Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
vien dai » hien dai
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
toc van » toc san, tac van, oc van
hoc van » hoc dan, hoc va, hoc vat
su tien » su kien, su hien, tu tieng
x hoi » xa hoi, o hoi, 5 hoi
vi su » va su, ve su, ki su

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ky nang ((x hoi) or (x ho)). hieu vien dai ((toc van) OR (hoc van)) hanh vi su tien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang ((x hoi) OR (x ho)). hieu vien dai ((toc van) OR (hoc van)) hanh vi su tien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky nang ((x hoi) or (x ho)). hieu vien dai ((toc van) OR (hoc van)) hanh vi su tien".
• Adding a wildcard symbol may retrieve word variants: su sach ky nang ((x hoi) or (x ho)). hieu vien dai ((toc van) OR (hoc van)) hanh vi su tien*.