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   265898篇
  免费   10286篇
  国内免费   4761篇
电工技术   8954篇
技术理论   2篇
综合类   5877篇
化学工业   41735篇
金属工艺   12665篇
机械仪表   10290篇
建筑科学   11098篇
矿业工程   2724篇
能源动力   7246篇
轻工业   23418篇
水利工程   3504篇
石油天然气   7001篇
武器工业   677篇
无线电   31638篇
一般工业技术   44729篇
冶金工业   37635篇
原子能技术   5309篇
自动化技术   26443篇
  2023年   1684篇
  2022年   3342篇
  2021年   4862篇
  2020年   3399篇
  2019年   3345篇
  2018年   4444篇
  2017年   4865篇
  2016年   4616篇
  2015年   4961篇
  2014年   7139篇
  2013年   13399篇
  2012年   10554篇
  2011年   13040篇
  2010年   10836篇
  2009年   11465篇
  2008年   11377篇
  2007年   11126篇
  2006年   10075篇
  2005年   8814篇
  2004年   7280篇
  2003年   6456篇
  2002年   6433篇
  2001年   6112篇
  2000年   5805篇
  1999年   5961篇
  1998年   12172篇
  1997年   8935篇
  1996年   7026篇
  1995年   5445篇
  1994年   4517篇
  1993年   4295篇
  1992年   3193篇
  1991年   2981篇
  1990年   2785篇
  1989年   2725篇
  1988年   2619篇
  1987年   2300篇
  1986年   2213篇
  1985年   2500篇
  1984年   2278篇
  1983年   2086篇
  1982年   1944篇
  1981年   1997篇
  1980年   1844篇
  1979年   1848篇
  1978年   1807篇
  1977年   2134篇
  1976年   2739篇
  1975年   1572篇
  1973年   1624篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
3.
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell.  相似文献   
4.
Zhao  Ziyu  Lin  Haitao  Ma  Pibo 《Applied Composite Materials》2022,29(4):1675-1694
Applied Composite Materials - In this paper, the low-velocity impact deformation behavior of biaxial warp-knitted flexible composite was investigated. A simplified finite element model (FEM) of the...  相似文献   
5.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
6.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  相似文献   
7.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  相似文献   
8.
Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface.  相似文献   
9.
B4C-TiB2 ceramics (TiB2 ranging 5~70 vol%) with Mo-Co-WC as the sintering additive were prepared by spark plasma sintering. In comparison with B4C-TiB2 without additive, the enhanced densification was evident in the sintered specimen with Mo-Co-WC additive. Core-rim structured grain was observed around TiB2 grains. The interface of the rim between TiB2 and B4C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B4C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B2 rim around the TiB2 core may occur as a result of the solid solution and dissolution-precipitation between TiB2 phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB2 content increased, alongside the decreased hardness. B4C-30 vol% TiB2 specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m1/2.  相似文献   
10.
The potential of using high metals containing coal gangue and lignite to prepare high-activity coal char-based catalysts is investigated for effective biomass tar decomposition. Loose structure and rough surface are formed for these char-based catalysts with heterogeneous distribution of a large number of inorganic particles. In the biomass tar decomposition, the performance of the coal char-based catalysts is significantly influenced by the content of the metals in the raw materials and coal gangue char (GC) with the ash content as high as 50.80% exhibits the highest activity in this work. A high biomass tar conversion efficiency of 93.5% is achieved at 800 °C along with a significant increase in the fuel gas product. During the five-time consecutive tests, the catalytic performance of GC increases a little at the second or third times reuse and remains relatively stable, showing the remarkable stability of the catalyst in biomass tar decomposition 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