Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
truc van » truc va, thuc van, truc ban
so sach » so sanh, bo sach, hoc sach
hanh ve » hanh vi, hanh va, hanh kem
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
co sach » bo sach, cuon sach, hoc sach
ve cau » ke cau, va cau, ve cac
ve cua » le cua, de cua, te cua
o hoi » co hoi, o hai, o hoa
o hoc » co hoc, mo hoc, so hoc

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 (co sach)) van dong ((o hoi) or (o hoc)). hieu ve cau truc van hanh ve cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((so sach) OR (co sach)) van dong ((o hoi) OR (o hoc)). hieu ve cau truc van hanh ve cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((so sach) OR (co sach)) van dong ((o hoi) or (o hoc)). hieu ve cau truc van hanh ve cua tre".
• Adding a wildcard symbol may retrieve word variants: ((so sach) OR (co sach)) van dong ((o hoi) or (o hoc)). hieu ve cau truc van hanh ve cua tre*.