Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
vien cac » vien bach, vien dai, vien da
xa dong » ha dong, van dong, lao dong
xa nong » xuat nong, may nong, cua nong
cac tac » cac toc, cac bac, cac dac
tu sach » thu sach, su sach, te sach
ky tang » ky nang, ky dang, kho tang
ky lang » ky nang, ky dang, tay lang
doi hoa » doi hoac, doi hoat, do hoa

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ky lang) OR (ky tang)) xa hoi. hieu vien cac tac ((xa nong) OR (xa dong)) doi hoa viet~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ky lang) OR (ky tang)) xa hoi. hieu vien cac tac ((xa nong) or (xa dong)) doi hoa viet~".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ky lang) OR (ky tang)) xa hoi. hieu vien cac tac ((xa nong) or (xa dong)) doi hoa viet*.