问题 问答题 简答题

试从化学结构上分析多潘立酮比甲氧氯普胺较少中枢副作用的原因。

答案

参考答案:

作为促动力药物的多潘立酮和甲氧氯普胺,是希望作用于消化系统的多巴胺D2受体,如促进胃肠道的蠕动等起作用。但这两个药物都能进入中枢,影响中枢的多巴胺D2受体,导致中枢神经的副作用。从结构上看多潘立酮比甲氧氯普胺含有较多的极性基团,极性较甲氧氯普胺大,不易透过血脑屏障。即相比之下,进人中枢的多潘立酮的量较少,故多潘立酮比甲氧氯普胺较少中枢的副作用。

选择题
阅读理解

BEIJING—Seven prestigious universities in China announced Sunday that they would begin using the same independent exam —besides the national one —to test students hoping to gain entrance to them in 2011.

The seven are Peking University, Beihang University, Beijing Normal University, Nankai University, Fudan University, Xiamen University and Hong Kong University.

Students who want to gain entrance to any of the seven universities will only have to sit one independent exam, according to the joint announcement.

“This will help lighten tile students’ load, otherwise they must take several exams for different universities,”said the announcement.

Passing the exam could result in more than one interview chance, giving the students more opportunities to choose their favorite universities.

China’ s college entrance exam system is undergoing reform as universities aim to select students based on independent criteria rather than just using the results of the national exam.

In 2003, Peking University and another 21 universities were allowed to pilot (试用) the reform by using their own criteria to independently select five percent of their students.

Now nearly 80 universities across the country have the right to select talented students based on their own exams.

Education experts regard universities selecting students according to independent examinations as conducive (有助的) to better understanding where the students’ talents lie.

Although this may be the case, it has also created problems as students may sit many different exams as they often apply for a number of universities.

To relieve students from such pressures, the national education outline (2010—2020) released in July this year encourages high-level universities to group together to use the same exams.

小题1: If students want to be admitted to the seven prestigious universities, they can______.

A.only pass the interview.

B.only take the national exam.

C.only take the independent exam.

D.either take the national exam or the take the independent exam.小题2: What’s the purpose of students sitting one independent exam to gain entrance to the seven universities?

A.It can reduce students’load to take several exams.

B.The universities will have the same standard to test students.

C.There will be less trouble marking students’ test papers.

D.It can avoid fierce competition among these universities.小题3: If students pass the independent exam,they will ______.

A.take the national exam.

B.have one or more interview chances.

C.be admitted to one of the universities.

D.he trained to be adapted to universities life and studies.小题4:What is the advantage of universities selecting students according to independent examinations?

A.Students needn’t take the national exam.

B.Students’education cost can be lowered.

C.Students abilities and talents can be better found.

D.It can encourage middle schools to recommend more qualified students.