Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
dang xay » dang van, van xay
nam thuc » nam thuoc, am thuc, nam tu
so sach » so sanh, bo sach, co sach
lang xa » lang ha, lang van
dan vai » dan va, dan tai, dan vat
vai cua » dai cua, hai cua, lai cua
cua tre » cua te, cuu tre, cua triet
va dan » ca dan, va dao, va dau

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) OR (nam thu)) va dan vai 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) OR (nam thu)) va dan vai 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) OR (nam thu)) va dan vai cua tre".
• Adding a wildcard symbol may retrieve word variants: so sach y ((lang xa) or (dang xay)) hoi. hieu quang ((nam thuc) OR (nam thu)) va dan vai cua tre*.