It's a question heard often from newer researches trying to learn about and get acquainted with period sources. Someone will suggest looking at a publication and the newer person wonders over the prospect of trying to find a 160 year old magazine. Researchers love Goolge Books and the like for the access they offer, librarians like them because we love showing people easy ways to find what they want. In the past decade a number of organizations have digitized a multitude of 19th century magazines, in some cases complete runs of really wonderful and significant titles. Most allow users to search the text, some allow users to page through as if they have the original paper in front of them. Unfortunately there is no one source to look at to see what is in these many digitization projects collectively, there isn't even a truly comprehensive source of all of the many digitization projects detailing their areas of focus. And in some cases the text is not searchable by Google or other search engines.
Am I cruel? I've just told you there are gold mines out there, pointed out that they are hidden, and didn't tell you where to look!
I have attempted to make this easier for people. I have something of an obsession with 19th century ladies' magazines and I have already done much hunting, pecking, and sorting. I have put my rather extensive list of bookmarks into a publically accessible list. This list is by no means complete, in fact I still have at least one more file I need to merge into this list. And of course there are more and more showing up all the time. I will update this as I remember to, this is much (MUCH) easier to update than building a webpage so updating is more likely to happen. Because my bookmarks started with fashion research there is some bias in the types of magazines I collected links to, if you want the Ladies Home Journals and Cosmos of the day they are there, if you want agriculture they aren't.
The list is in a Zotero group. Zotero is citation and research tracking software (and it's free!). Zotero tries to encourage collaboration and in that spirit they try to make it easy for researchers to share, the groups are part of that effort. The information offered right up front is minimal but you can add more (publication dates and such) with the icon to the far right over the list. When you open the group it will be sorted in alphabetical order but if you're looking for specific years more than titles you can resort it by date. If you sign up for an account with Zotero you can make your sorting and display "stick" from visit to visit. You can save these links to your regular bookmarks or set up a Zotero account and save them there where you can also annotate them (make notes, tag them, etc.)
Before you are totally bored and stop reading (those who didn't already) the list can be found at 19th Century Fashion Magazines.
