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排序方式: 共有42条查询结果,搜索用时 15 毫秒
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N. A. Borisevich D. K. Buslov V. N. Zhabinskii V. A. Khripach 《Journal of Applied Spectroscopy》2009,76(5):617-622
IR spectra of steroid phytohormones of the stigmastane series (22R, 23R)-28-homocastasterone and (22R,23R)-28-homosecasterol
and their isomers (22S,23S)-28-homocastasterone and (22S,23S)-28-homosecasterol have been analyzed. The 28-homocastasterone
molecule contains diol groups in ring A and in the side chain whereas that of 28-homosecasterol has one diol group in the
side chain. The lack of two OH groups in ring A of homosecasterol compared to homocastasterone results in the appearance of
stretching vibrational bands of H–C= (νmax = 3025 cm–1) and –C=C (νmax = 1656 cm–1) groups of ring A. Substantial changes are observed in the area of OH stretching vibrations. Homocastasterones pressed in
KBr possess twice as many OH groups as homosecasterols such that absorption band total intensities in IR spectra of both isomers
caused by H-bonds of the diol groups in the side chain amount to 65% whereas the share of the 2α,3α group is only 35% of the
total intensity. Hence the contribution from the side-chain OH groups of the studied brassinosteroids to the integral optical
density of the bands exceeds that from the ring-A OH groups. In dilute CHCl3 solutions of the brassinosteroids, the conformations
of the brassinosteroid side chains are not the same. As a result, intramolecular H-bonds of different energy are created.
The optical density Dmax in band maxima of free OH groups for homocastasterones is three times higher than that for the corresponding band maxima
of homosecasterol. This implies that Dmax for bands of free OH groups of the homocastasterone ring-A diol group is greater, in contrast with the relatively greater
Dmax for bands of homosecasterol side-chain OH groups bound by an intermolecular H-bond. The homocastasterone diol groups also
form intramolecular Hbonds more actively. The lack of the diol group in ring A of the homosecasterols does not affect the
frequencies of the C=O stretching vibrations. This leads to the conclusion that the C=O group forms intermolecular H-bonds
only with the side-chain OH groups of brassinosteroids pressed in KBr. 相似文献
3.
D. K. Buslov N. A. Nikonenko N. I. Sushko R. G. Zhbankov 《Journal of Applied Spectroscopy》2002,69(6):817-824
Deconvolution of the IR absorption spectrum of -D glucose in the spectral range 1500–450 cm–1 has been carried out. The results of the deconvolution were compared with the IR and Raman spectra recorded at room and low temperatures and with the data obtained by theoretical calculations for the frequencies of the normal vibrations of the -D glucose molecule in the crystalline state. It is shown that deconvolution of the IR spectra recorded at room temperature makes it possible to separate the bands observed experimentally only at a very low temperature of the sample and a number of components that were not resolved earlier. The number of bands separated on deconvolution of the IR spectra of -D glucose in the spectral range 1500–450 cm–1 is more than twice the number of visible absorption maxima in the usual spectrum. The results of deconvolution of the IR spectrum of -D glucose are in good agreement with the data of theoretical calculations for the frequencies of the normal vibrations of the -D glucose molecule in the crystalline state. The existence of the factor-group (Davydov) splitting of a number of frequencies of the nondegenerate fundamental vibrations of molecules in a crystal cell has been revealed in the IR spectrum of -D glucose. It was concluded that the model of an isolated molecule is insufficient for detailed theoretical interpretation of the vibrational spectra of carbohydrates. 相似文献
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Ivan Buslov Jeanne Becouse Simona Mazza Mickael Montandon‐Clerc Prof. Dr. Xile Hu 《Angewandte Chemie (International ed. in English)》2015,54(48):14523-14526
Chemoselective hydrosilylation of functionalized alkenes is difficult to achieve using base‐metal catalysts. Reported herein is that well‐defined bis(amino)amide nickel pincer complexes are efficient catalysts for anti‐Markovnikov hydrosilylation of terminal alkenes with turnover frequencies of up to 83 000 per hour and turnover numbers of up to 10 000. Alkenes containing amino, ester, amido, ketone, and formyl groups are selectively hydrosilylated. A slight modification of reaction conditions allows tandem isomerization/hydrosilylation reactions of internal alkenes using these nickel catalysts. 相似文献
6.
A system of hydrogen bonds in weakly hydrated PVA films containing up to ≤8.5 wt % water is investigated via IR spectroscopy.
It is shown that water molecules bind to only part of the hydroxyl groups of the polymer that are available for hydration
and form the first hydrating layer. In a completely dehydrated film, practically every hydroxyl group of PVA forms hydrogen
bonds with two other hydroxyl groups and serves as both a proton donor and a proton acceptor. In the hydrated film, one to
three water molecules directly bind with one hydroxyl group of PVA. 相似文献
7.
Yuko Uchio Yukio Isozaki Tsutomu Ota Atsushi Utsunomiya Mikhail M. Buslov Shigenori Maruyama 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(9):422
The Baratal limestone in the Gorny Altai Mountains, southern Siberia, occurs as large allochthonous blocks within a Cambrian accretionary complex that developed around the Siberia craton. Before the final accretion to Siberia in the Cambrian, the terrigenous clastic-free Baratal limestone was deposited directly upon a basaltic basement with a geochemical signature identical to that of modern oceanic plateau. The Baratal limestone with 598 ± 25 Ma (Early Vendian) Pb-Pb isochron age consists of three distinct facies; 1) massive lime mudstone with ooids and stromatolites, 2) bedded lime mudstone, and 3) limestone conglomerate/breccia dominated by ooid-bearing lime mudstone clasts. The first represents a shallow marine environment on top of an ancient oceanic plateau, while the latter two represent the deeper slope to bottom-of-slope facies of a plateau. The Vendian Baratal limestone provides the oldest example of a reconstructed shallow marine carbonate buildup complex developed on a plateau/seamount in a mid-ocean. 相似文献
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