Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
hanh vai » hanh vi, hanh va, hanh tai
van hanh » van thanh, ban hanh, van anh
dang xay » dang van, van xay
cac tac » cac toc, cac bac, cac dac
te sach » toc sach
sach ky » sac ky, sach y, sach ty
dang xa » lang xa, dang ha, dang va
vai va » mai va, dai va, hai va
thiet » thieu

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 ky ((dang xa) OR (dang xay)) hoi. hieu vien ((cac tac) or (dat nuoc)) van hanh vai va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach ky ((dang xa) OR (dang xay)) hoi. hieu vien ((cac tac) OR (dat nuoc)) van hanh vai va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sach ky ((dang xa) OR (dang xay)) hoi. hieu vien ((cac tac) or (dat nuoc)) van hanh vai va thiet".
• Adding a wildcard symbol may retrieve word variants: te sach ky ((dang xa) OR (dang xay)) hoi. hieu vien ((cac tac) or (dat nuoc)) van hanh vai va thiet*.