Perhaps you should try some spelling variations:
hoc viet » hoc hien
ban hanh » ban hang
van hanh » van thanh, van anh, van ban
hieu van » hieu va, thien van, lieu va
tang mai » tang ma, tang tai, lang mai
mai hoi » mai khoi, dai hoi, lai hoi
hieu ve » hieu va
cac tuc » cac toc, cac tu, cac tac
ky tang » ky nang, ky dang, kho tang
xac ky » cac ky, sac ky, bac ky
vi hoc » li hoc, va hoc
su xac » pu xac, su 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 xac ky tang mai hoi. ((hieu ve) OR (hieu van)) cac tuc ((van hanh) or (ban hanh)) vi hoc viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su xac ky tang mai hoi. ((hieu ve) OR (hieu van)) cac tuc ((van hanh) OR (ban hanh)) vi hoc viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su xac ky tang mai hoi. ((hieu ve) OR (hieu van)) cac tuc ((van hanh) or (ban hanh)) vi hoc viet".
• Adding a wildcard symbol may retrieve word variants: su xac ky tang mai hoi. ((hieu ve) OR (hieu van)) cac tuc ((van hanh) or (ban hanh)) vi hoc viet*.