Perhaps you should try some spelling variations:
thanh do » thanh de, thanh pho, thanh hoa
thanh di » thanh doi, thanh de, thanh dinh
te sach » toc sach
cac loc » cac lop, cac toc, cac hoc
hieu va » lieu va, hieu qua
mai hoi » mai khoi, lai hoi, mai doi
dai hoi » dai hoc, dai hai, dai moi
cua tre » cua te, cuu tre, cua triet
sach 7 » sach y, sach 2
loc va » hoc va, luc va
7 tang » 6 tang

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 7 tang ((mai hoi) OR (dai hoi)). hieu va cac loc va ((thanh di) or (thanh do)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach 7 tang ((mai hoi) OR (dai hoi)). hieu va cac loc va ((thanh di) OR (thanh do)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sach 7 tang ((mai hoi) OR (dai hoi)). hieu va cac loc va ((thanh di) or (thanh do)) cua tre".
• Adding a wildcard symbol may retrieve word variants: te sach 7 tang ((mai hoi) OR (dai hoi)). hieu va cac loc va ((thanh di) or (thanh do)) cua tre*.