Perhaps you should try some spelling variations:
sach doi » sach hoi, sach moi, sach dao
doi nang » dai nang, hoi nang, voi nang
quoc ban » quoc bao, quoc lan, quoc quan
cao quoc » cac quoc, cao thuoc, han quoc
tu sach » thu sach, su sach, te sach
hang di » hang doi, hang dien, hang dich
hang vi » hang va, hanh vi, khang voi
cua tuc » cua duc, cua tu, cua thuoc
hieu va » lieu va, hieu qua
dai hoi » dai hoc, dai hai, dai moi
mai hoi » mai khoi, lai hoi, mai doi
va cao » va cac, va co, va dao

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 doi nang ((mai hoi) or (dai hoi)). hieu va cao quoc ban ((hang vi) or (hang di)) cua tuc~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach doi nang ((mai hoi) OR (dai hoi)). hieu va cao quoc ban ((hang vi) OR (hang di)) cua tuc.
• Adding a wildcard symbol may retrieve word variants: tu sach doi nang ((mai hoi) or (dai hoi)). hieu va cao quoc ban ((hang vi) or (hang di)) cua tuc*.