Perhaps you should try some spelling variations:
thien van » thi van
trinh dai » trinh tai, trinh di, trinh da
hieu van » hieu va, lieu va, hieu ve
va trinh » van trinh, va tinh, lap trinh
te sach » toc sach
sach tu » sach thu, cach tu, sach ty
tu hang » thu hang, tu hanh, tu hung
cac dac » cac dan, cac dai, cac bac
cua tre » cua te, cuu tre, cua triet
hang o » hang do, hang o2, hoang o
dac va » duc va, day va, dat va
o hai » co hai, so hai, o lai

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 hai. ((hieu van) or (thien van)) cac dac va trinh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach tu hang o hai. ((hieu van) OR (thien van)) cac dac va trinh dai cua tre.
• Adding a wildcard symbol may retrieve word variants: te sach tu hang o hai. ((hieu van) or (thien van)) cac dac va trinh dai cua tre*.