Perhaps you should try some spelling variations:
"phat trien khoa hoc" » "phat trien nha hoc", "phat trien hoat hoc", "phat vien khoa hoc", "phat trien hoa hoc", "phan trien khoa hoc", "pham trien khoa hoc", "nhat trien khoa hoc"
"phap trien khoa hoc" » "phap trien nha hoc", "phap trien hoat hoc", "phap vien khoa hoc", "phap truyen khoa hoc", "phap tieng khoa hoc", "phap tiep khoa hoc", "phap trien hoa hoc"
"phat trien khai hoc" » "phat trien nha hoc", "phat trien thai hoc", "phat trien khi hoc", "phat trien khai thac", "phan trien khai hoc", "pham trien khai hoc", "nhat trien khai hoc"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (((("phat trien khoa hoc") OR ("phat trien khai hoc"))) or ("phap trien khoa hoc"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("phat trien khoa hoc") OR ("phat trien khai hoc"))) OR ("phap trien khoa hoc")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"phat trien khoa hoc\") OR (\"phat trien khai hoc\"))) or (\"phap trien khoa hoc\"))".
• Removing quotes may allow a broader search: (((( phat trien khoa hoc ) OR ( phat trien khai hoc ))) or ( phap trien khoa hoc )).
• Adding a wildcard symbol may retrieve word variants: (((("phat trien khoa hoc") OR ("phat trien khai hoc"))) or ("phap trien khoa hoc"))*.