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
hoc tan » hoc tang, hoc dan, hoc tap
va gian » va gianh, van gian, va giai
mo hoc » mon hoc, co hoc
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 mo hoc tan khoa hoc xa hoi va gian dan~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc ((sach hoi) OR (sach moi)) tap, nghien cuu mo hoc 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 mo hoc tan khoa hoc xa hoi va gian dan*.