Perhaps you should try some spelling variations:
tinh tai » trinh tai, tinh thai, tinh hai
duc manh » suc manh, duc anh, duc minh
tu sach » thu sach, su sach, te sach
tai cua » thai cua, tai cuc, tri cua
duc may » duc mau, duc man, dung may
qua cac » cua cac
sach ty » sach y, sach tu, sach thu
lang xa » lang ha, dang xay, lang van
tang ma » mang may, tang van
cua tre » cua te, cuu tre, cua triet

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 ty ((tang ma) or (lang xa)) hoi. hieu qua cac ((duc may) OR (duc manh)) tinh tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty ((tang ma) OR (lang xa)) hoi. hieu qua cac ((duc may) OR (duc manh)) tinh tai cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty ((tang ma) or (lang xa)) hoi. hieu qua cac ((duc may) OR (duc manh)) tinh tai cua tre*".