Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
hanh hai » thanh hai, nhanh hai, hang hai
so triet » su triet, so thiet, bo triet
su sach » so sach, vu sach
qua cac » cua cac
cac tuc » cac toc, cac tu, cac tac
tuc van » thuc van, truc van, tuc va
y nang » ky nang, ly nang, v nang
hai so » dai so, tai so, thai son
o hoi » co hoi, o hoc, o hoa
o hai » co hai, so hai, o lai

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 y nang ((o hoi) or (o hai)). hieu qua cac tuc van hanh hai so triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang ((o hoi) OR (o hai)). hieu qua cac tuc van hanh hai so triet.
• Adding a wildcard symbol may retrieve word variants: su sach y nang ((o hoi) or (o hai)). hieu qua cac tuc van hanh hai so triet*.