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
su sach » so sach, vu sach
sach ty » sach y, sach tu, sach thu
thuc va » thuc vat, thuc dan, thuc day
lang xa » lang ha, lang van
cua tre » cua te, cuu tre, cua triet
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va
vi cua » vai cua, di cua

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ty ((lang xa) or (((dang xay) OR (van xay)))) hoi. hieu quang nam thuc va dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ty ((lang xa) OR (((dang xay) OR (van xay)))) hoi. hieu quang nam thuc va dan vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ty ((lang xa) or (((dang xay) OR (van xay)))) hoi. hieu quang nam thuc va dan vi cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ty ((lang xa) or (((dang xay) OR (van xay)))) hoi. hieu quang nam thuc va dan vi cua tre*.