Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh tai » thanh tai, hang tai, han tai
lan hanh » ban hanh, van hanh, lan anh
quoc lan » quoc ban, nuoc luan, quoc quan
cac quoc » cac nuoc, cac cuoc, cao quoc
tai cua » thai cua, tai cuc, tri cua
qua cac » cua cac
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, nang cao
mang xa » lang xa, mang may, dang xay
nang xa » nang x, lang xa, ang xa

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 ky ((((nang xa) or (mang xa))) or (nang ma)) hoi. hieu qua cac quoc lan hanh tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky ((((nang xa) OR (mang xa))) OR (nang ma)) hoi. hieu qua cac quoc lan hanh tai cua tre.
• Adding a wildcard symbol may retrieve word variants: toc sach ky ((((nang xa) or (mang xa))) or (nang ma)) hoi. hieu qua cac quoc lan hanh tai cua tre*.