Perhaps you should try some spelling variations:
doanh dan » doanh ban, doanh van, doanh dao
va doanh » van doanh, vay doanh, va danh
tu sach » thu sach, su sach, te sach
vu cham » vu kham, tu cham, qua cham
dan cua » dan ca, ban cua, dai cua
cua tre » cua te, cuu tre, cua triet
va cham » va chat, va tham
y tang » ky tang, 6 tang, 7 tang
luc va » duc va, tuc va, loc va
ma hoi » mai hoi, ma hoa, me hoi

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: tu sach y tang ((ma hoi) OR (xa hoi)). hieu ((va cham) OR (vu cham)) luc va doanh dan cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y tang ((ma hoi) OR (xa hoi)). hieu ((va cham) or (vu cham)) luc va doanh dan cua tre~".
• Adding a wildcard symbol may retrieve word variants: tu sach y tang ((ma hoi) OR (xa hoi)). hieu ((va cham) or (vu cham)) luc va doanh dan cua tre*.