Air is made up of three main types of gases: oxygen, carbon dioxide, and nitrogen.
空气是成立的三种主要类型的气体：氧，二氧化碳和氮。
Three types of N? chloroacetyl substituted nitrogen? containing benzoheterocycles were introduced into pyrimidine by the formation of thioether.
三种n-氯乙酰取代的苯并含氮杂环化合物通过硫醚键的形成被导入嘧啶结构。
Total nitrogen contents of surface soil in three forest types changed with seasons distinctly, and overall extents were not big.
三个林型表层土壤全氮含量季节变化规律明显不同，总体变化幅度都不大。
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