Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
van hanh » van thanh, ban hanh, van anh
chai tu » cai tu, choi tu, chay tu
cham tu » pham tu, cam tu, chay tu
hieu vu » hieu va, hieu ve, hieu su
tu sach » thu sach, su sach, te sach
nang xa » nang x, lang xa, nang ma
lang ha » long ha
vi cau » va cau, ve cau, di cau

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 y ((nang xa) or (lang ha)) hoi. hieu vu ((cham tu) OR (chai tu)) van hanh vi cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y ((nang xa) OR (lang ha)) hoi. hieu vu ((cham tu) OR (chai tu)) van hanh vi cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y ((nang xa) or (lang ha)) hoi. hieu vu ((cham tu) OR (chai tu)) van hanh vi cau tren".
• Adding a wildcard symbol may retrieve word variants: tu sach y ((nang xa) or (lang ha)) hoi. hieu vu ((cham tu) OR (chai tu)) van hanh vi cau tren*.