Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
v nang » va nang, vu nang, van nang
va cao » va cac, va co, va dao
luc va » tuc va, loc va
dau di » da di, dau da, dau do
di cua » dai cua, doi cua, de cua
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: ((toc sach) OR (doc sach)) v nang xa hoi. hieu va cao ((luc va) or (duc va)) dau di cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) v nang xa hoi. hieu va cao ((luc va) OR (duc va)) dau di cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) v nang xa hoi. hieu va cao ((luc va) or (duc va)) dau di cua te".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) v nang xa hoi. hieu va cao ((luc va) or (duc va)) dau di cua te*.