Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
van cham » van chat, van tham, va cham
trung ha » trung hoc, trung tam, trung cap
dinh dao » dinh dat, minh dao, dinh cao
sach ky » sac ky, sach y, sach ty
dao cua » dai cua, day cua, dan cua
cua tre » cua te, cuu tre, cua triet

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 hoi) or (ma hoa)). hieu van cham ((thuc vat) or (trung ha)) dinh dao cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky nang ((xa hoi) OR (ma hoa)). hieu van cham ((thuc vat) OR (trung ha)) dinh dao cua tre.
• Adding a wildcard symbol may retrieve word variants: toc sach ky nang ((xa hoi) or (ma hoa)). hieu van cham ((thuc vat) or (trung ha)) dinh dao cua tre*.