全文获取类型
收费全文 | 4851篇 |
免费 | 760篇 |
国内免费 | 198篇 |
专业分类
电工技术 | 63篇 |
综合类 | 300篇 |
化学工业 | 1692篇 |
金属工艺 | 29篇 |
机械仪表 | 35篇 |
建筑科学 | 147篇 |
矿业工程 | 1018篇 |
能源动力 | 683篇 |
轻工业 | 225篇 |
水利工程 | 17篇 |
石油天然气 | 1080篇 |
武器工业 | 6篇 |
无线电 | 73篇 |
一般工业技术 | 204篇 |
冶金工业 | 86篇 |
原子能技术 | 41篇 |
自动化技术 | 110篇 |
出版年
2024年 | 10篇 |
2023年 | 86篇 |
2022年 | 162篇 |
2021年 | 180篇 |
2020年 | 190篇 |
2019年 | 207篇 |
2018年 | 222篇 |
2017年 | 207篇 |
2016年 | 194篇 |
2015年 | 208篇 |
2014年 | 351篇 |
2013年 | 257篇 |
2012年 | 354篇 |
2011年 | 361篇 |
2010年 | 259篇 |
2009年 | 262篇 |
2008年 | 214篇 |
2007年 | 260篇 |
2006年 | 237篇 |
2005年 | 226篇 |
2004年 | 166篇 |
2003年 | 160篇 |
2002年 | 136篇 |
2001年 | 131篇 |
2000年 | 100篇 |
1999年 | 98篇 |
1998年 | 93篇 |
1997年 | 81篇 |
1996年 | 96篇 |
1995年 | 70篇 |
1994年 | 66篇 |
1993年 | 37篇 |
1992年 | 24篇 |
1991年 | 27篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有5809条查询结果,搜索用时 15 毫秒
761.
综述了90年代以来CH4-CO2重整反应在改性镍基催化剂、贵金属负载型催化剂和分子筛催化材料研究方面的最新发展。 相似文献
762.
通过正交试验和梯度寻优试验,找到了二甲苯与甲醛合成二(二甲苯基)甲烷的优化工艺条件:二甲苯与甲醛的摩尔比8:1,硫酸-二甲基苯磺酸催化剂用量10.025%、反应温度120 ̄140℃及反应时间140min,在最优工艺条件下,二(二甲苯基)甲烷收率可达77.38%。 相似文献
763.
甲烷活化与转化是当今催化研究领域的前沿课题。本文对甲烷氧化偶联制乙烯、甲烷芳构化、甲烷部分氧化制合成气的催化剂进行了介绍。 相似文献
764.
During the conversion of methane to benzene in the absence of oxygen over a 2 wt% Mo/H-ZSM-5 catalyst at 700°C, three different
types of surface carbon have been observed by X-ray photoelectron spectroscopy: adventitious or graphitic-like C (284.6 eV),
carbidic-like C (282.7 eV), and hydrogen-poor sp-type C (283.2 eV), where the C 1s binding energies for the respective forms
of carbon are given in parentheses. Pretreatment of the catalyst at 700°C in CO also resulted in a strong signal at 283.2
eV; thus, the species responsible for this signal appears to be different from the usual aromatic-type coke. The coke with
dominantly sp hybridization is concentrated on the external surface of the zeolite and is responsible for the gradual deactivation
of the catalyst.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
765.
Kazuhiro Nomura Kiyoshi Noro Yasuhisa Nakamura Yoshiteru Yazawa Hisao Yoshida Atsushi Satsuma Tadashi Hattori 《Catalysis Letters》1998,53(3-4):167-169
The examination of the combustion of a trace amount of methane over Pd‐ion‐exchanged silicoaluminophosphate‐5 (Pd‐SAPO‐5)
at low temperature in the presence of water vapor reveals that water vapor strongly depresses methane combustion and causes
a significant decrease in catalytic activity with time. The newly prepared bimetallic catalyst Pd–Pt‐SAPO‐5, on the other
hand, shows higher performance for methane combustion under similar conditions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
766.
The adsorption, decomposition of CH3 and its reactions with CO2 were followed by means of Fourier transform infrared spectroscopy combined with mass spectrometry. Methyl radicals were produced
by the pyrolysis of azomethane. Absorption bands, observed at room temperature adsorption, were attributed to adsorbed CH3 and CH3O species. The decomposition of adsorbed CH3 in vacuum started above 400 K and was accelerated by CO2. In the study of the interaction of methane with titania, activated in different ways, we found no convincing spectroscopic
evidence for the activation of methane at 300 K.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
767.
Methane conversion to higher hydrocarbons in a “one‐step” process under non‐oxidative conditions at low temperature was here
first introduced and investigated over Co–Pd/SiO2 catalysts at 250°C as a function of hydrogen concentration in helium and of catalyst composition. A maximum in the production
of C2+ hydrocarbons including aromatics (benzene and toluene) was observed at 1.3 vol% H2/He mixture in which one pulse of methane was introduced. Additional hydrogenation with the same H2/He mixture at 400°C was efficient to remove the larger hydrocarbon fragments already existing on the surface. On pure Pd/SiO2 the one‐step process is not so efficient as on cobalt‐rich samples, but in the latter case the hydrocarbon removal is the
most efficient during high‐temperature hydrogenation. It was found that methane conversion in the one‐step process is at least
2.5 times greater than that measured in the “two‐step” process and, in some cases, 80% of the methane introduced is converted
to larger hydrocarbons. The results are discussed in terms of the hydrogen coverage ensuring the optimum hydrogen content
in the surface CHx species leading to chain growth.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
768.
769.
770.