The main reservoir of nitrogen is the atmosphere. 氮的主要蓄存库是大气层。
After harvesting the crops, he tested them for nitrogen content. 作物收获后，他测定了作物中氮的含量。
They contain nitrogen and usually occur as salts of asids such as citric, malic, and succinic acids such as citric, malic, and succinic acids. 它们是一类含氮的，一般由酸性盐如柠檬酸，苹果酸，琥珀酸所形成。
