Perhaps you should try some spelling variations:
hieu suat » hieu luat, hieu qua
cham duc » pham duc, cham soc, pham duy
toc sach » hoc sach, doc sach, thuoc sach
cua viet » ca viet, hoa viet, cua vat
tang mai » tang ma, tang tai, lang mai
mai hoi » mai khoi, dai hoi, lai hoi
hieu su » hieu sau, tieu su, hieu so
sach ty » sach y, sach tu, sach thu
ty tang » tay tang, ty xang, ty hang
hanh va » hang va

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ty tang mai hoi. ((hieu su) or (hieu suat)) cham duc va ((hanh va) or (hanh vi)) cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty tang mai hoi. ((hieu su) OR (hieu suat)) cham duc va ((hanh va) OR (hanh vi)) cua viet.
• Adding a wildcard symbol may retrieve word variants: toc sach ty tang mai hoi. ((hieu su) or (hieu suat)) cham duc va ((hanh va) or (hanh vi)) cua viet*.