Perhaps you should try some spelling variations:
sach ky » sac ky, sach ty, sach kem
qua bac » qua ban, qua cac, cua bac
mai hoi » mai khoi, dai hoi, lai hoi
cua tre » cua te, cuu tre, cua triet
ma hoi » xa hoi, ma hoa, me hoi
va anh » van anh, va danh, va hanh
anh va » hanh va
va cua » va chua, via cua, ca cua
bo va » bao va, do va, so 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 ky) OR (sach y)) nang ((ma hoi) or (mai hoi)). hieu qua bac bo va anh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so ((sach ky) OR (sach y)) nang ((ma hoi) OR (mai hoi)). hieu qua bac bo va anh va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so ((sach ky) OR (sach y)) nang ((ma hoi) or (mai hoi)). hieu qua bac bo va anh va cua tre".
• Adding a wildcard symbol may retrieve word variants: so ((sach ky) OR (sach y)) nang ((ma hoi) or (mai hoi)). hieu qua bac bo va anh va cua tre*.