Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
van hanh » van thanh, ban hanh, van anh
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hieu cua » hieu qua, dieu cua, bieu cua
cac luc » cau luc, coc luc, cac cuoc
nang xa » nang x, lang xa, nang ma
hanh di » hanh vi, hanh de, hang di
cua tre » cua te, cua triet, dua tren
cuu tre » cau tren, cau treo
y nang » ky nang, ly nang, v nang

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 y nang xa hoi. hieu cua ((cac luc) OR (cac nuoc)) van hanh di ((cua tre) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y nang xa hoi. hieu cua ((cac luc) OR (cac nuoc)) van hanh di ((cua tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y nang xa hoi. hieu cua ((cac luc) OR (cac nuoc)) van hanh di ((cua tre) or (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: toc sach y nang xa hoi. hieu cua ((cac luc) OR (cac nuoc)) van hanh di ((cua tre) or (cuu tre))*.