Perhaps you should try some spelling variations:
ban thanh » ban hanh, ban hang
sach van » sach han, sach va, bach van
van nang » van quang, van ban, van dong
va thanh » gia thanh, va tinh, le thanh
so sach » so sanh, bo sach, co sach
hieu he » hieu ve, hiem he, hieu le
lai roi » lai hoi, loi roi
mai hoi » mai khoi, dai hoi, lai hoi
vai hoa » van hoa, va hoa, dai hoa
he nam » ha nam, nghe nam

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach van nang ((mai hoi) or (lai roi)). hieu he nam thu ((va thanh) OR (ban thanh)) vai hoa viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach van nang ((mai hoi) OR (lai roi)). hieu he nam thu ((va thanh) OR (ban thanh)) vai hoa viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach van nang ((mai hoi) or (lai roi)). hieu he nam thu ((va thanh) OR (ban thanh)) vai hoa viet".
• Adding a wildcard symbol may retrieve word variants: so sach van nang ((mai hoi) or (lai roi)). hieu he nam thu ((va thanh) OR (ban thanh)) vai hoa viet*.