Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
sach vu » sach va, sach tu, sach uu
vu nang » vuc nang, va nang, vu dang
hieu va » lieu va
cam loc » cam lo
loc va » hoc va, luc va
va dan » ca dan, va dao, va dau
di cua » doi cua, de cua, do 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 vu nang x hoi. ((hieu va) OR (hieu qua)) cam loc va dan ((di cua) or (dai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach vu nang x hoi. ((hieu va) OR (hieu qua)) cam loc va dan ((di cua) OR (dai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach vu nang x hoi. ((hieu va) OR (hieu qua)) cam loc va dan ((di cua) or (dai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: toc sach vu nang x hoi. ((hieu va) OR (hieu qua)) cam loc va dan ((di cua) or (dai cua)) tre*.