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排序方式: 共有4055条查询结果,搜索用时 15 毫秒
41.
N‐trimellitylimido‐L ‐methionine ( 3 ) was prepared by reaction of trimellitic anhydride ( 1 ) with ‐L ‐methionine ( 2 ) in acetic acid solution at refluxing temperature. This diacid was reacted with thionyl chloride, and N‐trimellitylimido‐L ‐methionine diacid chloride ( 4 ) was obtained in quantitative yield. The resulting diacid chloride was reacted with p‐aminobenzoic acid in dry acetone and bis(p‐aminobenzoic acid)‐N‐trimellitylimido‐L ‐methionine ( 5 ) was obtained as a novel optically active amide–imide diacid monomer in high yield. The direct polycondensation of amide–imide diacid monomer 5 with several aromatic diamines was carried out with tosyl chloride (TsCl)/pyridine (Py)/dimetheylformamide (DMF) system. The resulting thermally stable poly(amide–imide)s (PAIs) were obtained in good yields and inherent viscosities ranging between 0.24 and 0.46 dL g?1 and were characterized with FTIR, 1H NMR, CHN, and TGA techniques. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1248–1254, 2007 相似文献
42.
Many high Miller index metals surfaces are naturally chiral, offering opportunities for performing enantiospecific chemistry. Previous theoretical treatments of adsorption on these surfaces have used surfaces truncated from bulk crystals. This paper examines the effect of surface relaxation on enantiospecific adsorption on chiral Pt surfaces by using relaxed surface structures determined using density functional theory. 相似文献
43.
44.
Phase calculation for nonequilibrium multicomponent systems is attempted using the stepwise-regression method. The experimental data (the amount and composition of glassy phase in a system of Al2 O3 –SiO2 ceramics as functions of the state of the original materials, the firing temperature, and the composition of the samples) are treated by the proposed method. The equations obtained are accurate in estimating the amount and composition of glassy phases in the system, showing that the stepwise-regression method is effective in phase calculation. 相似文献
45.
Cinchonidine and cinchonine have been grafted onto pure silica MCM-41. It has been shown that both supported alkaloids are active catalysts for the Michael addition of ethyl 2-oxocyclopentanecarboxylate and methyl vinyl ketone, anchored cinchonidine being more active and enantioselective than anchored cinchonine. The study of the influence of the polarity of the solvent and reaction temperature on the optical induction shows that there is not a direct correlation between solvent polarity and enantioselectivity, and the maximum optical yield was obtained between 278 and 273 K. 相似文献
46.
Robert G. Laughlin 《Journal of the American Oil Chemists' Society》1990,67(11):705-710
Recent phase studies of several surfactant-water systems, using new or refined methods, have revealed significant errors in
earlier phase diagrams. These diagrams had been determined largely using methods based on the isoplethal phase studies principle.
This principle has inherent limitations which do not exist in isothermal methods.
Isothermal nuclear magnetic resonance and refined calorimetric methods have been extensively used in recent surfactant phase
studies. Methods based on the new lyotrope gradient (swelling) principle show great promise as a means of improving the efficiency
and quality of surfactant phase studies. 相似文献
47.
48.
ON GENERALIZED FRACTIONAL PROCESSES 总被引:3,自引:0,他引:3
Abstract. A class of stationary long-memory processes is proposed which is an extension of the fractional autoregressive moving-average (FARMA) model. The FARMA model is limited by the fact that it does not allow data with persistent cyclic (or seasonal) behavior to be considered. Our extension, which includes the FARMA model as a special case, makes use of the properties of the generating function of the Gegenbauer polynomials, and we refer to these models as Gegenbauer autoregressive moving-average (GARMA) models. While the FARMA model has a peak in the spectrum at f = 0, the GARMA process can model long-term periodic behavior for any frequency 0 f 0.5. Properties of the GARMA process are examined and techniques for generation of realizations, model identification and parameter estimation are proposed. The use of the GARMA model is illustrated through simulated examples as well as with classical sunspot data. 相似文献
49.
Immobilization of new Mn(salen) complex over MCM-41 and its activity in asymmetric epoxidation of styrene 总被引:3,自引:0,他引:3
New tetradentate chelates of bis-Schiff bases were synthesized and then these chiral salen ligands were immobilized over mesoporous
MCM-41 by using the ion-exchange method. The efficiency of the chiral catalyst was examined in the asymmetric epoxidation
of styrene. Chiral Mn(salen) complexes immobilized onto mesoporous MCM-41 were stable during the reaction without any leaching
and exhibited relatively high enantioselectivity for epoxidation as compared with homogeneous complexes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
50.
J. H. Bordon J. R. Handley J. A. McLean R. M. Silverstein L. Chong K. N. Slessor B. D. Johnston H. R. Schuler 《Journal of chemical ecology》1980,6(2):445-456
The aggregation pheromone ofGnathotrichus retusus was isolated and identified as (S)-(+)-sulcatol (6-methyl-5-hepten-2-ol). In laboratory and field experiments,G. retusus responded to (S)-(+)-sulcatol, but not to (±)-sulcatol, which was attractive to the sympatric species,G. sulcatus. G. sulcatus did not respond to optically pure (S)-(+)-sulcatol, but began to respond when 1% (R)-(–)-sulcatol was present in an enantiomeric mixture.Research supported by the National Science Foundation, U.S.A. (Grant BMS-74-13643), and the Natural Sciences and Engineering Research Council of Canada (Co-op grant A0243 and Operating Grant A3881 and A3785). 相似文献