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   1615505篇
  免费   26827篇
  国内免费   7197篇
电工技术   35316篇
综合类   6640篇
化学工业   283069篇
金属工艺   67014篇
机械仪表   48152篇
建筑科学   48291篇
矿业工程   11683篇
能源动力   52108篇
轻工业   122946篇
水利工程   16224篇
石油天然气   38084篇
武器工业   192篇
无线电   204608篇
一般工业技术   304093篇
冶金工业   199339篇
原子能技术   34791篇
自动化技术   176979篇
  2021年   16950篇
  2020年   12879篇
  2019年   15737篇
  2018年   19200篇
  2017年   18741篇
  2016年   23922篇
  2015年   18659篇
  2014年   30553篇
  2013年   90436篇
  2012年   40161篇
  2011年   54878篇
  2010年   46913篇
  2009年   54766篇
  2008年   49509篇
  2007年   46647篇
  2006年   47457篇
  2005年   42485篇
  2004年   43908篇
  2003年   43745篇
  2002年   42376篇
  2001年   39434篇
  2000年   37525篇
  1999年   37309篇
  1998年   57215篇
  1997年   46275篇
  1996年   40056篇
  1995年   33477篇
  1994年   31019篇
  1993年   30874篇
  1992年   26893篇
  1991年   24144篇
  1990年   24364篇
  1989年   23409篇
  1988年   21954篇
  1987年   20179篇
  1986年   19612篇
  1985年   22864篇
  1984年   22731篇
  1983年   20634篇
  1982年   19473篇
  1981年   19635篇
  1980年   18237篇
  1979年   18707篇
  1978年   17945篇
  1977年   18070篇
  1976年   19664篇
  1975年   16153篇
  1974年   15658篇
  1973年   15764篇
  1972年   13161篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The properties of a spinel copper cobaltite obtained by thermal decomposition of mixed nitrates of both metals at 350°C and normal pressure are described. It has been shown that the maximum copper content (x) in the spinel CuxCo3?xO4 does not exceed 0.9. When the copper amount in the initial mixture is higher a second phase CuO is formed. The copper ions are distributed over the A- and the B-sites of the spinel lattice, i.e. the spinel is partially inverted. Such a model explains well the data obtained about the lattice parameter, IR-absorption and the magnetic susceptibility of the samples with different x.  相似文献   
992.
993.
A historical review of licensing among industrial/organizational (I/O) psychologists demonstrates that the American Psychological Association (APA) policy on such licensing is inconsistent. Arguments for and against licensure for this group are presented. Job analysis and APA data are drawn upon to show that few I/O activities may pose the personal risk that would seem to require the protection of a license. Alternatives are discussed for changes in present APA policy and state licensing requirements. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
994.
Haug  K. Maloberti  F. Temes  G.C. 《Electronics letters》1985,21(24):1156-1157
Compensated SC integrator stages are analysed and compared with respect to their sensitivities to finite amplifier gain effects. Simple single-stage amplifiers may be used in such circuits even in highly selective filtering applications. This may allow an extension of the present frequency range of SC circuits.  相似文献   
995.
The paper presents the results of research in the convection drying of unidirectional glass fibre bobbins on the basis of which the relations are suggested required to calculate the process of drying in the design of drying equipment.  相似文献   
996.
997.
The dynamic and equilibrium swelling behavior of polystyrene microparticles crosslinked with divinyl benzene was investigated in methyl ethyl ketone and cyclohexane. The dynamic studies gave new information about the mechanism of penetrant transport in this polymer. The equilibrium studies were used to determine important parameters of the crosslinked structure of these systems, including the average molecular weight between crosslinks, M?c  相似文献   
998.
Field surveys of a series of conjugated diunsaturated straight-chain primary alcohols, acetates, and aldehydes (dienes), including the 3,5-dode-cadienyl, 8,10-dodecadienyl, 3,5-tetradecadienyl, 8,10-tetradecadienyl, 9,11-tetradecadienyl, and 10,12-tetradecadienyl primary alcohols, acetates, and most aldehydes, and the related monounsaturated straight-chain primary alcohols, acetates, and aldehydes (monoenes), including the 3-dodecadienyl alcohol and acetates, attracted the following species from the title families. Diene attractants have been demonstrated for at least onePhyllonorycter sp.,Chionodes lugubrella (Fabr.),Leptostales ferruminaria (Zell.),Drepana bilineata (Pack.),Pyrausta fodinalis (Led.),Notocelia purpurissatana Heinr.,Phaneta alterana Heinr. Monoene attractants were demonstrated forHedya separatana (Kft.),Cydia fletcherana (Kft.),Barbara mappana Free.,Ancylis burgessiana (Zell.),Ancylis nubeculana Clem.,Evippe prunifoliella Cham.,Phlyctaenia coronata tertialis (Gn.), aChionodes sp., a Gelechiidae sp., and an unidentifiedPhyllonorycter sp. Replicated field experiments showed attraction-inhibition relationships for most species. Electroantennagram data are presented forLeptostales ferruminaria andDrepana bilineata.  相似文献   
999.
Summary Starting with Z-2, 3-diamino-2-butenedinitrile as diamine component the synthesis of the low molecular N,N,O,O-chelate 3.Co and its ligand 3 is optimized. An easy synthesis of the chelate 8.Co covalently bound on macroreticular resins is presented. The chelates 8.Co are the most active heterogenous catalysts for the valence isomerization of quadricyclane to norbornadiene today.  相似文献   
1000.
For the past three decades, IS managers have been faced with the tasks of honing their craft, improving productivity, and serving as the keepers of information technology for the corporation. For the most part, they have done a commendable job. However, the rules of the game are changing. Old solutions are no longer extensible to current problems, and today's problems are unlike any faced in the past. This article takes a fresh look at what the top priorities for IS managers should be in the coming years.  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