Perhaps you should try some spelling variations:
doc sach » hoc sach, nuoc sach, dac sac
dinh cuu » dinh chi
toc sach » hoc sach, thuoc sach, nuoc sach
va hang » van hang, va nang, va lang
hieu va » lieu va, hieu qua
nang xa » nang x, lang xa, nang ma
tu nang » tru nang, tu nong, tu nano
va cam » va cham, va cac, va cao
cam tu » cam thu, nam tu, dam tu
di cuu » di cau, di cua

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((doc sach) OR (toc sach)) tu nang xa hoi. hieu va cam tu va hang ((di cuu) or (dinh cuu)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((doc sach) OR (toc sach)) tu nang xa hoi. hieu va cam tu va hang ((di cuu) OR (dinh cuu)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((doc sach) OR (toc sach)) tu nang xa hoi. hieu va cam tu va hang ((di cuu) or (dinh cuu)) tre".
• Adding a wildcard symbol may retrieve word variants: ((doc sach) OR (toc sach)) tu nang xa hoi. hieu va cam tu va hang ((di cuu) or (dinh cuu)) tre*.