Perhaps you should try some spelling variations:
cua viet » ca viet, hoa viet, cua vat
ban hang » ngan hang
thuc ban » thuoc ban, thuc dan, thu ban
cau thuc » cau truc, cuu thuc, can thuc
hieu van » hieu va, thien van, lieu va
sach ky » sac ky, sach y, sach ty
van cau » van dau, van hau, van chat
tang ma » tang van
cua tre » cua te, cuu tre, cua triet
su sach » so sach, vu sach

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 ((tang ma) OR (mang may)) hoi. hieu van cau thuc ban hang va ((cua tre) or (cua viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky ((tang ma) OR (mang may)) hoi. hieu van cau thuc ban hang va ((cua tre) OR (cua viet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky ((tang ma) OR (mang may)) hoi. hieu van cau thuc ban hang va ((cua tre) or (cua viet))".
• Adding a wildcard symbol may retrieve word variants: su sach ky ((tang ma) OR (mang may)) hoi. hieu van cau thuc ban hang va ((cua tre) or (cua viet))*.