资料库：免费学习与研究链接

百科全书与综合参考

Wikipedia The fastest way to get oriented on almost any topic. Follow its footnotes to real sources.
Encyclopaedia Britannica Editor-reviewed articles you can safely cite when Wikipedia is not accepted.
Stanford Encyclopedia of Philosophy Peer-reviewed, in-depth entries, the standard reference for philosophy essays.
Wikimedia Commons Millions of freely licensed images and diagrams for presentations and projects.
Our World in Data Clear charts and datasets on global topics, ready to cite in essays.
CIA World Factbook Up-to-date country statistics (population, economy, geography) in one place.

OpenStax Complete peer-reviewed textbooks you can download instead of buying.
MIT OpenCourseWare Full MIT courses with lecture notes, problem sets, and exams to practise on.
Khan Academy Short video lessons with instant practice, good for filling gaps before an exam.
LibreTexts Huge open library of chemistry, biology, and maths texts organised by course.
Open Yale Courses Recorded Yale lectures in full, strong for humanities and psychology.
Coursera (audit) Most university courses can be audited free: skip the certificate, keep the content.
OpenLearn Free Open University short courses with built-in self-assessment.

Wolfram Alpha Solves equations step-free and answers computable questions. Great for checking work.
Desmos Instant in-browser graphing calculator: see what a function actually does.
GeoGebra Interactive geometry and algebra you can drag around to build intuition.
PhET Simulations Physics and chemistry experiments you can run in the browser when there is no lab.
Wolfram MathWorld Precise definitions and theorems when your textbook is vague.
NASA Real mission data, images, and explainers for space and earth science projects.
PubMed Search real biomedical research. Abstracts are free and citable.
Periodic Table (Ptable) Interactive periodic table with properties, isotopes, and orbitals on hover.
3Blue1Brown Visual explanations of calculus and linear algebra that make the ideas click.

Purdue OWL The standard guide for APA/MLA citation rules and academic writing structure.
Merriam-Webster Reliable dictionary with usage notes. Settles "which word is right" arguments.
Cambridge Dictionary Definitions in plain English plus translations, kinder to non-native speakers.
Thesaurus.com Fast synonyms when the same word keeps appearing in your essay.
Hemingway Editor Paste a draft and it highlights sentences that are too long or too dense.
Zotero Collects sources as you browse and formats the bibliography for you.
Etymonline Word origins, useful for language essays and remembering vocabulary.

Project Gutenberg Over 70,000 public-domain classics: every set text older than 1929, free.
Internet Archive Borrow scanned books and revisit dead web pages via the Wayback Machine.
JSTOR (free reading) Register free to read a quota of real academic papers each month.
World History Encyclopedia Well-sourced ancient and world history articles written for students.
The British Museum Search millions of objects from the collection with images and context.
Smithsonian Open Access Millions of museum images and 3D models, free to reuse in any project.
Google Arts & Culture Zoom into artworks in extreme detail and tour museums virtually.
Library of Congress Primary sources (photographs, maps, newspapers) for history projects.

Wiktionary A free dictionary in many languages, with full conjugation and declension tables.
WordReference Bilingual dictionaries with forum threads on the phrases textbooks miss.
Forvo Hear any word pronounced by native speakers before you say it in class.
Tatoeba Millions of example sentences with translations, so you can see words used in context.
DeepL Best-in-class machine translation for checking your own sentences.

Learning Scientists Six study techniques that actually work, explained with printable guides.
Anki Free spaced-repetition flashcards, the heavyweight option for long-term memory.
Pomofocus A clean Pomodoro timer if you want one outside Brainlag.
Crash Course Fast, funny video overviews of whole subjects, good before starting a topic.