Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
hanh thai » nhanh thai, hinh thai, hanh tai
vien cac » vien bach, vien dai, vien da
thai cua » than cua, tai cuc, tri cua
duc manh » suc manh, duc anh, duc minh
du manh » du hanh, tu manh, vu manh
sach ty » sach tu, sach thu, xach tay
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai

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 ty) or (sach y)) nang o hoi. hieu vien cac ((du manh) OR (duc manh)) hanh thai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach ty) OR (sach y)) nang o hoi. hieu vien cac ((du manh) OR (duc manh)) hanh thai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ty) or (sach y)) nang o hoi. hieu vien cac ((du manh) OR (duc manh)) hanh thai cua tre".
• Adding a wildcard symbol may retrieve word variants: te ((sach ty) or (sach y)) nang o hoi. hieu vien cac ((du manh) OR (duc manh)) hanh thai cua tre*.