阻环

The preparation and characterization of mono-and bispenta-phenylcyclopentadienyl lutetium chlorides were reported.

本文介绍高空间位阻的五苯基环戊二烯基氯化镥的合成及鉴定。

The partial substitution of acids on the triazole-ring of polymer 10 may arise from difference in acid strengths or from varying degrees of steric hinderance during protonation reactions.

在酸部分取代对三氮唑聚合物10环可能产生的酸强度的差异，或从不同的反应过程中的质子立体阻度。

The transition metal complex has a pentagon ring structure having an amido group connected by a phenylene bridge in which a stable bond is formed in the vicinity of a metal site, and thus, a sterically hindered monomer can easily approach the transition metal complex.

该过渡金属配合物具有由亚苯基桥连接的酰胺基的五边环结构，其中在金属位置附近形成稳定键，因此位阻单体可容易地接近过渡金属配合物。

It may be due to the following two reasons: 1 High steric hindrance caused by rigid structure of substituted fluorenone preventsthe approach of the chiral reductor;2 The prochiral center is, moreover, linked to two coplanar aromatic rings, which due to strong conjugation are highly electronically similar and thus it becomes extremely difficult to distinguish between them.

主要是以下两个原因：1取代芴酮的刚性结构产生高的空间位阻，阻止了手性催化剂的接近；2潜手性中心旁的两个芳香环不仅立体构型非常相似，而且高度的电子相似，很难被手性配体识别。

Laboratory test shows that the pump has realized the designation of friction free down stroke, self-sealing with no leakage upstroke, and long life with wear resistance seal ring.

室内试验表明该泵实现了下行"无"摩阻，上行自封"无"漏失，专用耐磨环实现了长寿命的目的。

With the size of alcohol ROH increasing, space steric block made solvolysis activity of propylene oxide decrease.

空间位阻的变化，使得环氧丙烷溶剂解反应活性随着醇类溶剂的分子增大而减小。

In order to improve the radiation resistance of condensed-type RTV silicone rubber, two kinds of crosslinking agents are synthesized successfully: triethoxysilane with acenaphthenyl groups m.p.

当三乙氧基硅烷和三乙氧基硅烷用作缩合型RTV硅橡胶的交联剂时，由于二者所含的稠环基团的空间位阻较大，因而样品硫化速度较慢。

The aconitic acid-acrylic acid copolymer, itaconic acid homopolymer and polyepoxysuccinic acid which were non-phosphorus scale and dispersing inhibitors were synthesized with the fermentation products citric acid, itaconic acid and maleic anhydride.

以生物发酵产品柠檬酸和衣康酸为主要原料，分别合成了无磷阻垢分散剂丙烯三羧酸－丙烯酸共聚物和衣康酸均聚物，利用马来酸酐合成了聚环氧琥珀酸。

No fluorescence of 2b hasbeen detected. Probably the planar conjugative effect is destroyed by the sterichindrance of methoxy group.

而蒽冠醚2b则几乎没有荧光，这可能是由于甲氧基的引入导致体系的空间位阻增大，从而破坏了蒽环的平面共轭效应所致。

Results An intracerebral echoless cyst could be visualized in all the three cases, in which" high-speed and low-resistance" blood signal could be detected by CDFI. There was direct communication between the vein of Galen and several basis cranii cerebral arteries without cerebral ventricle dilation. The dilated heart-breast rate could be visualized in all the three cases, two of which complicating with the dilation of superior vena cava and tricuspid regurgitation; two of which complicating with pleural fluid and abdominal dropsy; one of which complicating with edema of skin and polyhydramnios; one of which complicating with reversing blood signal of umbilical artery in diastolic phase.

结果 超声声像图显示3例胎儿在丘脑后下方、小脑上方有一无回声囊性结构，彩色多普勒超声提示无回声区内为高速低阻血流信号，与颅底动脉环间可见多条血管分支相通；脑室系统均未见扩大；胎儿心胸比增大，其中2例伴有上腔静脉内径增宽、三尖瓣反流；2例伴有胸腹水，1例全身皮肤水肿伴羊水过多，1例脐动脉舒张期血流反向。

Singer Leona Lewis and former Led Zeppelin guitarist Jimmy Page emerged as the bus transformed into a grass-covered carnival float, and the pair combined for a rendition of "Whole Lotta Love".

歌手leona刘易斯和前率领的飞艇的吉他手吉米页出现巴士转化为基层所涵盖的嘉年华花车，和一双合并为一移交&整个lotta爱&。

This is Kate, and that's Erin.

这是凯特，那个是爱朗。