Perhaps you should try some spelling variations:
cam thuc » am thuc, cam thu, can thuc
hanh vai » hanh vi, hanh va, hanh tai
nam thuc » nam thuoc, am thuc, nam thu
nang mai » nang ma, nang tai, lang mai
mai khoi » mai khoa, tai khoa, cac khoi
so sach » so sanh, co sach, hoc sach
va hanh » van hanh, va thanh, va danh
hieu ve » hieu va, hieu van
va nang » van nang, da nang, cam nang
bo sach » co sach, hoc sach
vai hoa » van hoa, va hoa, dai hoa

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) or (bo sach)) va nang mai khoi. hieu ve ((cam thuc) OR (nam thuc)) va hanh vai hoa viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((so sach) OR (bo sach)) va nang mai khoi. hieu ve ((cam thuc) OR (nam thuc)) va hanh vai hoa viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((so sach) or (bo sach)) va nang mai khoi. hieu ve ((cam thuc) OR (nam thuc)) va hanh vai hoa viet".
• Adding a wildcard symbol may retrieve word variants: ((so sach) or (bo sach)) va nang mai khoi. hieu ve ((cam thuc) OR (nam thuc)) va hanh vai hoa viet*.