Steven Goodman, a dean and professor of medicine at Stanford and the editor of the journal Clinical Trials, which has its own imitators, called this phenomenon “the dark side of open access,” the movement to make scholarly publications freely available.

The number of these journals and conferences has exploded in recent years as scientific publishing has shifted from a traditional business model for professional societies and organizations built almost entirely on subscription revenues to open access, which relies on authors or their backers to pay for the publication of papers online, where anyone can read them.

Open access got its start about a decade ago and quickly won widespread acclaim with the advent of well-regarded, peer-reviewed journals like those published by the Public Library of Science, known as PLoS. Such articles were listed in databases like PubMed, which is maintained by the National Library of Medicine, and selected for their quality.

But some researchers are now raising the alarm about what they see as the proliferation of online journals that will print seemingly anything for a fee. They warn that nonexperts doing online research will have trouble distinguishing credible research from junk. “Most people don’t know the journal universe,” Dr. Goodman said. “They will not know from a journal’s title if it is for real or not.”