usefullyadv.有用地usefuladj.有用的；有益的；实用的useful connected set有效连通集usefulness of English用途useful receiver power接收机有用功率useful in agriculture在农业方面有用的useful seam thickness可采层厚度useful detection area有效探测面积(γ照相机的)useful life longevity使用耐久性usefulness of studies读书无用论useful exposure range有效曝光范围usefulness of earnings盈余有用性