Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, nang cao
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
cac tu » cac thu, cach tu, cac du
dau vi » dau ve, dat vi, dau viet
dau va » dau ve, lau va

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