Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dua tren » dung tren
va danh » va dinh, va hanh, dia danh
cu tren » tu tren
cac luc » cau luc, coc luc, cac nuoc
hieu va » lieu va, hieu qua
lang xa » lang ha, dang xay, lang van
va dan » ca dan, va dao, va dau

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 _ lang xa hoi. hieu va cac luc ((va danh) OR (va dan)) di ((dua tren) or (cu tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach _ lang xa hoi. hieu va cac luc ((va danh) OR (va dan)) di ((dua tren) OR (cu tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach _ lang xa hoi. hieu va cac luc ((va danh) OR (va dan)) di ((dua tren) or (cu tren))".
• Adding a wildcard symbol may retrieve word variants: toc sach _ lang xa hoi. hieu va cac luc ((va danh) OR (va dan)) di ((dua tren) or (cu tren))*.