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   199861篇
  免费   4340篇
  国内免费   1557篇
电工技术   4439篇
技术理论   5篇
综合类   1432篇
化学工业   31916篇
金属工艺   9344篇
机械仪表   6549篇
建筑科学   6173篇
矿业工程   1544篇
能源动力   5449篇
轻工业   17923篇
水利工程   2062篇
石油天然气   4741篇
武器工业   152篇
无线电   22227篇
一般工业技术   36231篇
冶金工业   34396篇
原子能技术   4537篇
自动化技术   16638篇
  2021年   2282篇
  2020年   1708篇
  2019年   1917篇
  2018年   2865篇
  2017年   2866篇
  2016年   2876篇
  2015年   2512篇
  2014年   3842篇
  2013年   9300篇
  2012年   6025篇
  2011年   7902篇
  2010年   6398篇
  2009年   7178篇
  2008年   7102篇
  2007年   7038篇
  2006年   6290篇
  2005年   5787篇
  2004年   5145篇
  2003年   4773篇
  2002年   4674篇
  2001年   4581篇
  2000年   4454篇
  1999年   4699篇
  1998年   10919篇
  1997年   7789篇
  1996年   6042篇
  1995年   4598篇
  1994年   3887篇
  1993年   3744篇
  1992年   2749篇
  1991年   2643篇
  1990年   2502篇
  1989年   2481篇
  1988年   2436篇
  1987年   2164篇
  1986年   2089篇
  1985年   2399篇
  1984年   2210篇
  1983年   2028篇
  1982年   1892篇
  1981年   1953篇
  1980年   1809篇
  1979年   1824篇
  1978年   1779篇
  1977年   2109篇
  1976年   2689篇
  1975年   1559篇
  1974年   1552篇
  1973年   1609篇
  1972年   1352篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
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   
3.
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   
4.
Yarn-dyed fabric is often woven from warp and weft yarns in the same color depth to ensure a uniform color appearance. The difference in color depth between warp and weft tends to result in the uneven color of the yarn-dyed fabric. This article aims to establish a color tolerance for yarn-dyed fabric that can be woven with a qualified color appearance but from the warp and weft yarns in different color depths. A total of 27 yarn-dyed fabric samples in three color series (red, yellow, and blue) were evaluated by using the yarn-dyed fabric from warp and weft yarns in the same color depth of 2% (on weight of fabric, owf) as the standard. Visual assessment and instrumental measurement of color were carried out to establish the color tolerance ellipse that was defined as CMC (Color Measurement Committee) color differences (2:1) of no more than 1.00. It was found that the color strengths (K/S) and color differences (ΔECMC(2:1)) of these fabric samples for each color series had linear relationships with the color depths of warp and weft yarns. The color tolerance ellipses indicated that, even though the warp and weft yarns had an apparent color difference, they could be woven in fabrics with relatively uniform color appearance and meet the requirements for yarn-dyed fabric. This work provided valuable insight into the production of qualified yarn-dyed fabrics from unqualified dyed yarns.  相似文献   
5.
杜强国 《机械管理开发》2021,36(5):25-26,61
为了适应煤矿产能的提升和开采规模的不断加大,南岭矿对现有机电运输设备进行了重新的选型和升级.实际应用表明,优化后的井下运输设备的运输能力能够很好地满足矿井的安全高效生产.  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.
9.
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   
10.
Ultrawide band gap semiconductor materials have attracted considerable attention in recent years owing to their great potential in the photocatalytic field. In this study, Zn-doped Ga2O3 nanofibers with various concentrations were synthesized via electrospinning; they exhibited a superior photocatalytic degradation performance of rhodamine B dye compared to that of undoped Ga2O3 nanofibers. The Zn dopant replaced Ga sites via replacement doping, which could increase the concentration of oxygen vacancies and lead to enhanced photocatalytic properties. When the Zn concentration increased, a Ga2O3/ZnGa2O4 hybrid structure formed, which could further enhance the photocatalytic performance. The separation of photogenerated carriers due to Zn doping and heterojunctions were the primary causes of the enhanced photocatalytic performance. This study provides experimental data for the fabrication of high-performance photocatalysts based on Ga2O3 nanomaterials.  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