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   1702110篇
  免费   32354篇
  国内免费   11058篇
电工技术   40359篇
技术理论   2篇
综合类   12259篇
化学工业   289783篇
金属工艺   70539篇
机械仪表   51139篇
建筑科学   55139篇
矿业工程   13482篇
能源动力   52863篇
轻工业   133064篇
水利工程   18378篇
石油天然气   41592篇
武器工业   814篇
无线电   210120篇
一般工业技术   313527篇
冶金工业   219969篇
原子能技术   35274篇
自动化技术   187219篇
  2021年   19205篇
  2020年   14421篇
  2019年   16782篇
  2018年   20014篇
  2017年   20002篇
  2016年   24900篇
  2015年   21011篇
  2014年   33280篇
  2013年   93722篇
  2012年   44569篇
  2011年   59545篇
  2010年   50539篇
  2009年   58007篇
  2008年   54040篇
  2007年   51654篇
  2006年   52004篇
  2005年   46247篇
  2004年   46778篇
  2003年   46035篇
  2002年   44649篇
  2001年   41685篇
  2000年   39593篇
  1999年   39628篇
  1998年   63204篇
  1997年   50564篇
  1996年   43158篇
  1995年   35701篇
  1994年   32870篇
  1993年   32338篇
  1992年   27648篇
  1991年   24835篇
  1990年   24925篇
  1989年   23959篇
  1988年   22478篇
  1987年   20581篇
  1986年   20075篇
  1985年   23386篇
  1984年   23117篇
  1983年   20946篇
  1982年   19707篇
  1981年   19852篇
  1980年   18472篇
  1979年   18942篇
  1978年   18146篇
  1977年   18807篇
  1976年   21315篇
  1975年   16287篇
  1974年   15763篇
  1973年   15884篇
  1972年   13315篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Two‐dimensional arrangements of molecules can show remarkable cooperative electronic effects. Such effects can serve to achieve direct electronic sensing of chemical and physical processes via electrostatic effects, i.e., without transfer of charge or matter between the locus of sensing and that of detection.  相似文献   
992.
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   
993.
994.
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   
995.
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   
996.
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   
997.
998.
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   
999.
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   
1000.
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   
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