Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dat hang » dat khanh, dat quang, tat thang
day hang » dai hang, day nang, dai thang
cac thuc » cach thuc, cac thu, can thuc
hieu va » lieu va, hieu qua
hieu ve » hieu van
nang xa » nang x, lang xa, nang ma
dau cua » dai cua, day cua, cau cua
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach y nang xa hoi. ((hieu ve) or (hieu va)) cac thuc ((day hang) OR (dat hang)) dau cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y nang xa hoi. ((hieu ve) OR (hieu va)) cac thuc ((day hang) OR (dat hang)) dau cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y nang xa hoi. ((hieu ve) or (hieu va)) cac thuc ((day hang) OR (dat hang)) dau cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach y nang xa hoi. ((hieu ve) or (hieu va)) cac thuc ((day hang) OR (dat hang)) dau cua tre*.