她撕下两格纸巾，然后纵向对折。She tore off two sections of paper towel and folded them lengthwise.他把那沓纸揉得嚓嚓响。He crunched the sheets of paper in his hands.她拿起一张纸，把它哗哗啦啦地塞到打字机中。She took up a sheet and ratcheted it into the typewriter....
氨的合成主要经过四道工序.There are four major steps in ammonia synthesis.试计算氮在尿素及硫酸氨的质量百分率.Calculate the percentage by mass of nitrogen in urea and ammonium sulphate.这种肥料经过化验表明氨的含量很高.Tests of the manure showed a high ammonia content...