Perhaps you should try some spelling variations:
hieu luat » hieu qua
hieu vuc » hieu luc, hieu tuc, hieu thuc
hanh tai » thanh tai, hang tai, han tai
van nang » van quang, van ban, van dong
so sach » so sanh, bo sach, co sach
va hanh » van hanh, va thanh, va danh
va viet » hoa viet, san viet, mai viet
ma hoi » mai hoi, xa hoi, ma hoa
luc va » duc va, tuc va, loc va
v nang » va nang, vu nang, voi nang
tai va » thai va, mai va, tri va

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ((v nang) OR (van nang)) ma hoi. ((hieu vuc) or (hieu luat)) nang luc va hanh tai va viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ((v nang) OR (van nang)) ma hoi. ((hieu vuc) OR (hieu luat)) nang luc va hanh tai va viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ((v nang) OR (van nang)) ma hoi. ((hieu vuc) or (hieu luat)) nang luc va hanh tai va viet".
• Adding a wildcard symbol may retrieve word variants: so sach ((v nang) OR (van nang)) ma hoi. ((hieu vuc) or (hieu luat)) nang luc va hanh tai va viet*.