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   6227篇
  免费   635篇
  国内免费   114篇
电工技术   135篇
技术理论   1篇
综合类   144篇
化学工业   1550篇
金属工艺   285篇
机械仪表   415篇
建筑科学   152篇
矿业工程   53篇
能源动力   307篇
轻工业   513篇
水利工程   55篇
石油天然气   203篇
武器工业   11篇
无线电   946篇
一般工业技术   1208篇
冶金工业   229篇
原子能技术   52篇
自动化技术   717篇
  2024年   11篇
  2023年   81篇
  2022年   83篇
  2021年   252篇
  2020年   210篇
  2019年   194篇
  2018年   222篇
  2017年   238篇
  2016年   254篇
  2015年   231篇
  2014年   355篇
  2013年   436篇
  2012年   432篇
  2011年   483篇
  2010年   410篇
  2009年   387篇
  2008年   383篇
  2007年   238篇
  2006年   253篇
  2005年   261篇
  2004年   224篇
  2003年   206篇
  2002年   166篇
  2001年   131篇
  2000年   121篇
  1999年   147篇
  1998年   104篇
  1997年   78篇
  1996年   81篇
  1995年   56篇
  1994年   59篇
  1993年   28篇
  1992年   26篇
  1991年   26篇
  1990年   18篇
  1989年   22篇
  1988年   7篇
  1987年   8篇
  1986年   5篇
  1985年   5篇
  1984年   9篇
  1983年   7篇
  1982年   4篇
  1981年   5篇
  1979年   4篇
  1978年   4篇
  1977年   3篇
  1973年   3篇
  1972年   2篇
  1968年   1篇
排序方式: 共有6976条查询结果,搜索用时 15 毫秒
1.

LiFe2/3Mn1/3PO4/C composite was prepared by the rheological phase reaction using LiH2PO4, Li2CO3, FePO4, Mn(Ac)2·4H2O and ascorbic acid as starting materials. The crystal structure and morphology of as-synthesized sample were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The analysis of XRD results showed that the obtained sample was single-phase with orthorhombic olivine-type structure (Pnma space group). SEM micrographs revealed that the sample was aggregates, with an irregular morphology. The initial discharge capacity was 166.9, 149.1, 139.6, 112.8, 82.93 mAh g??1 at the rate of 0.1, 0.5, 1, 2, and 10 C, respectively. And when the rate was 0.1, 0.5, 1, 2, and 10 C, the capacity retention was 92.2%, 90%, 92.9%, 97.6%, 91.5% after 50, 100, 200, 200, 500 cycles, respectively.

  相似文献   
2.
Neural Processing Letters - Raman spectroscopy is often used for the composition determination and rapid classification of materials because it can reflect the molecular information of materials....  相似文献   
3.
4.
5.
Intelligent Service Robotics - A robust control designed for multiple degrees-of-freedom (DOF) robot manipulators performing complex tasks requiring frequent physical interaction with unknown...  相似文献   
6.
7.
The electrochemical reduction of carbon dioxide (CO2) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO2 to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO2 to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO2 in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions.  相似文献   
8.
膨胀套管的弹塑性理论分析   总被引:3,自引:3,他引:0  
分析认为,膨胀套管在膨胀过程中先进入弹性阶段,然后进入弹塑性阶段,最后进入塑性流动阶段。采用弹塑性分析方法,对膨胀套管膨胀过程中套管内壁的受力与变形进行了研究,模拟了其成形的过程,并建立了解析解,为膨胀套管膨胀操作过程中确定关键操作参数提供了理论支持。根据推导出的力学模型,计算出了外径107.9mm、钢级为J55的膨胀套管膨胀到直径139.7mm时膨胀芯头拉头处的轴向力为195.94kN。  相似文献   
9.
All-buried InP-InGaAsP ring resonators laterally coupled to bus waveguides are demonstrated. The buried configurations offer a lower built-in refractive index step along the resonator periphery, which affords enhanced optical coupling coefficients between the waveguides and reduced scattering losses caused by the resonator sidewall imperfections. Very low optical intensity attenuations of 0.4 cm/sup -1/ and coupling-limited quality factors of greater than 10/sup 5/ are observed from 200-/spl mu/m-radii ring resonators. The measured spectral linewidth is as narrow as 0.0145 nm.  相似文献   
10.
We have developed a new type of tunable band rejection filter, which provides high spectral-shaping flexibility in a wide tuning range. The filter consists of a long-period fiber grating (LPFG) with divided coil heaters. Each of the divided coil heaters is controlled individually to adjust a temperature distribution along the LPFG and to modify the spectral shape of the LPFG filter. The tunable band rejection filter is demonstrated to function properly when applied as an erbium-doped fiber amplifier gain-flattening filter.  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