查询词典 asymmetric system

The synthesis and characterization of asymmetric dinuclear and mononuclear vanadium complexes show that the pH value is very important for the products\' formation and isolation. In some pH range, theα-alkoxy bridge was easy to break and form asymmetric dinuclear and mononuclear vanadium structure.

三、不对称的双核钒和单核钒配合物的合成和表征显示，pH值对产物的形成和分离具有至关重要的作用。pH值在一定范围内，柠檬酸的烷氧基氧作为桥氧的化学键才容易断开，从而形成不对称的双核钒和单核钒结构。pH值不仅影响不对称双核V_2O_3钒配合物和单核钒配合物的形成，还关系到钒还原的速度。

In order to improve the luminescence and thermal performance of asymmetric ROPPVs, a series of poly derivatives with asymmetric alkoxyl substituents/ nanometer semiconductor composites were synthesized through dehydrochlorination in-situ polymerization.

为了进一步改善不对称ROPPVs的发光性能和热性能，首次采用原位脱氯化氢缩合聚合法，合成出一系列不对称烷氧基取代聚对(来源：9bab9bABC论文网www.abclunwen.com)苯乙炔衍生物／纳米半导体复合材料。

The asymmetric hydrogenation of prochiral ketones is one of the most efficient methods of producing enantiomerically enriched secondary alcohols. The ruthenium complex RuCl_2[P(C_6H_5)_3]_2--DPEN(DPEN=1, 2-diphenylethylene-diamine) was applied to the asymmetric hydrogenation of benzalacetone.

具有光学活性的烯丙基醇是合成许多生理活性药物的重要中间体，前手性酮不对称加氢反应是制备具有光学活性仲醇的一种重要方法。

Chiral auxiliary controlled asymmetric reaction is one of the main methods in asymmetric synthesis.

手性助剂控制的不对称反应是不对称合成的主要方法之一。

This work, concentrated on the asymmetric allylation of aldehydes controlled by different chiral auxiliaries prepared from rotational pure tartaric acid, can be divided into three parts.The first part aims to review the developments of chiral drugs and asymmetric synthesis, from which derived the present research topic backgrounds and works.Synthesis and applications of allylation from aldehydes are the second part of the thesis. By optimizing the reaction conditions, such as solvents, temperature, time and chiral auxiliaries like N,N\'-dibenzyl tartamide, N,N\'-p-dimethylphenyl tartamide, N,N\'-o-dimethylphenyl tartamide, N,N\'-o-dichlorophenyl tartamide, N,N\'-a-dinaphyl tartamide, N,N\'-dicyclohexyl tartamide and N,N\'-diphenyl tartamide, ideal experimenttal conditions are obtained according to HPLC monitoring, as well as the auxiliaries\' recoveries experiments. Starting from benzaldehyde and 3-bromopropaldehyde, N,N\'-dibenzyl tartamide is considered the best auxiliary in this reaction.

本文介绍了醛的不对称烯丙基化反应，以光学纯酒石酸为原料，研究了不同构型手性配体在醛的烯丙基化反应中的立体选择性，全文共分三部分十个章节：第一部分对当前手性药物和手性技术进行了概述，并由此展开了本文的研究背景和任务；第二部分为有机合成部分，对醛的不对称烯丙基化反应进行了深入探讨，以苯甲醛为原料对反应条件进行优化，在优化的反应条件下对制备的七种可回收手性酰胺配体(N-苄基酒石酸二酰胺、N-对甲苯基酒石酸二酰胺、N-邻甲苯基酒石酸二酰胺、N-邻氯苯基酒石酸二酰胺、N-a-萘基酒石酸二酰胺、N-环己基酒石酸二酰胺和N-苯基酒石酸二酰胺)进行筛选，优化配体回收实验条件，最终确定出N-苄基酒石酸二酰胺在苯甲醛的不对称烯丙基化反应中具有较大优越性，结晶回收的手性配体光学纯度保持不变。

The first asymmetric total synthesis of coumarinolignoids Daphneticin and it's enantiomer was accomplished starting from 7-hydroxycoumarin and 3, 4, 5-trimethoxybenzaldehyde, in which Sharpless asymmetric dihydroxy reaction was used to construct chiral center, and Mitsunobu reaction was used to obtain desired configuration.

并以7-羟基香豆素和3，4，5-三甲氧基苯甲醛为起始原料，用Sharpless不对称双羟化反应构筑手性中心，用Mitsunobu偶联反应作为关键步骤，合成了手性的香豆素木脂素Daphneticin及其异构体。

The first asymmetric synthesis of trans-β-hydroxy-γ-butyrolactones:-(3R, 4R, 5S)-4-(1-acetoxy-isopropyl)-3-hydroxy-butyrolactone 65a was achieved starting from isobutylaldehyde through nine steps. The key steps involve the construction of three chiral carbon centers by the Sharpless's asymmetric epoxidation and Substrate directable chemical reaction.

以异丁醛为起始原料，经过九步反应首次设计合成了具有三个手性中心的trans-β-羟基-γ-丁内酯：-（3R，4〓，5S）-4-（1-乙酰氧基-异丙基）-3-羟基-丁内酯65a，关键步骤是Sharpless不对称环氧化和底物定向不对称合成反应。

The first part of this dissertation described a new effective method for asymmetric synthesis of,α,α-disubstituted amino acids from the asymmetric Strecker reaction products of aldehydes.

在本论文的第一部分，我们开发了一条以醛为原料，以不对称Strecker反应和不对称烷基化为关键步骤的合成α，α双取代氨基酸的有效方法，并对其立体选择性结果进行了机理探讨。

Based on English definition of the six properties which a relation R defined on a set A and utilizing the logical characteristic of implications, two aspects of ordered-pair and the matrix MR are considered, and the properties of the R is analyzed one by one. A few useful conclusions are summarized as determining the properey of the R. The following collections are also analyzed between reflexive and irreflexive, symmetric and antisymmetric, symmetric and asymmetric and among irreflexive, antisymmetric and asymmetric.

根据定义在一个集合A上的关系R的六个性质的英文定义，利用蕴含式的逻辑特点，从有序对和关系R的矩阵M两个角度对每个性质逐一进行分析，得出在判定关系R的性质时可用的结论，并且分析了自反性与非自反性之间、对称性与反对称性之间、对称性与非对称性之间、非自反性和反对称性以及非对称性之间的联系。

An contemporary expansion of the model has assumed evidently that asymmetric information spreads among firms and customers , and explored their differently asymmetric behaviors of responding to others ' changes of pricing and the causes of sticky prices so that the problem field of model has been expanded from oligopolistic market to monopolistically competitive market .

模型当代的一个扩展，明确假设了在顾客与厂商之间信息分布不对称，探讨了他们对于价格变动的反应不对称行为的各异性和粘性价格的成因，将微观模型的问题域从寡头市场扩展至垄断竞争市场。

Article 144 The Government of the Hong Kong Special Administrative Region shall maintain the policy previously practised in Hong Kong in respect of subventions for non-governmental organizations in fields such as education, medicine and health, culture, art, recreation, sports, social welfare and social

第一百四十四条香港特别行政区政府保持原在香港实行的对教育、医疗卫生、文化、艺术、康乐、体育、社会福利、社会工作等方面的民间团体机构的资助政策。原在香港各资助机构任职的人员均可根据原有制度继续受聘。

Small wonder, then, that the Chinese spend more in the shop than any other group of foreign visitors do .

这样的小惊喜，使中国顾客比任何国家的人消费得更多。