Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
nam thuc » nam thuoc, am thuc, nam thu
dang xay » dang van, van xay
dan vat » dang vat, van vat, dan va
dan vai » dan va, dan tai, den vai
thuc va » thuc vat, thuc dan, thuc day
so sach » so sanh, bo sach, co sach
lang xa » lang ha, lang 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: so sach y ((lang xa) or (dang xay)) hoi. hieu quang nam thuc va ((dan vai) OR (dan vat)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y ((lang xa) OR (dang xay)) hoi. hieu quang nam thuc va ((dan vai) OR (dan vat)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y ((lang xa) or (dang xay)) hoi. hieu quang nam thuc va ((dan vai) OR (dan vat)) cua tre".
• Adding a wildcard symbol may retrieve word variants: so sach y ((lang xa) or (dang xay)) hoi. hieu quang nam thuc va ((dan vai) OR (dan vat)) cua tre*.