Perhaps you should try some spelling variations:
cac thuc » cach thuc, cac thu, can thuc
kho tang » cao tang
so sach » so sanh, bo sach, co sach
thuc va » thuc vat, thuc dan, thuc day
hieu va » hieu qua
ky tang » ky nang, ky dang, ky trong
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
va dan » ca dan, va dao, va dau
dan di » danh di, dan da, dan de
di cua » dai cua, doi cua, de cua

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 ((ky tang) OR (kho tang)) ma hoi. ((hieu va) or (lieu va)) cac thuc va dan di cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ((ky tang) OR (kho tang)) ma hoi. ((hieu va) OR (lieu va)) cac thuc va dan di cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ((ky tang) OR (kho tang)) ma hoi. ((hieu va) or (lieu va)) cac thuc va dan di cua tre".
• Adding a wildcard symbol may retrieve word variants: so sach ((ky tang) OR (kho tang)) ma hoi. ((hieu va) or (lieu va)) cac thuc va dan di cua tre*.