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   551743篇
  免费   90889篇
  国内免费   56328篇
电工技术   47205篇
技术理论   61篇
综合类   42136篇
化学工业   85499篇
金属工艺   42411篇
机械仪表   30336篇
建筑科学   40983篇
矿业工程   24581篇
能源动力   19195篇
轻工业   41906篇
水利工程   13234篇
石油天然气   36174篇
武器工业   6508篇
无线电   68619篇
一般工业技术   73185篇
冶金工业   27020篇
原子能技术   4983篇
自动化技术   94924篇
  2024年   3910篇
  2023年   9749篇
  2022年   14506篇
  2021年   19347篇
  2020年   19049篇
  2019年   26141篇
  2018年   28879篇
  2017年   31026篇
  2016年   29766篇
  2015年   32167篇
  2014年   34987篇
  2013年   38021篇
  2012年   38325篇
  2011年   37530篇
  2010年   32833篇
  2009年   28837篇
  2008年   26891篇
  2007年   25484篇
  2006年   25551篇
  2005年   22937篇
  2004年   18867篇
  2003年   16276篇
  2002年   14853篇
  2001年   13496篇
  2000年   13742篇
  1999年   14964篇
  1998年   12886篇
  1997年   10916篇
  1996年   10408篇
  1995年   9244篇
  1994年   7622篇
  1993年   6011篇
  1992年   5199篇
  1991年   3967篇
  1990年   3105篇
  1989年   2703篇
  1988年   2188篇
  1987年   1091篇
  1986年   863篇
  1985年   602篇
  1984年   416篇
  1983年   312篇
  1982年   357篇
  1981年   278篇
  1980年   233篇
  1976年   288篇
  1975年   228篇
  1972年   250篇
  1971年   137篇
  1960年   206篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The increasing complecity of many expert system application areas calls for the integration of the knowledge of multiple experts. The use of multiple experts introduces some interesting new problems during the process of knowledge acquisition. The problems are further complicated when the experts are geographically dispersed or unavailable for face-to-face interactions.

This article discusses the motivations for acquiring the knowledge of multiple experts, the problems related to knowledge acquisition, new issues that arise whens multiple experts interact, solutions that can be brought to bear in building multiple expert systems (particularly when experts are geographically dispersed), and new tools for knowledge engineers to use when dealing with multiple experts.  相似文献   

52.
The electrochemical faceting of polycrystalline (pc) platinum yielding a (100)-preferred oriented electrode surface was accomplished in HF solutions by applying to the pc platinum electrode a square wave potential perturbation at 1 kHz in the 0.2 to 1.3 V range (vs rhe). SEM patterns of the resulting surfaces were also obtained. For HF concentrations up to 2 M no appreciable influence of the electrolyte concentration on the electrochemical faceting was noticed. Otherwise, the voltammetric response of the (100)-type preferred oriented platinum surface in the H-adatom potential range when compared to previously reported data resulted remarkably sensitive to the electrolyte composition. The discussion of results was based on the non-equilibrium adsorption conditions for anions under the periodic perturbation.  相似文献   
53.
The effect of ion exchange conditions, such as Si/Al ratio, precursor copper salt, pH and concentration of the solution, on the catalytic activity in SCR of NO by propane and on the electronic state of copper ions in Cu-ZSM-5 has been studied. The NO conversion in NO SCR by C3H8 has been found to reach a maximum value at Cu/Al ratio about 0.37–0.4 and remain constant at higher Cu/Al.

ESR and UV–vis DR spectroscopy have been used to elucidate stabilization conditions of copper ions in Cu-ZSM-5 zeolites as isolated Cu2+ ions, chain copper oxide structures and square-plain oxide clusters. The ability of copper ions for reduction and reoxidation in the chain structures may be responsible for the catalytic activity of Cu-ZSM-5. These transformations of copper ions are accompanied by the observation of intervalence transitions Cu2+–Cu+ and CTLM of the chain structures in the UV–vis spectra.  相似文献   

54.
55.
介绍并分析了春光油田现代油藏经营管理模式的构建与运作及实施效果.  相似文献   
56.
57.
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry  相似文献   
58.
印染废水处理工艺研究及实例   总被引:1,自引:0,他引:1  
本文简要介绍了印染废水水质特征,提出了处理工艺,并利用两个工程实例说明了该工艺的可行性.  相似文献   
59.
60.
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