Perhaps you should try some spelling variations:
su sach » so sach, vu sach
va hanh » van hanh, va thanh, va danh
cac luc » cau luc, coc luc, cac nuoc
sach ty » sach y, sach tu, sach thu
hieu ve » hieu va, hieu van
su viet » so viet
cao hoc » co hoc, cho hoc, chat hoc
cao hoi » cau hoi, co hoi, tao hoi
ty nang » ky nang, ty xang, ty hang
va dan » ca dan, va dao, va dau
hoi su » hoi suc, khoi su, thoi su
ve cac » va cac, vien cac

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 ty nang ((cao hoi) OR (cao hoc)). hieu ve cac luc ((va hanh) or (va dan)) hoi su viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ty nang ((cao hoi) OR (cao hoc)). hieu ve cac luc ((va hanh) OR (va dan)) hoi su viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ty nang ((cao hoi) OR (cao hoc)). hieu ve cac luc ((va hanh) or (va dan)) hoi su viet".
• Adding a wildcard symbol may retrieve word variants: su sach ty nang ((cao hoi) OR (cao hoc)). hieu ve cac luc ((va hanh) or (va dan)) hoi su viet*.