positv.假定v.安置positivist discipline实证主义学科positronium chemistry正电子素化学positivist criminology实证主义犯罪学positivist sociologist实证主义社会学家positron radioactivity阳电子放射性positivistic sociology实证主义社会学posite sintered compact层状烧结坯positron-decay energy正电子衰变能量positron scintiscanning正电子闪烁扫描positron brain scanning正电子脑扫描