问题 问答题

什么是氢化物原子荧光法原理?

答案

参考答案:

待测元素(As、Sb、Bi、Ge,Sn、Pb、Se、,TE.等元素与还原剂硼氢化钠等发生反应时,可形成气态氢化物,生成的氢化物在常温下为气态,借助载气流导入原子化器中。原子荧光是原子蒸气受具有特征波长的光源照射后,其中一些自由原子被激发跃迁到较高能态,然后去活化回到某一较低能态(常常是基态)而发射出特征光谱的物理现象。各种元素都有其特定的原子荧光光谱,根据原子荧光强度的高低可测得试样中待测元素含量。

单项选择题
阅读理解

阅读理解。

     Today it seems perfectly natural for us to shake hands when we greet someone or say goodbye. But like

so many things that we do without thinking such actions at one time probably represented something.

     For example, in primitive (原始的) life the hand was used to fight enemies, kill animals, and make spears

and tools. So when the hand was extended to someone, it showed that the person was not armed or ready for

fight.

     We know that the hand was an important symbol in early religion, probably as a mark of power. The

Greeks prayed to their gods with raised hands. Presenting the hands palm to palm was at one time the way

an inferior (身份低的) person paid respect to a superior(身份高的) one.

     Among the Arabs, it was customary at one time to kiss the hand of a superior. Later on, polite Arabs

began to resist the efforts of people to kiss their hands, and sometimes they would end up shaking hands as

each tried to prevent the other from showing this mark of"inferiority (下级)."

     The early Greeks held out the right hand when they wished to show friendship to a stranger. So we can

see that the hand, and what was done with it, was full of meaning to people down through the ages. And

while we shake hands without thinking, we are really carrying on a custom that has been handed down to us

from ancient times.

1. The second paragraph tells us ________.

A. the handshake didn't mean greeting

B. what hands were used to do in primitive life

C. the handshake showed men's kindness

D. the handshake showed nothing

2. Human beings first made their living by ________.

A. hunting

B. fishing

C. hand

D. farming

3. Among the Arabs, at one time, ________.

A. people kissed each other whenever they met

B. men kissed the women whenever they met

C. less important person kissed more important person's hand

D. more important person kissed less important person's hand

4. Generally speaking, in different countries ________.

A. people shake hands in the same way

B. handshake has different meanings

C. strangers never have handshake

D. people only use handshake to show friendship

5. The phrase " hand down" in the last sentence means ________.

A. put down

B. leave down

C. give down

D. pass down