选择性的

Combining the performance evaluation (activity, selectivity and stability) and the characterization of the catalysts (XRD, TPD, FTIR and the pore structure measure), it can be concluded that :(1)The activity of modified β is higher than MCM-22, but the selectivity of ethylbenzene is lower about 3% than that of MCM-22;(2)The mounts of diethylbenzene and the other by-products are higher 1.7 times and 1.5 times than these of MCM-22 respectively;(3)The catalytic performance of zeolite mixture is nearly equal to modified β, but the selectivity of ethylbenzene is higher about 0.5% than that of modified β;(4)The catalytic activity of zeolite is mainly correlated with the number of acid sites, strength and distribution, and the distribution of products is determined by the binding energy of ethylbenzene and the pore structure, while the stability of catalyst is affected by the amount of poly-ring aromatic alkylate and the pore structure.

以性能评价和特性表征（XRD、TPD、FTIR和孔结构测定）相结合的方式，对上述三种催化剂性能比较的结果表明：（1）改性的活性明显高于MCM-22，但乙苯选择性却低于MCM-22绝对差约3%；（2）改性(上二乙苯和其他副产物的生成量分别约为MCM-22上对应值的1.7和1.5倍左右；（3）混合型催化剂的性能与改性相仿，但乙苯选择性提高0.5%左右；（4）对乙苯合成，沸石催化剂的活性主要取决于其B酸中心数、酸强度及酸分布，产物分布则取决于催化剂表面的乙苯脱附能垒值和孔道结构，而稠环芳烃的生成量和催化剂孔道结构是影响催化剂稳定性的主要因素。

THE FIRST TOTAL SYNTHESIS OF TAXAMAIRIN B Taxamairin B, representive of rare naturally-occuring rearrang-ed 9(10→20)-abeo-8, 11, 13-triene diterpenoids, has been firstsynthesized by a eleven-step route in an overall yield of 8.19%,starting from commercially available catechol and 1,3-cyclohexan-dione. The improved Friedel-Crafts annulation, thermodynamicallycontrolled-geminal pairing methylation, the selective oxidation ofallyl group and the selective reduction of the less-hindrancecarbon-carbon double bond are the key steps.

二。美丽红豆杉素B的全合成研究 1，美丽红豆杉素B的首次全合成以价廉，易得的邻苯二酚和1，3-环己二酮为原料，经过改良的Friedel-Crafts烷基化反应，热力学控制的α，β-不饱和酮结构的α一位双烷基化，烯丙位的选择性氧化，以及选择性还原位阻较小的碳碳双键等十一步反应，以8.19％的总收率首次完成了美丽红豆杉素B的全合成。

It was found that the MCM-22 zeolite catalyst prepared by the VPT method not only showed good crystallinity and high BET surface area, but also better crystal growth orientation and denser structure.The catalyst showed high activity, selectivity and good stability for alkylation of benzene with propylene, especially better selectivity to the end product cumene.The shaped MCM-22 zeolite catalyst prepared by the VPT method has good prospect of industrial application in synthesis of cumene.

结果表明：汽相法制备的MCM-22分子筛催化剂不仅具有较好的结晶度和较高的微孔表面积，而且具有更好的晶体生长取向性和更加致密的结构；在烷基化反应中也具有很好的活性、选择性和稳定性，特别是对目的产物异丙苯的选择性明显高于水热法合成的催化剂，在异丙苯合成上具有很好的应用前景。

Based on extended Linsker's network developed by Wimbauer et al.,we build a model for the receptive field of toad's R3 ganglion cell and a model for the receptive field of the nLM neuron of pigeon. Computer simulations on the 'head/tail preference' property,the configurational selectivity of the R3 neuron,and the selectivity for contrast,direction,orientation and the length of the moving edges of the nLM neuron,have been made. The simulation results are consistent with the physiological experiments qualitatively.

为揭示这类神经元的信息加工原理，以Wimbauer等人提出的时延Linsker网络为基础，通过将不同的时空动态感受野线性组合，建立了蟾蜍视神经节R3类神经元和家鸽扁豆核神经元的感受野模型，并模拟了R3神经元对蠕虫样刺激物的"头/尾偏爱"特征，细胞对刺激物的构型选择性以及nLM神经元对运动边缘的反差、方向、边缘朝向和长度的选择性。

For a peptide to act as part of the host defense system or to be of pharmaceutical interest, high antimicrobial activity must be combined by low hemolytic activity. Our results indicated that the antimicrobial activity increased with increasing charge and polar angle, with charge of ＋4 and polar angle of 140° exhibiting the highest antibacterial and membrane permeabilizing activity. Higher hydrophobicity and hydrophobic moment correlated with increased hemolytic activity, thus decreasing selectivity dramatically.

胜肽要扮演宿主免疫机制的一部分或要成为新型态的抗生素不仅要有强大的抗菌活性还需要有高度的选择性，由本实验的结果发现，当抗菌胜肽的正电荷及极性角度增加时，胜肽之抗菌活性会随之增加，当抗菌胜肽的电荷为＋4而极性角度为 140°时，胜肽有最强之抗菌能力及膜渗透活性；而随著胜肽疏水性以及疏水性矩的增加，会增加溶血活性，结果反而降低了抗菌胜肽的选择性。

Experiment on adaptation effects in cat striate cortex found no pronounced difference between simple cells and complex cells.

结果显示，相对于简单的平动刺激，复杂的光流刺激引起了更显著的适应及后效应：细胞的反应在适应期间及适应后衰减程度更大，多数细胞的方向选择性在适应后发生了显著变化；总体上，细胞对复杂光流的适应具有方向选择性，但细胞对平动刺激的适应与测试刺激的运动方向无关。

It is the fluorosilicic ion that exsits in the slurry and plays an important role in flotation, fluorosilicic ion not only reacted with Fe〓 on the surface of aegirine to form ionic compound, but also formed stable Si-F bond in Si-O etching reaction. Only ionic compound was obtained when it was attached to hematite surface according to the theories of coordination chemistry, Compared with SiF〓, Fatty acid ion preferentially acts with Fe〓 on the minerals surface, therefore, SiF〓 Can't obstruct the adsorption of collector on the surface of hematite completly, but can reduce the flotation recovery of aegirine selectively.

运用FTIR、XPS等测试方法仔细研究了氟硅酸盐抑制剂对含铁硅酸盐钠辉石的选择性抑制作用机理，氟硅酸盐在弱酸性条件下对赤铁矿浮选的抑制作用很微弱，而对含铁硅酸盐钠辉石强烈抑制，从而扩大了两者之间的浮选差异；SiF〓是矿浆中起抑制作用的主要成分，SiF〓不仅与钠辉石表面的Fe〓形成离子型配合物，而且还与Si-O键形成稳定的Si-F共价键，而与赤铁矿表面只能形成离子型配合物，根据晶体配位场理论，与SiF〓相比较羧酸根离子将优先与矿物表面Fe〓发生配位作用，因此SiF〓的存在并不能完全阻碍捕收剂在赤铁矿表面的吸附作用，却能够选择性地抑制钠辉石的上浮。

In the mixed solvent of dimethyl phthalate / TBP or phenyl ether / TBP, the selectivity for styrene oxide is good but the conversion of styrene is low due to the coordination to the catalyst of the solvent.

邻苯二甲酸二甲酯或二苯醚等与磷酸三丁酯的混合溶剂中环氧化的选择性较高，但由于溶剂对催化剂的配位作用抑制了催化剂的活性，苯乙烯转化率很低；当部分的邻苯二甲酸二甲酯或二苯醚被甲苯取代后，苯乙烯的转化率提高，生成环氧苯乙烷的选择性不变。

In this thesis, this system is used for epoxidation of propylene and styrenewith good results. The solvent effect is investigated for epoxidation of styrene. In the mixedsolvent of dimethyl phthalate / TBP or phenyl ether / TBP, the selectivity for styreneoxide is good but the conversion of styrene is low due to the coordination to thecatalyst of the solvent. When part of dimethyl phthalate or phenyl ether is replacedby toluene, the conversion increases and the selectivity keeps constant.

邻苯二甲酸二甲酯或二苯醚等与磷酸三丁酯的混合溶剂中环氧化的选择性较高，但由于溶剂对催化剂的配位作用抑制了催化剂的活性，苯乙烯转化率很低；当部分的邻苯二甲酸二甲酯或二苯醚被甲苯取代后，苯乙烯的转化率提高，生成环氧苯乙烷的选择性不变。

The facts influencing the high stereoselectivity were discussed. It is proposed that the stability of the tri- molecular transition state or the stereoelectronic effect of the vinyl anion intermediate formed by the nucleophilic addition of halide anion to the electron-deficient carbon- carbon triple bond might be responsible for the high Z-stereoselectivity.

通过对影响反应的高立体选择性因素的研究，认为反应的三分子过渡态的稳定性或生成的烯基负离子中间体的立体电子效应决定了反应的高度Z立体选择性。

In the negative and interrogative forms, of course, this is identical to the non-emphatic forms.

。但是，在否定句或疑问句里，这种带有"do"的方法表达的效果却没有什么强调的意思。

Go down on one's knees;kneel down

屈膝跪下。。。下跪祈祷