Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
hieu van » hieu va, thien van, lieu va
cau tren » cu tren, ca tren, cau treo
dong hoa » dong hoc, dong co
van hanh » van thanh, ban hanh, van anh
hanh va » hang va, hanh vi
co sach » bo sach, cuon sach, hoc sach
sach ky » sac ky, sach y, sach ty
van lam » van nam
lam so » lam son, nam so, ham so
so van » su van, vo van

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

• Performing a fuzzy search may retrieve terms with similar spellings: co sach ky ((dong hoa) or (van xay)) hoi. hieu van lam so van hanh va ((cau tren) OR (dau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: co sach ky ((dong hoa) OR (van xay)) hoi. hieu van lam so van hanh va ((cau tren) OR (dau tren))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "co sach ky ((dong hoa) or (van xay)) hoi. hieu van lam so van hanh va ((cau tren) OR (dau tren))*".