Perhaps you should try some spelling variations:
hoc sach » hoc sinh, hoc cac, hoc anh
hieu van » hieu va, thien van, lieu va
thuc day » thuc dan, thuc vat
hanh dai » hanh tai, hanh dao, vanh dai
tu sach » thu sach, su sach, te sach
nang xa » nang x, lang xa, nang ma
thuc va » thuc vat, thuc dan
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) or (hoc sach)) ky nang xa hoi. hieu van nam ((thuc va) OR (thuc day)) hanh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (hoc sach)) ky nang xa hoi. hieu van nam ((thuc va) OR (thuc day)) hanh dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (hoc sach)) ky nang xa hoi. hieu van nam ((thuc va) OR (thuc day)) hanh dai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (hoc sach)) ky nang xa hoi. hieu van nam ((thuc va) OR (thuc day)) hanh dai cua tre*.