题目内容

液相色谱分析中对色谱峰扩展的影响可以忽略不计的是( )。

A. 涡流扩散项;
B. 分子扩散项;
C. 传质扩散项;
D. 柱压效应。

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在液相色谱中,提高色谱柱柱效的最有效的途径是( )。

A. 减小填料粒度;
B. 适当升高柱温;
C. 降低流动相的流速;
D. 增大流动相的流速。

在液相色谱中,为了改变柱子的选择性,可以进行下列哪种操作。( )

A. 改变柱长;
B. 改变填料粒度;
C. 改变流动相或固定相种类;
D. 改变流动相的流速。

Focusing on the main ideas and complete the following paragraph with key information from the text.One day, at the registrar’s office of a college, I noticed how parents are behaving with their college-age children nowadays. Obviously students are young1 and can handle registration by2 , but their parents completely3 the situation. In a seminar for teaching assistants, I was surprised to hear that parents often go to their office to4 about marks and assignments their children have got. What I have seen and heard has left me feeling 5. Unlike my parents allowing me to make6 in my life, parents of today’s college students seem never to give their children a chance to take7 .

以下是元素作用的是()。

A. 该元素用来定义文档类型
B. 该元素用来声明命名空间
C. 该元素用来向搜索引擎声明网站关键字
D. 该元素用来向搜索引擎声明网站