Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dang xay » dang van, van xay
tinh ket » dinh ket, tinh yeu, tinh yen
va trien » va truyen, va thiet, va tuyen
lang xa » lang ha, lang van
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
va cao » va cac, va co, va dao
tuc va » thuc va, truc va, duc va
ket va » ket van

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 ky ((lang xa) OR (dang xay)) hoi. hieu va cao ((tuc va) or (tuc xa)) tinh ket va trien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky ((lang xa) OR (dang xay)) hoi. hieu va cao ((tuc va) OR (tuc xa)) tinh ket va trien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky ((lang xa) OR (dang xay)) hoi. hieu va cao ((tuc va) or (tuc xa)) tinh ket va trien".
• Adding a wildcard symbol may retrieve word variants: toc sach ky ((lang xa) OR (dang xay)) hoi. hieu va cao ((tuc va) or (tuc xa)) tinh ket va trien*.