Copyright laws are extremely complex, but let's look at Eons Terms of Use:
view link"Eons is the owner of this website as a whole and of any individual content on the website that is provided by Eons staff members or contributors who provide work under contract with Eons. All Eons content is protected under the copyright and intellectual property laws of the United States and other countries. The Eons website also includes works that are the property of others, such as individual contributors or experts; these works, too, are protected by copyright and other intellectual property laws. You may display and, unless otherwise noted, download and print out portions of Eons content solely for your own personal, non-commercial use. Any redistribution, retransmission or publication of any copyrighted material is strictly prohibited without the express written consent of the copyright owner. You agree not to change or delete any proprietary notices from materials downloaded from Eons."To sum this up: Eons owns the copyright of material produced by staff members and contracted contributors. If you, as a user of Eons, upload material to Eons, you own the copyright. Eons does not.
Keep in mind that when you post your material anywhere on the Web and it has not appeared elsewhere in publication, you MAY be actually "publishing" your work, thus killing the opportunity to sell "first rights." Also, many people infringe on other's copyright, either deliberately or because of ignorance. If you have concerns about infringement, DO NOT POST material that has value to you as a writer. Be especially careful about websites that may acquire your copyright through their own terms of use (unlike Eons) if you upload to those sites.
If you have any more questions on copyright, please let me know. I am not an attorney and cannot offer legal advice, but I have studied intellectual property in law school and can provide basic information.