的实际运行情况证明数据上报通讯准确率为100%,多次模拟线路故障,根据故障点的不同,一般在2~3min内系统都能可靠的隔离故障,恢复系统。  相似文献   
90.
This paper explains the manufacturing process of a composite train carbody with a sandwich composite structure for bodyshell and a stainless steel structure for the under frame. In addition, the structural behavior and safety of the composite carbody of the Korean tilting train was investigated by the static load tests. From the test results, the stiffness of the composite carbody met the specified design. In the aspect of strength, the maximum stress of the composite bodyshell was of 12.2% of strength of CF1263 carbon/epoxy.  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