Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
van hanh » van thanh, ban hanh, van anh
nuoc van » nuoc va, nuoc san, luoc van
hieu cua » hieu qua, dieu cua, bieu cua
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hoc sach » hoc sinh, hoc cac, hoc anh
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) OR (hoc sach)) y nang xa hoi. hieu cua 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) OR (hoc sach)) y nang xa hoi. hieu cua 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) OR (hoc sach)) y nang xa hoi. hieu cua cac nuoc van hanh di ((cua tre) or (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (hoc sach)) y nang xa hoi. hieu cua cac nuoc van hanh di ((cua tre) or (cuu tre))*.