density step灰度等级densityn.密度；浓度；比重density of an electron beam电子束密度density function estimation密度函数估计density dependent mortality密度制约死亡率, 密度依赖死亡率density gradient separation密度梯度分离法density determination phial[医] 密度测定瓶density evolution algorithm密度演变算法density of rock fill object堆石体密度density of charging current充电电流密度Density of pipeline crunodes管线点密度density dependent regulation密度制约调节作用