Perhaps you should try some spelling variations:
vuc nang » cuc nang, vu nang, chuc nang
van hanh » van thanh, ban hanh, van anh
sach vuc » sach duoc, sach nuoc, sach truc
tu sach » thu sach, su sach, te sach
hanh ki » hanh vi, hanh ky, hanh kien
vuc van » duc van, luc van, thuc van
so viet » hoc viet
mai hoi » mai khoi, dai hoi, lai hoi
va cao » va cac, va co, va dao
ma hoi » xa hoi, ma hoa, me hoi
va cam » va cham, va cac, va cai
ki so » khi so, ka so, ki 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 vuc nang ((ma hoi) or (mai hoi)). hieu ((va cam) or (va cao)) vuc van hanh ki so viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach vuc nang ((ma hoi) OR (mai hoi)). hieu ((va cam) OR (va cao)) vuc van hanh ki so viet.
• Adding a wildcard symbol may retrieve word variants: tu sach vuc nang ((ma hoi) or (mai hoi)). hieu ((va cam) or (va cao)) vuc van hanh ki so viet*.