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   256300篇
  免费   3117篇
  国内免费   885篇
电工技术   5043篇
综合类   200篇
化学工业   37031篇
金属工艺   9623篇
机械仪表   7623篇
建筑科学   6134篇
矿业工程   881篇
能源动力   7317篇
轻工业   21339篇
水利工程   2207篇
石油天然气   3245篇
武器工业   15篇
无线电   34556篇
一般工业技术   50725篇
冶金工业   49149篇
原子能技术   5193篇
自动化技术   20021篇
  2022年   1493篇
  2021年   2259篇
  2020年   1596篇
  2019年   1969篇
  2018年   3329篇
  2017年   3364篇
  2016年   3468篇
  2015年   2269篇
  2014年   4032篇
  2013年   11633篇
  2012年   6385篇
  2011年   8783篇
  2010年   7047篇
  2009年   8025篇
  2008年   8548篇
  2007年   8464篇
  2006年   7489篇
  2005年   6627篇
  2004年   6394篇
  2003年   6651篇
  2002年   6113篇
  2001年   6575篇
  2000年   6045篇
  1999年   6460篇
  1998年   16714篇
  1997年   11548篇
  1996年   8886篇
  1995年   6695篇
  1994年   5976篇
  1993年   5914篇
  1992年   4181篇
  1991年   4070篇
  1990年   3890篇
  1989年   3688篇
  1988年   3591篇
  1987年   3053篇
  1986年   2979篇
  1985年   3250篇
  1984年   2962篇
  1983年   2860篇
  1982年   2671篇
  1981年   2577篇
  1980年   2490篇
  1979年   2332篇
  1978年   2131篇
  1977年   2626篇
  1976年   3614篇
  1975年   1777篇
  1974年   1740篇
  1973年   1674篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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   
32.
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   
33.
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   
34.
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   
35.
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   
36.
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   
37.
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   
38.
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype.  相似文献   
39.
40.
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