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排序方式: 共有219条查询结果,搜索用时 31 毫秒
191.
192.
Andrzej Machocki Andrzej Denis Wieslaw Grzegorczyk Wojciech Gac 《Applied Surface Science》2010,256(17):5551-102
The usefulness of nano- and micro-powders of ceria and zirconia as a support of the cobalt-based catalyst as well as additional modification of zirconia-supported cobalt catalysts with cerium for the production of hydrogen in the steam reforming of bio-ethanol (SRE) for fuel cell applications was studied. It was found that mainly different structural features of the nano- and micro-powder of ceria- and zirconia-supported cobalt catalysts are higher cobalt surface area and much smaller average sizes of cobalt crystallites for the catalysts with high-dispersed support. Similarly, the presence of high-dispersed ceria introduced to the zirconia-supported catalysts simultaneously with the deposition of cobalt increases their total and active surface area as well as decreases the size of cobalt crystallites, regardless of the initial dispersion of zirconia support. The results of the temperature-programmed reduction and the temperature-programmed desorption of hydrogen showed that small crystallites of the cobalt phase strongly interact with high-dispersed ceria.Ceria has a great influence on the effects of the SRE. For the nano-powder ceria-supported cobalt catalyst and for the nano-powder zirconia-supported catalysts with the cobalt-ceria active phase the yield of hydrogen formed from one molecule of ethanol supplied to the SRE process was the highest; even at the relatively low temperature of 420 °C it is close to 5.5 mol H2/mol EtOH. At the same time there were achieved: complete conversion of ethanol, very close to that of water and 92%, 81-84%, 5-6% selectivities to hydrogen, carbon dioxide and carbon monoxide, respectively. 相似文献
193.
This paper describes the preparation and characterization of ZrO2 thin films deposited on silicon wafer by spin coating method. Nanocrystalline ZrO2 was synthesized by hydrothermal method using zirconium (IV)-n-propoxide as a precursor material. Surface of the ZrO2 particles was then modified with 2-acetoacetoxyethyl methacrylate used as a copolymer for coatings. The optical properties, nanostructure and surface morphology of the thin films prepared from surface modified ZrO2 nanoparticles were examined by optical spectroscopy, X-ray diffraction and scanning electron microscopy, respectively. It was found that the films deposited on silicon wafer have crystalline structure of monoclinic (111) at temperature of 150 °C. It was observed that films depict very dense material that does not present any granular or columnar structure. It was found that optical transparency of thin ZrO2 films distributed in the range of 30-40 percent in the spectral range 400-800 nm. Refractive index of ZrO2 films were determined as functions of ZrO2 content and it was found that the refractive index increases from 1.547 to 1.643 with increased ZrO2 content. 相似文献
194.
195.
Silica monoliths were fabricated inside fused-silica capillaries. Then the monolithic columns were coated with membrane-like zirconia. The zirconia-coated silica monoliths exhibited different EOF behavior comparing with that of bare silica monoliths. The magnitude and direction could be manipulated by changing the running buffers. Due to the amphoteric characteristic of zirconia, the silica monoliths with zirconia surface facilitate the separation of basic compounds. Aromatic amines and alkaloids were separated without obvious peak tailing. The zirconia surface was easily modified with octadecylphosphonic acid for the separation of neutral compounds. Column efficiency as high as 90,000 and 80,000 m−1 was obtained for beberine and naphthalene, respectively. Furthermore, the zirconia coating increased the stability of the monolithic columns. Even after being exposed to severe condition, there was no apparently efficiency decrease for the test samples. 相似文献
196.
H. Liu V. Adeeva G. D. Lei W. M. H. Sachtler 《Journal of molecular catalysis. A, Chemical》1995,100(1-3):35-48
The isomerization of n-butane to i-butane has been studied at 11 bar in a microflow reactor over sulfated zirconia (SZ) and platinum containing sulfated zirconia (Pt-SZ) catalysts. In the presence of H2 a significantly higher temperature is required for isomerization over SZ than in its absence. The rate over SZ is higher with n-butane containing 33 ppm butene as an impurity than with a feed that is pre-equilibrated over a Pt/SiO2 catalyst to a much lower butene content. Over Pt-SZ the reaction rate is higher, because any butene consumed is rapidly regenerated; the conversion is perfectly stable in 83 h runs, selectivity to i-butane is 95%; i-pentane and propane are the main byproducts. The activation energy is 53 kJ mol−1. Upon increasing the pressure of H2 from 1.1 to 6.6 bar, the reaction rate was found to decrease in a perfectly reversible fashion. Kinetic analysis reveals that the reaction order is negative in H2 (−1.1 to −1.3 depending on the temperature) and positive in n-butane (+ 1.3 to +1.6), indicating that the mechanism of this isomerization is intermolecular: butene is formed and reacts with adsorbed C4-carbenium ions to adsorbed C8 intermediates which isomerize and undergo β-fission to fragments with i-C4 structure. This mechanism is confirmed over Pt-SZ by isotopic labelling experiments, though at much lower pressure, using double labelled 13CH3---CH2---CH2---13CH3. The primary reaction product consists of i-butane molecules, containing zero, one, two, three and four 13C atoms in a binomial distribution. 相似文献
197.
S. Sarish Biju M. Devassy Walter Bhringer Jack Fletcher S.B. Halligudi 《Journal of molecular catalysis. A, Chemical》2005,240(1-2):123-131
The liquid-phase alkylation of phenol with 1-dodecene was carried out over WOx/ZrO2 solid acid catalysts. The catalysts were prepared by wet impregnation method using zirconium oxyhydroxide and ammonium metatungstate. Catalysts with different WO3 loading (5–30 wt.%) were prepared and calcined at 800 °C and catalyst with 15% WO3 was calcined from 700–850 °C. All the catalysts were characterized by surface area, XRD, and FTIR. The catalyst with 15% WO3 calcined at 800 °C (15 WZ-800) was found to be the most active in the reaction. The effect of temperature, molar ratio and catalyst weight on dodecene conversion and products selectivity was studied in detail. Under the optimized reaction conditions of 120 °C, phenol/1-dodecene molar ratio 2 and time 2 h, the catalyst 15 WZ-800 gave >99% dodecene conversion with 90% dodecylphenol selectivity. Comparison of the catalytic activity of 15 WZ-800 with sulfated zirconia calcined at 500 °C (SZ-500) and Hβ zeolite showed that activity of SZ-500 was lower than that of 15 WZ-800, while Hβ zeolite showed negligible activity. It is observed that the presence of water in the reaction mixture was detrimental to the catalytic activity of WOx/ZrO2. The catalyst 15 WZ-800 also found to be an efficient catalyst for alkylation of phenol with long-chain olefins like 1-octene and 1-decene. 相似文献
198.
镧助剂对Fe/ZrO2催化剂结构及F-T反应性能的影响 总被引:10,自引:1,他引:10
用XRD,Mossbauer谱,TPR,CO-TPD和CO加氢反应性能测试等手段研究了镧助剂对Fe/ZrO2催化剂结构及F-T合成催化剂性能的影响。结果表明,不同的制备方法明显影响催化剂的结构及反应的性能,镧助剂以La2O3形式存在时,催化剂上甲烷选择降低,烯烃选择性提高;镧助剂以LaFeO3形式存在时,催化剂的催化活性大大提高,但同时甲烷选择性上升,烯烃选择性下降。 相似文献
200.
CO2重整甲烷反应高效稳定Ni/ZrO2催化剂的纳米结构特点 总被引:4,自引:0,他引:4
分别通过在常压流动N2气中加热处理ZrO(OH)2醇凝胶和在空气中焙烧ZrO(OH)2水凝胶制备了含不同晶相组成和不同尺寸ZrO2纳米粒子的Ni/ZrO2催化剂.Ni/ZrO2催化剂上CO2重整CH4反应的活性和稳定性以及多种催化剂表征(XRD,TEM,TPR及TPD等)数据表明,高效稳定的Ni/ZrO2催化剂必须具有“金属/氧化物”纳米复合物的特征.ZrO2纳米粒子的晶相组成对CO2重整甲烷反应中纳米复合物型Ni/ZrO2催化剂的稳定性没有明显影响. 相似文献