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   202464篇
  免费   2759篇
  国内免费   738篇
电工技术   3615篇
综合类   114篇
化学工业   33408篇
金属工艺   8271篇
机械仪表   5551篇
建筑科学   5539篇
矿业工程   1203篇
能源动力   5309篇
轻工业   18052篇
水利工程   1914篇
石油天然气   3368篇
武器工业   3篇
无线电   21493篇
一般工业技术   37171篇
冶金工业   38945篇
原子能技术   4530篇
自动化技术   17475篇
  2021年   1713篇
  2019年   1581篇
  2018年   2500篇
  2017年   2429篇
  2016年   2651篇
  2015年   1936篇
  2014年   3310篇
  2013年   9388篇
  2012年   5455篇
  2011年   7502篇
  2010年   5915篇
  2009年   6825篇
  2008年   6958篇
  2007年   6848篇
  2006年   5940篇
  2005年   5499篇
  2004年   5177篇
  2003年   4809篇
  2002年   4777篇
  2001年   4585篇
  2000年   4298篇
  1999年   4496篇
  1998年   10840篇
  1997年   7816篇
  1996年   6116篇
  1995年   4702篇
  1994年   4054篇
  1993年   3977篇
  1992年   3011篇
  1991年   2793篇
  1990年   2796篇
  1989年   2795篇
  1988年   2701篇
  1987年   2505篇
  1986年   2399篇
  1985年   2789篇
  1984年   2625篇
  1983年   2392篇
  1982年   2233篇
  1981年   2225篇
  1980年   2087篇
  1979年   2145篇
  1978年   2054篇
  1977年   2346篇
  1976年   2902篇
  1975年   1792篇
  1974年   1752篇
  1973年   1811篇
  1972年   1503篇
  1971年   1356篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
51.
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   

52.
Filled fibrous sorbents modified with transition metal ferro- and ferricyanides capable to recover americium(III) and rare-earth metals(III) from nitric acid solutions were prepared. The most complete and rapid recovery is attained on complex-forming and cation-exchange sorbents (as filled fibrous materials) saturated with nickel ions. The sorbents are characterized by good kinetic properties and can be used for recovery of the above metals.  相似文献   
53.
54.
Robert Cravotta 《电子设计技术》2006,13(9):80-80,82-84,86
新的特性必须更加智能,在增加价值的同时不会分散驾驶者的注意力和增加事故的风险。  相似文献   
55.
56.
57.
Visibility of collaboration on the Web   总被引:14,自引:3,他引:11  
The emerging influence of new information and communication technologies (ICT) on collaboration in science and technology has to be considered. In particular, the question of the extent to which collaboration in science and in technology is visible on the Web needs examining. Thus the purpose of this study is to examine whether broadly similar results would occur if solely Web data was used rather than all available bibliometric co-authorship data. For this purpose a new approach of Web visibility indicators of collaboration is examined. The ensemble of COLLNET members is used to compare co-authorship patterns in traditional bibliometric databases and the network visible on the Web. One of the general empirical results is a high percentage (78%) of all bibliographic multi- authored publications become visible through search of engines in the Web. One of the special studies has shown Web visibility of collaboration is dependent on the type of bibliographic multi-authored papers. The social network analysis (SNA) is applied to comparisons between bibliographic and Web collaboration networks. Structure formation processes in bibliographic and Web networks are studied. The research question posed is to which extent collaboration structures visible in the Web change their shape in the same way as bibliographic collaboration networks over time. A number of special types of changes in bibliographic and Web structures are explained. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
58.
The difference in the turbulent diffusion between the active (heat) and passive (mass) scalars in a thermally stably stratified medium is investigated. The axisymmetric problem is treated on the formation of a turbulent circulation flow above a heated disk and on the turbulent diffusion of a passive scalar (impurity) from a continuous surface source in a stably stratified medium. The results indicate that the thermal stratification causes appreciable differences in the coefficients of turbulent transfer between the active (heat) and passive (mass) scalars. This means that the assumption of the identity of the coefficient of turbulent diffusion of heat and mass, employed in conventional models of turbulence, produces significant errors in estimating the heat and mass transfer in a thermally stably stratified medium.  相似文献   
59.
Thermal Transformations of an Aluminoborophosphate Binder   总被引:1,自引:0,他引:1  
Thermal transformations of a commercial aluminoborophosphate binder are studied in a broad temperature range by optical microscopy, x-ray diffraction, IR spectroscopy, and thermal analysis. The introduction of B2O3 reduces the temperature of phosphate polycondensation, enhances the stability of cyclometaphosphates in a broad temperature range (180–1100°C), and reduces the stability of hydrogen phosphates.  相似文献   
60.
This paper describesMicroScope, a framework for developing analysis tools for Lisp programs. MicroScope uses a knowledge-intensive approach for program representation and analysis. The analysis tools share a common object oriented program database, and a common Prolog inference engine. The use of Prolog and a declarative representation for programs permits sharing of information, and provides high bandwidth communication between diverse analysis tools. It also supports program specification and debugging activities in the same framework. Extensions to Prolog to support analysis are described, and two tools, theCritic and theExpector, are presented.This work supported in part by Hewlett-Packard Company, the National Science foundation Under Grant Number MCS81-21750 and the Defense Advanced Research Projects Agency under contract number DAAK11-84-K-0017.  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