Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
van hanh » van thanh, ban hanh, van anh
hieu van » hieu va, thien van, lieu va
ty nang » ky nang, ty hang, ly nang
cua tre » cua te, cuu tre, cua triet
co hai » co dai, co hoi, o hai
cac so » cac co, cac ho, cac o
cac bo » bac bo, cac co
vi cua » vai cua, 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: toc sach ((ty nang) OR (ty xang)) co hai. hieu van ((cac so) or (cac bo)) van hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ty nang) OR (ty xang)) co hai. hieu van ((cac so) OR (cac bo)) van hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ty nang) OR (ty xang)) co hai. hieu van ((cac so) or (cac bo)) van hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ty nang) OR (ty xang)) co hai. hieu van ((cac so) or (cac bo)) van hanh vi cua tre*.