Perhaps you should try some spelling variations:
hieu cua » hieu qua, dieu cua, bieu cua
thai cua » than cua, tai cuc, tri cua
sach ky » sac ky, sach y, sach kem
sach ty » sach y, sach tu, sach thu
cac dac » cac dan, cac dai, cac bac
hai cua » dai cua, hoi cua, lai cua
dac va » duc va, day va, dat va
va dau » va dao

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu ((sach ky) or (sach ty)) nang x ho. hieu cua cac dac va dau ((hai cua) OR (thai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu ((sach ky) OR (sach ty)) nang x ho. hieu cua cac dac va dau ((hai cua) OR (thai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu ((sach ky) or (sach ty)) nang x ho. hieu cua cac dac va dau ((hai cua) OR (thai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: thu ((sach ky) or (sach ty)) nang x ho. hieu cua cac dac va dau ((hai cua) OR (thai cua)) tre*.