Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
sang mai » sang ma, sang tai, lang mai
sach ky » sac ky, sach y, sach ty
ky sang » ky nang, ky dang, ky tang
mai hoi » mai khoi, dai hoi, lai hoi
hieu ve » hieu van
hieu va » lieu va, hieu qua
cac tuc » cac toc, cac tu, cac tac
dap dai » tap dai, dap bai
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach ky sang mai hoi. ((hieu ve) or (hieu va)) cac tuc xa ((dap dai) OR (dat dai)) cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky sang mai hoi. ((hieu ve) OR (hieu va)) cac tuc xa ((dap dai) OR (dat dai)) cua te*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ky sang mai hoi. ((hieu ve) or (hieu va)) cac tuc xa ((dap dai) OR (dat dai)) cua te*".