Perhaps you should try some spelling variations:
sach hoi » sach doi, cach thoi, hoach hoi
sach moi » sach doi, bach mai, sach bai
tan khoa » toan khoa, tran khoa, san khoa
khoa hoc » hoa hoc
gian dan » gian lang
cuu mot » cua mot, cuu mo, huu mot
goc tan » ngoc tan, hoc tan, goc tao
va gian » va gianh, van gian, va giai
hoc xa » hoc ma

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc ((sach hoi) or (sach moi)) tap, nghien cuu mot goc tan khoa hoc xa hoi va gian dan~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc ((sach hoi) OR (sach moi)) tap, nghien cuu mot goc tan khoa hoc xa hoi va gian dan.
• Adding a wildcard symbol may retrieve word variants: toc ((sach hoi) or (sach moi)) tap, nghien cuu mot goc tan khoa hoc xa hoi va gian dan*.