Perhaps you should try some spelling variations:
trinh nghien » trinh nghe, kinh nghiem, trinh thiet
sach trinh » sach tranh, hanh trinh, sach kinh
bai nghiem » trai nghiem, thi nghiem, bai nghe
nghiem ve » nghiem va, nghiem vi, nghiem de
nghien d » nghiem d, nghien o, nghiem de
sach bai » sach dao, cac bai, sach xa
so sach » so sanh, bo sach, hoc sach
co sach » bo sach, cuon sach, hoc sach
ve hoc » te hoc, va hoc, vi hoc
d hoc » du hoc, ad hoc, de hoc

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 trinh nghien d hoc ) or ( co sach bai nghiem ve hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( so sach trinh nghien d hoc ) OR ( co sach bai nghiem ve hoc )).
• Adding a wildcard symbol may retrieve word variants: (( so sach trinh nghien d hoc ) or ( co sach bai nghiem ve hoc ))*.