Perhaps you should try some spelling variations:
cua triet » cua viet, su triet, va triet
hieu vien » hieu hien, hieu viec, thieu nien
hanh tai » thanh tai, hang tai, han tai
van hanh » van thanh, ban hanh, van anh
nuoc van » nuoc va, nuoc san, luoc van
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
vien cac » vien bach, vien dai, vien da
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, dua tren
tu sach » thu sach, su sach, te sach
co loi » co hoi
o hoc » co hoc, mo hoc, so hoc

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky nang ((o hoc) or (co loi)). hieu vien cac nuoc van hanh tai ((cua tre) OR (cua triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hoc) OR (co loi)). hieu vien cac nuoc van hanh tai ((cua tre) OR (cua triet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((o hoc) or (co loi)). hieu vien cac nuoc van hanh tai ((cua tre) OR (cua triet))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoc) or (co loi)). hieu vien cac nuoc van hanh tai ((cua tre) OR (cua triet))*.