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991.
《Magnetic resonance in chemistry : MRC》2002,40(2):133-138
Non‐selective and selective versions of several proton‐detected 1D NMR experiments to be applied to 15N are proposed. Clean, artifact‐free 1D spectra are easily obtained by the effective coherence selection by pulsed‐field gradients and the attainable sensitivity is maximized using modern pulse schemes. Despite the low sensitivity inherent to 15N NMR spectroscopy, the successful application of these experiments is demonstrated for resonance assignments and accurate measurement of both one‐bond and long‐range proton–nitrogen coupling constants on a model tripeptide at natural abundance. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
992.
Betti base‐derived tetradentate ligand 2 has been successfully designed and synthesized through the condensation of Betti base with glyoxal. Its application in N‐arylation of imidazoles has been investigated which opens a new field for application of Betti base derivatives in organic transformation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
993.
994.
We use Janelidze's Categorical Galois Theory to extend Brown and Ellis's higher Hopf formulae for homology of groups to arbitrary semi-abelian monadic categories. Given such a category A and a chosen Birkhoff subcategory B of A, thus we describe the Barr-Beck derived functors of the reflector of A onto B in terms of centralization of higher extensions. In case A is the category Gp of all groups and B is the category Ab of all abelian groups, this yields a new proof for Brown and Ellis's formulae. We also give explicit formulae in the cases of groups vs. k-nilpotent groups, groups vs. k-solvable groups and precrossed modules vs. crossed modules. 相似文献
995.
Alexandre Gabard 《Archiv der Mathematik》2008,90(3):267-274
We show that (a variation of) the Prüfer surface, which is an example of a separable non-metrizable 2-manifold, does not have
the homotopy type of a CW-complex.
Received: 6 February 2007 Revised: 21 August 2007 相似文献
996.
997.
Tomohiro Hirano Shuhei Masuda Shou Nasu Koichi Ute Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》2009,47(4):1192-1203
Radical polymerization of N,N‐dimethylacrylamide (DMAAm) was investigated in the presence of tartrates, such as diethyl L ‐tartrate, diisopropyl L ‐tartrate, and di‐n‐butyl L ‐tartrate, in toluene at low temperatures. Syndiotactic polymers were obtained in the presence of tartrates, whereas isotactic polymers were obtained in the absence of tartrates. The syndiotactic‐specificity increased with increasing amount of tartrates and with decreasing polymerization temperature. NMR analysis suggested that DMAAm and tartrates formed a 1:1 complex through double hydrogen bonding. A mechanism for the syndiotactic‐specific radical polymerization of DMAAm is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1192–1203, 2009 相似文献
998.
Tomohiro Hirano Shou Nasu Akihiro Morikami Koichi Ute 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6534-6539
Radical polymerization of N‐methylacrylamide (NMAAm), N,N‐dimethylacrylamide (DMAAm), and N‐methyl‐N‐phenylacrylamide (MPhAAm) was investigated in toluene at low temperatures. Atactic, isotactic, and syndiotactic polymers were obtained by the polymerization of NMAAm, DMAAm, and MPhAAm, respectively, indicating that the stereospecificity of the radical polymerization of acrylamide derivatives depended on the N‐substituents of the monomer used. From the viewpoint of monomer structure, the origin of the stereospecificity of radical polymerization of NMAAm derivatives is discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6534–6539, 2009 相似文献
999.
1000.
In this paper, a mixture representation for the joint distribution function of progressively Type-II censored order statistics from heterogeneous distributions is established. Applications of this representation to stochastic orderings and inequalities are then illustrated. 相似文献