Perhaps you should try some spelling variations:
thuat sach » thuat lanh, thuat san
mai khoi » mai khoa, tai khoa, cac khoi
tu sach » thu sach, su sach, te sach
hanh di » hanh vi, hanh de, hang di
va hanh » van hanh, va thanh, va danh
cac duc » cac du, cao duc, cac dac
qua cac » cua cac
su viet » so viet
mai hoi » dai hoi, lai hoi, mai doi
di su » doi su, ki su, da 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) or (thuat sach)) ty xang ((mai hoi) OR (mai khoi)). hieu qua cac duc va hanh di su viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thuat sach)) ty xang ((mai hoi) OR (mai khoi)). hieu qua cac duc va hanh di su viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (thuat sach)) ty xang ((mai hoi) OR (mai khoi)). hieu qua cac duc va hanh di su viet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (thuat sach)) ty xang ((mai hoi) OR (mai khoi)). hieu qua cac duc va hanh di su viet*.