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