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排序方式: 共有825条查询结果,搜索用时 375 毫秒
771.
772.
Jinsong Chai Sha Yang Ying Lv Hanbao Chong Haizhu Yu Manzhou Zhu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(44):15818-15821
Bimetallic nanomaterials are of major importance in catalysis. A Au‐Cu bimetallic nanocluster was synthesized that is effective in catalyzing the epoxide ring‐opening reaction. The catalyst was analyzed by SCXRD and ESI‐MS and found to be Au24Cu6(SPhtBu)22 (Au24Cu6 for short). Six copper atoms exclusively occupy the surface positions in two groups with three atoms for each, and each group was bonded with three thiolate ligands to give a planar motif reminiscent of a benzene ring. In the epoxide‐ring opening reaction, Au24Cu6 exhibited superior catalytic activity compared to other homometallic and Au‐Cu alloy NCs, such as Au25 and Au38?xCux. Control experiments and DFT calculations revealed that the π conjugation among the Cu?S bonds played a pivotal role. This study demonstrates a unique π conjugation established among the Cu?S bonds as a critical structural motif in the nanocluster, which facilitates the catalysis of a ring‐opening reaction. 相似文献
773.
Filyakova V. I. Kuznetsova O. A. Ulomskii E. N. Rybalova T. V. Gatilov Yu. V. Kodess M. I. Rusinov V. L. Pashkevich K. I. 《Russian Chemical Bulletin》2002,51(2):332-336
The reactions of Li enolates of fluorine-containing -diketones with 3-aminopyrazoles afforded (7-polyfluoroalkyl)pyrazolo[1,5-a]pyrimidines. The structure of 3-bromo-2-methyl-5-phenyl-7-trifluoromethylpyrazolo[1,5-a]pyrimidine was established by X-ray diffraction analysis. 相似文献
774.
The purpose of this paper is to study the eigenvalue problems for a class of positive nonlinear operators. Using projective metric techniques and the contraction mapping principle, we establish existence, uniqueness and continuity results for positive eigensolutions of a particular type of positive nonlinear operator. In addition, we prove the existence of a unique fixed point of the operator with explicit norm-estimates. Applications to nonlinear systems of equations and to matrix equations are considered. 相似文献
775.
We describe Hopf algebras which are central extensions of quantum current groups. For a special value of the central charge, we describe Casimir elements in these algebras. New types of generators for quantum current algebra and its central extension for quantum simple Lie groups, are obtained. The application of our construction to the elliptic case is also discussed. 相似文献
776.
Michel Dubois-Violette 《Letters in Mathematical Physics》1990,19(2):121-126
By using the results of S. L. Woronowicz, we show that for the twisted version of the classical compact matrix groups, the Hopf algebraA
h
of representative elements is isomorphic as a co-algebra to the Hopf algebraA
O
of representative functions on the classical group. As a consequence,A
h
can be identified withA
O
as a co-algebra but with an associative product, called the star-product, which is a deformation of the original commutative product ofA
O
. Furthermore, the construction of this star product from the original product is connected to the Fourier transformation in a manner which is similar to the construction of quantum mechanics from classical mechanics on phase space. In fact, we shall describe the analog of the Weyl correspondence. 相似文献
777.
Cornelia Dru?u 《Topology》2004,43(5):983-1033
We prove that the filling order is quadratic for a large class of solvable groups and asymptotically quadratic for all -rank one lattices in semisimple groups of -rank at least 3. As a byproduct of auxiliary results we give a shorter proof of the theorem on the nondistorsion of horospheres providing also an estimate of a nondistorsion constant. 相似文献
778.
Tetsuya Masuda Katsuhisa Mimachi Yoshiomi Nakagami Masatoshi Noumi Yutaka Saburi Kimio Ueno 《Letters in Mathematical Physics》1990,19(3):195-204
Some series of unitary representations of the quantum group SU
q
(1, 1) are introduced. Their matrix elements are expressed in terms of the basic hypergeometric functions. Operator realization of the coordinate elements of SU
q
(1, 1) and aq-analogue of some classical identities are discussed. 相似文献
779.
We obtain a quantitative estimate for the measure of the set of large values of the zeta-function on the critical line which is related to the Lindelöf hypothesis and give its application to extreme values (-results). We also investigate the problem of small values. 相似文献
780.
Summary. In standard first-passage percolation on (with ), the time-minimizing paths from a point to a plane at distance are expected to have transverse fluctuations of order . It has been conjectured that with the inequality strict (superdiffusivity) at least for low and with . We prove (versions of) for all and .
Received: 30 August 1995 / In revised form: 28 March 1996 相似文献