Perhaps you should try some spelling variations:
hieu viec » nhieu viec, hieu ve, sieu viet
hieu vien » hieu hien, thieu nien, hieu tieng
tu sach » thu sach, su sach, te sach
dinh va » dinh van, dinh ve, tinh va
va dinh » van dinh, va kinh, va tinh
cac bao » cach bao, cac bai, cac ban
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
bao va » bao ve, tao va, ban va
va cua » va chua, via cua, ca cua

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 xa) or (nang ma)) hoi. ((hieu vien) OR (hieu viec)) cac bao va dinh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky ((nang xa) OR (nang ma)) hoi. ((hieu vien) OR (hieu viec)) cac bao va dinh va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky ((nang xa) or (nang ma)) hoi. ((hieu vien) OR (hieu viec)) cac bao va dinh va cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky ((nang xa) or (nang ma)) hoi. ((hieu vien) OR (hieu viec)) cac bao va dinh va cua tre*.