选择性

It is reported that alkannin and shikonin isolated from the roots of Lithospermum erthyrorhizon or Alkanna tinctoria and their acylshikonin derivatives are potent selective inhibitors of DNA Topoisomerase Ⅰ.

文献报导紫草素和酰基紫草素等具有DNA拓扑异构酶Ⅰ的选择性抑制活性。本组曾合成得到少量环异紫草素（8），它对小鼠白血病P-388肿瘤细胞具有强烈的抑制作用。

The preparation of potassium malonyloxyborohydride in situ and its seletive hydroborating alkene are described.

介绍了丙二酰氧基硼氢化钾的制备及其原位与烯烃的选择性硼氢化。

Supercritical conditions can enhance the conversion of isooctane but lower the alkene selectivity simultaneously.

超临界条件与常压相比能提高异辛烷的转化率，但同时使烯烃选择性降低。

When the mol quantity of Cu2+ dissolved was 5% of those of AlCl3 in ionic liquids, alkylation results from ionic liquids is comparable with those obtained with concentrated sulfur acid: the yield of alkylate reaching 178% of the volume of butene inputted, the selectivity of C8 reaching 75% and the octane number of alkylate reaching 92.2.

溶入Cu2+和Cu+后，离子液体的催化性能有显著的改善，当Cu2+的摩尔加入量为三氯化铝的5%时，烷基化油收率达到丁烯体积的178%，对C8的选择性为75%，烷基化油辛烷值为92.2，并且离子液体可以重复使用。

During the reaction of alkylation, general contained 0.2%~2.0% butadiene will produce viscous heavy composite materials, which will raise final boiling point of alkylate and decrease octane, what is more, it will react with acid to produce corresponding ester, which will increase the consumption of acid, Therefore, we must remove butadiene by selective hydrogenation, at the same time, it will convert some of 1- butane to 2- butane by isomerization and raise octane of alkylate.

一般含有0.2%~2.0%的丁二烯，其在烷基化反应中，可生成一种分子量很高的粘稠重质迭合物，使烷基化油的干点升高，辛烷值降低，并且它还和酸反应生成相应的酯而加大酸耗量。因此必须经过选择性加氢除掉丁二烯，同时，将部分1-丁烯异构化为2-丁烯，以提高烷基化油的辛烷值。

These ligands were found to be very effective in construction of quaternary carbon centers by using asymmetric allylic alkylation.

这类配体在前手性亲核试剂的不对称烯丙基化构筑手性季碳中心的反应中，显示了较好的反应活性及对映选择性。

And the mole ratio of benzene to propylene on the alkylation process have been studied.

统计了中试研究数据并进行了数学关联，获得了BPA分子筛催化剂对异丙苯、二异丙苯选择性和反应器床层温升的关联式。

The ligands were found to be effective in palladium-catalyzed asymmetric allylic alkylation to construct chiral quaternary carbon center.

这类配体在前手性亲核试剂的不对称烯丙基化构筑手性季碳中心的反应中，显示了较好的反应活性及对映选择性。

Some advantages of this invention are that it provides desirable catalyst lifetime and activity, minimizes resin swelling, and provides a desirable, sustained selectivity to alkylene glycol.

本发明的优点是，它提供了所希望的催化剂寿命和活性，最大程度地减少了树脂溶胀和提供了理想的、持久的对亚烷基二醇的选择性。

After hydrogenation of the double bond and the addition of alkyne to a carbonyl we introduced the N-hydroxy group by SN2 reaction.

不对称氢化和炔负离子对羰基的立体选择性加成构建了两个新的手性中心，之后用羟胺衍生物对羟基的SN2取代反应引入了羟胺片断。

Breath, muscle contraction of the buttocks; arch body, as far as possible to hold his head, right leg straight towards the ceiling (peg-leg knee in order to avoid muscle tension).

呼气，收缩臀部肌肉；拱起身体，尽量抬起头来，右腿伸直朝向天花板（膝微屈，以避免肌肉紧张）。

The cost of moving grain food products was unchanged from May, but year over year are up 8%.

粮食产品的运输费用与5月份相比没有变化，但却比去年同期高8％。