Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dua tren » dung tren
cau tren » cu tren, dau tren, ca tren
dang xay » dang van, van xay
hieu va » lieu va, hieu qua
va hanh » van hanh, va thanh, va danh
hanh di » hanh vi, hanh de, hang di
lang xa » lang ha, lang van
cac luc » cau luc, coc luc, cac nuoc
luc va » duc va, tuc va, loc va

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