Perhaps you should try some spelling variations:
thong cong » trong cong, tong cong, thong thong
hieu sang » chieu sang, hieu lang, hieu quang
hanh sinh » hanh tinh, hanh dinh, hinh sinh
bang cong » dang cong, bang song, hang cong
quang dac » quan dac, quang dai, quang dam
doc hieu » toc thieu, hoc thieu, hoc hien
sinh va » sinh vat, tinh va, dinh van

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc hieu sang - hanh sinh va ((thong cong) or (bang cong)) tinh quang dac~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu sang - hanh sinh va ((thong cong) OR (bang cong)) tinh quang dac*.