Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
dong cua » dung cua, cong cua, huong cua
dao hanh » dao thanh, dang hanh, ban hanh
day hanh » day nhanh, day thanh, day manh
nam thuc » nam thuoc, am thuc, nam thu
hieu van » thien van, lieu va, hieu ve
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
nang xa » nang x, lang xa, nang ma
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: doc sach ky nang xa hoi. ((hieu van) or (hieu va)) nam thuc ((day hanh) OR (dao hanh)) dong cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky nang xa hoi. ((hieu van) OR (hieu va)) nam thuc ((day hanh) OR (dao hanh)) dong cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky nang xa hoi. ((hieu van) or (hieu va)) nam thuc ((day hanh) OR (dao hanh)) dong cua tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ky nang xa hoi. ((hieu van) or (hieu va)) nam thuc ((day hanh) OR (dao hanh)) dong cua tre*.