Perhaps you should try some spelling variations:
thai nghien » thi nghiem, phap nghien, phan nghien
thai nguyen » toan nguyen, tran nguyen
sach trac » sach truc, sach tranh, sach tham
trac nghe » trac nghiem, thai nghe, cac nghe
nghe duoc » nghiem duoc, nghe nuoi, che duoc
duoc hoc » quoc hoi
so sach » so sanh, bo sach, co sach

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( so sach ((thai nghien) or (thai nguyen)) cuu khoa ) or ( so sach trac nghe duoc hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( so sach ((thai nghien) OR (thai nguyen)) cuu khoa ) OR ( so sach trac nghe duoc hoc )).
• Adding a wildcard symbol may retrieve word variants: (( so sach ((thai nghien) or (thai nguyen)) cuu khoa ) or ( so sach trac nghe duoc hoc ))*.