Bartleby: Free-of-charge and chock-full of content, Bartleby allows users to search for information about various fiction, nonfiction, verse, and other published works. The site's offerings include a full digital version of the classic medical textbook, Gray's Anatomy, and fully transcribed versions of 70 different works included in the Harvard Classics collection.

 Full versions of Bartlett's Familiar Quotations, Oxford's Shakespeare, Strunk's Elements of Style, and other time-honored texts are also available in full.

 Visitors may buy books published on Bartleby or download free e-book versions for their electronic reading device.

  This collection of lesson plans touches on mathematics at all grade levels, from elementary-level arithmetic to advanced disciplines like calculus and trigonometry. The site features calculators, study plans and sample tests, games, and other learning materials.

 The Math Tutoring section includes tips for finding a tutor, evaluating his/her methods, and retaining long-term tutorial services.

 Math Help: With the tagline ‘Your Personal Math Teacher,' Math Help is geared toward online learners who struggle in particular areas of the subject. Live study sessions, practice problems, tests, and graded report cards are all included.

 Specific sections target math for elementary and secondary students, community college enrollees, and individuals currently studying for collegiate entrance exams.

 The Textbook Search tool allows users to find lesson plans that correspond to their specific assignments.

 PatrickJMT (Just Math Tutorials): The administrator of this site (a college-level math instructor with nearly a decade of experience) provides an extensive collection of instructional videos for thousands of basic mathematical operations.

 The offerings include nearly 400 guides for algebra, 275 for calculus, and just over 150 for trigonometry.

 Most videos range between 6 and 10 minutes, providing a clear explanation of the subject at hand.

 A search tool allows users to find videos pertaining to specific operations or functions.

 Science World: The guides on this site are divided into five categories: Physics, Chemistry, Astronomy, Mathematics, and Biography. Each was created by researchers from Wolfram using Mathematica software, and are available to users free-of-charge.

 Many guides feature .GIF images, 3D animation, and other high-resolution media resources.

 A large portion of the articles are user-generated; contributors upload content, and site administrators edit the submissions for accuracy and readability.

 Famous figures in the sciences are searchable by name, nationality, historical period, and/or prizes won during their lifetime.

 Science.gov: This bare-bones site features links to more than 200 contemporary science topics. The list is alphabetized, and each entry will redirect users to all federal agencies and organizations associated with that particular field.

 The site curates information from more than 55 databases, 2,100 websites, and 200 million individual pages.

 The Science.gov homepage also features a news bulletin, video clips, and other science-oriented resources.

Thomas Adewumi University

 Eformulae.com: This site is a collection of scientific and mathematical formulas used in fields like engineering, physics, chemistry, and statistics. The layout is fairly rudimentary, but the materials are easy to access and the information is reviewed and edited by experts in these respective fields.

 For each formula, all variables and operations are clearly defined. See the ‘Engineering Formulas‘ page as an example.

 For fields with differing schools of thought, different formulas are housed in their own sections (as is the case with ‘Applied Mechanics‘, and others).

 Biology Online: Registration is free on this site, which hosts digital books, article links, tutorials, and a dictionary of biology-related terminology.

 The site's forum lets users post questions and take part in biology-oriented discussions.

 Another popular feature of the site is a monthly blog that covers topics like allergy season, botany, and obesity.

 Published authors are invited to share their work on the site and receive feedback from other registered users.

 Published authors are invited to share their work on the site and receive feedback from other registered users.

 Biology Reference: Simple and easy-to-use, this alphabetized directory of biology topics features detailed encyclopedic entries written by on-site authors.

 All articles feature a bibliography of sources and comment field for readers to provide feedback.

 A significant amount of interlinking between entries allows users to browse similar topics with relative ease.

 Ptable: This illustrated guide to the Periodic Table of Elements features definitions of all elements, as well as information related to orbitals, isotopes, compounds, and other fundamentals of chemistry.

 All element definitions are linked to their corresponding Wikipedia pages.

 The interactive diagrams allow users to toggle boiling/melting point, electronegativity, density, and other comparative aspects of different elements.

 ChemnetBase: This database of reference materials includes guides to specific scientific topics, such as the ‘Combined Chemical Dictionary‘ and the ‘Dictionary of Drugs.' Subscriptions to the site are not free, but all new members receive a free thirty-day trial.

 The site also includes a section dedicated to ‘Librarian Resources.'

 ‘Subject Collections‘ of e-books pertaining to 43 different professional fields are housed on individual pages.