| #541 | The Princeton University Library chronicle. -- Princeton : Friends of the Princeton University Library, 1939-. -- ISSN 0032-8456 |
| #542 | Priroda. -- Moskva : Nauka, 1912-. -- ISSN 0032-874X |
| #543 | Priroda. -- Sofia : Balgarska Akademija na Naukite, 1952-. -- ISSN 0032-8731 |
| #544 | Príroda a spoločnosť. -- Slovensko : Martin : Matica slovenská, 1991 Martin : Osveta Bratislava : Obzor Bratislava :, 1952-. -- ISSN 0322-7707 |
| #545 | Prírodovedecká príloha. -- Slovensko : Bratislava : Klub inžinierov Slovákov,, 1940-1942 |
| #546 | Proceedings. -- London : Royal Society, 1990-1996. -- ISSN 0962-8444 |
| #547 | Proceedings in print. -- [Arlington] : [Proceedings in Print], 1964-1997. -- ISSN 0032-9568 |
| #548 | Proceedings of the Academy of Natural Sciences of Philadelphia. -- Philadelphia : Academy of Natural Sciences of Philadelphia, 1841-. -- ISSN 0097-3157 print. -- ISSN 1938-5293 online |
| #549 | Proceedings of the Bournemouth Natural Science Society. -- Bournemouth : Bournemouth Natural Science Society, 1922-. -- ISSN 0962-5364 |
| #550 | Proceedings of the Indian National Scientific Academy, Pt. A. Physical sciences. -- New Delhi : Indian National Sceince Academy, 1970-. -- ISSN 0370-0046 |