Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
dua tren » dung tren
sach ky » sac ky, sach y, sach ty
cac luc » cau luc, coc luc, cac cuoc
cua tre » cua te, cuu tre, cua triet
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va

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 x ho. hieu van ((cac luc) or (cac nuoc)) va dan vi ((cua tre) or (dua tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky nang x ho. hieu van ((cac luc) OR (cac nuoc)) va dan vi ((cua tre) OR (dua tren)).
• Adding a wildcard symbol may retrieve word variants: toc sach ky nang x ho. hieu van ((cac luc) or (cac nuoc)) va dan vi ((cua tre) or (dua tren))*.