Perhaps you should try some spelling variations:
su sach » so sach, vu sach
sach yu » sach y, sach tu, sach uu
yu wang » yun wang, yi wang, yu hang
mai hoi » mai khoi, dai hoi, lai hoi
qua cac » cua cac
cac loc » cac lop, cac toc, cac hoc
hanh va » hanh vi
loc va » hoc va, luc va

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 yu wang ((mai hoi) or (ma hoa)). hieu qua cac loc va ((hanh va) OR (hang va)) hoa viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach yu wang ((mai hoi) OR (ma hoa)). hieu qua cac loc va ((hanh va) OR (hang va)) hoa viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach yu wang ((mai hoi) or (ma hoa)). hieu qua cac loc va ((hanh va) OR (hang va)) hoa viet".
• Adding a wildcard symbol may retrieve word variants: su sach yu wang ((mai hoi) or (ma hoa)). hieu qua cac loc va ((hanh va) OR (hang va)) hoa viet*.