Perhaps you should try some spelling variations:
dieu cua » dieu tra
van hanh » van thanh, ban hanh, van anh
truc van » truc va, thuc van, truc ban
sach van » sach han, sach va, bach van
so sach » so sanh, bo sach, co sach
hieu ke » hieu kem, chieu ke, hieu ky
so hoc » co hoc, mo hoc, so hoa
ke cau » ket cau
de cua » le cua, te cua
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: so sach van dong ((o hoi) or (so hoc)). hieu ke cau truc van hanh ((de cua) or (dieu cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach van dong ((o hoi) OR (so hoc)). hieu ke cau truc van hanh ((de cua) OR (dieu cua)) tre.
• Adding a wildcard symbol may retrieve word variants: so sach van dong ((o hoi) or (so hoc)). hieu ke cau truc van hanh ((de cua) or (dieu cua)) tre*.