They are tech trading constantly. This is a huge part of the game and you won't realize this till you lose your first game and wonder how the heck they outpaced you in tech so quickly.
Once you realize they are tech trading and you make a race with some diplomacy you can control the tech trade and profit greatly. You will have thousands of credits. I have 20,000 while everyone else has about 100 trying to keep up with paying for any new techs I have either bought off the humans or someone else and sold to everyone else before they had a chance.
So basically you have to buy any new tech that comes along and sell it to everyone else before the one who created the tech has a chance to do it themselves. You won't make that much off each sale but selling one tech for 400 a piece to each civ gets you about 3200 credits more or less per high level tech. Basically, this game is teaching you to become Microsoft.

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Some of the later techs can get expensive to buy off other races, especially the humans, which charge me about 3000 for some of the more powerful techs like phasors. So if you can't get a powerful tech it's probably because you don't have the funds to buy it, they get expensive. But like I said, if you play their game, you can easily beat them at it and have plenty of money to buy any new tech that comes along and sell it to recoup the loss in money. Pick one area of tech to keep for yourself as an advantage and never trade this area. I do this with missile tech to keep an edge. When you research mid game, only go for the techs that will give you an advantage and let everyone else research the other techs for you.
Right now in my medium galaxy, diplomatic race, my competitors are the humans. The humans are my biggest competitors since they alone have a higher diplomacy rating than me (I go for some research and military bonuses in my race) and sometimes create the tech and get a few sales if I become less diligent. They can do this because they created a pool of money in the early game with tech trading that they use now to fund their economy for research. I still have a major lead over them 20,000 to 5000.
Until this is fixed you "have" to tech trade to keep up with the tech.