Perhaps you should try some spelling variations:
sang mai » sang ma, sang tai, lang mai
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, am thuc, nam thu
hanh vit » hanh vi, danh viet, hanh tiet
so sach » so sanh, bo sach, co sach
sach ky » sac ky, sach y, sach ty
ky sang » ky nang, ky dang, ky tang
mai hoi » mai khoi, dai hoi, lai hoi
hieu ve » hieu va
thuc va » thuc vat, thuc dan, thuc day
va hanh » van hanh, va thanh, va danh
vit hoa » viet hoan

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 sang mai hoi. ((hieu ve) or (hieu van)) nam thuc va hanh vit hoa viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ky sang mai hoi. ((hieu ve) OR (hieu van)) nam thuc va hanh vit hoa viet.
• Adding a wildcard symbol may retrieve word variants: so sach ky sang mai hoi. ((hieu ve) or (hieu van)) nam thuc va hanh vit hoa viet*.