Perhaps you should try some spelling variations:
nhanh thai » nhanh thi, nhanh thanh, nhanh thang
van nhanh » van thanh, van hanh, van khanh
sach thu » sach thue, sach thieu, sach tham
thu nang » thi nang, thu hang, thu bang
cau tren » cu tren, dau tren, cau treo
tu sach » thu sach, su sach, te sach
duc van » duc va, duc tan, duc manh
cac duc » cac du, cao duc, cac dac
ca tren » cu tren, la tren, co tren
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

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 thu nang ((o hoi) or (o hai)). hieu ve cac duc van nhanh thai ((cau tren) OR (ca tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach thu nang ((o hoi) OR (o hai)). hieu ve cac duc van nhanh thai ((cau tren) OR (ca tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach thu nang ((o hoi) or (o hai)). hieu ve cac duc van nhanh thai ((cau tren) OR (ca tren))".
• Adding a wildcard symbol may retrieve word variants: tu sach thu nang ((o hoi) or (o hai)). hieu ve cac duc van nhanh thai ((cau tren) OR (ca tren))*.