Perhaps you should try some spelling variations:
cua triet » cua viet, su triet, va triet
sach vuc » sach duoc, sach nuoc, sach truc
toc sach » hoc sach, doc sach, thuoc sach
vuc nang » cuc nang, vu nang, chuc nang
cua tre » cua te, cuu tre, dua tren
nang o » nang co, nang ho, nang ro
va cam » va cham, va cao, va cai
luc va » duc va, tuc va, loc va
va dan » ca dan, va dao, va dau
dan di » danh di, dan da, dan de
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: toc sach vuc nang o hoi. hieu ((va cam) or (va cac)) luc va dan di ((cua tre) OR (cua triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach vuc nang o hoi. hieu ((va cam) OR (va cac)) luc va dan di ((cua tre) OR (cua triet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach vuc nang o hoi. hieu ((va cam) or (va cac)) luc va dan di ((cua tre) OR (cua triet))".
• Adding a wildcard symbol may retrieve word variants: toc sach vuc nang o hoi. hieu ((va cam) or (va cac)) luc va dan di ((cua tre) OR (cua triet))*.