Perhaps you should try some spelling variations:
nam thuc » nam thuoc, am thuc, nam thu
sang mai » sang ma, sang tai, lang mai
thuc va » thuc vat, thuc dan, thuc day
va viet » hoa viet, san viet, mai viet
ca viet » hoa viet, san viet, mai viet
va hanh » van hanh, va thanh, va danh
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
mai hoi » mai khoi, dai hoi, lai hoi
ky sang » ky nang, ky dang, ky tang
co viet » so viet, o viet, hoc viet
ve nam » he nam, va nam, le nam

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 ky sang mai hoi. hieu ve nam thuc va hanh vi ((((ca viet) OR (va viet))) or (co viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky sang mai hoi. hieu ve nam thuc va hanh vi ((((ca viet) OR (va viet))) OR (co viet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky sang mai hoi. hieu ve nam thuc va hanh vi ((((ca viet) OR (va viet))) or (co viet))".
• Adding a wildcard symbol may retrieve word variants: su sach ky sang mai hoi. hieu ve nam thuc va hanh vi ((((ca viet) OR (va viet))) or (co viet))*.