Perhaps you should try some spelling variations:
dung tren » dung trong, dung trung
toc sach » hoc sach, doc sach, thuoc sach
sach tru » sach truc, sach thu, sach tu
tru nang » tra nang, tri nang, truc nano
va triet » va thiet, va trien, ve triet
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
cac tuc » cac toc, cac tu, cac tac
tuc van » thuc van, truc van, tuc va
van van » van ban, tan van, san van
van tai » von tai, van tuan

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 tru nang xa hoi. hieu va cac tuc van van tai ((dung tren) or (va triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach tru nang xa hoi. hieu va cac tuc van van tai ((dung tren) OR (va triet)).
• Adding a wildcard symbol may retrieve word variants: toc sach tru nang xa hoi. hieu va cac tuc van van tai ((dung tren) or (va triet))*.