Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dua tren » dung tren
va triet » va thiet, va trien, ve triet
tru nang » tra nang, tri nang, thi nang
hieu va » lieu va, hieu qua
tuc van » thuc van, truc van, tuc va
van han » van hanh, van phan, van nhan
han tai » hang tai, nhan tai, van tai
cac tuc » cac toc, cac tu, cac tac

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) OR (truc nano)) xa hoi. hieu va cac tuc van han tai ((dua tren) or (va triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((tru nang) OR (truc nano)) xa hoi. hieu va cac tuc van han tai ((dua tren) OR (va triet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((tru nang) OR (truc nano)) xa hoi. hieu va cac tuc van han tai ((dua tren) or (va triet))".
• Adding a wildcard symbol may retrieve word variants: toc sach ((tru nang) OR (truc nano)) xa hoi. hieu va cac tuc van han tai ((dua tren) or (va triet))*.