树脂从树皮的裂口自然地流出来.Pitch bleeds freely from break in the bark.有些树产树脂.Some trees afford resin.用于提取这种油的树脂取自于一种矮小坚韧的树。The resin from which the oil is extracted comes from a small, tough tree....
悲观的人,即使走在平坦的大道,也会被小石子绊跌.The pessimist stumbles over pebbles even on a wide and well - paved road.少年人扛磨石, 孩童背木柴,都绊跌了.Young men toil at the millstones; boys stagger under loads of wood.不一会儿他绊跌到捕熊人设的陷阱里.In a moment he stumb...
方法: 用溴代及胺化反应合成了四甲基吡嗪衍生物.METHODS: The target compound was prepared by the bromination and amination reaction.用溴—甲醇溶解Al_2O_3, 其回收率在91%以上.If Al 2 O 3 is dissolved by Br 2 - CH 3 OH, its Recovery rate is above 91 %.用溴比用氯时产出率...