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排序方式: 共有411条查询结果,搜索用时 15 毫秒
71.
Chong-il Lee Qing-long MengHiroshi Kaneko Yutaka Tamaura 《International Journal of Hydrogen Energy》2013
The role played by the dopant in the H2-generation step of two-step water splitting has been investigated with CeO2–ZrO2–MOx (M = Mg, Ca, Sr, Ba, Sc, Y, Lu, La, Nd, Sm, Eu, Gd, Dy, Tm, Tb and Pr). The relationship between ionic radius, valence of the dopant, and oxidation ratio was investigated for its effect on H2 yield. The oxidation ratio increases with an increase in the ionic radii. This tendency increases with an increase in the ionic valence (divalent < trivalent < tetravalent). This suggests that the surface process affects the chemical equilibrium of the reaction. The ionic conductivity measured by AC impedance spectroscopy showed that the increase in ionic conductivity speeds the reaction rate of H2 generation. This indicates that a bulk diffusion process is the rate-determining step of H2-generation reaction. 相似文献
72.
Presented paper deals with the catalytic decomposition of hydrocarbons (methane and toluene) in the aspect of H2 production and types of obtained carbon deposits. The catalyst used in our studies was nickel supported on ceria–zirconia (Ni/CeZrO2). The aim of this work was to investigate the reactivity of obtained carbon deposits with H2O. Both issues are of great importance for determining the mechanisms of carbon deposits formation and their suppression during steam reforming reaction. 相似文献
73.
M. Casapu J.-D. Grunwaldt M. Maciejewski F. Krumeich A. Baiker M. Wittrock S. Eckhoff 《Applied catalysis. B, Environmental》2008,78(3-4):288-300
Differences in the NOx storage-reduction (NSR) behavior of Pt/Ba/CeO2 and Pt/Ba/Al2O3 have been identified and traced to their different chemical and structural properties. The results show that Pt/Ba/CeO2 exhibits inferior NOx storage and, particularly, reduction (regeneration) activity compared to the Al2O3 supported catalyst. The incomplete reduction of the stored NOx-species in Pt/Ba/CeO2 seems to be caused by a faster and more profound reoxidation of Pt particles during the lean period as evidenced by in situ X-ray absorption spectroscopy. Interestingly, the reduction activity could be significantly improved by a pre-reduction step at mild conditions. Exposure of the Pt/Ba/CeO2 catalyst to reducing H2 atmosphere in the temperature range 300–500 °C lead to a moderate increase of Pt particle size which beneficially influenced the regeneration activity. In contrast, pre-reduction at temperatures above 500 °C was unfavorable and resulted in a severe decrease of the regeneration activity, probably due to migration of the partially reduced CeO2 onto the surface of Pt particles. 相似文献
74.
F.C. Meunier G. Yablonsky D. Reid S.O. Shekhtman C. Hardacre R. Burch M. Lazman 《Catalysis Today》2008,138(3-4):216
The kinetics of the water-gas shift reaction were studied on a 0.2% Pt/CeO2 catalyst between 177 and 300 °C over a range of CO and steam pressures. A rate decrease with increasing partial pressure of CO was experimentally observed over this sample, confirming that a negative order in CO can occur under certain conditions at low temperatures. The apparent reaction order of CO measured at 197 °C was about −0.27. This value is significantly larger than that (i.e. −0.03) reported by Ribeiro and co-workers [A.A. Phatak, N. Koryabkina, S. Rai, J.L. Ratts, W. Ruettinger, R.J. Farrauto, G.E. Blau, W.N. Delgass, F.H. Ribeiro, Catal. Today 123 (2007) 224] at a similar temperature. A kinetic peculiarity was also evidenced, i.e. a maximum of the reaction rate as a function of the CO concentration or possibly a kinetic break, which is sometimes observed in the oxidation of simple molecules. These observations support the idea that competitive adsorption of CO and H2O play an essential role in the reaction mechanism. 相似文献
75.
The oxidation of carbon black, CB, in presence of CeO2 is investigated to gain a better understanding of the effect of the contact between the two solids during this reaction. Different CB/CeO2 mixtures are tested in a fixed bed reactor. The experimental data are used to propose a model for CB oxidation in presence of CeO2. It accounts for the size distribution of CeO2 particles, the contact area between CB and CeO2, the mass of CB in the sample and the initial ratio CB/CeO2. Corresponding kinetic parameters are determined. 相似文献
76.
Robinson L. ManfroAline F. da Costa Nielson F.P. RibeiroMariana M.V.M. Souza 《Fuel Processing Technology》2011,92(3):330-335
Nickel catalysts supported on CeO2 were prepared and evaluated in aqueous-phase reforming of glycerol. Three different methodologies of synthesis were used: wet impregnation, co-precipitation and combustion, and the catalysts were characterized by chemical composition, textural analysis, crystalline structure and reducibility. The reaction was carried out in a batch reactor with solution of 1 and 10 wt.% glycerol, at 523 and 543 K. A maximum glycerol conversion of 30% was achieved by the catalyst prepared by combustion at 543 K using solution 1% glycerol. In the gas phase, the molar fraction of H2 was always higher than 70% and formation of CH4 was very low (< 1%). The increase in glycerol concentration decreases the conversion and H2 formation. 相似文献
77.
Xiaoyu Fan Famin QiuHangsheng Yang Wei TianTianfeng Hou Xiaobin Zhang 《Catalysis communications》2011,12(14):1298-1301
Mn-Ce-OX catalysts loaded on TiO2-carbonaceous materials were prepared by sol-gel method. Selective catalytic reduction of NOX was conducted in a fixed-bed flow-reactor over catalysts coated on aluminum plates. A de-NOX efficiency of more than 90% was obtained over the Mn-Ce-OX/TiO2-carbon nanotubes (CNTs) catalyst between 75 °C and 225 °C under a gas hourly space velocity (GHSV) of ~ 36,000 h−1. This activity improvement is attributed to the increase of the BET surface area, and the occurrence of reaction between adsorbed NOX and NH3. Moreover, the de-NOX efficiency was increased to 99.6% by adding 250 ppm SO2 between 100 °C and 250 °C. 相似文献
78.
The effects of ceria (CeO2) abrasives in chemical mechanical polishing (CMP) slurries were investigated on silicon dioxide (SiO2) and silicon nitride (Si3N4) polishing process. The ceria abrasives were prepared by the flux method, using potassium hydroxide (KOH) as the grain growth accelerator. The primary particle size of the ceria abrasives was controlled in the range of ~ 84-417 nm by changing the concentration of potassium hydroxide and the calcination temperature without mechanical milling process. The removal rate of silicon dioxide film strongly depended upon abrasive size up to an optimum abrasive size (295 nm) after CMP process. However, the surface uniformity deteriorated as abrasive size increases. The observed polishing results confirmed that there exists an optimum abrasive size (295 nm) for maximum removal selectivity between oxide and nitride films. In this study, polishing behaviors of the ceria abrasives were discussed in terms of morphological characteristics. 相似文献
79.
Shohei Tada Ochieng James Ochieng Ryuji Kikuchi Takahide Haneda Hiromichi Kameyama 《International Journal of Hydrogen Energy》2014
The effect of CeO2 loading amount of Ru/CeO2/Al2O3 on CO2 methanation activity and CH4 selectivity was studied. The CO2 reaction rate was increased by adding CeO2 to Ru/Al2O3, and the order of CO2 reaction rate at 250 °C is Ru/30%CeO2/Al2O3 > Ru/60%CeO2/Al2O3 > Ru/CeO2 > Ru/Al2O3. With a decrease in CeO2 loading of Ru/CeO2/Al2O3 from 98% to 30%, partial reduction of CeO2 surface was promoted and the specific surface area was enlarged. Furthermore, it was observed using FTIR technique that intermediates of CO2 methanation, such as formate and carbonate species, reacted with H2 faster over Ru/30%CeO2/Al2O3 and Ru/CeO2 than over Ru/Al2O3. These could result in the high CO2 reaction rate over CeO2-containing catalysts. As for the selectivity to CH4, Ru/30%CeO2/Al2O3 exhibited high CH4 selectivity compared with Ru/CeO2, due to prompt CO conversion into CH4 over Ru/30%CeO2/Al2O3. 相似文献
80.
《应用陶瓷进展》2013,112(2):123-127
AbstractThis article describes the synthesis of a CeO2 fine powder by thermal decomposition of cerium oxalate and cerium nitrate powders using a microwave furnace. Plate-like crystalline CeO2 particles were obtained using the cerium oxalate precursor powder. Using the cerium nitrate powder as a precursor, spherical crystalline CeO2 particles were obtained with a primary particle diameter of 30?nm and secondary particle size of 550?nm. 相似文献