问题 问答题 简答题

简述分子筛的结构构型三种层次。

答案

参考答案:

⑴基本结构单元是硅氧四面体(SiO4)和铝氧四面体(AlO4)。

⑵硅氧四面体和铝氧四面体可通过氧原子(氧桥)联结起来形成环。由四个四面体形成一个环就叫四元氧环。以此类推有五元氧环、六元氧环,八元氧环,十元氧环和十二元氧环等。窗口氧环的孔口对通过的分子起筛分作用。

⑶各种不同的环通过氧桥相互联接又可形成三维空间的多面体。各种各样的多面体构成中空的笼,笼进一步相互联接形成分子筛。

阅读理解

阅读理解。

     It was getting late. There was no noise in the forest. We could only hear the birds singing. And then,

a bear-a big brown bear-came into the forest.

     The bear stopped under a tall tree. He was very hungry. He looked up into the tree. There in the nut

tree was his supper-a supper of nice nuts. But the nuts were high up in the tree. The hungry  bear  could

not reach them. But he knew how to get his supper. He climbed up the tree.

     Up and up he climbed. He climbed onto a big branch of the tree. He sat there  and  then shook(摇)

the branch again and again. At last the branch broke. The brown bear fell down  with  the branch  and

nuts.

     The bear sat up and looked around. With his big paws he picked up the nuts and ate them up.

1.How did the brown bear get his supper?                  

A. He climbed up the tree and ate the nuts there.

B. He shook the apples off a tree and ate them.

C. He picked up the nuts on the ground and ate them.

D. He fell down with the branch of the tree. Then he took the nuts and ate them.

2.The bear was         .

A. black        

B. brown    

C. black and white    

D. brown and black

3.The story took place          .

A. in the morning  

B. at noon

C. before evening ca        

D. at midnight

4.The word "branch" in this passage means          in Chinese.

A. 树干        

B. 树叶        

C. 树枝            

D. 树桩

5.Where did the bear eat the nuts?

A. in a forest.  

B. outside the forest.

C. near a forest.  

D. in front of the forest.

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