Penn has a number of popular Japanese magazines in the collection for you to use, in the library. Unfortunately, the majority of them cannot be checked out. Feel free to use them in the Van Pelt Current Periodicals reading area (fourth floor) or the East Asia Seminar Room (fifth floor) depending on where they are shelved. Most of what you will be looking for are in the East Asia Seminar Room or in East Asia Stacks!
Penn has many, many academic journals in print in Japanese, on topics ranging from literature and history to dentistry! Of course, the ones you'll find in Van Pelt are related to social science and humanities. Many of our older issues are housed in LIBRA. You can request an article copy straight from LIBRA or another Penn library and they'll scan it for you and email you a PDF.
The article request form can be accessed by clicking "Scan & Deliver" on the journal's record in Franklin. (The library will scan something for you no matter what its location is.) To get a citation to fill out the form (in ROMAJI ONLY) use one of the below databases to find the information on your article. Page numbers are particularly important!