Perhaps you should try some spelling variations:
can thiet » dan thiet, cac thiet, cad thiet
ban hanh » ban hang
luc sang » lam sang, luc canh, duy sang
va danh » va dinh, va dan, va hanh
dau luc » cau luc, dau luan, dau nuoc
so sach » so sanh, bo sach, co sach
lo sang » lam sang, cao sang, lee sang
hieu va » lieu va, hieu qua
ma hoi » mai hoi, xa hoi, ma hoa
va dau » va dao
vi can » voi can, vi van, i can

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 ((lo sang) or (luc sang)) ma hoi. hieu va dau luc ((va danh) or (ban hanh)) vi can thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ((lo sang) OR (luc sang)) ma hoi. hieu va dau luc ((va danh) OR (ban hanh)) vi can thiet.
• Adding a wildcard symbol may retrieve word variants: so sach ((lo sang) or (luc sang)) ma hoi. hieu va dau luc ((va danh) or (ban hanh)) vi can thiet*.