Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cua viet » ca viet, hoa viet, cua vat
hieu va » hieu qua
lang de » vang de, dang de, lang du
y nang » ky nang, ly nang, v nang
xuc va » duc va, tuc va, xac va
luc va » duc va, tuc va, loc va
de cua » le cua, te cua, dieu cua
x hoi » xa hoi, o hoi, x ho

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 y nang x hoi. ((lieu va) or (hieu va)) cam ((xuc va) OR (luc va)) lang de cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y nang x hoi. ((lieu va) OR (hieu va)) cam ((xuc va) OR (luc va)) lang de cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y nang x hoi. ((lieu va) or (hieu va)) cam ((xuc va) OR (luc va)) lang de cua viet".
• Adding a wildcard symbol may retrieve word variants: toc sach y nang x hoi. ((lieu va) or (hieu va)) cam ((xuc va) OR (luc va)) lang de cua viet*.