Perhaps you should try some spelling variations:
sach van » sach han, sach va, bach van
van nang » van quang, van ban, van dong
van hanh » van thanh, ban hanh, van anh
truc van » truc va, thuc van, truc ban
su sach » so sach, vu sach
hanh de » hanh ve, hanh kem
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
ve cau » ke cau, va cau, ve cac
de cua » le cua, te cua, dieu cua
o hoa » do hoa, so hoa, o ha
o hoi » co hoi, o hoc
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 van nang ((((o hoi) OR (o hoa))) or (o hai)). hieu ve cau truc van hanh de cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach van nang ((((o hoi) OR (o hoa))) OR (o hai)). hieu ve cau truc van hanh de cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach van nang ((((o hoi) OR (o hoa))) or (o hai)). hieu ve cau truc van hanh de cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach van nang ((((o hoi) OR (o hoa))) or (o hai)). hieu ve cau truc van hanh de cua tre*.