Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
hieu van » hieu va, thien van, lieu va
van phat » va phat, van chat, van phan
phat day » phap day, phan day, phan dau
hanh hai » thanh hai, nhanh hai, hang hai
xang ma » tang ma, nang ma, sang ma
va hanh » van hanh, va thanh, va danh
hai cua » thai cua, dai cua, hoi cua
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa

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) or (doc sach)) ty xang ma hoi. hieu van phat day va hanh hai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) ty xang ma hoi. hieu van phat day va hanh hai cua tre.
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (doc sach)) ty xang ma hoi. hieu van phat day va hanh hai cua tre*.