Perhaps you should try some spelling variations:
su triet » su viet, su tien, ve triet
luoc van » luoc can, luoc va, luot van
mai khoi » mai khoa, tai khoa, cac khoi
hanh ki » hanh vi, hanh ky, hanh kien
luc van » luu van, duc van, luc va
tu sach » thu sach, su sach, te sach
sach vu » sach va, sach tu, sach uu
mai hoi » dai hoi, lai hoi, mai doi
vu nang » vuc nang, va nang, vu dang
hieu va » lieu va, hieu qua
va cao » va cac, va co, va dao
ki su » ky su

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach vu nang ((mai hoi) OR (mai khoi)). hieu va cao ((luc van) or (luoc van)) hanh ki su triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach vu nang ((mai hoi) OR (mai khoi)). hieu va cao ((luc van) OR (luoc van)) hanh ki su triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach vu nang ((mai hoi) OR (mai khoi)). hieu va cao ((luc van) or (luoc van)) hanh ki su triet".
• Adding a wildcard symbol may retrieve word variants: tu sach vu nang ((mai hoi) OR (mai khoi)). hieu va cao ((luc van) or (luoc van)) hanh ki su triet*.