Perhaps you should try some spelling variations:
duc tien » duc thien, luc tieng, thuc tien
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
dang mai » dang hai, dang mau, dang bai
hanh tai » thanh tai, hang tai, han tai
duc tre » duoc tren
va hanh » van hanh, va thanh, va danh
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
hieu ve » hieu van
mai hoa » mai khoa, ma hoa, dai hoa
ky dang » ky nang, ky danh

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 dang mai hoa. ((hieu ve) OR (hieu va)) cac nuoc va hanh tai ((duc tre) or (duc tien))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky dang mai hoa. ((hieu ve) OR (hieu va)) cac nuoc va hanh tai ((duc tre) OR (duc tien)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky dang mai hoa. ((hieu ve) OR (hieu va)) cac nuoc va hanh tai ((duc tre) or (duc tien))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky dang mai hoa. ((hieu ve) OR (hieu va)) cac nuoc va hanh tai ((duc tre) or (duc tien))*.