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991.
S. Ye. Yakovenko 《Liquid crystals》1999,26(1):23-30
We present the results of an experimental study of the Raman depolarization ratio for the cyano stretching mode in two mesogens, 5CB and 80CB, under variable temperature and pressure. In contrast to previous observations, the Raman results do not yield any indication of molecular association, even in such an expectedly strongly associated liquid crystal as 80CB, which has a re-entrant nematic phase at elevated pressure. Possible explanations for this are discussed. 相似文献
992.
Ding Wang Ye Liu Chun‐Yan Hong Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2005,43(21):5127-5137
Novel hyperbranched poly(amido amine)s containing tertiary amines in the backbones and acryl as terminal groups were synthesized via the Michael addition polymerizations of trifunctional amines with twofold molar diacrylamide. The hyperbranched structures of these poly(amido amine)s were verified by 13C NMR (INVGATE). The polymerization mechanisms were clarified by following the polymerization process with NMR method, and the results show that the reactivity of secondary amine formed in situ is much lower than that of the secondary amine in 1‐(2‐aminoethyl) piperazine (AEPZ) ring and the primary amine. The secondary amine formed in situ was almost kept out of the reaction before the primary and secondary amines in AEPZ were consumed, leading to the formation of the AB2 intermediate, and the further reaction of the AB2 yielded the hyperbranched polymers. The molecular weights and properties of poly(amindo amine)s obtained were characterized by GPC, DSC, and TGA, respectively. Based on the reaction of active acryl groups in the polymers obtained with glucosamine, hyperbranched polymers containing sugar were formed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5127–5137, 2005 相似文献
993.
W.A.Strauss等人已证明了广义非线性 Euler-Poisson-Darboux方程初边值问题整体解的存在唯一性 .本文应用一个差分不等式研究了整体解的渐近性质 . 相似文献
994.
995.
In our early researches, lanthanum and cerium could enter plant and bind to porphyrin of chlorophyll to form Ln3+-chllorophyll. La and Ce greatly increase photosystem II (PSII) activity and PSII electron transport rate, and the fluorescence emission peaks of PSII are blue-shifted [1—4]. Do REEs coordinate with PSII reaction center complex in vivo? Moreover, do REEs coordinate with D1(30 kD)/D2(32 kD)/Cytb559 (~9 kD) reaction center complex of site of producing pri-mary reaction-p… 相似文献
996.
997.
介绍一种改进的Oligo诱导DNA定点突变方法,此法制备的含U野生型模板DNA在JM107中的存活率从5%~10%下降至1%~2%;诱变反应终产物转染JM107产生的斑数比原法提高15~20倍,诱导连续4个核苷酸替换产生的突变频率达80%~85%,即使诱导连续12个核苷酸的缺失,也能获得40%~50%的突变频率. 相似文献
998.
MNA/PMMA有机薄膜光波导 总被引:2,自引:0,他引:2
研究出MNA/PMMA有机薄膜光波导。用棱镜耦合器进行了波导参数的测量,发现薄膜呈现各向异性,有较大的双折射。 相似文献
999.
The anodic voltammetric behavior of methotrexate was studied at glassy carbon electrode in acetate buffer (pH = 3.6) solution using cyclic, square-wave voltammetric and chronocoulometric techniques. The oxidation of methotrexate is an irreversible diffusion-controlled process. The oxidation mechanism was proposed and discussed in this work. The dependence of the current on pH, the concentration and nature of buffer, and instrumental parameters were investigated to optimize the experimental conditions for the determination of methotrexate. It was found that in the range of 8.0 × 10−7–2.0 × 10−5 mol/L, the currents measured by square-wave voltammetry presented a good linear property as a function of the concentrations of methotrexate. In addition, validation parameters, such as reproducibility, sensitivity and recovery were evaluated as well. The proposed method was also successfully applied for the determination of methotrexate in diluted human urine with good satisfactory. 相似文献
1000.
Received: 14 August 1997 相似文献