Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » thien van, lieu va, hieu ve
dinh dat » dinh ket, dinh van, dinh lam
cau thuc » cau truc, cuu thuc, can thuc
tu sach » thu sach, su sach, te sach
thuc va » thuc vat, thuc dan, thuc day
dat cua » dai cua, day cua, mat cua
ky tang » ky nang, ky dang, kho tang
tang xa » trang xa, tang ma, lang xa
hieu va » lieu va, hieu qua
va dinh » van dinh, va kinh, va tinh
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu sach) or (toc sach)) ky tang xa hoi. ((hieu van) or (hieu va)) cau thuc va dinh dat cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky tang xa hoi. ((hieu van) OR (hieu va)) cau thuc va dinh dat cua te.
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky tang xa hoi. ((hieu van) or (hieu va)) cau thuc va dinh dat cua te*.