Perhaps you should try some spelling variations:
danh cong » dang cong, hanh cong, anh cong
hieu van » hieu va, thien van, lieu va
cong cua » cong cu, dong cua, huong cua
tu sach » thu sach, su sach, te sach
va danh » va dinh, va dan, va hanh
cac duc » cao duc, cac dac, cac nuoc
sach ky » sac ky, sach y, sach ty
mang xa » lang xa, mang may, dang xay
cua tre » cua te, cuu tre, cua triet

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