全文获取类型
收费全文 | 4644篇 |
免费 | 169篇 |
国内免费 | 168篇 |
专业分类
电工技术 | 119篇 |
综合类 | 195篇 |
化学工业 | 585篇 |
金属工艺 | 105篇 |
机械仪表 | 292篇 |
建筑科学 | 407篇 |
矿业工程 | 48篇 |
能源动力 | 284篇 |
轻工业 | 169篇 |
水利工程 | 61篇 |
石油天然气 | 440篇 |
武器工业 | 19篇 |
无线电 | 730篇 |
一般工业技术 | 608篇 |
冶金工业 | 50篇 |
原子能技术 | 200篇 |
自动化技术 | 669篇 |
出版年
2024年 | 3篇 |
2023年 | 31篇 |
2022年 | 81篇 |
2021年 | 100篇 |
2020年 | 95篇 |
2019年 | 58篇 |
2018年 | 76篇 |
2017年 | 99篇 |
2016年 | 131篇 |
2015年 | 113篇 |
2014年 | 222篇 |
2013年 | 233篇 |
2012年 | 200篇 |
2011年 | 377篇 |
2010年 | 251篇 |
2009年 | 273篇 |
2008年 | 248篇 |
2007年 | 310篇 |
2006年 | 291篇 |
2005年 | 242篇 |
2004年 | 215篇 |
2003年 | 174篇 |
2002年 | 178篇 |
2001年 | 119篇 |
2000年 | 128篇 |
1999年 | 127篇 |
1998年 | 121篇 |
1997年 | 102篇 |
1996年 | 94篇 |
1995年 | 57篇 |
1994年 | 52篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1959年 | 4篇 |
排序方式: 共有4981条查询结果,搜索用时 46 毫秒
51.
改善高平均功率固体激光器光束质量的研究 总被引:5,自引:0,他引:5
本文首先概述了内含热透镜的激光谐振腔的分析方法,提出影响高平均功率固体激光器光束质量的主要因素是激光介质的热效应,尤其是非对称的热透镜象差。因此,改善光束质量的途径是补偿或修正透镜象差,使光束质量达到非相干多模振荡的理论值。 相似文献
52.
In this note, we show that any distributive lattice is isomorphic to the set of reachable configurations of an Edge Firing Game. Together with the result of James Propp, saying that the set of reachable configurations of any Edge Firing Game is always a distributive lattice, this shows that the two concepts are equivalent. 相似文献
53.
在压水堆核电站应急计划和应急响应中,堆底熔穿事故占有重要位置。本文用法国核电厂事故源项S3(对应于堆底熔穿事故)计算了在典型气象条件下的场外放射学的后果,根据一般防护决策原则和我国颁布的干预水平,提出了保护公众的应急防护措施的建议。 相似文献
54.
本文较详细地描述了多孔硅的电致发光(EL),以及发光的量子限制效应的机制,并且讨论了目前已经制备出的几种多孔硅发光二级管:Ps/电解液型,Schot-tky-Like,PN结等二极管。最后,讨论了多孔硅作为半导体光电材料所存在的一些问题。 相似文献
55.
56.
微机控制多功能晶闸管逆变弧焊电源研究 总被引:2,自引:0,他引:2
本文介绍了微机控制多功能晶闸管逆变弧焊电源的主要功能硬件及软件程序设计,微机主芯片采用了单片机 MCS—51,焊机能输出四种静特性,实现一机多用。 相似文献
57.
The catalytic cracking of coal tar asphaltene (CTA) pyrolysis vapors was carried out over transition met-alion modified zeolites to promote the generation of light aromatic hydrocarbons (L-ArHs) in a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) micro-reactor system.The effects of ultra stable Y(USY),Co/USY and Mo/USY on the selectivity and yield of L-ArHs products and the extent of deoxygena-tion (Edeoxygenation),lightweight (Elightweight) from CTA pyrolysis volatiles were investigated.Results showed that the yields of L-ArHs are mainly controlled by the acid sites and specific surface area of the catalysts,while the deoxygenation effect is determined by theirs pore size.The Elightweight of CTA pyrolysis volatiles over USY is 9.65%,while the Edeoxygenation of CTA pyrolysis volatiles over Mo/USY reaches 20.85%.Additionally,the modified zeolites (Mo/USY and Co/USY) exhibit better performance than USY on L-ArHs production,owing to the synergistic effect of metal ions (Mo,Co) and acid sites of USY.Compared with the non-catalytic fast pyrolysis of CTA,the total yield of L-ArHs obtained over USY (4032 mg·kg-1),Co/USY (4363 mg·kg-1) and Mo/USY (4953 mg·kg-1) were increased by 27.03%,38.19% and 54.78%,respectively.Furthermore,the possible catalytic conversion mechanism of transition metal ion (Co and Mo) modified zeolites was proposed based on the distribution of products and the characterizations of catalysts. 相似文献
58.
全面分析铸件浇注成型过程中气体的气源后,指出正确认识气孔的形成,从气孔的大小,位置、分布、形态反过程分析形成气孔的气源,有针对性地采取措施解决铸件中的气孔弊病问题。 相似文献
59.
聚乙烯转光棚膜的加工及应用研究 总被引:8,自引:3,他引:8
本文对聚乙烯转光棚膜的加工和光转换剂的作用、配比关系及物理性能进行了讨论。 相似文献
60.
The direct catalytic conversion of alkanes into aromatics has found potentially important industrial applications. Initially only alkanes with 6 and more carbon atoms in the chain were concerned. Supported platinum catalysts were found active for the aromatization of alkanes; the drawbacks of these catalysts were their deactivation with time on stream and the existence of simultaneous parallel reactions. Much discussion has been published on the aromatization of C6+ alkanes. A bifunctional mechanism which involves both the metal and the acid sites of the support and a monofunctional mechanism involving only the metallic sites operate over, respectively, Pt supported on acidic support and Pt supported on nonacidic support. In the present review the mechanisms proposed for the aromatization of alkanes are described. Over monofunctional Pt catalysts two possible mechanisms prevail: 1,6 ring closure on the Pt surface involving primary and secondary C-H bond rupture, followed by dehydrogenation of the cycloalkanes into aromatics (1,5 ring closure to a lesser extent also contributes to aromatic production); or dehydrogenation of the alkanes into olefins, dienes, and trienes followed by thermal ring closure. Zeolites were found most suitable as support for preparing catalysts more active and more selective in the alkane aromatization. In addition catalysts based on noble metals supported on zeolite appeared more resistant against deactivation by coke. In this review the aromatization of hexane, heptane, and octane over Pt-zeolite catalysts is discussed in detail. Comparisons between different zeolite structures and different dehydrogenation sites are given. In particular a critical analysis of the results and interpretation concerning Pt-KL catalysts strongly suggests that the exceptional high selectivity towards aromatization of n-hexane exhibited by Pt-KL could not be explained by only the nest or constraint effect exerted by the channel dimension and morphology, not by only the terminal cracking properties, not by only the partial electron transfer from the zeolite support to the Pt particles, and not by only the Pt particle size. Zeolite structure also affects the aromatic product distribution, in particular when the alkane contains more than 7 carbon atoms. It is shown how Pt on medium-pore zeolites such as In-ZSM-5, silicalites will favor the aromatization of C8 alkane isomers into ethylbenzene-styrene with respect to other C8 aromatics. Aromatization of light alkanes, C2-C5, requires the increase of the hydrocarbon chain length up to 6 carbon atoms and higher, followed by cyclization reaction. Recently new processes to convert C2-C5 alkanes into aromatics have been disclosed, M2-forming from Mobil, Cyclar from BP-UOP, and Aroforming from IFP-Saluted. In general these processes use bifunctional catalysts possessing a dehydrogenating and an acid function. The catalysts consist of a metal ion or metal oxide supported on a microporous acid solid. In this review we analyze the results concerning mainly platinum supported on pentasil-type zeolite. It is shown that althoug Pt has better dehydrogenating properties as compared with gallium and zinc, the efficiency of catalysts based on Pt-ZSM-5 for light alkane aromatization is less because undersirable reactions such as hydrogenolysis and ethene (olefins) hydrogenation occur on the platinum surface, resulting in the production of unreactive alkanes, CH2, C2H6. These drawbacks could be partially suppressed by alloying Pt and by increasing the reaction temperature. 相似文献