全文获取类型
收费全文 | 67篇 |
免费 | 0篇 |
专业分类
化学 | 46篇 |
数学 | 6篇 |
物理学 | 15篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2018年 | 1篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2007年 | 3篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有67条查询结果,搜索用时 62 毫秒
11.
12.
Mayra G. Álvarez Adriana Urdă Vicente Rives Silvia R.G. Carrazán Cristina Martín Didier Tichit Ioan-Cezar Marcu 《Comptes Rendus Chimie》2018,21(3-4):210-220
The catalytic properties of ZnAlVO mixed oxides derived from decavanadate-exchanged ZnAl–layered double hydroxide (LDH) precursors prepared by a sol–gel method (ZnAlVO–LDHx,y) were investigated in the oxidative dehydrogenation of propane and compared with those of supported catalysts obtained by conventional impregnation of NH4VO3 on ZnO (ZnVO-I,y) and ZnAlO mixed oxide (ZnAlVO-I,y) supports. The effects of composition and calcination time on the catalytic behavior were particularly examined. Higher propane conversions were achieved at higher vanadium content and calcination time of the precursors. The LDH-derived catalysts were the most active ones in all the temperature range studied (300–425 °C). The order of activity for propane conversion for the different catalyst families varies as ZnAlVO–LDHx,y > ZnAlVO-I > ZnVO-I and follows the strength of the Lewis and Brønsted acid sites determined by monitoring of pyridine adsorption by Fourier transform infrared spectroscopy, whereas the propene selectivities are close together in agreement with the similar densities of basic sites determined by CO2–temperature-programmed desorption measurements. It was indeed established that the acidity, rather than the nature of the crystalline phases, the reducibility, or the specific surface area of the samples, governs the catalytic activity. 相似文献
13.
Laura Marcu Warren S. Grundfest Jean-Michel I. Maarek 《Photochemistry and photobiology》1999,69(6):713-721
To study the photobleaching of the main fluorescent compounds of the arterial wall, we repeatedly measured the time-resolved fluorescence of elastin, collagen and cholesterol during 560 s of excitation with nitrogen laser pulses. Three fluence rate levels were used: 0.72, 7.25 and 21.75 microW/mm2. The irradiation-related changes of the fluorescence intensity and of the time-resolved fluorescence decay constants were characterized for the emission at 390, 430 and 470 nm. The fluorescence intensity at 390 nm decreased by 25-35% when the fluence delivered was 4 mJ/mm2, a common value in fluorescence studies of the arterial wall. Cholesterol fluorescence photobleached the most, and elastin fluorescence photobleached the least. Photobleaching was most intense at 390 nm and least intense at 470 nm such that the emission spectra of the three compounds were markedly distorted by photobleaching. The time-resolved decay constants and the fluorescence lifetime were not altered by irradiation when the fluence was below 4 mJ/mm2. The spectral distortions associated with photobleaching complicate the interpretation of arterial wall fluorescence in terms of tissue content in elastin, collagen and cholesterol. Use of the time-dependent features of the emission that are not altered by photobleaching should increase the accuracy of arterial wall analysis by fluorescence spectroscopy. 相似文献
14.
Ionel Popescu Adriana Urda Tatiana Yuzhakova Ioan-Cezar Marcu Jozsef Kovacs Ioan Sandulescu 《Comptes Rendus Chimie》2009,12(9):1072-1078
Unsupported and γ-Al2O3-supported Ba and Pb titanate catalysts were prepared, characterized and studied in the combustion of methane, as a test reaction for VOCs’ catalytic combustion. They present good catalytic activities, and after dispersion (5%) on γ-Al2O3 the specific activity of the supported perovskite phase increased 25 and 30 times, respectively, compared with the unsupported samples. PbTiO3/γ-Al2O3 shows the best catalytic properties among the tested samples. 相似文献
15.
Esterification of acetic acid with n-Butanol has been studied in a heterogeneous reaction system using two γ-alumina-supported vanadium oxide catalysts with different V loadings, which were prepared by the impregnation of a precipitated alumina. The alumina support and the supported catalysts were characterized using X-ray diffraction, N2 adsorption, EDX analysis and NH3-TPD techniques. The effects of the reaction time, of the molar ratio of the reactants, of the speed of agitation and of the mass fraction of the catalyst on the catalytic properties were studied. In the presence of the supported catalyst containing 10 wt % V2O5 (10V-Al2O3 sample) the conversion reached 87.7% after 210 min of reaction at 100 °C with an n-Butanol-to-acetic acid mole ratio equal to one. The conversion as well as the total acidity measured by TPD of NH3 increased in the following order: Al2O3 < 5V-Al2O3 (5 wt % V2O5/Al2O3) < 10V-Al2O3. In all cases the reaction was completely selective to n-butyl acetate. Nevertheless, a loss in catalytic activity after three reaction cycles with 10 V2O5–Al2O3 catalyst was observed. 相似文献
16.
Argon-ion-laser photoetching was performed at various wavelengths, around the absorption edge of ZnSe and CdS. The surface etch pit density is observed to decrease with increasing penetration depth of the light. This observation is explained in terms of the recent theory of non-uniform charge flow within semiconductor junctions.Incumbent of Helen and Milton A. Kitmmelman Career Development Chair in perpetuity, established by Helen and Milton A. Kimmelman, N.Y.Formerly: Department of Plastics ResearchIncumbent of Jacob and Alphonse Laniado (Montreal, Canada) Career Development Chair 相似文献
17.
18.
19.
C. Crăciun L. David D. Rusu M. Rusu O. Cozar G. Marcu 《Journal of Radioanalytical and Nuclear Chemistry》2001,247(2):307-310
The sandwich-type uranium(IV)-polyoxometalate Na6 [U3 (SbW9 O33 )2 ]·22H2 O was prepared and investigated by FT-IR and UV-VIS methods. The uranium(IV) coordination at the trilacunary Keggin units shifts the as (W-Ob,c -W), as (W=Od ), as (W-Oa ) antisymmetric stretching vibration bands in the 700 ÷ 950 cm-1 region of the FT-IR spectrum of U(IV)-complex. The visible electronic absorption spectrum of the complex indicates a 3 H4 electronic ground state of uranium ions and a quasicubic local symmetry around them. The UV electronic spectra of the U(IV)-POM complex and of the ligand present the broad bands assigned to p -d electronic transitions in the W=O bonds (at 46640 cm-1 for the ligand and 47280 cm-1 for the complex) and d -p -d transitions in tricentric W-O-W bonds (at 40880 cm-1 for the ligand and 39920 cm-1 for the complex). 相似文献
20.
Carmen Racles Viorica Gaina Mihai Marcu Maria Cazacu Mihaela Simionescu 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(9):1605-1617
Abstract Organofunctional siloxane oligomers containing maleimide were synthesized by condensation reaction of α. ω-hydroxypropylsiloxane oligomers with n-[4-(chlorocarbonyl)phenyl]maleimide. A model compound [bis(maleimide-ester)disiloxane] was obtained to facilitate the characerization of the oligomers. Then, the heterogeneous catalyzed ring-opening cationic polymerization technique was applied to obtain an oligomer starting from the model compound and octamethylcyclotetrasiloxane. The structures of the resulting oligomers were confirmed by elemental analysis, IR and 1H-NMR spectroscopy. They were characterized by determining softening points, solubility and studying their thermal behavior by thermogravimetric (TGA and differential scanning calorimetry (DSC) measurements. 相似文献