查询词典 lewis

The free phosphonic groups shielded most of the Lewis-acid sites on the surface of zirconia and imparted negative charges on the surface at high pH, resulting in excellent resolution for phenols and a great improvement for the separation of benzoic acids.

在该固定相上，酸性化合物的色谱性能得到明显改善，硝基酚、苯二酚等在氧化锆上通常难以洗脱的酚类化合物，均得到了高效分离。

Lewis acidity is considered to be responsible for the high photoactivity at 950 °C.

而路易士酸被认为是锻烧950 ℃之样品有高活性的主要原因。

Lewis Carroll. Halftone photomechanical reproduction of photograph.

路易士。卡洛尔的照片，以网版照相技术翻印。

We screened a set of Lewis base organocatalysts derived from chiral pipecolinic acid and tert-butanesulfinamide for the reduction of-N-Cbz-1- phenylpropenamine, including newly designed ones and some of those previously developed in our lab. However, only moderate stereoselectivities, albeit high yields were obtained.

在本课题组前期研究的基础上，我们筛选并设计了一系列以手性哌啶酸和叔丁基亚磺酰胺为母体的有机小分子路易斯碱催化剂，它们能催化三氯氢硅对-N-苄氧羰基-1-苯基丙烯胺的不对称还原，获得很高的收率和中等的对映选择性，并且具有很好的底物普适性。

Starting from chiral proline, pipecolinic acid, piperazine-2-carboxylic acid and 1,2-diphenyl amino alcohol, a series of structurally simple and easily prepared amides were developed as highly effective Lewis basic organocatalysts for the asymmetric reduction of imines with trichlorosilane as the reducing agent, which promoted the reduction of N-aryl imines with high yields and excellent enantioselectivities with an unprecedented substrate spectrum.

本文分别由手性脯氨酸、哌啶酸、哌嗪酸以及氨基醇出发，设计和合成了一系列结构新颖、合成简便、性能优良的酰胺类有机小分子路易斯碱催化剂，以廉价的三氯氢硅为氢源，用这些催化剂催化亚胺不对称还原，得到了非常优良的收率、对映选择性和前所未有的底物普适性。

The normally brominated Baylis-Hillman adducts were formed as the major product at low temperature. While at room temperature or heating, the α,γand β,β-dibrominated compounds were formed as the major products using 3-butyn-2-one and methyl propiolate or propynenitrile as substrate, respectively.

贫电子炔类化合物的Baylis-Hillman反应的研究在这部分工作中我们发现在用TiBr〓或BBr〓为Lewis酸催化贫电子炔类化合物和芳香醛的Baylis-Hillman反应时，温度对反应的影响很大：当反应在低温下进行时，通常生成的是正常的β-溴代的Baylis-Hillman反应产物；而在室温或加热条件下反应，以丁炔酮为底物时，主要生成的是α，γ-二溴化合物，而以丙炔酸甲酯及丙炔腈为底物时，主要生成的是β，β-二溴化合物。

In order to further improve the catalytic activity and investigate the influence of catalyst acidic properties on the catalytic activity, acid-treated montmorillonite and molecular sieve Hβwere modified by loading Lewis acid and protonic acid treatment.

为了进一步提高催化剂的催化活性和考察催化剂酸性质对催化剂活性的影响，对酸化蒙脱土和Hβ分子筛进行了改性处理并考察了它们改性后的催化活性。

Voted NO on allowing reimportation of prescription drugs

Ron Lewis 美国不应该允许从加拿大进口处方药品。

In the Lewis and Chambers example, restaurants have been seedily increasing their prices.

在刘易斯和商会例如，餐馆已seedily提高其价格。

In the Lewis and Chambers example, restaurants have been seedily increasing their prices.

以里维斯和詹姆波斯的经历来看，饭店涨价措施是极为拙劣和不理智的。

It has been put forward that there exists single Ball point and double Ball points on the symmetrical connecting-rod curves of equilateral mechanisms.

从鲍尔点的形成原理出发，分析对称连杆曲线上鲍尔点的产生条件，提出等边机构的对称连杆曲线上有单鲍尔点和双鲍尔点。

The factory affiliated to the Group primarily manufactures multiple-purpose pincers, baking kits, knives, scissors, kitchenware, gardening tools and beauty care kits as well as other hardware tools, the annual production value of which reaches US$ 30 million dollars.

集团所属工厂主要生产多用钳、烤具、刀具、剪刀、厨具、花园工具、美容套等五金产品，年生产总值3000万美元，产品价廉物美、选料上乘、质量保证，深受国内外客户的青睐