Here are some of our favorite science books. Though we are not yet middle or high school level at our house, I have compiled some I think you might like. I have also included some traditional texbooks from the 21st century. They are categorized by a broad range below. There are many more on Google Books. You can use some of the words in these titles as key words in your search. You can read more about searching for free ebooks on Finding Free Textbooks on Google Books or Searching the Internet Archive.
You can find more science for primary in Narrative Style Science Readers
First Year Science-with experiments
Science for Beginners: A First Book in General Science for … with exercises to illustrate principles
Science for Beginners with exercises to illustrate principles
General Science: First Course with questions and excercises