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   197496篇
  免费   4154篇
  国内免费   1583篇
电工技术   4459篇
技术理论   2篇
综合类   1462篇
化学工业   31267篇
金属工艺   8917篇
机械仪表   6467篇
建筑科学   6329篇
矿业工程   1616篇
能源动力   5249篇
轻工业   17562篇
水利工程   2044篇
石油天然气   4618篇
武器工业   123篇
无线电   22013篇
一般工业技术   35817篇
冶金工业   34122篇
原子能技术   4521篇
自动化技术   16645篇
  2021年   2175篇
  2020年   1619篇
  2019年   1847篇
  2018年   2740篇
  2017年   2805篇
  2016年   2795篇
  2015年   2376篇
  2014年   3817篇
  2013年   8981篇
  2012年   5931篇
  2011年   7774篇
  2010年   6318篇
  2009年   7030篇
  2008年   6994篇
  2007年   6933篇
  2006年   6169篇
  2005年   5775篇
  2004年   5116篇
  2003年   4705篇
  2002年   4609篇
  2001年   4598篇
  2000年   4364篇
  1999年   4635篇
  1998年   10827篇
  1997年   7778篇
  1996年   6007篇
  1995年   4589篇
  1994年   3856篇
  1993年   3703篇
  1992年   2732篇
  1991年   2649篇
  1990年   2502篇
  1989年   2503篇
  1988年   2429篇
  1987年   2154篇
  1986年   2096篇
  1985年   2378篇
  1984年   2195篇
  1983年   2018篇
  1982年   1890篇
  1981年   1948篇
  1980年   1798篇
  1979年   1819篇
  1978年   1778篇
  1977年   2108篇
  1976年   2687篇
  1975年   1557篇
  1974年   1549篇
  1973年   1607篇
  1972年   1350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.
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   
5.
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   
6.
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   
7.
8.
Various products, including foods and pharmaceuticals, are sensitive to temperature fluctuations. Thus, temperature monitoring during production, transportation, and storage is critical. Facile indicators are required to monitor temperature conditions via color changes in real time. This study aimed to prepare and apply thiol-functionalized covalent organic frameworks (COFs) as a novel indicator for monitoring thermal history and temperature abuse. The COFs underwent obvious color changes from bright yellow to purple after exposure to different temperatures for varying durations. The reaction kinetics are analyzed under isothermal conditions, which reveal that the order of reaction rates is k−20°C < k4°C < k20°C < k35°C < k55°C. The activation energy (Ea) of the COFs is calculated using the Arrhenius equation as 50.71 kJ moL−1. The COFs are capable of sensitive color changes and offer a broad temperature tracking range, thereby demonstrating their application potential for the monitoring of temperature and time exposure history during production, transportation, and storage. This excellent performance thermal history indicator also shows promise for expanding the application field of COFs.  相似文献   
9.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic.  相似文献   
10.
Fibre Chemistry - An analysis of the aramid fiber market including the range of industrial textile materials containing chemical fibers for specialized protective clothing of metallurgical workers,...  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