filtermask过滤式防毒面具filtern.过滤器；滤色镜；滤光器v.过滤；渗透filter of graded density分级比重过滤Filter bag dust removing布袋除尘filtered Possion process过滤泊松过程filter-ponding control滤池积水控制filter leaf for residual残液过滤叶片filter-type respirator过滤式口罩filter back-projection滤波反投影filtering medium of sand砂滤料Filter out impurities.滤除杂质filter backwashing water滤池反冲水