全文获取类型
收费全文 | 5230篇 |
免费 | 365篇 |
国内免费 | 177篇 |
专业分类
电工技术 | 7篇 |
综合类 | 176篇 |
化学工业 | 3384篇 |
金属工艺 | 145篇 |
机械仪表 | 58篇 |
建筑科学 | 5篇 |
矿业工程 | 22篇 |
能源动力 | 134篇 |
轻工业 | 106篇 |
水利工程 | 2篇 |
石油天然气 | 1382篇 |
武器工业 | 5篇 |
无线电 | 76篇 |
一般工业技术 | 182篇 |
冶金工业 | 61篇 |
原子能技术 | 11篇 |
自动化技术 | 16篇 |
出版年
2024年 | 15篇 |
2023年 | 78篇 |
2022年 | 145篇 |
2021年 | 187篇 |
2020年 | 130篇 |
2019年 | 145篇 |
2018年 | 124篇 |
2017年 | 129篇 |
2016年 | 174篇 |
2015年 | 168篇 |
2014年 | 257篇 |
2013年 | 247篇 |
2012年 | 307篇 |
2011年 | 295篇 |
2010年 | 250篇 |
2009年 | 253篇 |
2008年 | 253篇 |
2007年 | 286篇 |
2006年 | 260篇 |
2005年 | 284篇 |
2004年 | 239篇 |
2003年 | 224篇 |
2002年 | 203篇 |
2001年 | 146篇 |
2000年 | 156篇 |
1999年 | 126篇 |
1998年 | 119篇 |
1997年 | 82篇 |
1996年 | 64篇 |
1995年 | 71篇 |
1994年 | 82篇 |
1993年 | 54篇 |
1992年 | 46篇 |
1991年 | 39篇 |
1990年 | 24篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 28篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1951年 | 8篇 |
排序方式: 共有5772条查询结果,搜索用时 20 毫秒
31.
对抚顺石油化工分公司石化三厂白油加氢装置进行技术改造,通过调整加氢工艺,采用一段加氢工艺生产高品级的加氢尾油,再经分馏系统生产出多种优级品的白油,满足了市场需求,并创造了可观的经济效益和社会效益。 相似文献
32.
An anomalous rate enhancement with increasing conversion has been observed during the liquid phase hydrogenation of nitrobenzene and crotonaldehyde over Ge/Pd/C catalysts at ambient temperature and atmospheric pressure. Inductive coupled plasma atomic emission spectroscopy and electrochemical measurement of the oxidation state of catalysts during reaction revealed that the bimetallic particles were partially oxidized by the reactants, which resulted in Ge-dissolution and increased exposure of Pd on the surface. It is proposed that the surface and bulk composition of Ge/Pd catalysts are a function of their oxidation state. This behaviour is due to the unusually high mobility of Ge in the Pd lattice and to the good solubility of GeO2 in polar solvents. The influence of hydrogen transport on the corrosion process and the stability of other X/Pd type bimetallic catalysts during liquid phase hydrogenation are also discussed. 相似文献
33.
P. Da Costa C. Potvin J.-M. Manoli M. Breysse G. Djega-Mariadassou 《Catalysis Letters》2003,86(1-3):133-138
Hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene on alumina-supported Mo2C has been studied. These catalysts are stable and active under deep HDS conditions (0-250 wt ppm S). However, although they are well known to have hydrogenation properties, they lead preferentially to a non-hydrogenated product of the HDS reaction: dimethylbiphenyl. For the same reaction, supported platinum and sulfided molybdenum oxide lead to the hydrogenated products dimethyldicyclohexyl and methylcyclohexyltoluene, respectively. The ranking of HDS activity is as follows: MoS2/Al2O3 < Mo2C/Al2O3 < Pt/SiO2. 相似文献
34.
35.
The macro-kinetics of benzene hydrogenation over porous Ni/γ-Al_2O_3 catalyst was measured with asingle-pellet diffusion reactor.Based on the dusty-gas model,the differential equations by taking into account ofthe variation of effective diffusivities with the composition were derived to describe the diffusion and reactionprocesses of reacting species over porous catalyst.Using the tortuosity factors determined under the condition ofsteady physical diffusion,the global reaction rates were calculated by solving the equations,and the results are ingood agreement with the experimental data obtained. 相似文献
36.
The activities of several commercial nickel catalysts were determined by measuring their activation energies. Among these
catalysts, G95E, Resan 22, Nysosel 222 and 325, all with low activation energy, were more active than DM3 and G95H, which
had higher activation energy. However, the less active catalysts increased the linoleate selectivity of soybean oil during
hydrogenation. The yields of bothtrans isomers and winterized oil were higher for the more selectively hydrogenated oil catalyzed by the less active catalysts.
In the sensory evaluation, the fractionated solid fat that contained moretrans isomers was lower in flavor scores than the fractionated liquid oil after hydrogenation and winterization of soybean oil. 相似文献
37.
38.
The relationship between chemical structure and reactivity for thermal hydroprocessing was studied for five gas oils derived from Alberta bitumens. Chemical structure was characterized by combining data from 1 H and 13 C nuclear magnetic resonance spectroscopy, class fractionation, and elemental analysis to calculate structural parameters. Thermal hydrotreating was performed in a continuous-flow stirred reactor at 420 and 440°C, 13.9 MPa hydrogen pressure, and 1.5 h1 LHSV. Conversion of the 343–525°C boiling fraction of the gas oils was correlated with the concentration of naphthenic methylene groups in the feed. Formation of methane and ethane was dependent on the degree of condensation of the aromatic rings in the feed oils. Thermal desulfurization was highly correlated with the amount of saturates in the feed, and the aromaticity of the resin fraction. Hydrogen consumption increased with the aromaticity of the gas oil… 相似文献
39.
40.