Perhaps you should try some spelling variations:
thanh doi » thanh loi, thanh moi, thanh do
thi hang » thi hanh, thi nang, thi hong
hieu van » hieu va, thien van, hieu ve
sach thi » sach thu, sach tai, sach thieu
thanh di » thanh de, thanh do, thanh dinh
te sach » toc sach
cac luc » cau luc, coc luc, cac nuoc
cua tre » cua te, cuu tre, cua triet
luc va » duc va, tuc va, loc va
hang o » hang do, hang o2, hoang o
o hoi » co hoi, o hoc, o hai

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