Well I think I've cracked the theme as I did it by solving a few examples and finding other words that mean the same. I've come back to the forum with six still to get including two themes (23ac and 25ac). Thanks for the hint about 5/9 being this what we're doing. I don't think I'd have spotted it without that.
I could still use a hint for 16d and 13d.
I couldn't parse 22d, but I'm a vegetarian. But I did find a physicist! I had 6d wrong which held me up getting 9ac right