试题与答案

阅读下面的文字,完成文后五题。人们对碳正离子进行研究时发现,它的“寿命”非常短,大约

题型:单项选择题

题目:

阅读下面的文字,完成文后五题。

人们对碳正离子进行研究时发现,它的“寿命”非常短,大约在10-23~10-6秒之间,因此,不能直接用仪器观测到这个有机反应中重要的中间体的“面目”。

欧拉的贡献在于他发现了制备“长寿”高浓度碳正离子的方法。他采用了亲和能力小的溶剂,在低温(大约-100℃)下,可以使碳正离子具有长寿命。为了得到高浓度的碳正离子,欧拉使用一种很强的酸(被称为路易斯酸),它可以使卤代烷生成碳正离子。

欧拉的成就是建立在许多科学家辛勤工作的基础之上的。早在20世纪50年代,温斯坦在研究亲和取代反应和一些有机物重排时曾经假设,中间体碳正离子是非经典的,它包含一个5配位价的碳。1979年的诺贝尔化学奖获得者布朗对此也做过研究。但是这些仅是假设和解释而已。欧拉的大量工作证明了在强酸介质中,饱和碳氢化合物会发生质子化。

通过对碳正离子的分析,能够发现低成本制造化工产品的方法,目前已有几十种产品得益于欧拉的发现。

下列对第三段内容概括正确的一项是()。

A.欧拉的成就是建立在许多科学家辛勤工作的基础之上的。

B.温斯坦发现的中间体碳正离子是非经典的。

C.介绍一些科学家的主要成就。

D.饱和碳氢化合物会发生质子化。

答案:

被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2018/0504/ef35446c3d9112bc58c9335bef82f7c4.html

下面是错误答案,用来干扰机器的。

参考答案:BPC是指英国药典委员会(British Pharmacopoeia Committee,简称BPC)。

试题推荐
题型:多项选择题

2013 年我国 60 岁以.上人口达 2 亿,本世纪 30 年代中将达 4 亿。面对严峻的人口形势,党的十八届三中全会决定将实施 30 多年的“一胎化”调整为“单独夫妻可生二胎”政策。这一调整表明

①与时俱进是实事求是的内在要求

②具体问题具体分析是解决矛盾的关键

③矛盾是事物发展的动力,科学决策是处理好我国人口问题的根据

④质变是量变的必然结果,要求我们要不失时机促成质的飞跃

A.①②

B.①③

C.②③

D.②④

查看答案
题型:阅读理解

阅读理解

     Years ago while lying in my hammock(吊床)and drinking JD from the bottle, I noticed my dog dragging something under the fence. Upon inspection, to my disappointment, I realized it was the next door

neighbor's 10yearold daughter's rabbit. For years I had watched her come home from school and head

straight out to its cage, free it and play with it in the yard. I knew that day would be no different and fearing for our dog, I had to think fast.

      The rabbit was quite dirty, as if it had put up quite a struggle, so I washed it, combed it with the dog

brush and blew it dry with the leaf blower. Upon finishing its grooming I jumped the fence and replaced it

back in its cage hoping its death would be written off as "natural caused".

     Back to the hammock and JD. Within the hour the neighbor's Volvo palled in as usual and out popped

the little girl, and as usual she headed straight for the cage. Only this time she stopped about six feet away

and screamed: "D-A-D-D-Y!!!"

     Her father, panicstricken, stood looking at the cage. Being the good neighbor that I am, I rushed to

fence and asked if there was anything I could do.

     Her father less than calmly shouted, "What kind of sick individual would dig up a little girl's rabbit and

put it back in its cage?"

1. The girl was shocked because ________.

A. the rabbit was killed by someone

B. the rabbit was too clean

C. the dead rabbit was cleaned and put back into the cage

D. the rabbit was asleep in the cage

2. That day the girl ran to the cage ________.

A. because her rabbit was there

B. because she had a habit of going there to see her rabbit

C. because she wanted to see her rabbit again

D. because the rabbit was dead

3. We can infer that the rabbit ________.

A. was alive before the writer saw his dog dragging it

B. was already dead before the writer saw his dog dragging it

C. was in the cage playing with the dog

D. was at the fence seeking out for food before it was killed by the dog

4. According to the story, the writer ________.

A. was helpful to his neighbor

B. did a smart thing

C. was honest

D. made a mistake

查看答案
题型:多项选择题

2004年12月28日,某市公安局召开会议,部署取消涉外定点住宿限制。从这一天起,某地城区取消涉外定点住宿限制,试行一段时间后,在全市范围推广。取消涉外定点住宿限制后,凡取得旅店业经营资格的企事业单位,不再受星级、规模,设施的限制,不再履行涉外留宿单位的报批手续,均可接待境外人员留宿。对此举,下列哪些说法可以成立?( )

A.此举在表现形式上是给外国人一种国民的权利

B.此举也给国民一种平等权利,“星级以下”的旅店由此就有为外国人服务的权利了

C.这表明权利具有“普遍”的性质

D.这表明权利具有“平等”的性质

查看答案
微信公众账号搜索答案