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排序方式: 共有40条查询结果,搜索用时 15 毫秒
1.
A new preconditioned conjugate gradient (PCG)-based domain decomposition method is given for the solution of linear equations
arising in the finite element method applied to the elliptic Neumann problem. The novelty of the proposed method is in the
recommended preconditioner which is constructed by using cyclic matrix. The resulting preconditioned algorithms are well suited
to parallel computation. 相似文献
2.
G. Ya. Remennikov I. V. Boldyrev N. A. Kapran L. K. Kurilenko 《Chemistry of Heterocyclic Compounds》1993,29(3):325-329
Using a modification of the Biginelli reaction, we have synthesized 6-methyl- and 1,6-dimethyl-5-nitro-4-phenyl-2-oxo-1,2,3,4-tetrahydropyrimidines. We have studied some of their chemical conversions involving the methyl group on the C(6) atom, the nitrogen atoms of the pyrimidine ring, and the phenyl substituent.Translated from Khimiya Geterosiklicheskikh Soedinenii, No. 3, pp. 388–392, March, 1993. 相似文献
3.
V. M. Cherkasov G. Ya. Remennikov A. A. Kisilenko E. A. Romanenko 《Chemistry of Heterocyclic Compounds》1980,16(2):179-182
The corresponding σ complexes of the Meisenheimer type, viz., anions of the potassium salts of 6H-5-nitro-6-acetonylpyrimidines,
were obtained and isolated in the reaction of 5-nitro-, 5-nitro-4-methoxy-, 5-nitro-2-methoxy-, and 5-nitro-2,4-dimethoxypyrimidines
with acetone in the presence of potassium hydroxide. The structures of the complexes were proved by means of the PMR, IR,
and UV spectra. It is shown that the acetone anion in all cases adds to the methoxy-unsubstituted position of the pyrimidine
ring, whereas nucleophilic attack takes place at the C4 atom when the 2 and 4 positions are free.
See [1] for communication 1.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 239–242, February, 1980. 相似文献
4.
T. Szitó J. G. Kiss GY. I. Garab L. A. Mustárdy Á. Faludi-Dániel 《Photochemistry and photobiology》1984,40(1):113-117
Abstract Orientation pattern of the Qy absorption and emission dipoles of chlorophyll a were studied in wild type Scenedesmus obliquus and in mutants deficient in chlorophyll b and carotenoids. Fluorescence polarization ratio at –140°C and linear dichroism at 25°C were measured in whole cells and thylakoids aligned in polyacrylamide gel. Unlike normal thylakoids, mutants displayed fluorescence polarization ratios significantly lower than 1.0 and showed a negative LD signal around 672 nm, indicating the tendency of the Qy dipoles to tilt out from the membrane plane. Such an orientation pattern can also be artificially induced by treating normal thylakoids with linolenic acid. 相似文献
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9.
Seeliger F Berger ST Remennikov GY Polborn K Mayr H 《The Journal of organic chemistry》2007,72(24):9170-9180
The kinetics of reactions of acceptor-stabilized carbanions 2a-m with benzylidenebarbituric and -thiobarbituric acids 1a-e has been determined in a dimethyl sulfoxide solution at 20 degrees C. Second-order rate constants were employed to determine the electrophilicity parameters E of the benzylidenebarbituric and -thiobarbituric acids 1a-e according to the correlation equation log k(20 degrees C) = s(N + E). With E parameters in the range of -10.4 to -13.9, the electrophilicities of 1a-e are comparable to those of analogously substituted benzylidenemalononitriles. 相似文献
10.
G. Ya. Remennikov V. V. Pirozhenko S. I. Vdovenko S. A. Kravchenko 《Chemistry of Heterocyclic Compounds》1998,34(1):104-110
We have studied the reaction of isomeric 7-and 5-methoxyfuroxano[3,4-d]pyrimidines with carbanions of some CH acids. We have shown that regardless of the position of the substituent in the pyrimidine ring, nucleophilic attack occurs regioselectively at the C(7) atom. As a result, we have obtained the products of substitution at the methoxy group, and also anionic complexes and covalent adducts.For Communication 12 see [1].Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, Kiev 253660. Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 34, No. 1, pp. 112–119, January, 1998. 相似文献