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烟草中含有多种 ,主要 。烟碱又名 ,是由 、 两种杂环组成的含氮碱。 它不仅可以使红色石蕊变 色 ,还可以使酚酞试剂变 色 ,并可以被 KMnO 4 溶液氧化生成 ,与 试剂 作用产生沉淀。 烟碱能与 结合生成烟碱盐酸盐而溶于水中,在此提取液中加入 后,可使烟碱游离出来。游离烟碱在 °C 左右具有一定的蒸气压。因此,可利用 法 分离提取。
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【单选题】—Who is Ren Changxia? —A great policewoman. She always thought _____ of others than of herself. [ ]
A.
more
B.
much
C.
less
D.
most
【简答题】Those who enjoy total may not find themselves happy.
【简答题】Mr White works in an office. He liked reading in bed when he was at school. It was bad for his 41 and now he has near sight (近视). But he wouldn’t want 42 to know about it and he never wears a pair of ...
【多选题】关于生态规划方法之一的“多目标规划法”,下列说法不准确:
A.
多目标规划法是运筹学的一个重要分支，它是在线性规划的基础上，为解决多目标决策问题而发展起来的一种科学管理的数学方法。
B.
多目标规划法是研究与分析一个系统 ( 或模型 ) 的状态或输出变化对系统参数或周围条件变化的敏感程度的方法。
C.
多目标规划法是通过分析社会经济系统内部各变量之间的结构关系来研究系统整体行为的理论，用于地区和国家级规划模型。
D.
多目标规划法是通过分析经济与环境之间的关系来研究系统整体行为的理论。
【单选题】-Who is Ren Changxia? -A great policewoman. She always thought ________ of others than herself. [ ]
A.
much
B.
more
C.
less
D.
most
【简答题】Mr White works in an office. He liked reading in bed when he was at school. It was bad for his 1 and now he has near sight (近视) . But he wouldn’t want 2 to know about it and he never wears a pair of g...
【简答题】Mr. White works in an office. He liked reading in bed when he was at school. It was bad for his eyes and now he is near-sighted. But he wouldn’t want anybody else to know about it and he never wears a...
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