density step灰度等级densityn.密度；浓度；比重density temperature coefficient密度温度系数density-dependent competition密度制约竞争density of network of waterways河网密度density gradient centrifugation密度梯度离心,密度梯度离心分离法,密度梯度离心法density vertical representation密度函数垂直表示density-strength relationship密度与强度关系density of residential building居住建筑面积密度Density gradient centrifigation密度梯度离心Density based hierarchical tree密度树density-tapered array antenna密度递减阵天线