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921.
922.
LI Jing SHANG Yan-mei XIAO Chuan SONG Zhi-guang LI Ye-zhi HUANG Hua-min .College of Chemistry Jilin University .School of Public Health Changchun P.R.China .Key Laboratory for Supramolecular Structure Materials of Ministry of Education Changchun 《高等学校化学研究》2009,25(1)
(R)-4-Hydroxymethyl-2-thioxo thiazolidine as a new chiral catalyst in the asymmetric addition of diethyl-zinc to benzaldehyde was synthesized from (R)-4-hydroxymethyl-2-thioxo thiazolidine carboxylic acid and its crystal structure was determined by X-ray diffraction method. The compound was crystallized in the orthorhombic system, space group P212121 with unit cell dimensions a=0.67253(12) nm; b=0.89164(17) rim; c=1.06146(19) nm, volume 0.6365(2) nm3; Z=4, calculated denisity 1.557 Mg/m3; absorption coefficient 0.733 mm-1; F(000)=312. The X-ray crystal structure analysis reveals that the compound has a thione group. 相似文献
923.
1IntroductionShadowmoireinterferometryisawholefieldnoncontact3Dmeasurementtechnique.ItisfirstappliedbyH.Takasaki[1]in1970.In... 相似文献
924.
925.
926.
地空导弹武器系统效能评估指标体系研究 总被引:4,自引:0,他引:4
地空导弹武器系统效能评估是地空导弹武器系统研制和使用过程中的关键环节.效能评估指标体系的建立是保证效能评估科学、合理的重要基础.针对现代地空导弹武器系统的使用特点,在W SE IAC模型的框架下,构建了地空导弹武器系统效能评估指标体系,并给出了指标的分解及确定方法.研究结果可为地空导弹武器系统效能评估提供支持. 相似文献
927.
In our previous theoretical studies [Meng-Tao Sun, Yong-Qing Lee, and Feng-Cai Ma, Chem. Phys.Lett. 371 (2003) 342], we have reported the quantum interference on collision-induced rotational energy transfer on CO (A1П, v = 3) with inert gases, which originates from the difference between the two A-related collision potential energy surfaces. The interference angle, which measures the degree of coherence, is presented in this paper. Based on the time-dependent first order Born approximation, taking into account the anisotropic Lennard-Jones interaction potentials, the relation of the interference angle with the factors, including experimental temperature, partner, and rotational quantum number, are obtained. The changing tendencies with them are discussed. This theoretical model is important to understanding and performing this kind of experiment. 相似文献
928.
Chitin 1 is a biodegradable and nontoxic polysaccharide widely spread among marine and terrestrial invertebrates and fungi. It is usually obtained from waste materials of the sea food-processing industry, mainly shells of crab, shrimp, prawn and krill. Native chitin occurs in such natural composite materials usually combined with inorganics, proteins, lipids and pigments. Its isolation calls for chemical treatments to eliminate these contaminants, some of which maybe coimmercially explored. By treating crude chitin with aqueous 40~50% sodium hydroxide at 110~115℃ chitosan is obtained. However, the fully deacetylated product is rarely obtained due to the risks of side reactions and chain deplolymerization. Chitosan and chitin are closely related since both are linear polysaccharides containing 2-acetamido-2-deoxy-D-glucopyranose and 2-amino-2-deoxy-D-glucopyranose units joined by β (1→4) glycosidic bonds. They can be distinguished by their contents of the above-mentioned units and by their solubilities in aqueous media. The acetylated units predominate in chitin while chitosan chains contain mostly deacetylated units. Chitin is soluble in a very limited number of solvents while chitosan is soluble in aqueous dilute solutions of a number of mineral and organic acids, being the most common ones, the hydrochloric and acetic acids. In aqueous dilute acid media chitosan forms salts, producing polyelectrolyte chains bearing positive charges on the nitrogen atoms of their amine groups. In fact the salt of chitosan may be formed in a separate step or as a consequence of the presence of acid in the water suspension of the neutralized form of chitosan. 相似文献
929.
930.
A kind of predator-prey system of Holling typeⅡand interaction perturbation with impulsive effect is presented.By using Floquet theory and small amplitude perturbations skills,the locally asymptotical stability of prey-eradication periodic solution and the permanence of the system are discussed and the corresponding threshold conditions are given respectively.Finally,the existence of positive periodic solution is investigated by the bifurcation theory. 相似文献