Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
kho tang » cao tang
vien cac » vien bach, vien dai, vien da
te sach » toc sach
cac duc » cac du, cao duc, cac dac
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cua triet, dua tren
cuu tre » cau tren, cau treo
ma hoi » mai hoi, xa hoi, ma hoa

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 ((kho tang) or (ky nang)) ma hoi. hieu vien cac duc va hanh vi ((cua tre) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach ((kho tang) OR (ky nang)) ma hoi. hieu vien cac duc va hanh vi ((cua tre) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: te sach ((kho tang) or (ky nang)) ma hoi. hieu vien cac duc va hanh vi ((cua tre) or (cuu tre))*.