Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
cac toc » cac toi, cac nuoc, cac thoi
cac tuc » cac tu, cac tac, cac nuoc
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
hieu ve » hieu van
sang ma » tang ma, nang ma, sang tao
ky sang » ky nang, ky dang, ky tang
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va
vi cua » vai cua, di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky sang ma hoi. ((hieu ve) or (hieu va)) ((cac tuc) OR (cac toc)) va dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky sang ma hoi. ((hieu ve) OR (hieu va)) ((cac tuc) OR (cac toc)) va dan vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky sang ma hoi. ((hieu ve) or (hieu va)) ((cac tuc) OR (cac toc)) va dan vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky sang ma hoi. ((hieu ve) or (hieu va)) ((cac tuc) OR (cac toc)) va dan vi cua tre*.