Perhaps you should try some spelling variations:
nam thuc » nam thuoc, nam thu, nam tu
dan manh » dang manh, doan manh, van manh
vai cua » dai cua, hai cua, lai cua
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
vai ca » vai cac, bai ca, vai va
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai

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 nang o hoi. hieu ve ((nam thuc) OR (am thuc)) dan manh ((vai ca) or (vai cua)) viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang o hoi. hieu ve ((nam thuc) OR (am thuc)) dan manh ((vai ca) OR (vai cua)) viet*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang o hoi. hieu ve ((nam thuc) OR (am thuc)) dan manh ((vai ca) or (vai cua)) viet*".