Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
sach tra » sach tranh, sach tham, sach tren
tra nang » thi nang, kha nang, da nang
dua tren » dung tren
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
thiet » thieu

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