全文获取类型
收费全文 | 602947篇 |
免费 | 8010篇 |
国内免费 | 1868篇 |
专业分类
电工技术 | 10248篇 |
综合类 | 2823篇 |
化学工业 | 88847篇 |
金属工艺 | 24443篇 |
机械仪表 | 18105篇 |
建筑科学 | 14695篇 |
矿业工程 | 2803篇 |
能源动力 | 15564篇 |
轻工业 | 50286篇 |
水利工程 | 6394篇 |
石油天然气 | 9657篇 |
武器工业 | 37篇 |
无线电 | 68568篇 |
一般工业技术 | 116497篇 |
冶金工业 | 105883篇 |
原子能技术 | 10776篇 |
自动化技术 | 67199篇 |
出版年
2022年 | 3159篇 |
2021年 | 4893篇 |
2020年 | 3479篇 |
2019年 | 4556篇 |
2018年 | 21323篇 |
2017年 | 20100篇 |
2016年 | 17305篇 |
2015年 | 6114篇 |
2014年 | 9424篇 |
2013年 | 24201篇 |
2012年 | 17502篇 |
2011年 | 28914篇 |
2010年 | 23441篇 |
2009年 | 22857篇 |
2008年 | 24350篇 |
2007年 | 24969篇 |
2006年 | 15604篇 |
2005年 | 15296篇 |
2004年 | 14613篇 |
2003年 | 14467篇 |
2002年 | 13127篇 |
2001年 | 12912篇 |
2000年 | 12029篇 |
1999年 | 12643篇 |
1998年 | 32856篇 |
1997年 | 22917篇 |
1996年 | 17485篇 |
1995年 | 13041篇 |
1994年 | 11292篇 |
1993年 | 10980篇 |
1992年 | 7922篇 |
1991年 | 7439篇 |
1990年 | 7261篇 |
1989年 | 7013篇 |
1988年 | 6476篇 |
1987年 | 5766篇 |
1986年 | 5655篇 |
1985年 | 6265篇 |
1984年 | 5900篇 |
1983年 | 5170篇 |
1982年 | 4900篇 |
1981年 | 4966篇 |
1980年 | 4705篇 |
1979年 | 4609篇 |
1978年 | 4408篇 |
1977年 | 5334篇 |
1976年 | 6971篇 |
1975年 | 3796篇 |
1974年 | 3550篇 |
1973年 | 3665篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A three-stage study has been carried out with rainbow trout (Oncorhyncus mykiss) to develop analytical approaches which can provide a fingerprint for tainting by oil sands chemicals from process-affected waters and natural sources. The objective was to find a simpler alternative to sensory evaluation. In the first stage, a set of seven test compounds was added to fish tissue which was analysed by headspace and solvent (dichloromethane, DCM) extraction followed by gas chromatography-mass spectrometry (GC-MS). In the second stage, fingerlings (5-20 g) were exposed for 96 hours to the test compound mixture at 1.0 and 0.5 times the estimated tainting threshold concentrations. In the final stage, fingerlings were exposed for 96 hours to an oil sands process water at 5, 10, 20 and 50% concentrations in clean water. None of the test compounds was identified in DCM extracts of tissue from exposed fish. Two long-chain aldehydes, hexadecanal and 9-octadecenal, were tentatively identified in these extracts by matching of mass spectra with library spectra. 相似文献
992.
993.
994.
K. F. Müller Dr.-Ing. 《Materials and Structures》1985,18(6):463-472
The development in recent years with increasing air pollution, increasing need of energy saving and last not least the growing number of damage in old structures leads to a raising demand to calculate the durability of structures, too. The paper has been prepared by request of the RILEM Technical Committee 45-LTO to show that, in principle, it is possible to evolve a theory for predicting the service life of r.c. structures and to sketch a way how that could be achieved. A lot of necessary basic data can be found scattered in the literature. To collect these data will be the first step to take. 相似文献
995.
In this study, the effects of low energy ultrasound irradiation on landfill leachate treatment by means of sequencing bath reactor were investigated. The aim of this work was to estimate the influence of leachate irradiation time on aerobic treatment efficiency. The sonification of the leachate was carried out in static conditions using the disintegrator UD-20. The field frequency of 22 kHz (the power output equals to 180 W) and amplitude of 12 microm was applied. The sonification time was changed in the range of 30-140 s. It was found that ultrasonic pretreatment enhances the subsequent aerobic digestion resulting in a better degradation of landfill leachate. The sonification of raw leachate leads to enhancement of COD and ammonia removal as compare to experiment without ultrasound. 相似文献
996.
Yadin Y. Nazarathy M. Bilenca A. Orenstein M. 《Lightwave Technology, Journal of》2007,25(6):1431-1440
The recently introduced multichip differential phase-shift keying (MC-DPSK) optical transmission format, entailing the modulation of relative phases over a moving transmission window of successive chip intervals, is analytically and numerically analyzed. The maximum-likelihood optimal MC-DPSK receiver is derived and synthesized using integrated-optic Mach-Zehnder delay interferometers, whose electrical outputs are interpreted as generalized Stokes' parameters. The MC-DPSK performance over a nonlinear fiber channel, limited by the combination of amplified spontaneous emission noise and self-phase modulation, is further derived and simulated, demonstrating that the lowest complexity three-chip binary-phase MC-DPSK receiver provides an ~1-dB Q-factor advantage over conventional DPSK. 相似文献
997.
998.
A calorimetric measurement technique developed for NASA's Deep Space Network (DSN) transmitters that does not require data on the coolant's thermal parameters is described. Calibration of the measurement system is achieved by measuring the DC input power to the klystron and relating coolant temperature increase to this known power dissipation. Agreement between calorimetric and electrical measurements of total system power was good, the difference being less than 2%. The operation of the system was not greatly affected by the composition of the coolant, which was varied from pure water to 40% ethylene glycol by mass. Good accuracy was also shown at output power levels, which varied over a 3.6:1 range 相似文献
999.
1000.