Perhaps you should try some spelling variations:
nghien cac » nghiep cach, nghien cuu, nghiep cay
hoc doanh » hoa doanh, hoc danh, hoc dan
thu sach » tu sach, thuat sach, thuoc sach
sach hoc » cach hoc, sach hoi, mach hoc
cac cong » cua cong
cong hoc » dong hoc, cong hoa, cong coc
dan nhan » danh nhan, dan chan, van nhan
nhan dan » phan dau, gian dan, nhan tai

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach hoc tap, nghien cac cong hoc doanh ((khoa hoc) or (hoa hoc)) ma hoa dan nhan dan~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach hoc tap, nghien cac cong hoc doanh ((khoa hoc) OR (hoa hoc)) ma hoa dan nhan dan.
• Adding a wildcard symbol may retrieve word variants: thu sach hoc tap, nghien cac cong hoc doanh ((khoa hoc) or (hoa hoc)) ma hoa dan nhan dan*.