短語詞組短語background d concentration 背景濃度background sediment concentration 背景含沙量background ion concentration 本底離子濃度background equivalent concentration 本底等效濃度;背景當(dāng)量濃度background concentration of tracer 示蹤劑背景濃度co background concentration co ＿2背景濃度natural background concentration 自然背景濃度atmospheric co background concentration 大氣coco 2 background concentration co 本底濃度 返回 background concentration