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排序方式: 共有57条查询结果,搜索用时 15 毫秒
11.
Robert D Gilbertson Drew Gorman-Lewis Hans-Christoph Weiss Michael M Haley 《Tetrahedron》2004,60(5):1215-1223
Several 1,2-diphenyl- and 1,2,3-triphenyl-3-alkynylcyclopropenes have been prepared in moderate to very good yields by the reaction of acetylenic nucleophiles with the appropriate cyclopropenylium salt. Single crystal X-ray structures of four of the cyclopropenes were obtained. Stereoselective reduction of the triple bond failed in all cases, whereas model compounds lacking the cyclopropene moiety were reduced successfully. A rational for this lack of reactivity is proposed. The solution-phase thermochemistry of the 3-alkynyl-1,2,3-triphenylcyclopropenes was explored, affording 3-alkynyl-1H-indenes in moderate to good yields. 相似文献
12.
We are concerned with the semilinear polyharmonic model problem (–)K v = v +v|v|
s–1 inB,D
v|B = 0 for ¦|<-K – 1. HereK ,B is the unit ball in n,n >2K,
is the critical Sobolev exponent. Let 1 denote the first Dirichlet eigenvalue of (-)K inB. The existence of a positive radial solutionv is shown for
相似文献
13.
14.
UV irradiation of η5-C5H5Nb(CO)4 in the presence of the phosphine ligands L (L = 2 PEt3, Ph2P(CH2)2PPh2 (p2(n), n = 1–5), cis-Ph2PCH=CHPPh2 (c-dpe)), and the mixed arsine-phosphine ligands Ph2AsCH2CH2PPh2 (arphos) and o-C6H4(AsPh2)(PPh2) (pab) yields the well defined complexes cis-[η5-C5H5Nb(CO)2L]. The monosubstituted species η5-C5H5Nb(CO)3L have been characterized spectroscopically. P2Ph4 forms mono- and dinuclear, mono- and biligate carbonylniobium complexes.Shielding of the 93Nb nucleus increases in the sequences (i) Ph2As- < Ph2P-, (ii) chelate 4-ring < chelate 5-ring and (iii) η5-C5H5Nb(CO)2L < η5-C5H5Nb(CO)3L < η5-C5H5Nb(CO)4, and 31P coordination shifts decrease in the order c-dpe > pab > arphos > p2(2) > p2(5) > p2(4) ~ PEt3 > p2(3) > p2(1). The trends generally parallel those for the corresponding NMR parameters of the vanadium complexes. Paramagnetic contributions to the overall shielding are smaller for the 93Nb than for the 51V nucleus, and this is explained in terms of increased covalency and decreased π-interaction in the niobium complexes. 相似文献
15.
Hans-Christoph Kaiser Hagen Neidhardt Joachim Rehberg 《Monatshefte für Mathematik》2009,45(3):179-185
The negative quantum mechanical particle density in its dependence on the potential in the Hamiltonian is a nonlinear operator.
We give an explicit proof of the monotonicity of this operator for a large class of admissible thermodynamic equilibrium distribution
functions. In particular the zero temperature case is included. 相似文献
16.
Filippo Gazzola Hans-Christoph Grunau Guido Sweers 《Annali di Matematica Pura ed Applicata》2010,189(3):475-486
We prove that the best constant for the critical embedding of higher order Sobolev spaces does not depend on all the traces.
The proof uses a comparison principle due to Talenti (Ann Scuola Norm Sup Pisa Cl Sci 3(4): 697–718, 1976) and an extension
argument which enables us to extend radial functions from the ball to the whole space with no increase of the Dirichlet norm.
Similar arguments may also be used to prove the very same result for Hardy-Rellich inequalities. 相似文献
17.
18.
Hans-Christoph Kaiser Hagen Neidhardt Joachim Rehberg 《Integral Equations and Operator Theory》2003,45(1):39-63
We describe an embedding of a quantum mechanically described structure into a macroscopic flow. The open quantum system is partly driven by an adjacent macroscopic flow acting on the boundary of the bounded spatial domain designated to quantum mechanics. This leads to an essentially non-selfadjoint Schrödinger-type operator, the spectral properties of which will be investigated. 相似文献
19.
We prove existence and uniqueness (up to rescaling) of positive radial entire solutions of supercritical semilinear biharmonic
equations. The proof is performed with a shooting method which uses the value of the second derivative at the origin as a
parameter. This method also enables us to find finite time blow up solutions. Finally, we study the convergence at infinity
of smooth solutions towards the explicitly known singular solution. It turns out that the convergence is different in space
dimensions n ≤ 12 and n ≥ 13.
Financial support by the Vigoni programme of CRUI (Rome) and DAAD (Bonn) is gratefully acknowledged. 相似文献
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