全文获取类型
收费全文 | 991篇 |
免费 | 9篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 2篇 |
综合类 | 43篇 |
化学工业 | 636篇 |
金属工艺 | 4篇 |
机械仪表 | 5篇 |
建筑科学 | 20篇 |
矿业工程 | 27篇 |
能源动力 | 86篇 |
轻工业 | 7篇 |
水利工程 | 5篇 |
石油天然气 | 42篇 |
一般工业技术 | 101篇 |
冶金工业 | 15篇 |
原子能技术 | 6篇 |
自动化技术 | 12篇 |
出版年
2023年 | 9篇 |
2022年 | 30篇 |
2021年 | 25篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 13篇 |
2017年 | 20篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 55篇 |
2012年 | 43篇 |
2011年 | 52篇 |
2010年 | 48篇 |
2009年 | 82篇 |
2008年 | 106篇 |
2007年 | 61篇 |
2006年 | 50篇 |
2005年 | 42篇 |
2004年 | 42篇 |
2003年 | 32篇 |
2002年 | 17篇 |
2001年 | 27篇 |
2000年 | 32篇 |
1999年 | 26篇 |
1998年 | 17篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有1011条查询结果,搜索用时 15 毫秒
71.
Effect of the activation procedure on the performance of Mo/H-MFI catalysts for the non-oxidative conversion of methane to aromatics 总被引:1,自引:0,他引:1
Sharifah B. Derouane-Abd Hamid J. Ross Anderson Iver Schmidt Christophe Bouchy Claus J. H. Jacobsen Eric G. Derouane 《Catalysis Today》2000,63(2-4):461-469
The effect of pre-treatment on the performance of Mo/H-MFI zeolite catalysts applied to the non-oxidative conversion of methane to aromatics has been investigated. It is demonstrated that catalyst performance depends on activation conditions. Activation of the Mo-oxide/H-MFI precursor with an n-butane/hydrogen mixture results in higher catalyst stability and benzene selectivity which are tentatively attributed to the formation of the -MoC1−x carbide, with f.c.c. structure as revealed by XRD. 相似文献
72.
Unusual selectivity of oxygenate synthesis: Formation of acetic acid from syngas over unpromoted Rh in NaY zeolite 总被引:1,自引:0,他引:1
Syngas conversion over Rh/zeolite-NaY catalysts at high-pressure lead to high yields of acetic acid. This unusual selectivity toward one oxygenate in the absence of any catalyst promoter is most pronounced at lower temperature; the apparent activation energy for overall CO-hydrogenation is 23.7 kcal/mol, but for the formation of acetic acid it is 11.9 kcal/mol. The selectivity is little affected by the protons formed during the reduction of Rh. In stiu FT-IR measurement reveals that changes in activity and selectivity during the start-up period are caused by thorough catalyst reconstruction, converting the original Rh0 clusters to multinuclear Rh6(CO)16 and CH3Rhy(CO)x and/or mononuclear CH3Rh(CO)x carbonyl complexes, and smaller Rh0 clusters. Stable acetate groups, but not the surface bound acetyls, are formed and detected by FT-IR. Most of the cooperating Rh species survive when the pressure is lowered from 1.0 to 0.1 MPa, maintaining a high acetic acid selectivity that is vastly superior to that of the fresh catalyst. 相似文献
73.
Zhiyong Wang Mohammed A. Al-Daous Elizabeth R. Kiesel Fan Li Andreas Stein 《Microporous and mesoporous materials》2009,120(3):351-358
Zeolite NaY nanocrystals (20−50 nm) were hydrothermally grown on polyelectrolyte-coated three-dimensionally ordered macroporous (3DOM) activated zirconia. The zeolite nanocrystallites uniformly coated the macropore walls of 3DOM sulfated zirconia, but sulfate groups were lost during the hydrothermal reaction. 3DOM tungstated zirconia was found to be more stable in the strong basic environment of the zeolite precursor solution. Further, ion-exchange of zeolite NaY with ruthenium followed by hydrogen-reduction formed a composite of RuNaY and 3DOM activated zirconia. The presence of ruthenium was confirmed by X-ray photoelectron spectroscopy and the external shape of zeolite nanoparticles was maintained after ion-exchange, but the zeolite lattice fringes could not be observed by transmission electron microscopy after incorporation of reduced ruthenium. Although the catalytic activity of the materials has not yet been tested, these hierarchical nano- and microstructures bring multiple catalyst components (modified zeolite Y, a typical Fischer–Tropsch catalyst, and activated zirconia, an isomerization catalyst) together in intimate contact for potential multi-reaction processes. 相似文献
74.
In this study mine waters obtained from coal mining operations in South Africa were used as a substitute for pure water during the synthesis of zeolites from South African coal fly ash. Procedures that had been optimized to produce single phase zeolite Na-P1 and X using pure water were employed independently. The use of circumneutral mine water resulted in similar quality zeolite Na-P1 and X whereas the use of acidic mine drainage led to the formation of a single phase hydroxysodalite zeolite. Since these two wastes (fly ash and mine waters) are found in close proximity to each other, this study demonstrates that they can be used to ameliorate each other and at the same time produce saleable zeolitic products that can be used to offset their costs of disposal and treatment. 相似文献
75.
Rutger A. van Santen 《Catalysis Today》1999,50(3-4):511-515
The combined use of quantum chemistry and spectroscopy to provide a basis of microkinetics modelling is discussed. 相似文献
76.
Hiromi Yamashita Yo Fujii Yuichi Ichihashi Shu Gou Zhang Keita Ikeue Dal Ryung Park Keiko Koyano Takashi Tatsumi Masakazu Anpo 《Catalysis Today》1998,45(1-4):221-227
Highly dispersed titanium oxide catalysts have been prepared within zeolite cavities as well as in the zeolite framework and utilized as photocatalysts for the reduction of CO2 with H2O to produce CH4 and CH3OH at 328 K. In situ photoluminescence, ESR, diffuse reflectance absorption and XAFS investigations indicate that the titanium oxide species are highly dispersed within the zeolite cavities and framework and exist in tetrahedral coordination. The charge transfer excited state of the highly dispersed titanium oxide species play a significant role in the reduction of CO2 with H2O with a high selectivity for the formation of CH3OH, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce CH4, being similar to reactions on the powdered TiO2 catalysts. Ti-mesoporous molecular sieves exhibit high photocatalytic reactivity for the formation of CH3OH, its reactivity being much higher than the powdered TiO2 catalysts. The addition of Pt onto the highly dispersed titanium oxide catalysts promotes the charge separation which leads to an increase in the formation of CH4 in place of CH3OH formation. 相似文献
77.
This is a comparative study of the synthesis of zeolite A from metakaolinite using both conventional and microwave-assisted heating. The effects of reaction conditions on the rate of formation, crystallinity and actual % yield of zeolite A were investigated. Reaction parameters such as different NaOH molarities (1.0–5.0 M), temperatures (70 and 80 °C), durations (1–8 h) as well as the effect of seeding percentage (1–4%) were tested. The rate of zeolite A formation was found to increase by 2–3 times in microwave treated samples with a notable enhancement in the product crystallinity and % yield whether seeded or un-seeded. 相似文献
78.
Kang Shanjiao Dou Tao Li Qiang Duan Aijun Zheng Yanying Pan Huifang 《Journal of Porous Materials》2008,15(2):159-162
This paper presents the direct synthesis of super-low SiO2/Al2O3 ratio zeolite beta molecular sieve through a novel route, by which some of aluminium species are added during crystaling
process. The IR results show that with the increase of aluminium content in the framework, the frequency of the band in the
range of framework vibration (1060–1090 cm−1) shifts to the lower wave-number; the BET surface-area decreases and the basicity of zeolite becomes stronger. In a second
step, new adsorbents were obtained by solid-state ion exchanging zeolite beta with Cu(I), Ag(I) cations. The deep-desulfurization
(sulfur levels of <1 ppmw) tests were performed using fixed-bed adsorption technique, the sulfur content of the treated and
untreated gasoline was analyzed by microcoulometry. The experimental results show that the desulfurization performance of
sorbents decreases in order: Cu(I)beta > Ag(I)beta > Na-beta. The best sorbent, Cu(I)beta, has breakthrough adsorption capacities
of 0.236 mmolS/g of sorbent for model gasoline. 相似文献
79.
D. Karami S. Rohani 《Chemical Engineering and Processing: Process Intensification》2009,48(8):1288-1292
Four methods were used for the synthesis of pure zeolite Y using soluble silicate as a silica source: (1) the gelling of soluble silicate to silica–alumina gel, by aluminate (or aluminium sulphate), (2) the precipitation of soluble silicate to precipitated silica–alumina gel, by aluminate (or aluminium sulphate), (3) the gelling of soluble silicate by sulphuric acid plus alumina impregnation, and (4) the precipitation of soluble silicate by sulphuric acid plus alumina impregnation. A 24 two-level factorial design was used to study the influence of four different variables on the purity of zeolite Y (expressed in terms of degree of crystallinity). The ageing time turned out to be the most significant variable. Synthesis time, alkalinity and mixing rate were also found to be statistically significant. X-ray diffraction patterns were used to characterize the samples, which ranged from well-crystallized faujasite structures to amorphous materials. The highest purity achieved in method (1) was 38%. The best synthesis condition derived from method (1) was applied to the other three methods. Only method (4) yielded the pure zeolite Y. Therefore, the effect of silica–alumina precursor preparation on producing the pure zeolite Y is extremely important. 相似文献
80.
Sergio M. Bonesi Esther Carbonell Hermenegildo Garcia Maurizio Fagnoni Angelo Albini 《Applied catalysis. B, Environmental》2008,79(4):368-375
Solid photocatalysts in which the 2,4,6-triphenylpyrylium (TP) or 2,4,6-triphenylthiapyrylium cation (TTP) are encapsulated within zeolite Y or deposited on mesoporous silica are used as photosensitizers for the oxidation of sulfides, both aromatic and aliphatic, in solvents of various polarity. Contrary to the same cations in solution, these solid sensitizers are not significantly degraded during operation. An effective oxygenation takes place leading to sulfoxides, disulfides, sulfinic and sulfenic esters as well as sulfonic acids. This large scope method shows a limited dependence on the substrate structure and on conditions and is suitable for the abatement of sulfur-containing pollutants. 相似文献