Perhaps you should try some spelling variations:
su triet » su viet, su tien, ve triet
van hanh » van thanh, ban hanh, van anh
vuc nang » cuc nang, chuc nang, van nang
hanh ki » hanh vi, hanh ky, hanh kien
duc van » duc va, duc tan, duc manh
tu sach » thu sach, su sach, te sach
mai hoi » mai khoi, dai hoi, lai hoi
vu nang » va nang, vu dang, v nang
va cam » va cham, va cao, va cai
ki su » ky su

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ((vu nang) OR (vuc nang)) mai hoi. hieu ((va cam) or (va cac)) duc van hanh ki su triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((vu nang) OR (vuc nang)) mai hoi. hieu ((va cam) OR (va cac)) duc van hanh ki su triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((vu nang) OR (vuc nang)) mai hoi. hieu ((va cam) or (va cac)) duc van hanh ki su triet".
• Adding a wildcard symbol may retrieve word variants: tu sach ((vu nang) OR (vuc nang)) mai hoi. hieu ((va cam) or (va cac)) duc van hanh ki su triet*.