利用液体各组分在溶剂中溶解度的差异,从而分离混合物的单位操作称为()。
参考答案:萃取
No wonder he looks tired! He's been studying for the exams all week, ____ he's been working in a bar
at night. [ ]
A. while
B. but
C. plus
D. as
计算题:有一伤损在100mm声程处的伤波比120mm声程φ3横孔反射波高5dB,求其当量横孔直径。