全文获取类型
收费全文 | 506398篇 |
免费 | 14584篇 |
国内免费 | 5485篇 |
专业分类
电工技术 | 13206篇 |
技术理论 | 6篇 |
综合类 | 6565篇 |
化学工业 | 76918篇 |
金属工艺 | 20191篇 |
机械仪表 | 18752篇 |
建筑科学 | 19457篇 |
矿业工程 | 4207篇 |
能源动力 | 13961篇 |
轻工业 | 49550篇 |
水利工程 | 4932篇 |
石油天然气 | 9021篇 |
武器工业 | 818篇 |
无线电 | 65589篇 |
一般工业技术 | 87316篇 |
冶金工业 | 79490篇 |
原子能技术 | 6539篇 |
自动化技术 | 49949篇 |
出版年
2022年 | 3529篇 |
2021年 | 6690篇 |
2020年 | 4985篇 |
2019年 | 5004篇 |
2018年 | 6641篇 |
2017年 | 7070篇 |
2016年 | 7065篇 |
2015年 | 7461篇 |
2014年 | 10517篇 |
2013年 | 24941篇 |
2012年 | 16401篇 |
2011年 | 21259篇 |
2010年 | 16941篇 |
2009年 | 18255篇 |
2008年 | 19144篇 |
2007年 | 19249篇 |
2006年 | 18084篇 |
2005年 | 16556篇 |
2004年 | 14472篇 |
2003年 | 14039篇 |
2002年 | 13511篇 |
2001年 | 13494篇 |
2000年 | 12546篇 |
1999年 | 13331篇 |
1998年 | 26008篇 |
1997年 | 19250篇 |
1996年 | 15528篇 |
1995年 | 12336篇 |
1994年 | 10886篇 |
1993年 | 10065篇 |
1992年 | 7746篇 |
1991年 | 7213篇 |
1990年 | 6733篇 |
1989年 | 6382篇 |
1988年 | 6075篇 |
1987年 | 5019篇 |
1986年 | 4945篇 |
1985年 | 6043篇 |
1984年 | 5565篇 |
1983年 | 4802篇 |
1982年 | 4471篇 |
1981年 | 4415篇 |
1980年 | 4152篇 |
1979年 | 4044篇 |
1978年 | 3725篇 |
1977年 | 4501篇 |
1976年 | 6055篇 |
1975年 | 3084篇 |
1974年 | 2973篇 |
1973年 | 2851篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Faulkner D.W. Payne D.B. Stern J.R. Ballance J.W. 《Lightwave Technology, Journal of》1989,7(11):1741-1751
Some of the options for optical technology within the local loop environment are examined. In particular, passive shared access networks have been considered in some detail. These networks show great promise for delivering existing telephone services to small to medium business customers (4-30 lines) economically by the early 1990s. Extending fiber to the home will also be possible by virtue of a similar passive network infrastructure for customers requiring new broadband services beyond the single telephone line. For one-line plain old telephone service (POTS) customers, an intermediate approach of terminating the fiber network at the final network distribution point, with copper retained for the final leg, may be used prior to the provision of broadband services. A key feature of the passive optical network architecture is the use of wavelength-division multiplexing (WDM) as an upgrade strategy, allowing graceful upgrading from telephone services to multichannel high-definition television (HDTV) on gigabit/second bearers and full two-way switched broadband services employing wavelength routing across the network 相似文献
992.
A. J. Hugo D. M. Jakelski G. Stanitsas G. R. Sullivan R. R. Hudgins P. L. Silveston 《加拿大化工杂志》1986,64(2):349-351
In the approach to a cycle-invariant state in the forced feed concentration cycling of the CO oxidation over a NiO catalyst, a very long transient has been observed lasting 80 ks or more. This transient appears to be associated only with CO pretreatment of the catalyst and is not a general phenomenon. The slow convergence to the cycle-invariant state reported in certain modelling calculations in the literature appears to have a different cause. 相似文献
993.
Nelson Douglas L.; Canas Jose J.; Bajo Maria T.; Keelean Patricia D. 《Canadian Metallurgical Quarterly》1987,13(4):542
Cued recall with word stems as cues and fragment completion rely on different types of letter cues and also differ in the explicit–implicit nature of the retrieval orientation. Despite these differences, variables effective in one task may be effective in the other because both rely on letter cues. Two variables known to affect cued recall were manipulated: Lexical set size (number of words that fit the letter cue) and meaning set size (number of associates generated to the studied words). Across four experiments, subjects in each task were less likely to recover targets from larger lexical sets. However, meaning set size affected cued recall but not fragment completion. These results indicate that fragment completion and letter-cued recall are based on lexical search but that cued recall also involves a semantic search component. Furthermore, type of retrieval cue had a greater effect than type of retrieval orientation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
994.
Zhibin Xiong Haitao Liu Chunxiang Zhu Sin J.K.O. 《Electron Devices, IEEE Transactions on》2005,52(12):2629-2633
In this paper, a new polysilicon CMOS self-aligned double-gate thin-film transistor (SA-DG TFT) technology is proposed and experimentally demonstrated. The self-alignment between the top- and bottom-gate is realized by a backlight exposure technique. The structure has an ultrathin channel region (300 /spl Aring/) and a thick source/drain region. Experimental results show that this technology provides excellent current saturation due to a combination of the effective reduction in the drain field and the full depletion of the ultrathin channel. Moreover, for n-channel devices, the SA-DG TFT has a 4.2 times higher on-current (V/sub gs/=20V) as compared to the conventional single-gate TFT. Whereas for the p-channel devices, the SADG TFT has a 3.6 times higher on-current (V/sub gs/=-20V) compared to the conventional single-gate device. 相似文献
995.
The comfort diagrams and the so-called PMV-PPD values are already used today directly and indirectly in a wide field in technical practice, even at a standard level. This theory is known also in Hungary, and the PMV-PPD values have been used by us for the solution of a design problem. The task was to elaborate a calculation method, an index number suitable for the determination of the thermal confort effect in the case of occasional underheating of residential and communal buildings in winter.The results of this work are presented in this paper. 相似文献
996.
M. Delgado-Pinar J. Mora A. Diez J.L. Cruz M.V. Andres 《Photonics Technology Letters, IEEE》2005,17(3):552-554
We report a wavelength-switchable fiber ring laser that includes a Bragg grating-based acoustooptic superlattice modulator. Wavelength switching of the laser emission is achieved by controlling the peak reflectivity of the different reflection bands that appear on both sides of the Bragg wavelength when a longitudinal acoustic wave propagates along the grating. 相似文献
997.
It has been demonstrated recently that it is possible to guide broadband Terahertz pulses utilising a novel coaxial waveguide. This technique is hindered by the difficulty in exciting the radially polarised fundamental mode of the waveguide. To optimise mode matching, a novel radially symmetric photoconductive Terahertz antenna is proposed. Using finite element method simulations and analytical calculations, it is shown that this antenna can generate the desired radial polarisation. 相似文献
998.
A multi-channel continuous toxicity monitoring system developed in our laboratory, based on two-stage mini-bioreactors, was successfully implemented in the form of computer-based data acquisition. The multi-channel system consists of a series of a two-stage minibioreactor systems connected by a fiber optic probe to a luminometer, and uses genetically engineered bioluminescent bacteria for the detection of the potential toxicity from the soluble chemicals. This system can be stably and continuously operated due to the separation of the culture reactor from the test reactor and accomplish easy and long-term monitoring without system shut down by abrupt inflows of severe polluting chemicals. Four different recombinant bioluminescent bacteria were used in different channels so that the modes of the samples toxicities can be reasonably identified and evaluated based upon the response signature of each channel. The bioluminescent signatures were delivered from four channels by switching one at once, while the data is automatically logged to an IBM compatible computer. We also achieved the enhancement of the system through the manipulation of the dilution rate and the use of thermo-lux fusion strains. Finally, this system is now being implemented to a drinking water reservoir and river for remote sensing as an early warning system. 相似文献
999.
Lessons learnt from 15 years of ICA in anaerobic digesters. 总被引:1,自引:0,他引:1
Anaerobic digestion plants are highly efficient wastewater treatment processes with inherent energy production. Despite these advantages, many industries are still reluctant to use them because of their instability confronted with changes in operating conditions. There is therefore great potential for application of instrumentation, control and automation (ICA) in the field of anaerobic digestion. This paper will discuss the requirements (in terms of on-line sensors needed, modelling efforts and mathematical complexity) but also the advantages and drawbacks of different control strategies that have been applied to AD high rate processes over the last 15 years. 相似文献