If all you want to learn is technical scientific terms, you might be better just reading science journals in your field of interest and using a scientific dictionary to double-check terms. Alternatively, just get a good Greek dictionary to look up the roots of the words ("Let's see . . . epidermis = epi 'on' + dermis 'skin' = the outer layer of skin! Of course!").
If you have a desire to read ancient Greek literature, though, you've come to the right place. In the "Library" section of this website, there are old-but-useful Greek books in PDF, downloadable for free! If you want to start with classical Greek, download White's First Greek Book. If you want to start with Homeric, download Pharr's Homeric Greek. These books are a bit "old-school" - they're heavy on straight memorization. Get started there, and start reading the forums. If White and Pharr aren't working out for you, the posters here can help you identify exactly what you need, and point you in the direction of other resources.