Perhaps you should try some spelling variations:
su triet » su viet, su tien, ve triet
trinh do » trinh ky
tinh doi » trinh doc, tinh hoc, tinh son
dang xay » dang van, van xay
cac tac » cac toc, cac bac, cac dac
vu sach » vu bach, su sach, vu khach
sach ty » sach y, sach tu, sach thu
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
tac va » tac da, tac xa, tuc va

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: vu sach ty ((nang xa) or (dang xay)) hoi. hieu va cac tac va ((tinh doi) or (trinh do)) su triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach ty ((nang xa) OR (dang xay)) hoi. hieu va cac tac va ((tinh doi) OR (trinh do)) su triet.
• Adding a wildcard symbol may retrieve word variants: vu sach ty ((nang xa) or (dang xay)) hoi. hieu va cac tac va ((tinh doi) or (trinh do)) su triet*.