Perhaps you should try some spelling variations:
"astronomy and astrophysics gamma" » "astronomy and astrophysics data", "astronomy and astrophysics summary", "astronomy and astrophysics a"
"astronomy and astrophysics sun" » "astronomy and astrophysics _"

Try widening your search to All Fields.

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• If you are trying to use Boolean operators, they must be ALL CAPS: (("astronomy and astrophysics gamma") OR ("astronomy and astrophysics sun")).
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