Perhaps you should try some spelling variations:
dieu hieu » dieu hien, dien chieu, dieu kien
dua tren » dung tren
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
cac cao » cac co, ca cao, bac cao
va dinh » van dinh, va kinh, va tinh
cuu tre » cua tre, cau tren, cau treo
cao va » cao van, tao va, co va
x hoi » xa hoi, o hoi, x ho

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 x hoi. ((dieu hieu) OR (dieu khien)) cac cao va dinh van ((dua tren) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang x hoi. ((dieu hieu) OR (dieu khien)) cac cao va dinh van ((dua tren) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang x hoi. ((dieu hieu) OR (dieu khien)) cac cao va dinh van ((dua tren) or (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang x hoi. ((dieu hieu) OR (dieu khien)) cac cao va dinh van ((dua tren) or (cuu tre))*.