effective way有效方法effectiveadj.有效的；生效的；实际的effective picture area有效图像面积effective scale length有效刻度长effective orifice area有效孔区effective machine time有效工作时间effective stack height烟囱有效高度effective width method有效宽度法effective earth radius有效地球半径effective current flow有效电流effective intervention有效干预effective-pure state有效纯态