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排序方式: 共有308条查询结果,搜索用时 15 毫秒
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N. V. Vasil'ev V. M. Koshelev D. V. Romanov K. A. Lyssenko M. Yu. Antipin G. V. Zatonskii 《Russian Chemical Bulletin》2005,54(7):1680-1685
Cycloaddition reactions of polyfluorinated 1,3-oxazoles with cyclic and acyclic alkenes were studied. The results of these
reactions were interpreted using quantum chemical calculations. An unusual product, viz., fluorine-containing acylpyrrole, was studied by X-ray diffraction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1630–1635, July, 2005. 相似文献
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Rossmeisl J Kristensen I Gregersen M Jacobsen KW Nørskov JK 《Journal of the American Chemical Society》2003,125(52):16383-16386
The natural amino acids have different preferences of occurring in specific types of secondary protein structure. Simulations are performed on periodic model beta-sheets of 14 different amino acids, at the level of density functional theory, employing the generalized gradient approximation. We find that the statistically observed beta-sheet propensities correlate very well with the calculated binding energies. Analysis of the calculations shows that the beta-sheet propensities are determined by the local flexibility of the individual polypeptide strands. 相似文献
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An instability criterion based on the positivity of a Lyapunov-type exponent is used to study the stability of the Euler equations governing the motion of an inviscid incompressible fluid. It is proved that any flow with exponential stretching of the fluid particles is unstable. In the case of an arbitrary axisymmetric steady integrable flow, a sufficient condition for instability is exhibited in terms of the curvature and the geodesic torsion of a stream line and the helicity of the flow. 相似文献
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We propose a model to describe correlated two-electron dynamics in strong laser fields during laser-induced recollision between an electron and its parent ion. We derive an effective interaction potential which describes the effect of the laser-driven electron collision with an ion while retaining the correlation between the colliding and the bound electron. Using dissociative ionization of molecular hydrogen as an example, we analyze the dynamics of correlation-driven electron localization in a dissociating hydrogen molecular ion. 相似文献
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We derive the power of direct radiation into free space induced by Josephson oscillations in intrinsic Josephson junctions of layered superconductors. We consider the superradiation regime for a crystal cut in the form of a thin slice parallel to the c axis. We find that the radiation correction to the current-voltage characteristic in this regime depends only on crystal shape. We show that at a large number of junctions oscillations are synchronized providing high radiation power and efficiency in the terahertz frequency range. We discuss the crystal parameters and bias current optimal for radiation power and crystal cooling. 相似文献
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B. A. Gorelik L. A. Sokolova A. G. Grigoriev S. D. Koshelev E. I. Semenenko G. A. Matiushin L. Rychla 《Macromolecular Symposia》1989,28(1):249-265
The thermo and radiation aging of polyolefins and their blends were studied. It was shown that near the inversion point of phase there is the most marked interaction between continuous and dispersed components of blend. This interaction results in an improvement of blend stability higher than expected. The investigation of the influence of supermolecular structure of PP stability revealed the small spherulite samples are more stable under irradiation in air than large spherulite ones. The possibility of obtaining composites of polyolefins and silicon liquids urns shown. 相似文献
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王柏懿 《应用数学和力学(英文版)》2003,24(8):928-935
By using Lagrangian method, the flow properties of a dusty-gas point source in a supersonic free stream were studied and the particle parameters in the near-symmetry-axis region were obtained . It is demonstrated that fairly inertial particles travel along oscillating and intersecting trajectories between the bow and termination shock waves . In this region, formation of " mufti- layer structure" in panicle distribution with alternating low- and high density layers is revealed. Moreover, sharp accumulation of particles occurs near the envelopes of particle trajectories . 相似文献