Perhaps you should try some spelling variations:
ban thanh » ban hanh, ban hang
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, nam thu, nam tu
thanh vi » hanh vi, thanh va, thanh ve
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai
khach » khac, khanh
thiet » thieu

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

• Performing a fuzzy search may retrieve terms with similar spellings: vay khach y nang o hoi. hieu van ((nam thuc) OR (am thuc)) ban thanh vi ((cua tre) or (va thiet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vay khach y nang o hoi. hieu van ((nam thuc) OR (am thuc)) ban thanh vi ((cua tre) OR (va thiet))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "vay khach y nang o hoi. hieu van ((nam thuc) OR (am thuc)) ban thanh vi ((cua tre) or (va thiet))*".