Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
truc van » truc va, thuc van, truc ban
sach van » sach han, bach van, cach van
hieu ke » hieu kem, chieu ke, hieu ky
sach va » sach xa, sach ha, sach dao
nang o » nang co, nang ho, nang ro
ke cau » ket cau
te cua » tue cua, de cua
le cua » ly 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: su ((sach van) or (sach va)) nang o hoi. hieu ke cau truc van hanh ((te cua) OR (le cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach van) OR (sach va)) nang o hoi. hieu ke cau truc van hanh ((te cua) OR (le cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach van) or (sach va)) nang o hoi. hieu ke cau truc van hanh ((te cua) OR (le cua)) tre".
• Adding a wildcard symbol may retrieve word variants: su ((sach van) or (sach va)) nang o hoi. hieu ke cau truc van hanh ((te cua) OR (le cua)) tre*.