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31.
Formation Mechanism of the First Carbon–Carbon Bond and the First Olefin in the Methanol Conversion into Hydrocarbons 下载免费PDF全文
Dr. Yue Liu Dr. Sebastian Müller Dr. Daniel Berger Dr. Jelena Jelic Prof. Dr. Karsten Reuter Dr. Markus Tonigold Dr. Maricruz Sanchez‐Sanchez Prof. Dr. Johannes A. Lercher 《Angewandte Chemie (International ed. in English)》2016,55(19):5723-5726
The elementary reactions leading to the formation of the first carbon–carbon bond during early stages of the zeolite‐catalyzed methanol conversion into hydrocarbons were identified by combining kinetics, spectroscopy, and DFT calculations. The first intermediates containing a C?C bond are acetic acid and methyl acetate, which are formed through carbonylation of methanol or dimethyl ether even in presence of water. A series of acid‐catalyzed reactions including acetylation, decarboxylation, aldol condensation, and cracking convert those intermediates into a mixture of surface bounded hydrocarbons, the hydrocarbon pool, as well as into the first olefin leaving the catalyst. This carbonylation based mechanism has an energy barrier of 80 kJ mol?1 for the formation of the first C?C bond, in line with a broad range of experiments, and significantly lower than the barriers associated with earlier proposed mechanisms. 相似文献
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Meng Wang Dr. Oliver Y. Gutiérrez Dr. Donald M. Camaioni Prof. Dr. Johannes A. Lercher 《Angewandte Chemie (International ed. in English)》2018,57(14):3747-3751
Palladium on carbon catalyzes C?O bond cleavage of aryl ethers (diphenyl ether and cyclohexyl phenyl ether) by alcohols (R?OH) in H2. The aromatic C?O bond is cleaved by reductive solvolysis, which is initiated by Pd‐catalyzed partial hydrogenation of one phenyl ring to form an enol ether. The enol ether reacts rapidly with alcohols to form a ketal, which generates 1‐cyclohexenyl?O?R by eliminating phenol or an alkanol. Subsequent hydrogenation leads to cyclohexyl?O?R. 相似文献
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Community noise exposure and stress in children 总被引:3,自引:0,他引:3
Evans GW Lercher P Meis M Ising H Kofler WW 《The Journal of the Acoustical Society of America》2001,109(3):1023-1027
Although accumulating evidence over the past two decades points towards noise as an ambient stressor for children, all of the data emanate from studies in high-intensity, noise impact zones around airports or major roads. Extremely little is known about the nonauditory consequences of typical, day-to-day noise exposure among young children. The present study examined multimethodological indices of stress among children living under 50 dB or above 60 dB (A-weighted, day-night average sound levels) in small towns and villages in Austria. The major noise sources were local road and rail traffic. The two samples were comparable in parental education, housing characteristics, family size, marital status, and body mass index, and index of body fat. All of the children were prescreened for normal hearing acuity. Children in the noisier areas had elevated resting systolic blood pressure and 8-h, overnight urinary cortisol. The children from noisier neighborhoods also evidenced elevated heart rate reactivity to a discrete stressor (reading test) in the laboratory and rated themselves higher in perceived stress symptoms on a standardized index. Furthermore girls, but not boys, evidenced diminished motivation in a standardized behavioral protocol. All data except for the overnight urinary neuroendocrine indices were collected in the laboratory. The results are discussed in the context of prior airport noise and nonauditory health studies. More behavioral and health research is needed on children with typical, day-to-day noise exposure. 相似文献
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The elementary steps of sorption and transport of benzene, toluene, and o- and p-xylene from the gas phase to hydroxy groups of zeolite H/ZSM-5 on the outer surface (SiOH groups) and in the pores (SiOHAl groups) were studied using pressure modulations followed by fast time-resolved IR spectroscopy. Sorption on these acid sites occurs via a common physisorbed state on the outer surface. The equilibration of the molecules in this state is fast compared to the sorption rates on SiOH and SiOHAl groups. The relative rates of equilibration of functional groups with the aromatic molecules suggest that the aromatic molecules move freely on the surface of the outer surface before reversibly binding to OH groups, entering the micropores or desorbing. Molecules able to enter into the pores (benzene, toluene, p-xylene) adsorb faster on SiOHAl groups than on SiOH groups. If the access of the molecules into the pores is sterically constrained (o-xylene), the rate of adsorption on the remaining accessible SiOH groups is strongly enhanced. 相似文献
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Lifetimes of high spin states up to {
}=22+ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in 72, 74Se. The Q
t values derived from these measurements indicate that prolate shape stabilizes for 72Se, while a triaxial shape develops for 74Se at higher spins. Comparison of the observed trend in Q
t with spin for 72, 74Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency. 相似文献
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