It's a little difficult to keep a tech lead in civ3, because once one civ has already researched a tech (that being you), the price in beakers comes down for all the others. So there's a built-in bias against letting any civ get too far out in front. (Note that this can also work *for* you if you are behind.)
Some tips to maintain a lead:
- build roads everywhere; you get one extra commerce for every roaded tile your citizens are working
- switch to republic and/or democracy; these governments give you one more commerce for every tile that's already producing commerce
- build marketplaces, banks, stock exchanges (PTW only), Wall Street (all of these will increase your available cash, which means the same 80% research setting actually gets you more research)
- build libraries/universities
- build happiness improvements to allow more of your citizens to be productive and/or get bigger cities
- build harbors in your coastal cities (this allows more citizens to work ocean tiles by increasing the food you get from them; each ocean tile produces three or two commerce) in PTW build commercial docks
- build courthouses and police stations in towns that are marginally corrupt; this will allow more of the commerce they produce to actually make it into your coffers
Many wonders are useful for research too. Copernicus/Newton's are self-explanatory - try building them in a city that's already producing a lot of uncorrupted commerce. Pyramids/Sun Tzu's/Smith's reduce maintenance costs, therefore freeing up more cash for research. Pyramids also helps your growth rate. Oracle/Hanging Gardens/Sistine/Bach's all keep more citizens happy, which means fewer entertainers and/or a lower luxury slider, which also means more cash. Leo's can be useful, too, in the 'more free cash' category, especially if you have a largeish military that needs a lot of upgrades.
Finally, check your city screens to see how many of your citizens are entertainers. If it's a large number, you may be able to get better productivity by putting them all back to work and using the lux slider instead to keep them happy.
Good luck!
Renata