Perhaps you should try some spelling variations:
thien van » thi van
trinh dai » trinh tai, trinh di, trinh da
va trinh » van trinh, va tinh, lap trinh
hieu van » hieu va, lieu va, hieu ve
cua tre » cua te, cua triet, dua tren
cac duc » cac du, cao duc, cac dac
te sach » toc sach
sach tu » sach thu, cach tu, sach ty
tu hang » thu hang, tu hanh, tu hung
cuu tre » cau tren, cau treo
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 tu hang o hoi. ((hieu van) or (thien van)) cac duc va trinh dai ((cua tre) OR (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach tu hang o hoi. ((hieu van) OR (thien van)) cac duc va trinh dai ((cua tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sach tu hang o hoi. ((hieu van) or (thien van)) cac duc va trinh dai ((cua tre) OR (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: te sach tu hang o hoi. ((hieu van) or (thien van)) cac duc va trinh dai ((cua tre) OR (cuu tre))*.