Perhaps you should try some spelling variations:
sach thi » sach thu, sach tai, sach thieu
thi hang » thi hanh, thi nang, thi hong
te sach » toc sach
cua tre » cua te, cua triet, dua tren
hanh di » hanh vi, hanh de, hang di
cuu tre » cau tren, cau treo
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
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 ve cac ((duc tan) or (duc va)) hanh di ((cua tre) OR (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach thi hang o hoi. hieu ve cac ((duc tan) OR (duc va)) hanh di ((cua tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sach thi hang o hoi. hieu ve cac ((duc tan) or (duc va)) hanh di ((cua tre) OR (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: te sach thi hang o hoi. hieu ve cac ((duc tan) or (duc va)) hanh di ((cua tre) OR (cuu tre))*.