Perhaps you should try some spelling variations:
thanh dai » thanh hai, thanh tai, thanh dat
hieu van » hieu va, thien van, lieu va
quoc ban » quoc bao, quoc quan, quoc binh
quoc lan » nuoc luan, quoc quan, quoc danh
su sach » vu sach
so sach » so sanh, bo sach, co sach
xang xa » lang xa, mang xa, ang xa
van cau » van dau, van hau, van chat
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((su sach) or (so sach)) ty xang xa hoi. hieu van cau ((quoc ban) OR (quoc lan)) thanh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (so sach)) ty xang xa hoi. hieu van cau ((quoc ban) OR (quoc lan)) thanh dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (so sach)) ty xang xa hoi. hieu van cau ((quoc ban) OR (quoc lan)) thanh dai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((su sach) or (so sach)) ty xang xa hoi. hieu van cau ((quoc ban) OR (quoc lan)) thanh dai cua tre*.