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排序方式: 共有252条查询结果,搜索用时 140 毫秒
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E.W. Abel A. Rauf Khan K. Kite K.G. Orrel V. Sˇik 《Journal of organometallic chemistry》1982,225(1):357-363
The1H NMR spectra of the complexes [PtXMe3(Me2E)2], X - Cl and Br, E - S and Se, show a non-equivalence of the Me2E methyl groups at low temperatures arising from a lack of symmetry at the metal centre. Inversion at the E atoms equalises the environments, and activation energies for the process have been computed for three complexes. 相似文献
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In this paper, we investigate the problem of robust global exponential stability analysis for a class of neutral-type neural networks. The interval time-varying delays allow for both slow and fast time-varying delays. The values of the time-varying uncertain parameters are assumed to be bounded within given compact sets. Improved global exponential stability condition is derived by employing new Lyapunov-Krasovskii functional and the integral inequality. The developed nominal and robust stability criteria is delay-dependent and characterized by linear-matrix inequalities (LMIs). The developed results are less conservative than previous published ones in the literature, which are illustrated by representative numerical examples. 相似文献
24.
Michael Barfield Abdulla S. Babaqi David M. Doddrell Hans P.W. Gottlieb 《Molecular physics》2013,111(1):153-164
The anisotropic hyperfine coupling constants (AHCC) from the electron spin resonance (E.S.R.) spectra of a variety of atoms in organic radicals have been calculated by means of semiempirical molecular orbital wavefunctions in the INDO approximation. Hyperfine tensors involving 1H, 13C and 19F nuclei are obtained for the ?H, ?H3, CH3?H2, (CH3)3? hydrocarbon radicals, malonic acid radical, ?H2F, ?F2H, ?F3 and CF3?H2 radicals. The calculated values are compared with available experimental, non-empirical and semiempirical values for these radicals. All integrals of the operator entering the electronic contributions have been evaluated over Slater type orbitals. The introduction of deorthogonalized wavefunctions gives generally better calculated results. In particular, the tensor components of the 19F AHCC are in good agreement with the experimental results without the necessity of readjusting the effective nuclear charges. 相似文献
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The associated prime ideals of powers of polymatroidal ideals are studied, including the stable set of associated prime ideals of this class of ideals. It is shown that polymatroidal ideals have the persistence property and for transversal polymatroids and polymatroidal ideals of Veronese type the index of stability and the stable set of associated ideals is determined explicitly. 相似文献
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Mohamed M. Abdulla 《Monatshefte für Chemie / Chemical Monthly》2008,139(6):697-705
A series of pyridines, pyrimidinone, oxazinones, and their derivatives were synthesized as anti-inflammatory agents using abietic acid (7-isopropyl-1,4a-dimethyl-1,2,3,4,4a,4b,5,6,10,10a-decahydrophenanthrene-1-carboxylic acid) as the starting material. The arylidiene derivative was treated with cyanothioacetamide to give cyano pyridine-thione, which was reacted with ethyl chloroacetate to yield the corresponding cyano ester. The ester was hydrolysed to the sodium salt, which was reacted with acetic anhydride to afford 2-methyloxazinone, which was treated with ammonium acetate to afford 2-methylpyrimidinone followed by methylation with methyl iodide to yield 2,3-dimethyl- pyrimidinone. In addition, the oxazinone derivative was reacted with aniline or hydrazine hydrate to give 3-phenyl- or 3-aminopyrimidinones. The latter reacted with thiophene-2-carboxaldehyde or phenylisothiocyanate to afford Schiff’s bases or thiosemicarbazide derivatives. The pharmacological screening showed that many of these compounds have good anti-inflammatory activity comparable to Prednisolone® as reference drug. 相似文献
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Tao Wu Rahima Abdulla Yongxin Zhao Yi Yang Jun Chen Haji Akber Aisa 《Chromatographia》2008,67(5-6):467-470
Species of the genus Achillea have been used in traditional folk medicine for centuries. In Europe taxa of the Achillea millefolium group are widely spread, their correct taxonomic differentiation by morphological and anatomical characteristics encounters
some difficulties. Several species of the polyploid A. millefolium group however, can be characterised by their distinct sesquiterpene pattern. Analysis is usually performed by LC using conventional
RP stationary phases. Likewise, it has been proven that non-porous RP stationary phases are an excellent alternative for sensitive
and more rapid separations of plant extracts. In the present work a Kovasil MS-C18 1.5 μm non-porous packing was used with
an acetonitrile-water gradient for the analysis of Achillea flower extracts. Detection and identification of the respective sesquiterpenes has been achieved by diode array detection
and LC coupled APCI+ and ESI+ mass spectrometry. 相似文献