Perhaps you should try some spelling variations:
ban thanh » ban hanh, ban hang
hieu van » hieu va, thien van, lieu va
toc sach » hoc sach, doc sach, thuoc sach
va thanh » gia thanh, va tinh, le thanh
cac duc » cac du, cao duc, cac dac
van cac » van hac, van cau, van bac
ty hang » ly hang, ty xang, thi hang
cua tre » cua te, cuu tre, cua triet
hang x » nang x, hoang xa, chang xu
x hoi » xa hoi, o hoi, x ho

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

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