全文获取类型
收费全文 | 55191篇 |
免费 | 6819篇 |
国内免费 | 3320篇 |
专业分类
电工技术 | 1991篇 |
技术理论 | 8篇 |
综合类 | 3225篇 |
化学工业 | 19567篇 |
金属工艺 | 4291篇 |
机械仪表 | 1747篇 |
建筑科学 | 2892篇 |
矿业工程 | 1198篇 |
能源动力 | 3084篇 |
轻工业 | 3300篇 |
水利工程 | 478篇 |
石油天然气 | 2567篇 |
武器工业 | 194篇 |
无线电 | 3618篇 |
一般工业技术 | 11273篇 |
冶金工业 | 3552篇 |
原子能技术 | 1583篇 |
自动化技术 | 762篇 |
出版年
2024年 | 302篇 |
2023年 | 1268篇 |
2022年 | 1859篇 |
2021年 | 2031篇 |
2020年 | 2201篇 |
2019年 | 2102篇 |
2018年 | 1969篇 |
2017年 | 2244篇 |
2016年 | 2299篇 |
2015年 | 2112篇 |
2014年 | 3109篇 |
2013年 | 3346篇 |
2012年 | 3978篇 |
2011年 | 4256篇 |
2010年 | 3095篇 |
2009年 | 3182篇 |
2008年 | 2568篇 |
2007年 | 3296篇 |
2006年 | 3195篇 |
2005年 | 2675篇 |
2004年 | 2315篇 |
2003年 | 2117篇 |
2002年 | 1727篇 |
2001年 | 1374篇 |
2000年 | 1229篇 |
1999年 | 930篇 |
1998年 | 795篇 |
1997年 | 598篇 |
1996年 | 558篇 |
1995年 | 450篇 |
1994年 | 431篇 |
1993年 | 304篇 |
1992年 | 278篇 |
1991年 | 217篇 |
1990年 | 185篇 |
1989年 | 116篇 |
1988年 | 107篇 |
1987年 | 89篇 |
1986年 | 84篇 |
1985年 | 84篇 |
1984年 | 69篇 |
1983年 | 56篇 |
1982年 | 38篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1959年 | 9篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Renjith Devasia CP Reghunadhan Nair P Sivadasan KN Ninan 《Polymer International》2005,54(8):1110-1118
Polyacrylonitrile terpolymers of various compositions consisting of acrylonitrile (AN), itaconic acid (IA) and methyl acrylate (MA) were synthesized by solution polymerization in dimethylsulfoxide. Increase in concentration of either IA or MA retarded the overall polymerization rate and the polymer molecular weight. The system consisting of AN + MA and varying IA concentration was more prone to retardation in comparison with the system composed of AN + IA with variable MA concentration. The retardation factors were quantified. Minor quantities of MA boost the reactivity of IA in the terpolymer system. The terpolymer was richer in MA vis‐à‐vis the feed. The thermal characteristics of the terpolymer were examined as a function of its composition. In contrast to the copolymer of AN and IA requiring 1–1.5 mol% IA, the terpolymer required an IA content of approximately 2.5 mol% for optimum thermal stability. The polymer with 90 mol% AN, 2.5 mol% IA and 7.5 mol% MA exhibited reasonably good char‐forming characteristics and thermal stability. The overall crystallinity and crystallite size of the polymers were found to decrease on incorporation of the comonomers. The ‘aromatization index’ of the copolymer increased with the temperature of pyrolysis through re‐organization of the tetrahydropyridine ladder structure. Copyright © 2005 Society of Chemical Industry 相似文献
102.
103.
Wang Xuegang Yan Fengjie Yan Qian Li Xingeng 《Frontiers of Materials Science in China》2007,1(2):225-227
An iron-based amorphous foil (FeNiCrSiB) was used as an interlayer for the amorphous diffusion bonding of low carbon steel
pipes under argon flux. The microstructure and mechanical properties of the joint were analyzed using an electron probe micro-analyzer
(EPMA), tensile test, bending test and impact test. The results show that the joint microstructure resembles that of the base
metal and no precipitates form at the joint. Melting point depressants (B, Si) diffuse far away from the joint and the base
metal element is homogenous across the joint. The joint impact toughness is greater than the base metal toughness and the
mechanical properties of the joint are similar around the pipe. 相似文献
104.
矿山岩土工程系统环境质量评价指标体系 总被引:1,自引:0,他引:1
矿山现行的环境影响评价及其提交的环境影响报告书,是将矿山开发视为单个建设项目且只注重污染物排放和简单数量分析的单要素评价.本文将矿山开发视为统一系统,充分考虑系统内矿石开采、废石场、尾矿库等岩土工程及其矿岩氧化淋滤产生的毒害物质对矿区及其区域水土环境潜在而长期的影响,建立矿山岩士工程系统环境质量评价的指标体系,以改变矿山环境评价的传统旧式,规范和监督矿山开采行为,实现矿业开发与环境保护的协调发展. 相似文献
105.
C. Athanassiou G. Pekridis N. Kaklidis K. Kalimeri S. Vartzoka G. Marnellos 《International Journal of Hydrogen Energy》2007
In the present work, the prospects and trends of solid electrolyte membrane reactors (SEMRs) towards hydrogen production, are discussed. Initially, an overview of the principles, the properties and the techniques related to the usage of the SEMRs, are presented. In the following, a literature survey covering earlier and recent developments of the various methods (e.g. reforming or partial oxidation or dehydrogenation of hydrocarbons, steam electrolysis) employed in the SEMRs for the production of hydrogen, is performed. Finally, the current status of this research field is analyzed and future research topics are proposed. 相似文献
106.
107.
Preparation and Properties of Rare Earth Modified Carbon Black/Natural Rubber Composites 总被引:2,自引:2,他引:0
Lin Yaling Xiao Kongqing Zhang Anqiang Wang Lianshi 《中国稀土学报(英文版)》2005,23(6):720-720
The oxides Eu, Ho, Er and Dy were used to prepare the hydroxides of rare earth modified carbon black. Then natural rubber latex (NRL) was added into the reactor. The system reacted at 85 ℃ with stirring for 1 h to prepare powdered HAF-Ln(OH)3/NR composites. The effects of the kind and content of Ln on the particle size distribution of P [ NR/HAF-Ln (OH)3 ] and mechanical properties of its vulcanizate were studied respectively. It is found that rare earth can help to get the powder of the composite, the product particle with a diameter less than 0.9mm will be get when the composites containing the compound of Ho, Er and Dy with dosage of 1.0, 1.0, O. 5 percent, respectively. The adding of Ln can improve the tensile strength and tear strength of the vulcanizate effectively, what's more, Er and Dy can decrease the permanent set of vulcanizate significantly. The SEM studies shows that P[ NR/HAF-Dy (OH)3 ] vulcanizate shows superior mechanical properties that depend primarily on the absence of free carbon black, the fine dispersion of carbon black in the rubber matrix and better polymer-filler interaction. 相似文献
108.
MIP-CGP工艺专用催化剂CGP-1的开发与应用 总被引:11,自引:3,他引:8
阐述了生产汽油组分满足欧Ⅲ排放标准并多产丙烯的催化裂化工艺(简称MIP-CGP)专用催化剂(简称CGP-1)的研究开发与工业应用结果。CGP-1催化剂的基质具有良好的容炭性能,使活性组元受到良好保护,其优势作用在第二反应区得以充分发挥,具有更高的氢转移活性和强的汽油小分子烯烃裂化活性。中国石化九江分公司和镇海炼化公司的MIP-CGP工业试验标定结果表明,与常规FCC相比,采用CGP-1催化剂的MIP-CGP技术在生产烯烃体积分数小于18%的汽油组分的同时,丙烯产率达到8%以上。此外,汽油诱导期大幅提高,抗爆指数增加;总液体收率有所提高,干气产率下降,焦炭选择性良好。 相似文献
109.
土壤碳固定问题已成为陆地生态系统碳循环研究的热点问题。土壤碳固定是缓解温室效应加剧的有效方法之一。土壤有机碳含量变化受土地利用方式和耕作措施的强烈影响。将自然土壤转变为耕作土壤会导致土壤碳库的迅速下降,使土壤损失有机碳4.1-5.0×1013kg之间。采用新的农业措施会使碳损失量的60-70%重新被固定。这些措施有保护性耕作(少耕或免耕)、合理施用肥料、覆盖作物、应用深根且富含木质素的作物等。土壤除了固定有机碳外,干旱和半干旱地区土壤还具有固定无机碳的巨大潜力。文章还简要介绍了评价土壤有机碳的两种方法,并对今后的工作提出了几点建议。 相似文献
110.