查询词典 asymmetric

Our main work is as follows: the stable laser mode theory in uniform plasmas is extended to non-uniform plasma cases; the discussion of the sufficient and necessary conditions for laser self-focusing in uniform plasmas is developed to non-uniform plasma cases; a quantitative approach to judge the impact of different plasma density distribution on laser self-focusing is proposed; the evolution properties of asymmetric laser filed in non-uniform and uniform plasmas are discussed and mechanisms that symmetric channel-like plasmas can confine the laser centroid around the plasma channel axes and symmetrize initially asymmetric laser beams are proposed; the formation of solitary standing wave in moderate plasma density is studied by PIC simulations and can be explained by stimulated Raman scattering of laser beams in plasmas.

主要工作为：把均匀等离子体中激光的稳定模理论推广到横向非均匀等离子体情形；把均匀等离子体中激光自聚焦的充分和必要条件的讨论推广到横向非均匀等离子体情形；给出横向密度分布不同的等离子体影响激光自聚焦的定量判据。讨论了初始不对称的激光场在横向非均匀及均匀等离子体中的演化特性，并提出了具有对称腔道结构的等离子体箍缩激光质心和对称化初始不对称激光场的物理机制。用粒子模拟讨论了激光场在等离子体中形成孤立驻波的过程，认为前向受激拉曼散射是发生此现象的可能机制。

In the downstream, a sudden expansion microchannel with asymmetric pairs of microelectrodes is designed. The multi-electrodes are formed beside the expansion microchannel and result in the trap of micro-particles. AC electric potentials are applied to each pair of asymmetric electrodes creating a non-uniform electric field. The tangential component of the field produces a force on the induced charges in the diffused double layer.

此外在扩张管道上采用一种可调控式的微粒子撷取装置，主要是在扩张管道的侧边镀上多对的电极，利用电极间电场所引起的局部的电渗流(Electro-Osmotic Flow， EOF)和轴向压力驱动流彼此间相反的运动方向，进而在管道壁面电极区间产生回流区。

The E-TOF will also be feasible and practical to assist chemists in screening the optimal reaction condition or evaluating the overall efficiency of different catalytic systems for a specific asymmetric reaction.4.For the first time,we explored chiralγ-hydroxy-α,β-acetylenic esters,which were prepared via asymmetric alkynylation,as key intermediates to the synthesis of chiralγ-butyrolactones. This convergent and enantioselective approach to chiralγ-butyrolactones is practical and easily handled with protecting group free.

这一概念包括反应产率、对映选择性、配体用量以及反应时间四个重要反应参数，不仅适用同一反应不同催化体系的横向综合性评价，而且适用于某一特定反应催化体系的优化过程，有助于研究人员选择最佳的反应条件。4、我们发展了以手性γ-羟基-α，β-炔酸酯为关键中间体完成了手性γ-丁内酯类天然产物的对映立体选择性全合成，该关键中间体能够以我们的催化体系方便的对映选择性合成，之后的官能团转换方法成熟，易于操作，无需进行繁琐的官能团保护和脱保护过程，绿色经济。

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。

As she looked at Warrington's manly face, and dark, melancholy eyes, she had settled in her mind that he must have been the victim of an unhappy attachment.

每逢看到沃林顿那刚毅的脸，那乌黑、忧郁的眼睛，她便会相信，他一定作过不幸的爱情的受害者。

Maybe they'll disappear into a pothole.

也许他们将在壶穴里消失