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   100830篇
  免费   5946篇
  国内免费   3797篇
电工技术   4896篇
技术理论   5篇
综合类   4195篇
化学工业   15474篇
金属工艺   6542篇
机械仪表   4819篇
建筑科学   6030篇
矿业工程   1665篇
能源动力   3182篇
轻工业   5984篇
水利工程   1406篇
石油天然气   4511篇
武器工业   500篇
无线电   11213篇
一般工业技术   17747篇
冶金工业   9709篇
原子能技术   1541篇
自动化技术   11154篇
  2024年   323篇
  2023年   1155篇
  2022年   1963篇
  2021年   2880篇
  2020年   2088篇
  2019年   1881篇
  2018年   2374篇
  2017年   2564篇
  2016年   2427篇
  2015年   2852篇
  2014年   3598篇
  2013年   5807篇
  2012年   5114篇
  2011年   5822篇
  2010年   5045篇
  2009年   5077篇
  2008年   5039篇
  2007年   5034篇
  2006年   4687篇
  2005年   4017篇
  2004年   3140篇
  2003年   2866篇
  2002年   2936篇
  2001年   2780篇
  2000年   2415篇
  1999年   2551篇
  1998年   3247篇
  1997年   2660篇
  1996年   2412篇
  1995年   1781篇
  1994年   1414篇
  1993年   1255篇
  1992年   1028篇
  1991年   892篇
  1990年   739篇
  1989年   663篇
  1988年   526篇
  1987年   502篇
  1986年   429篇
  1985年   437篇
  1984年   339篇
  1983年   323篇
  1982年   333篇
  1981年   314篇
  1980年   368篇
  1979年   349篇
  1977年   415篇
  1976年   629篇
  1975年   308篇
  1973年   311篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Thin films on aluminum-tungsten alloys were prepared by co-deposition of pure aluminum and pure tungsten, each sputtered by an independently controlled magnetron source, on glass and sapphire substrates. Completely amorphous films were obtained in the Al80W20-Al67W33 composition range. Passivity and corrosion behavior of amorphous Al-W alloys were investigated in 1 M deaerated hydrochloric acid solution using polarization and impedance spectroscopy measurements and have been correlated with the properties of pure alloy components. Tungsten and sputter-deposited Al-W thin films are inherently passive materials while aluminum undergoes pitting corrosion in hydrochloric acid solution. The passive film formed at the OCP on each alloy possesses excellent electric and dielectric properties comparable to those of the isolating film on tungsten. The absolute impedance increases with increasing tungsten content in the alloy. According to electrochemical polarization measurements, alloying Al with W in solid solution significantly enhances the material's resistance to pitting corrosion by shifting the breakdown potential above 2000 mV (Al67W33) and lowering the corrosion rate at the OCP by more than two orders of magnitude. The most likely mechanism explaining the passivity of amorphous Al-W alloys, the Solute Vacancy Interaction Model (SVIM), involves the formation of complexes between highly oxidized solute atoms (W+6) and mobile cation vacancies, which restrict the transport of Cl through the oxide film and inhibit its breakdown in hydrochloric acid solution. The role that film stress relaxation effects and microscopic defects in amorphous Al-W films, of the some composition, and deposited on various substrates play in their corrosion resistance is discussed.  相似文献   
63.
移动IP综述     
论述了移动IP的概念和发展过程,分析了国内外对移动IP研究的重点问题及其方法,对移动IP的发展方向进行了归纳和总结,并提出了有关用的问题。  相似文献   
64.
ZnGa2O4纳米晶的制备和结构表征   总被引:2,自引:0,他引:2  
采用喷射共沉淀法制备了ZnGa2O4 纳米晶,XRD、SEM和TEM结构分析结果表明,喷射共沉淀法制备的ZnGa2O4的纳米晶颗粒细小均匀,形状完整,与化学共沉淀法相比,粒子尺寸明显减小,小于10nm,同时ZnO杂相峰消失,分析了喷射共沉淀法的机理,并对实验结果进行了解释。  相似文献   
65.
隔震结构在省防震减灾中心大楼工程中的应用   总被引:2,自引:1,他引:1  
结合工程实例介绍了隔震结构在工程设计中的应用  相似文献   
66.
67.
We have grown cubic centimeter-size crystals of YBa2Cu3O x suitable for neutron studies, by a top-seeded melt-growth technique. Growth conditions were optimized with an eye toward maximizing phase purity. It was found that the addition of 2% Y2BaCuO5 and 0.5% Pt (by mass) were required to prevent melt loss and to obtain the highest crystallinity. A neutron diffraction study on a mosaic of six such crystals found that the final Y2BaCuO5 concentration was 5%, while other impurity phases comprised less than 1% by volume. The oxygen content was set to x = 6.5, the crystals were detwinned, and then carefully annealed to give the well-ordered ortho-II phase. The neutron study determined that 70% of the mosaic's volume was in the majority orthorhomic domain. The neutron (006) and (110) rocking curve widths were ~1° per crystal and ~2.2° for the mosaic, and the oxygen chain correlation lengths were >100 Å in the a- and b-directions and ~50 Å in the c-direction.  相似文献   
68.
标准物质在分析测试中的重要地位及发展前景   总被引:2,自引:0,他引:2  
标准物质在分析测试领域中无论在定值,方法的研究,误差确定等方面都有着重要地位。标准物质的质量保证及正确使用也应引起我们重视。随着科学技术迅速发展标准物质有着广阔发展前景。  相似文献   
69.
The inertia effect on the onset of thermal instability in natural convection flow over heated horizontal and inclined flat plates embedded in fluid-saturated porous media is analyzed. The linear non-parallel flow model is employed in the instability analysis, which takes into account the streamwise variation as well as the transverse variation of the disturbance amplitude functions. The set of partial differential equations for the disturbance amplitude functions are converted to a system of homogeneous linear ordinary differential equations with homogeneous boundary conditions by the local non-similarity method. The resulting eigenvalue problem is then solved by an implicit finite-difference method. Representative neutral stability curves and critical Rayleigh numbers are presented. It has been found that as the angle of inclination relative to the horizontal increases, the surface heat transfer rate increases, whereas the flow becomes more stable to the vortex mode of instability. Also, as the inertia effect, expressed in terms of Forchheimer number, Fr, increases, the heat transfer rate decreases, but the flow becomes more stable. It is demonstrated that the non-parallel flow model predicts a more stable flow than the parallel flow model.  相似文献   
70.
京移通信设计院从1997年启动ISO9000质量管理体系标准贯彻落实(简称贯标)工作至今已八年多。八年来本院质量管理工作上了两个台阶。  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