Perhaps you should try some spelling variations:
dung tren » dung trong, dung trung
doc sach » hoc sach, toc sach, nuoc sach
sach tru » sach truc, sach thu, sach tu
va triet » va thiet, va trien, ve triet
tru nang » tra nang, tri nang, truc nano
hieu va » hieu qua
tac van » tac vang, cac van, tac va
van han » van hanh, van phan, van nhan
han tai » hang tai, nhan tai, van tai
nang xa » nang x, lang xa, nang ma
cac tac » cac toc, cac bac, cac dac

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach tru nang xa hoi. ((hieu va) or (lieu va)) cac tac van han tai ((dung tren) or (va triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach tru nang xa hoi. ((hieu va) OR (lieu va)) cac tac van han tai ((dung tren) OR (va triet)).
• Adding a wildcard symbol may retrieve word variants: doc sach tru nang xa hoi. ((hieu va) or (lieu va)) cac tac van han tai ((dung tren) or (va triet))*.