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排序方式: 共有421条查询结果,搜索用时 15 毫秒
101.
William N. Setzer Brian R. Coleman George S. Wilson Richard S. Glass 《Tetrahedron》1981,37(16):2743-2747
The helium I photoelectron spectra of the mesocyclic polythioethers 1,4-dithiacycloheptane (1,4-DTCH), 1,5-dithiacyclooctane (1,5-DTCO), 1,5-dithiacyclononane (1,5-DTCN), 1,4,7-trithiacyclononane (1,4,7-TTCN), and 1,6-dithiacyclodecane (1,6-DTCD) are reported. The conformations of these molecules in the gas phase are deduced from correlations of the observed spectra with semi-empirical MO calculations, as well as molecular mechanics analysis. 相似文献
102.
T. W. Beihoffer J. E. Glass 《Journal of polymer science. Part A, Polymer chemistry》1988,26(2):343-353
Vinylbenzyl acetate was synthesized in yields greater than 80% via the reaction of vinylbenzyl chloride with potassium acetate. Radical copolymerization of the monomer with styrene and methylmethacrylate were studied at 60°C. Reactivity ratios determined from FT-IR analysis of low conversion copolymerizations with styrene (M1) were r1 = 0.78 ± 0.07 and r2 = 1.33 ± 0.13. Polymers and copolymers of vinylbenzyl acetate were found to completely hydrolyze in dioxane/water/base solution to yield hydroxymethyl functionality. Size exclusion chromatography studies indicated that the hydrolysis proceeded without crosslinking. This procedure is a useful method for the introduction of hydroxyl functionality on polymers and avoids crosslinking problems common in previously reported methods. 相似文献
103.
Summary In this paper the techniques of étale sheaf cohomology are used to estimate trigonometric sums on certain singular algebraic
surfaces. This involves the computation of Betti numbers, made complicated by the presence of singularities. This leads to
the introduction of some new (non-singular) surfaces. Their Betti numbers are then computed and related to the original problem
which is thereby solved.
Riassunto In questo lavoro si utilizza la coomologia étale per valutare le somme trigonometriche per certe superfici algebriche singolari. Per il calcolo dei numeri di Betti necessari, reso difficile per la presenza delle singolarità, si utilizzano delle superfici ausiliari lisce i cui numeri di Betti consentono di risolvere il problema iniziale.相似文献
104.
以新鲜怀菊花为原料,用芦丁为对照品,硝酸铝作为显色剂,正交设计优化怀菊花中总黄酮提取条件,采用超声波和水浴提取法等2种工艺提取怀菊花中总黄酮,研究单因素对总黄酮提取率的影响,确定提取总黄酮的最佳条件,同时用碘量法研究对猪油的抗氧化性作用.水浴提取怀菊花总黄酮以A1B1C3组合为最佳提取条件,提取率为109.74mg/g.超声波提取怀菊花总黄酮以A2B2C2组合为最佳提取条件,提取率为114.47mg/g.实验结果表明,超声波法提取效果优于水浴提取法,怀菊花黄酮对猪油有一定的抗氧化能力. 相似文献
105.
Vitreous Pb5Ge3O11 was prepared by water quenching and by roller quenching. The crystallization was studied by DTA, X-ray diffraction, and TEM. After a glass transition at 325°C, meta-stable Pb5Ge3O11 crystallized exothermically at 370°C. This was subsequently followed by the formation of the stable phase of the same composition, again exothermically at 490°C. 相似文献
106.
107.
Laminar boundary layer flows behind constant speed shock waves moving into a dusty gas are analyzed numerically. The basic equations of two-phase flows are derived in shock fixed coordinates and solved by an implicit finite-difference method for the side wall boundary layer in a dusty gas shock tube. The development of the boundary layer and resulting velocity and temperature profiles, respectively, for the gas and particles are given from the shock front to far downstream. The effects of diaphragm pressure ratio, mass loading ratio of particles and particle size upon the flow properties are discussed in detail.This article was processed using Springer-Verlag TEX Shock Waves macro package 1990. 相似文献
108.
Block E Dikarev EV Glass RS Jin J Li B Li X Zhang SZ 《Journal of the American Chemical Society》2006,128(46):14949-14961
More than 40 new 4- to 12-membered ring heterocycles containing various combinations of Group 14 and 16 elements Si, Sn, S, Se, and Te have been synthesized and fully characterized. Synthesis of these small-ring as well as medium-ring (mesocyclic) heterocycles from alpha,omega-dihalides is facilitated by the presence of gem-dialkylsilyl and gem-dialkylstannyl groups in the precursors. Conformations of several of the new ring systems in the solid state have been determined by X-ray crystal structure analysis. Oxidation of mixed S(Se, Te)/Si eight-membered ring mesocycles with NOPF6 or Br2 gives dications or a bicyclic dibromide, respectively, which can be characterized by NMR methods. On treatment with nucleophiles, mesocyclic dications, or the corresponding radical cations undergo ring contraction, giving five- or six-membered ring heterocycles. Photolysis of a S/Se four-membered ring heterocycle gives selenoformaldehyde, trapped in 80% yield with 2,3-dimethyl-1,3-butadiene. 相似文献
109.
V. V. Bludov A. M. W. Glass 《Transactions of the American Mathematical Society》2006,358(12):5179-5192
In 1974, J. Martinez introduced the variety of weakly Abelian lattice-ordered groups; it is defined by the identity
110.
G. Karczewski M. Klimkiewicz I. Glass A. Szczerbakow R. Behrendt 《Applied Physics A: Materials Science & Processing》1982,29(1):49-52
Photovoltaicp-n junctions inn-type Pb1–xMn
x
Sx0.04, have been made by sulphur diffusion. Current-voltage and resistance-voltage characteristics have been examined at various temperatures. The spectral responses of the diodes have been measured within the temperature range from 5 to 300 K at a zero bias. From these measurements the energy band gap of Pb1–x
Mn
x
S solid solution has been determined as a function of temperature and manganese content. A phenomenological expression describing the variation of the energy gap of Pb1–x
Mn
x
S with temperature and alloy composition has been proposed. 相似文献