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   346174篇
  免费   3723篇
  国内免费   1344篇
电工技术   6339篇
综合类   600篇
化学工业   48857篇
金属工艺   17276篇
机械仪表   13524篇
建筑科学   7708篇
矿业工程   2232篇
能源动力   7661篇
轻工业   23564篇
水利工程   4072篇
石油天然气   7051篇
武器工业   43篇
无线电   39854篇
一般工业技术   74022篇
冶金工业   56185篇
原子能技术   8428篇
自动化技术   33825篇
  2021年   2191篇
  2019年   2102篇
  2018年   11399篇
  2017年   11950篇
  2016年   8233篇
  2015年   2989篇
  2014年   4467篇
  2013年   12147篇
  2012年   9502篇
  2011年   17453篇
  2010年   15016篇
  2009年   14988篇
  2008年   15177篇
  2007年   17042篇
  2006年   7897篇
  2005年   10583篇
  2004年   9010篇
  2003年   8489篇
  2002年   7323篇
  2001年   6912篇
  2000年   6625篇
  1999年   6802篇
  1998年   16323篇
  1997年   11609篇
  1996年   8948篇
  1995年   6870篇
  1994年   6065篇
  1993年   6097篇
  1992年   4425篇
  1991年   4227篇
  1990年   4085篇
  1989年   4070篇
  1988年   3769篇
  1987年   3403篇
  1986年   3404篇
  1985年   3760篇
  1984年   3480篇
  1983年   3225篇
  1982年   3032篇
  1981年   3049篇
  1980年   3038篇
  1979年   2836篇
  1978年   2877篇
  1977年   3147篇
  1976年   4104篇
  1975年   2421篇
  1974年   2380篇
  1973年   2400篇
  1972年   2019篇
  1971年   1784篇
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
61.
62.
63.
In this work was investigated the effect of the addition of barium titanate (BaTiO3) on electrical properties of two chemically recyclable thermosets, polyhemiaminal (PHA) and polyhexahydro‐s‐triazine (PHT), both fabricated from 4,4′‐oxydianiline (ODA), an ether derivative of aniline and paraformaldehyde. Thermal and mechanical properties as well as chemical recyclability of the two polymers and their nanocomposites/nanodielectrics were also investigated. In addition, a quantitative analysis was conducted of the nanoparticle dispersion in the PHA‐/PHT‐based BaTiO3‐containing nanocomposites using transmission electron microscopy imaging and the nearest‐neighbor distance index and this index was used to analyze the investigated properties in connection with the proper mechanisms. Regarding the electrical properties for both neat polymers, conductivity values of the order of 10?8 S m?1 at 100 Hz were observed and dielectric constant values close to 2.80 for both polymers at 1 kHz. The addition of 0.5 wt% of BaTiO3 ferroelectric nanoparticles increased by about 44% the dielectric constant (1 kHz) and conductivity (102 Hz) of the PHA‐based nanocomposite. PHA and PHT exhibited glass transition temperature (Tg) values in the range 125–180 °C. An increase of 7 °C in Tg was observed after the incorporation of 0.5 wt% of BaTiO3 into PHA. Concerning the mechanical properties, values in the range 4.00–4.45 GPa for reduced modulus and 0.30–0.43 GPa for nanohardness for PHA and PHT polymers were observed. Independently of filler content or polymer matrix, both mechanical properties were enhanced after the addition of BaTiO3. The chemical recycling of PHA/PHT and all nanocomposites in the initial ODA reagent after sulfuric acid treatment was successfully characterized using the NMR and Fourier transform infrared spectroscopic techniques. © 2018 Society of Chemical Industry  相似文献   
64.
Russian Journal of Non-Ferrous Metals - The synthesis and sintering of the (AlN)x(SiC)1 – x solid solution have been studied under conditions of self-propagating high-temperature synthesis...  相似文献   
65.
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result...  相似文献   
66.
Journal of Communications Technology and Electronics - This paper implements mathematically rigorous extended trial function algorithm to address cubic–quartic optical solitons in...  相似文献   
67.
Powder Metallurgy and Metal Ceramics - The properties of sintered and heat-treated steels produced from the Catamold 8740 material by powder injection molding were examined. Parts made of the...  相似文献   
68.
69.
70.
Magnetic MnFe2O4 nanopowders were synthesized by an original solvothermal method in the absence and in the presence of tetra-n-butylammonium bromide (TBAB) and Tween 80 (TW) as surfactants. Manganese ferrite/polyaniline (PANI) hybrid materials were synthesized by in situ polymerization of aniline on the surface of MnFe2O4 using ammonium persulfate as oxidant. The purpose of the study was to investigate the influence of the two surfactants on the properties of the MnFe2O4 powders and of their composites with PANI. The specific surface area, the cumulative surface area of pores and the cumulative volume of pores are influenced by the nature of surfactant in case of MnFe2O4 powders and are higher by comparison to those of the MnFe2O4/PANI hybrid materials. The values of saturation magnetization in case of MnFe2O4 powders are higher than those of the hybrid materials and are not influenced by the surfactant nature. These features revealed that MnFe2O4 powders can be efficiently used as adsorbents for the purification of wastewaters. The values of the electrical conductivity of the composites exhibit a significant increase in comparison to the MnFe2O4 powders and depend on the surfactant nature. The highest value of electrical conductivity was achieved by the composite obtained using Tween 80 as surfactant (σDC = 54.5·10?5S?m?1) which was close to that of PANI (σDC = 61.2·10?5 S?m?1). The fact that the magnetic and electric properties of the synthesized MnFe2O4/PANI composites can be changed by design, demonstrate the high potential of these materials to be used in magneto-electric applications.  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