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   253307篇
  免费   3043篇
  国内免费   867篇
电工技术   4808篇
综合类   193篇
化学工业   36227篇
金属工艺   9509篇
机械仪表   7574篇
建筑科学   6109篇
矿业工程   880篇
能源动力   7227篇
轻工业   21301篇
水利工程   2207篇
石油天然气   3230篇
武器工业   15篇
无线电   34294篇
一般工业技术   50178篇
冶金工业   48608篇
原子能技术   5075篇
自动化技术   19782篇
  2021年   2177篇
  2020年   1566篇
  2019年   1924篇
  2018年   3280篇
  2017年   3322篇
  2016年   3402篇
  2015年   2223篇
  2014年   3970篇
  2013年   11490篇
  2012年   6287篇
  2011年   8658篇
  2010年   6922篇
  2009年   7900篇
  2008年   8472篇
  2007年   8346篇
  2006年   7406篇
  2005年   6529篇
  2004年   6307篇
  2003年   6584篇
  2002年   6067篇
  2001年   6534篇
  2000年   5985篇
  1999年   6398篇
  1998年   16499篇
  1997年   11419篇
  1996年   8807篇
  1995年   6620篇
  1994年   5910篇
  1993年   5846篇
  1992年   4137篇
  1991年   4028篇
  1990年   3860篇
  1989年   3653篇
  1988年   3564篇
  1987年   3019篇
  1986年   2946篇
  1985年   3208篇
  1984年   2930篇
  1983年   2831篇
  1982年   2641篇
  1981年   2546篇
  1980年   2464篇
  1979年   2305篇
  1978年   2108篇
  1977年   2604篇
  1976年   3568篇
  1975年   1766篇
  1974年   1729篇
  1973年   1665篇
  1972年   1466篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.  相似文献   
2.
Clean Technologies and Environmental Policy - Food production and consumption is one of the major causes of global environmental degradation. One way to address environmental impacts in the food...  相似文献   
3.
4.
Theoretical Foundations of Chemical Engineering - New research results, as well as those published earlier by the authors, on the synthesis of azo compounds based on nitroanilines obtained by the...  相似文献   
5.
At the hydroelectric unit No. 11 of the Nizhnekamsk hydroelectric power plant, the filling wedges of a rotor were investigated by ultrasound in the free st  相似文献   
6.
Metallurgical and Materials Transactions B - The process of obtaining titanium tetrachloride (TiCl4) from the quartz-leucoxene concentrate (QLC) from the Yaregskoe oil-titanium field was studied....  相似文献   
7.
Hassan  Lovelu  Khan  K. A. 《Microsystem Technologies》2020,26(3):1031-1041

The efficiency of any electric cell or battery is very important. To keep it in mind it has been studied the columbic efficiency, voltaic efficiency and energy efficiency of a PKL (Pathor Kuchi Leaf) Quasi Voltaic Cell or Modified Voltaic Cell. It was found that the columbic efficiency data illustrated that this efficiency was lower comparing to other efficiencies may be the absence of salt bridge or separator between the electrodes. Because, our designed and fabricated PKL cell does not have any salt bridge. So that the internal resistance is lower than the traditional voltaic cell and as a result more current was found. The voltage and current changes with time and I–V characteristics for PKL unit cell, module, panel and array have also been studied. It is shown that the voltaic and energy efficiency have been studied. However, the highest efficiency was obtained for 40% PKL sap with 5% secondary salt in 55% aqueous solution, which implies that the concentration of PKL juice can play an important role regarding efficiency. It was also found that the average energy efficiency was 97.43% and it was also found that the average voltaic efficiency was 57.29%. Finally, morphological study FESEM (Field Emission Scanning Electron Microscopy) has also been performed. It is seen that the results confirmed that Zn was deposited on the Cu surface during the electro deposition process in PKL solution. Using AAS, it has been measured the concentration of [Cu2+] as a reactant ion and the concentration of [Zn2+] as a product ion those have been tabulated and graphically discussed. The variation of pH has also been studied with time and which was also tabulated and graphically discussed.

  相似文献   
8.
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   
9.
Wu  Li  Li  Jing  Fu  Caixia  Kühn  Bernd  Wang  Xiaolin 《Magma (New York, N.Y.)》2019,32(4):501-509
Magnetic Resonance Materials in Physics, Biology and Medicine - To investigate the value of using diffusion-weighted imaging (DWI) and intravoxel incoherent motion DWI (IVIM-DWI) to assess the...  相似文献   
10.
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y...  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