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   214026篇
  免费   27235篇
  国内免费   6954篇
电工技术   10339篇
技术理论   9篇
综合类   9863篇
化学工业   44945篇
金属工艺   10980篇
机械仪表   11516篇
建筑科学   12538篇
矿业工程   4196篇
能源动力   4759篇
轻工业   17854篇
水利工程   3766篇
石油天然气   9923篇
武器工业   1187篇
无线电   25421篇
一般工业技术   38391篇
冶金工业   11958篇
原子能技术   4986篇
自动化技术   25584篇
  2023年   2491篇
  2022年   4842篇
  2021年   7227篇
  2020年   6565篇
  2019年   7291篇
  2018年   8341篇
  2017年   9190篇
  2016年   9112篇
  2015年   10029篇
  2014年   11822篇
  2013年   14669篇
  2012年   13208篇
  2011年   13695篇
  2010年   12216篇
  2009年   11727篇
  2008年   11199篇
  2007年   10477篇
  2006年   9568篇
  2005年   8057篇
  2004年   6343篇
  2003年   6220篇
  2002年   6199篇
  2001年   5617篇
  2000年   4930篇
  1999年   3866篇
  1998年   2734篇
  1997年   2316篇
  1996年   2043篇
  1995年   1794篇
  1994年   1519篇
  1993年   1294篇
  1992年   1238篇
  1991年   1110篇
  1990年   1118篇
  1989年   1039篇
  1988年   915篇
  1987年   861篇
  1986年   778篇
  1985年   728篇
  1984年   707篇
  1982年   672篇
  1981年   677篇
  1979年   748篇
  1978年   782篇
  1977年   750篇
  1976年   763篇
  1975年   717篇
  1974年   719篇
  1973年   725篇
  1972年   708篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
在铝材生产中,熔炼、铸造工序是能源与资源消耗多的工序,因此,节约资源、降低烧损与能耗有着重要意义。降低能耗还可以相应地减少温室气体与有害、有毒物质排放,对环保有利。中国当前铝合金熔炼铸造能源与资源节约的主要措施:调整加工用锭坯供应结构,大幅提高电解铝厂供应的锭坯,由2013年供应的42%提高到"十三五"末的65%-70%;加快走出去的力度,到国外去办铝厂,将在国外生产的铝合金锭坯运回来,争取2020年出口的铝材与铝制品全部以进口锭坯加工,这是最大的资源与能源节约;加强废铝回收与有效再生利用;加强创新,大力采用新装备、新技术与新工艺;加强管理,精心操作,管理中还有较大的能源与资源节约潜力。  相似文献   
63.
64.

Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.

  相似文献   
65.
66.
67.
A layer-by-layer analysis of the structures, the phase compositions, and the defect substructures of differentially hardened rails has been carried by optical and transmission electron microscopy. It is found that the material volume of the rail head fillet is cooled faster than the volume located along the central axis.  相似文献   
68.
69.
Lobster krill (Munida genus) represents an under‐valued crustacean frequently caught on European fishing banks. In this work, its sensory, microbiological and biochemical qualities were evaluated during chilled storage. Additionally, the effects of a prestorage antimelanosic treatment consisting of soaking in sodium metabisulphite (SMB) solutions at two different concentrations (0.25% and 0.75%) were also studied. SMB prestorage treatment provided lobster specimens that still exhibited acceptable sensory quality after 10 days of storage, while control specimens were unacceptable at that time. SMB treatment also resulted in a significant (P < 0.05) inhibition of microbial growth, mainly of Enterobacteriaceae, psychrotrophes and proteolytic bacteria. Low lipid oxidation levels were observed for all batches; however, a significantly higher (P < 0.05) retention of polyunsaturated fatty acids was found in SMB‐treated lobster, especially in the 0.75% SMB batch. The results presented here open the way to the potential commercialisation of currently under‐utilised lobster krill as a chilled product.  相似文献   
70.
Cable‐shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable‐shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable‐shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil‐type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical‐electrochemical stability. The CASECs show excellent charge–discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm−3), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets.  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