问题 单项选择题

层析法分离物质的基本原理是

A.利用各物质的密度不同,从而使各物质以不同速度移动而达到分离

B.利用各物质的电荷多少,从而使各物质以不同速度移动而达到分离

C.利用各物质分子量不同,从而使各物质以不同速度移动而达到分离

D.利用各物质溶解度不同,从而使各物质以不同速度移动而达到分离

E.利用各物质的理化性质差异,以不同程度分布在两个相中,从而使各物质以不同速度移动而达到分离

答案

参考答案:E

解析: 层析法是利用不同物质理化性质的差异而建立起来的技术,所有层析系统都由两相组成:固定相和流动相,当待分离混合物随流动相通过固定相时,由于各组分的理化性质存在差异,与两相发生相互作用(吸附、溶解、结合等)的能力不同,在两相中的分配不同,而且随着流动相向前移动,各组分不断地在两相中进行再分配,与固定相相互作用越弱的组分,受阻滞作用小,向前移动速度越快,反之则越慢,分部收集流出液,可得到样品中所含的各单一组分,从而达到将各组分分离的目的。

选择题
阅读理解

阅读理解。

     New York has taken the title of the world's top fashion capital from Milan. The annual survey suggest

that the top five fashion cities are facing competition from Asia and Australia. New York had been the top fashion city for five years, but Milan took the title in 2009. The survey was made by the Global Language Monitor, a US based organization. It tracks the frequency(频率) of words and phrases in the media, on

the Internet and throughout the blog. With the US economy recovering, New York once again took the

top title. Hong Kong took second place. It was followed by London, Paris and Los Angeles. The other

top 10 cities were Milan, Sydney, Miami, Barcelona and Madrid.

    "Because of the new economic situation, the global fashion centers have also changed a lot, "said Bekka Payack. the Manhattan-based fashion reporter for the Global Language Monitor. "The new list shows that global fashion centers will change now and then. Compared with the traditional fashion cities, some new ones are performing better and better. "She said that perhaps this is new trend, and it is the first sign that the

traditional top five fashion cities--New York, Paris, London, Milan, and Rome--do not control global

fashion any more.

    The biggest changes in the list are Hong Kong, Madrid and Melbourne. The Group said that the top

newcomers to the list include Amsterdam at number 17, Cape Town at 23, Johannesburg at 25 and

Vienna at 27.

    The following are the 10 top fashion cities of 2010 and the changes from 2009.

  1. New York(up 1)      2. Hong Kong(up 5)

  3. London(up 2)           4. Paris(down 1)

  5. Los Angeles(up 1)    6. Milan(down 5)

  7. Sydney(up 2)            8. Miami(up 5)

  9. Barcelona(up 5)       10. Madrid(up 11)

1. New York has regained the title of the world's top fashion capital mainly because __________.

A. the US economy has been recovering

B. Milan faced competition from other cities

C. few big cities took part in the competition

D. the survey was made by an American organization

2. Compared with the 2009 list, which of the following has the greatest change?

A. Hong Kong    

B. Milan   

C. Madrid

D. Barcelona

3. We can infer from the text that __________. 

A. New York has lost the top title several times

B. all the traditional fashion cities are in the 2010 list

C. economic situations influence global fashion centers

D. new fashion cities have performed better than traditional ones

4. The text is probably taken from a __________. 

A. science report    

B. fashion magazine

C. geography textbook

D. history book