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   50331篇
  免费   4345篇
  国内免费   1505篇
电工技术   2055篇
技术理论   2篇
综合类   2020篇
化学工业   9607篇
金属工艺   2606篇
机械仪表   3147篇
建筑科学   2396篇
矿业工程   675篇
能源动力   1880篇
轻工业   4202篇
水利工程   684篇
石油天然气   1422篇
武器工业   193篇
无线电   7100篇
一般工业技术   8338篇
冶金工业   2716篇
原子能技术   685篇
自动化技术   6453篇
  2024年   131篇
  2023年   786篇
  2022年   1020篇
  2021年   1828篇
  2020年   1355篇
  2019年   1356篇
  2018年   1656篇
  2017年   1587篇
  2016年   1781篇
  2015年   1757篇
  2014年   2390篇
  2013年   3109篇
  2012年   3284篇
  2011年   3852篇
  2010年   3051篇
  2009年   3014篇
  2008年   2814篇
  2007年   2496篇
  2006年   2327篇
  2005年   1998篇
  2004年   1631篇
  2003年   1642篇
  2002年   1799篇
  2001年   1613篇
  2000年   1184篇
  1999年   1102篇
  1998年   1155篇
  1997年   827篇
  1996年   779篇
  1995年   579篇
  1994年   384篇
  1993年   326篇
  1992年   266篇
  1991年   204篇
  1990年   152篇
  1989年   152篇
  1988年   137篇
  1987年   105篇
  1986年   91篇
  1985年   64篇
  1984年   53篇
  1983年   42篇
  1982年   45篇
  1981年   34篇
  1980年   44篇
  1979年   23篇
  1977年   23篇
  1976年   39篇
  1975年   21篇
  1974年   19篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
11.
苏宇  张吉  王沁 《机械与电子》2020,38(3):66-71
设计了一款四功能水下机械臂,并对驱动关节进行了模块化设计和密封测试。为了保证水下机械臂的可靠性,在水下机械臂水下测试前,进行了强度校核和模态分析。为了验证水下机械臂的性能,通过 D- H法建立了其运动学模型,在此基础上分别进行了正、逆运动学分析。此外还采用蒙特卡洛法,在正运动学分析的基础上研究了工作空间特点。研究结果将为进一步的运动控制提供有益的帮助。  相似文献   
12.
Food Science and Biotechnology - Aluminum based reflective nanolens arrays were developed via a series of aluminum electropolishing and anodization steps with subsequent selective dissolution of...  相似文献   
13.
14.
15.
Semiconductor particles doped Al2O3 coatings were prepared by cathode plasma electrolytic deposition in Al(NO3)3 electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings.  相似文献   
16.
Lin  Haicheng  Huang  Wantong  Zhao  Kun  Qiao  Shuang  Liu  Zheng  Wu  Jian  Chen  Xi  Ji  Shuai-Hua 《Nano Research》2020,13(1):133-137
Nano Research - The isostructural and isoelectronic transition-metal-dichalcogenides 1T-TaS2 and 1T-TaSe2 are layered materials with intricate electronic structures. Combining the molecular beam...  相似文献   
17.
A series of anionic conjugated polyelectrolytes (CPEs) is synthesized based on poly(fluorene-co-phenylene) by varying the side-chain ionic density from two to six per repeat units (MPS2-TMA, MPS4-TMA, and MPS6-TMA). The effect of MPS2, 4, 6-TMA as interlayers on top of a hole-extraction layer of poly(bis(4-phenyl)-2,4,6-trimethylphenylamine (PTAA) is investigated in inverted perovskite solar cells (PeSCs). Owing to the improved wettability of perovskites on hydrophobic PTAA with the CPEs, the PeSCs with CPE interlayers demonstrate a significantly enhanced device performance, with negligible device-to-device dependence relative to the reference PeSC without CPEs. By increasing the ionic density in the MPS-TMA interlayers, the wetting, interfacial defect passivation, and crystal growth of the perovskites are significantly improved without increasing the series resistance of the PeSCs. In particular, the open-circuit voltage increases from 1.06 V for the PeSC with MPS2-TMA to 1.11 V for the PeSC with MPS6-TMA. The trap densities of the PeSCs with MPS2,4,6-TMA are further analyzed using frequency-dependent capacitance measurements. Finally, a large-area (1 cm2) PeSC is successfully fabricated with MPS6-TMA, showing a power conversion efficiency of 18.38% with negligible hysteresis and a stable power output under light soaking for 60 s.  相似文献   
18.
19.
20.
The evaluation of cell's weatherability is of practical interest. To further improve the soluble lead flow battery's weatherability, physiochemical properties of electrolytes containing fluoborate, perchlorate, methanesulfonate and trifluoromethanesulfonate are investigated from ?60 to 50 °C. Activities of CF3SO3H and HClO4 are poor in trifluoromethanesulfonate and perchlorate solutions due to common anion effect. The solubility of lead salt can be improved by increasing temperature, but worsened by increasing acid's content. With the temperature increasing, the conductivity is enhanced, and the viscosity is lowered for four solutions. The same results have been found by increasing acid's content except for CF3SO3H. The high energy efficiency can be achieved for cells over ?40–0 °C using fluoborate and perchlorate solutions, 73.2% at ?40 °C and 78.1% at ?30 °C respectively. Over the temperature range of 20–50 °C, the cells with methanesulfonate and trifluoromethanesulfonate solutions have good performance, 77.4% and 73.7% at 50 °C respectively.  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