向下向上焊
welding upward and downward
纵向参照坐标的民族性
vertical reference to nationalism
凹向下的
concave downward
concave downward‘ concave down
保持定向参数变换
orientation preserving parameter transformation
船舶纵向下水
ship end launching
ship longitudinal launching
longitudinal vessel launching
单向下行展开
unidimensional descending development