Perhaps you should try some spelling variations:
thu sach » thuat sach, thuoc sach, thu hoach
tu sach » su sach, te sach, tu cach
cac toc » cac toi, cac nuoc, cac thoi
hieu va » lieu va, hieu qua
hieu ve » hieu van
tang ma » mang may, tang van
ty tang » tay tang, ty xang, ty hang
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
toc va » hoc va, toc ta, tuc va
va dao » ca dao
dao va » dao van, tao va, do va
va cua » va chua, via cua, ca cua

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

• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu sach)) ty tang ma hoi. ((hieu ve) OR (hieu va)) cac toc va dao va cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) OR (thu sach)) ty tang ma hoi. ((hieu ve) or (hieu va)) cac toc va dao va cua tre~".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) OR (thu sach)) ty tang ma hoi. ((hieu ve) or (hieu va)) cac toc va dao va cua tre*.