Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
duc hanh » duc thanh, duc anh, du hanh
duc xanh » duc anh, duc manh, duc lanh
hieu van » hieu va, thien van, lieu va
ve triet » va trien, su triet
lang xa » lang ha, dang xay, lang van
sach ty » sach y, sach tu, sach thu
van cao » van dao, van bao, van hao
nang xa » nang x, nang ma, mang xa
vi ve » va ve, gi ve, ve ve

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 ty ((nang xa) or (lang xa)) hoi. hieu van cao ((duc xanh) OR (duc hanh)) hanh vi ve triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty ((nang xa) OR (lang xa)) hoi. hieu van cao ((duc xanh) OR (duc hanh)) hanh vi ve triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ty ((nang xa) or (lang xa)) hoi. hieu van cao ((duc xanh) OR (duc hanh)) hanh vi ve triet".
• Adding a wildcard symbol may retrieve word variants: toc sach ty ((nang xa) or (lang xa)) hoi. hieu van cao ((duc xanh) OR (duc hanh)) hanh vi ve triet*.