Perhaps you should try some spelling variations:
thanh dai » thanh hai, thanh tai, thanh dat
doc sach » hoc sach, toc sach, nuoc sach
mai khoi » mai khoa, tai khoa, cac khoi
truc va » thuc va, trung va
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
va cam » va cham, va cac, va cao
ma hoi » mai hoi, xa hoi, ma hoa

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

• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach y nang ((ma hoi) OR (mai khoi)). hieu va cam ((truc va) OR (thuc vat)) thanh dai cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach y nang ((ma hoi) or (mai khoi)). hieu va cam ((truc va) OR (thuc vat)) thanh dai cua tre~".
• Adding a wildcard symbol may retrieve word variants: doc sach y nang ((ma hoi) or (mai khoi)). hieu va cam ((truc va) OR (thuc vat)) thanh dai cua tre*.