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   179788篇
  免费   15724篇
  国内免费   8490篇
电工技术   11418篇
技术理论   13篇
综合类   11694篇
化学工业   29391篇
金属工艺   9949篇
机械仪表   11302篇
建筑科学   13771篇
矿业工程   5488篇
能源动力   5306篇
轻工业   12466篇
水利工程   3274篇
石油天然气   10749篇
武器工业   1405篇
无线电   21606篇
一般工业技术   21556篇
冶金工业   8749篇
原子能技术   1933篇
自动化技术   23932篇
  2024年   905篇
  2023年   3427篇
  2022年   6367篇
  2021年   8520篇
  2020年   6406篇
  2019年   5072篇
  2018年   5734篇
  2017年   6410篇
  2016年   5716篇
  2015年   7609篇
  2014年   9424篇
  2013年   11294篇
  2012年   12273篇
  2011年   12905篇
  2010年   11025篇
  2009年   10411篇
  2008年   9933篇
  2007年   9163篇
  2006年   9330篇
  2005年   7987篇
  2004年   5325篇
  2003年   4483篇
  2002年   4015篇
  2001年   3613篇
  2000年   3542篇
  1999年   4170篇
  1998年   3468篇
  1997年   2942篇
  1996年   2752篇
  1995年   2229篇
  1994年   1812篇
  1993年   1308篇
  1992年   1048篇
  1991年   790篇
  1990年   574篇
  1989年   469篇
  1988年   373篇
  1987年   255篇
  1986年   210篇
  1985年   130篇
  1984年   117篇
  1983年   86篇
  1982年   86篇
  1981年   70篇
  1980年   62篇
  1979年   29篇
  1978年   25篇
  1977年   24篇
  1976年   26篇
  1975年   16篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
通过3种不同的碱来制备2,4-二氯-5-氟苯甲酰乙酸甲酯,优选得到了其最佳缩合剂甲醇钠;同时应用正交设计实验,研究了原料配比、反应时间、反应温度对收率的影响,在优选条件下收率为78.5%。  相似文献   
92.
The coal filter cake is a product of fine coal after floatation which has an ash content of 7-13%, water content of 30±2%, and a particle size of less than 1 mm. The ash content was measured by the intensity of the single backscattered gamma-ray, and its accuracy is mainly dependent on the energy of the gamma-ray. The 238Pu low energy photon source is selected in this work. The energy of its gamma-ray is 15 keV, which can result not only in the best sensitivity, but also in the lowest contribution to the environment radiation. The root mean square deviation of the ash measurement is±0.33% (±1σ).  相似文献   
93.
With the “orthogonal experimental design” (OED), the dependence of conductivity and transparency of tin oxide films and open circuit voltage Voc of SIS solar cells on the spray deposition process factors was studied. The OED technique was found to be a powerful method for realizing the best factor combination. Using OED, curves were obtained which clearly depict the effects of each factor on the SIS characteristics. The results of the experiments also illustrate exactly which variation in fabrication technique most affects the sheet resistance, Voc, and film transparency. Under the optimal combination of conditions, a thin film doped with NH4F was obtained, with about 90% transmission and a sheet resistance of about 80 Ω/□, along with an SIS structure with a Voc of about 0.61 V.  相似文献   
94.
A method is proposed which avoids many limitations associated with traditional B-coefficient loss coefficient calculation. The proposed method, unlike the traditional B-coefficient method, is very fast and can handle line outages. The method utilizes network sensitivity factors which are established from DC load flow solutions, Line outage distribution factors (ODFs) are formulated using changes in network power generations to simulate the outaged line from the network. The method avoids the use of complicated reference frame transformations based upon Kron's tenser analysis. The necessity of data normalization used in least squares and the evaluation of the slope of &thetas;j versus PGn is not necessary with the proposed method. Using IEEE standard 14-bus and 30-bus systems, the method's results are compared against results obtained from an AC load flow program (LFED). The method's solution speed is compared to that of the LFED method, the base case database method and the conventional B-coefficient method based on Ajn-factor. The proposed method is easy to implement and, when compared to other methods, has exhibited good accuracy and rapid execution times. The method is well suited to online dispatch applications  相似文献   
95.
96.
专家系统在化工中的应用进展   总被引:2,自引:0,他引:2  
本文综述了近年来专家系统在化工领域的应用状况,并指出今后的发展趋势。  相似文献   
97.
王惠华  周仁公 《化学与粘合》1996,(4):241-242,233
本文提出采用高分子有机材料配合,生产石膏制品防水防潮剂的生产方法和工艺。该剂还可以应用到氧化镁系列板材,同时提出开发珠光或彩色防水防潮剂,能达到满足的装饰效果,值提开发推广。  相似文献   
98.
��Consulting the relevant documents at home and abroad,the author finisheid the derivation of quations about critical flow quantity,critical flow rate,contrast flow quantity,contrast flow rate which are necessary to the continuous water withdrawal through the flow string with different diameters and the rational flow string formula that should be selected when the contrust parameter1.The author also works out the solving programme for TI-59 computer and designs and draws up the nomograrn of mathematical mode.The evident economical results have been obtained from practice of optimizing the flow string for water withdrawal in gas production in Southern Sichuan and from studying the gas-water two-phase flow characteristics through vertical pipe.  相似文献   
99.
本文介绍北京核电站模拟器硬件构成并分析其功能和特点。  相似文献   
100.
There have been extensive attempts in recent years to perform spatial equilibrium analysis of commodity markets, particularly that of energy. Most of these attempts have been based on linear programming transportation models, and more recently quadratic programming models. Unfortunately, neither of these modelling approaches can deal with the case of multi-commodity analysis with non-symmetric regression coefficients. In this paper, we overcome this problem by employing the linear complementarity programming model. In addition, we show how the model can be applied to coal and gas energy flows within a single region. Future potential applications of the model are also implied.  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