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   183571篇
  免费   18627篇
  国内免费   11198篇
电工技术   14963篇
技术理论   5篇
综合类   15167篇
化学工业   25806篇
金属工艺   11114篇
机械仪表   12369篇
建筑科学   15674篇
矿业工程   6085篇
能源动力   5538篇
轻工业   13794篇
水利工程   4474篇
石油天然气   9217篇
武器工业   2080篇
无线电   22303篇
一般工业技术   18692篇
冶金工业   7390篇
原子能技术   2092篇
自动化技术   26633篇
  2024年   906篇
  2023年   2979篇
  2022年   5934篇
  2021年   8220篇
  2020年   6163篇
  2019年   4773篇
  2018年   5307篇
  2017年   6346篇
  2016年   5460篇
  2015年   8154篇
  2014年   10264篇
  2013年   12231篇
  2012年   14125篇
  2011年   14679篇
  2010年   13627篇
  2009年   12788篇
  2008年   12684篇
  2007年   11942篇
  2006年   10930篇
  2005年   8665篇
  2004年   6007篇
  2003年   5115篇
  2002年   4971篇
  2001年   4352篇
  2000年   3573篇
  1999年   2934篇
  1998年   1939篇
  1997年   1586篇
  1996年   1477篇
  1995年   1268篇
  1994年   1034篇
  1993年   638篇
  1992年   521篇
  1991年   412篇
  1990年   312篇
  1989年   262篇
  1988年   174篇
  1987年   123篇
  1986年   103篇
  1985年   50篇
  1984年   43篇
  1983年   35篇
  1982年   37篇
  1981年   44篇
  1980年   48篇
  1979年   26篇
  1978年   10篇
  1976年   10篇
  1959年   10篇
  1951年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The ennoblement of corrosion potential (Ecorr) of passive metal immersed in seawater was investigated with electrochemical technology and epifluorescence microscopy. The in situ observation showed that the bacteria number increased on the metal surface according to an exponential law which was in the same way with the ennoblement of Ecorr. At the same time, the anodic polarization current of high‐Mo stainless steel decreased in the initial days. According to the mix‐potential theory and the characteristics of polarization curves of high‐Mo steel in natural seawater, the ennoblement of corrosion potential may be induced by the decrease of the passive current density.  相似文献   
62.
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results.  相似文献   
63.
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications.  相似文献   
64.
65.
缺乏有力的监督和制约机制是我国行政判决执行难的重要原因之一.主张赋予检察机关时行政诉讼执行环节实施法律监督的权利.从而有效防止执行程序违法.抑制怠于执行和拖延执行现象的发生.阐述了由检察机关实施监督的法理依据,介绍了检察监督的方式.  相似文献   
66.
从关联分析法看如何改善沥青抗老化性能   总被引:1,自引:1,他引:0  
用灰色关联分析法研究了沥青抗老化性能与沥青化学组成之间的关联程度,结果表明,影响再生沥青性质的主要因素是沥青中的芳烃和胶质的含量。通过添加芳香组分能改善沥青四组分之间的配伍性,从而可以改善再生沥青的抗老化性能。并通过对再生剂进行富芳处理,验证了上述结论。  相似文献   
67.
68.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm.  相似文献   
69.
LaNiO3 was synthesized by sol-gel method in which lanthanum nitrate and nickel nitrate were used as start materials and citric acid was used as complex for gel formation.The precursor was dried and subsequently heated at elevated temperature to form the desired product.XRD analysis shows that pure LaNiO3 was synthesized.Electrical conductivity and electrochemical performance of the material were tested.The electrical conductivity decreases from 34.5that there are current peaks in the curve, which is the evidence of the electrochemical activity of LaNiO3.  相似文献   
70.
Spectral and structural characteristics of distributed Bragg reflector (DBR) in vertical-cavity surface-emitting lasers were studied with photoluminescence and double- crystal X- ray diffraction measurement. The expected high quality epitaxial DBR structure was verified. In the X- ray double- crystal rocking curves of DBR the zeroth- order peak, the first and second order satellite peaks were measured. Splitting of diffraction peak appeared in the rocking curves was analyzed. The effects of introduced deep energy levels on the structural perfection and optical properties were discussed.  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