Perhaps you should try some spelling variations:
hieu cua » hieu qua, dieu cua, bieu 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
dau hai » dai hai, dau ha, cau hai
hai cua » thai cua, dai cua, hoi cua
cua tre » cua te, cuu tre, cua triet
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 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 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 tre*.