Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » thien van, lieu va, hieu ve
ve triet » va trien, su triet
dang xay » dang van, van xay
xay hoi » xa hoi, tay hoi, cay phoi
ty dang » ty xang, ky dang, ty hang
sach ty » sach y, sach tu, sach thu
tinh te » kinh te, tinh tu, tinh he
hieu va » lieu va, hieu qua
luc va » tuc va, loc va
te ve » te va, te vi, de 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 dang xay hoi. ((hieu van) OR (hieu va)) cam ((luc va) or (duc va)) tinh te ve triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty dang xay hoi. ((hieu van) OR (hieu va)) cam ((luc va) OR (duc va)) tinh te ve triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ty dang xay hoi. ((hieu van) OR (hieu va)) cam ((luc va) or (duc va)) tinh te ve triet".
• Adding a wildcard symbol may retrieve word variants: toc sach ty dang xay hoi. ((hieu van) OR (hieu va)) cam ((luc va) or (duc va)) tinh te ve triet*.