Perhaps you should try some spelling variations:
thanh vai » thanh hai, thanh van, thanh tai
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
duc van » duc tan, duc manh, duc phan
vai cua » dai cua, hai cua, lai cua
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
va bao » va bai
x hoi » xa hoi, o hoi, 5 hoi

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 y nang ((x hoi) or (x ho)). hieu va bao ((duc van) OR (duc va)) thanh vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang ((x hoi) OR (x ho)). hieu va bao ((duc van) OR (duc va)) thanh vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang ((x hoi) or (x ho)). hieu va bao ((duc van) OR (duc va)) thanh vai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang ((x hoi) or (x ho)). hieu va bao ((duc van) OR (duc va)) thanh vai cua tre*.