Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
mai khoi » mai khoa, tai khoa, cac khoi
thu sach » thuat sach, thuoc sach, thu hoach
hanh vai » hanh vi, hanh va, hanh tai
vien cac » vien bach, vien dai, vien da
vai cua » dai cua, hai cua, lai cua
va hanh » van hanh, va thanh, va danh
cac luc » cau luc, coc luc, cac nuoc
tu sach » su sach, te sach, tu cach
mai hoi » dai hoi, lai hoi, mai doi
cua tre » cua te, cuu tre, cua triet
luc va » duc va, tuc va, loc va

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 (thu sach)) ky nang ((mai hoi) OR (mai khoi)). hieu vien cac luc va hanh vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu sach)) ky nang ((mai hoi) OR (mai khoi)). hieu vien cac luc va hanh vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (thu sach)) ky nang ((mai hoi) OR (mai khoi)). hieu vien cac luc va hanh vai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (thu sach)) ky nang ((mai hoi) OR (mai khoi)). hieu vien cac luc va hanh vai cua tre*.