Perhaps you should try some spelling variations:
tham thuc » nham thuc, pham thuc, tam thuc
may thoi » gay thoi, may thi, tay thoi
thuc ban » thuoc ban, thuc dan, thu ban
ban hang » ngan hang
hang vai » hang va, hang tai, hang hai
cua viet » ca viet, hoa viet, cua vat
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
ky mang » ky nang, ke mang, ky dang
may hoi » tay hoi, mai hoi, may hmi
hieu va » lieu va, hieu qua
va tham » van tham, va cham, va thanh
vai cua » dai cua, hai cua, lai cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky mang ((may hoi) or (may thoi)). hieu va tham thuc ban hang vai cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky mang ((may hoi) OR (may thoi)). hieu va tham thuc ban hang vai cua viet.
• Adding a wildcard symbol may retrieve word variants: tu sach ky mang ((may hoi) or (may thoi)). hieu va tham thuc ban hang vai cua viet*.