Perhaps you should try some spelling variations:
sach van » sach han, sach va, bach van
van nang » van quang, van ban, van dong
dan hanh » dang hanh, dan khanh, dan thanh
thuc dan » thuc hanh, hoc dan, thuc vat
su sach » so sach, vu sach
hanh de » hanh ve, hanh kem
cua tre » cua te, cuu tre, cua triet
ve cac » va cac, vien cac
de cua » le cua, te cua, dieu cua
ve cau » ke cau, va cau, le cau
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach van nang ((x hoi) OR (o hoi)). hieu ((ve cau) or (ve cac)) thuc dan hanh de cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach van nang ((x hoi) OR (o hoi)). hieu ((ve cau) OR (ve cac)) thuc dan hanh de cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach van nang ((x hoi) OR (o hoi)). hieu ((ve cau) or (ve cac)) thuc dan hanh de cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach van nang ((x hoi) OR (o hoi)). hieu ((ve cau) or (ve cac)) thuc dan hanh de cua tre*.