Perhaps you should try some spelling variations:
nam thuc » nam thuoc, am thuc, nam thu
mai khoi » mai khoa, tai khoa, cac khoi
vu sach » vu bach, su sach, vu khach
ca viet » va viet, hoa viet, san viet
va hanh » van hanh, va thanh, va danh
thuc va » thuc vat, thuc dan, thuc day
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
mai hoi » dai hoi, lai hoi, mai doi
ky sang » ky nang, ky dang, ky tang
co viet » so viet, o viet, hoc viet
va nam » van nam, ha nam, va nay

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

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