Perhaps you should try some spelling variations:
sach hoc » cach hoc, mach hoc, sach duoc
sach hoi » sach doi, sach moi, cach thoi
dan khoa » dang khoa, da khoa, san khoa
nhan dan » phan dau, gian dan, nhan tai
cuu hoa » cuu khoa, cuu hoan, cau hoa
hoc xa » hoc ma
hoi ca » hoi cua, hoi cac, hoi cau

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

• Performing a fuzzy search may retrieve terms with similar spellings: te ((sach hoc) OR (sach hoi)) tap, nghien cuu hoa hoc dan khoa hoc xa hoi ca nhan dan~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach hoc) OR (sach hoi)) tap, nghien cuu hoa hoc dan khoa hoc xa hoi ca nhan dan".
• Adding a wildcard symbol may retrieve word variants: te ((sach hoc) OR (sach hoi)) tap, nghien cuu hoa hoc dan khoa hoc xa hoi ca nhan dan*.