Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
dang xay » dang van
hieu va » lieu va, hieu qua
dao bai » dao hai, dao lai, dap bai
cao bai » cao tai, cac bai, cap bai
cua tre » cua te, cuu tre, cua triet
va hoc » van hoc
nuoc » quoc, duoc, ngoc

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 y ((dang xay) OR (van xay)) hoi. hieu va hoc nuoc va ((dao bai) or (cao bai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach y ((dang xay) OR (van xay)) hoi. hieu va hoc nuoc va ((dao bai) OR (cao bai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach y ((dang xay) OR (van xay)) hoi. hieu va hoc nuoc va ((dao bai) or (cao bai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: thu sach y ((dang xay) OR (van xay)) hoi. hieu va hoc nuoc va ((dao bai) or (cao bai)) cua tre*.