Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
cao bang » cao dang, cao tang, cao nang
hieu van » hieu va, thien van, lieu va
can bang » can ban, van ban, von bang
te sach » toc sach
keo cua » keo sua, kho cua, khoe cua
van tom » van tam, van toi, van toa
cua te » cua tu
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: ((te sach) or (doc sach)) ky nang x hoi. hieu van tom luoc ((can bang) OR (cao bang)) keo cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (doc sach)) ky nang x hoi. hieu van tom luoc ((can bang) OR (cao bang)) keo cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (doc sach)) ky nang x hoi. hieu van tom luoc ((can bang) OR (cao bang)) keo cua te".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (doc sach)) ky nang x hoi. hieu van tom luoc ((can bang) OR (cao bang)) keo cua te*.