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991.
High chemical yields and good enantiomeric excesses are obtained by using soluble polymer-supported tartrate ester in the epoxidation of trans-hex-2-en-1-ol using Ti(OPri)4/tert-butyl hydroperoxide. 相似文献
992.
993.
Let G be a finite group and
e(G) the set of element orders of G. Denote by h(
e(G)) the number of isomorphism classes of finite groups H satisfying
e(H) =
e(G). We prove that if G has at least three prime graph components, then h(
e
(G)){1, }. 相似文献
994.
High-efficiency coupling structure for a single-line-defect photonic-crystal waveguide 总被引:1,自引:0,他引:1
Prather DW Murakowski J Shi S Venkataraman S Sharkawy A Chen C Pustai D 《Optics letters》2002,27(18):1601-1603
We present the design and fabrication of a planar structure for coupling light from a multimode feed waveguide into a single-line-defect photonic-crystal waveguide. Finite-difference time-domain calculations predict a coupling efficiency of greater than 90%, and preliminary experimental results indicate successful coupling through a single-line-defect photonic-crystal waveguide. Device design, fabrication, and characterization are presented. 相似文献
995.
Highly ordered Prussian blue nanowires with diameter of about 50 nm and length up to 4 m have been fabricated by an electrodepositing technology with two-step anodizing anodic aluminum oxide films. The Mössbauer spectra taken between 15 and 300 K indicate that the hyperfine parameters decrease as the temperature increases. The temperature dependence of the quadrupole splitting, the isomer shift and the spectra area are discussed. A decrease of Debye temperature for Prussian blue nanowires was found with respect to that of Prussian blue bulk. 相似文献
996.
Gd,-.Na.CuO#, an interesting compound with complex magnetic behavior, has beensynthesized by a PbO-based flux method (l) and a solid state reaction (2) at temperaturesabout 1000"C. Its X-ray diffraction pattern has been indexed with tetragonal latticeparameters (l,3). Here we report a low temperature synthetic route in which the newmonoclinic form of Gd,-.Na.CuO# is obtained directly by precipitation from a moltenKOH/NaOH/KNO, solution. The SEM, EDX, XRD, XPS and magnetic characte… 相似文献
997.
A simple method for quantitative analysis of aesculin and aesculetin in Cortex fraxini was developed using capillary zone electrophoresis (CZE). Berberin was employed as an internal standard, The running buffer was 6 mM Na(2)B(4)O(7) and 10 mM NaH(2)PO(4) (pH 6.70). The linear calibration range was 32-256 mug ml(-1) (r=0.9996) for aesculin and 23-230 mug ml(-1) (r=0.9993) for aesculetin. The contents of aeculin and aesculetin in C. fraxini were easily determined within 12 min the pKa values of aesculin and asculetin determined by CZE were 6.56 and 5.62, respectively. A simple method for estimation of the temperature inside the capillary during running was also proposed. 相似文献
998.
Shi XF Sun WY Zhang L Li CD 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(3):603-613
In order to provide theoretical evidence for the existence and effect of NH-S hydrogen bonding in the zinc enzyme model complex [Zn(S-2-C6H4NHCOC6H5)2(1-MeIm)2] (1-MeIm = 1-methylimidazole) in addition to the spectroscopic and crystallographic investigations, normal coordinate analysis (NCA) was carried out using a modified Urey-Bradley force field. The vibrational frequencies of the complex with and without the NH-S hydrogen bonding as well as the corresponding internal coordinates were obtained. The good agreement found between the calculated and observed frequencies in the presence of the NH-S hydrogen bond, supports the reliability of the analysis. The stretching force constant of the NH-S hydrogen bond obtained from the calculation is 0.18 mdyne per A. The calculation shows that the N-H bond is weakened by formation of the NH-S hydrogen bond. The results are indicative of the existence of the NH-S hydrogen bond in the complex. 相似文献
999.
1000.
单丁基磷酸酯的合成与表征 总被引:1,自引:0,他引:1
本文报道用三氯氧磷酯化、水解方法制备单丁基磷酸酯,用红外、核磁共振,质谱等方法对其结构进行了分析与表征。 相似文献