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   98385篇
  免费   8235篇
  国内免费   4209篇
电工技术   5580篇
技术理论   6篇
综合类   6234篇
化学工业   16333篇
金属工艺   6165篇
机械仪表   6952篇
建筑科学   7979篇
矿业工程   3354篇
能源动力   2912篇
轻工业   6267篇
水利工程   1649篇
石油天然气   7267篇
武器工业   808篇
无线电   10613篇
一般工业技术   11441篇
冶金工业   4795篇
原子能技术   1011篇
自动化技术   11463篇
  2024年   364篇
  2023年   1656篇
  2022年   2858篇
  2021年   4192篇
  2020年   3231篇
  2019年   2620篇
  2018年   2858篇
  2017年   3219篇
  2016年   2998篇
  2015年   4093篇
  2014年   4889篇
  2013年   5804篇
  2012年   6313篇
  2011年   6735篇
  2010年   5790篇
  2009年   5517篇
  2008年   5368篇
  2007年   5085篇
  2006年   5419篇
  2005年   4719篇
  2004年   3001篇
  2003年   2843篇
  2002年   2663篇
  2001年   2416篇
  2000年   2330篇
  1999年   2625篇
  1998年   2077篇
  1997年   1724篇
  1996年   1692篇
  1995年   1399篇
  1994年   1146篇
  1993年   732篇
  1992年   640篇
  1991年   436篇
  1990年   347篇
  1989年   295篇
  1988年   219篇
  1987年   140篇
  1986年   112篇
  1985年   68篇
  1984年   45篇
  1983年   40篇
  1982年   41篇
  1981年   26篇
  1980年   23篇
  1979年   16篇
  1978年   1篇
  1965年   1篇
  1959年   2篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 162 毫秒
991.
The PbO2 and F-doped PbO2 (F-PbO2) film electrodes have been prepared by an electrodeposition process onto platinum substrate. The changes of their electrochemical activity for oxygen evolution (OE) reaction with accelerated electrolysis time have been studied. The results show that the activity of the electrodes decreases with increasing electrolysis time. This can be attributed to the conductivity variations, which are caused by the decrease of the oxygen vacancy concentration in PbO2 films during OE. The mechanism of the decrease of the oxygen vacancies has been investigated. For F-PbO2 film electrodes, though its electrochemical activity is somewhat lower than that of undoped one, its activity stability is much higher in comparison with that of PbO2. The influence of F doping on the activity of PbO2 film electrodes has been also discussed.  相似文献   
992.
改性胶粉/SBR共混胶料的结构性能研究   总被引:4,自引:0,他引:4       下载免费PDF全文
研究了硫黄、促进剂、改性胶粉用量对胶粉/SBR共混胶料性能的影响。结果表明;改性胶粉用量在10-35份的范围内.对共混胶料的静态力学性能影响不大:在10-22份的范围内对动态压缩疲劳生热影响不大.适当调整基质胶中硫黄、促进剂的用量.有利于降低胶料的动态压缩疲劳生热。扫描电子能谱微区分析的研究表明:由于硫黄的迁移形成了具有特殊结构的界面过渡层.该过渡层是降低动态压缩疲劳生热的关键。  相似文献   
993.
水体中苯胺类化合物测定方法的改进   总被引:1,自引:0,他引:1  
本文分别利用活性炭吸附、三氯甲烷萃取和前两种方法联用对显色剂 N-(1 -萘基 )乙二胺进行了提纯 ,从而使水体中苯胺类化合物测定方法的显色时间由 1 2 0 min(未提纯法 )缩短至 90 min(经三种方法提纯 ) ,显色剂溶液的稳定性有了明显的提高 ,测定方法的精密度得到了显著的改善 ,同时检出限也由 0 .3 0 mg/L (未提纯法 )分别降至 0 .0 48mg/L (活性炭吸附提纯法 )、0 .0 59mg/L(三氯甲烷萃取提纯法 )和 0 .0 3 1 mg/L(两种方法联用提纯法 ) ,用经三种方法提纯后的显色剂溶液测定水样中的苯胺 ,测定结果均令人满意  相似文献   
994.
A brown coal, peat and oil shale were subjected to a rapid pyrolysis process and medium-heat-value gases together with tar were collected. The char residue was of high activity and suitable for gasification to create a two-stage gasification system. The coal-tar is used for manufacturing liquid fuels and chemicals.  相似文献   
995.
Ultra-high-purity silicon tetrachloride (SiCl4) is demanded as an electronic-grade chemical to meet the stringent requirements of the rapidly developing semiconductor industry. The high requirement for ultra-high-purity SiCl4 has created the need for a high-efficient process for reducing energy consumption as well as satisfying product quality. In this paper, a mass of production technology of ultra-high-purity SiCl4 was successfully developed through chlorination reaction in the ultraviolet (UV)-based photo microreactor coupled with the distillation process. The influences of key operational parameters, including temperature, pressure, UV wavelength and light intensity on the product quality, especially for hydrogen-containing impurities, were quantified by the infrared transmittance of Fourier transform infrared spectroscopy (FT-IR) at 2185 cm-1 and 2160 cm-1 indicating that characteristic vibrational modes of Si—H bonds, as well as the operating conditions of distillation were also investigated as key factors for metal impurities removing. The advanced intensification of SiCl4 manufactured by the integration of photo microreactor and distillation achieves the products with superior specifications higher than the standard commercial products.  相似文献   
996.
正1 RecurDyn如何在仿真之前检查模型的各种设置是否正确?在动力学分析之前,若要检验样机,可以先进行运动学分析,且在施加作用力之前确定各种约束是否正确.在RecurDyn中,还提供模型预分析功能,在simulation type中有预分析功能(pre analysis),检查模型自由度、是否有冗余约束及其相关信息.2 RecurDyn怎样解决有冗余约束的问题?当模型存在冗余约束时,软件在求解过程中会  相似文献   
997.
Without use of any surfactant or oxidant, a series of Co3O4 catalysts have been prepared from cobalt nitrate aqueous solution via a very simple liquid-precipitation method with ammonium acid carbonate followed by calcination at various temperatures. The catalytic performance of the Co3O4 for CO oxidation has been studied with a continuous flowing laboratory microreactor system. The results show that the CO conversion of all the samples can reach 100% at ambient temperature. The catalyst calcined at 300 °C is able to maintain its activity for CO complete oxidation more than 500 min at 25 °C and about 240 min even at −78 °C. High reaction temperature results in a high catalytic stability, while the catalytic stability decreases with further increasing the reaction temperature. Characterizations with X-ray powder diffraction and transmission electron microscopy suggest that all the samples exist as a pure Co3O4 phase with the spinel structure, the samples are apt to aggregate and the specific surface area gradually decreases with increasing the calcination temperature, which directly leads to the decrease of catalytic stability. Furthermore, the amount of active oxygen species measured by CO titration experiments appears to be critical for catalytic performance.  相似文献   
998.
Ultra-high-purity silicon tetrachloride (SiCl4) is demanded as an electronic-grade chemical to meet the stringent requirements of the rapidly developing semiconductor industry. The high requirement for ultra-high-purity SiCl4 has created the need for a high-efficient process for reducing energy consumption as well as satisfying product quality. In this paper, a mass of production technology of ultra-high-purity SiCl4 was successfully developed through chlorination reaction in the ultraviolet (UV)-based photo microreactor coupled with the distillation process. The influences of key operational parameters, including temperature, pressure, UV wavelength and light intensity on the product quality, especially for hydrogen-containing impurities, were quantified by the infrared transmittance of Fourier transform infrared spectroscopy (FT-IR) at 2185 cm−1 and 2160 cm−1 indicating that characteristic vibrational modes of SiH bonds, as well as the operating conditions of distillation were also investigated as key factors for metal impurities removing. The advanced intensification of SiCl4 manufactured by the integration of photo microreactor and distillation achieves the products with superior specifications higher than the standard commercial products.  相似文献   
999.
轻质油品氧化脱硫技术进展   总被引:9,自引:1,他引:9  
介绍了国内外轻质油品氧化脱硫技术的研究进展情况,分析了选择性氧化脱硫、超声波氧化脱硫、光催化氧化脱硫、等离子体液相氧化脱硫等技术的优缺点,展望了氧化脱硫技术应用前景。  相似文献   
1000.
Over the past decade, ionic liquids (ILs) have become one of the fastest growing “green” media for chemists and engineers due to their superb physicochemical properties. The applications of these remarkable salts in reactions and extraction processes have been extensively investigated and reviewed. This review, however, highlights recent advances of ILs as versatile “green” engineering liquids in a variety of industrial applications including heat transfer fluids, azeotrope-breaking liquids, lubricants, electrolytes, liquid crystals, supported IL membranes, plasticizers, and more. This review is not intended to be comprehensive, but rather to discuss the potentials of ILs for diverse industrial 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