gravel bed短语¹¹⁴⁴⁶⁷⁺⁴ 基本例句 机砂砾层 The results show that the aerodynamic roughness length of gravel bed is a function of gravel size, coverage, free velocity, friction velocity and the atmospheric stratification stability; 得出以下结论：戈壁风蚀面上空气动力学粗糙度长度与砾石粒径、高度、覆盖度、自由风速、摩擦速度以及大气层结稳定度有关； cnki