全文获取类型
收费全文 | 390664篇 |
免费 | 4102篇 |
国内免费 | 779篇 |
专业分类
电工技术 | 6600篇 |
综合类 | 216篇 |
化学工业 | 60691篇 |
金属工艺 | 21054篇 |
机械仪表 | 14230篇 |
建筑科学 | 7348篇 |
矿业工程 | 4752篇 |
能源动力 | 7878篇 |
轻工业 | 20933篇 |
水利工程 | 5905篇 |
石油天然气 | 16122篇 |
武器工业 | 41篇 |
无线电 | 36816篇 |
一般工业技术 | 91871篇 |
冶金工业 | 59029篇 |
原子能技术 | 13973篇 |
自动化技术 | 28086篇 |
出版年
2021年 | 4027篇 |
2019年 | 3932篇 |
2018年 | 7426篇 |
2017年 | 7676篇 |
2016年 | 8150篇 |
2015年 | 4490篇 |
2014年 | 7645篇 |
2013年 | 16489篇 |
2012年 | 11029篇 |
2011年 | 13950篇 |
2010年 | 11313篇 |
2009年 | 12609篇 |
2008年 | 12847篇 |
2007年 | 12393篇 |
2006年 | 10350篇 |
2005年 | 9323篇 |
2004年 | 8859篇 |
2003年 | 8611篇 |
2002年 | 8341篇 |
2001年 | 8247篇 |
2000年 | 8005篇 |
1999年 | 7524篇 |
1998年 | 16273篇 |
1997年 | 12015篇 |
1996年 | 9128篇 |
1995年 | 7077篇 |
1994年 | 6395篇 |
1993年 | 6684篇 |
1992年 | 5376篇 |
1991年 | 5452篇 |
1990年 | 5383篇 |
1989年 | 5200篇 |
1988年 | 5109篇 |
1987年 | 4796篇 |
1986年 | 4754篇 |
1985年 | 5191篇 |
1984年 | 4964篇 |
1983年 | 4761篇 |
1982年 | 4429篇 |
1981年 | 4459篇 |
1980年 | 4517篇 |
1979年 | 4706篇 |
1978年 | 4827篇 |
1977年 | 5026篇 |
1976年 | 5767篇 |
1975年 | 4445篇 |
1974年 | 4462篇 |
1973年 | 4556篇 |
1972年 | 4051篇 |
1971年 | 3701篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
The biochemical composition can be seen as a good indicator of both the biodegradability and the methane potential of a given waste. The work presented here is an attempt to elaborate a typology of wastes and to compare it to the anaerobic degradation characteristics. The first data indicate that there is a link between the ligno-cellulosic content of the waste and the biodegradability. When dealing with application to anaerobic digestion processes, having a tool to predict the ability of the waste to be degraded could be of the greatest interest for preventing failures, estimating biogas production, methane content, or for the management of co-digestion processes. 相似文献
972.
Yu. A. Brodskii V. I. Bazikov I. V. Zubkov A. I. Krylov V. D. Stepanenko 《Chemical and Petroleum Engineering》2006,42(9-10):552-559
Modern designs are examined, and technical data presented for vibratory electric and convection driers, driers with infra-red sources, and steam driers. 相似文献
973.
We address the problem of estimating the instantaneous frequency (IF) of a phase signal using its level-crossing (LC) information based on front-end auditory processing motivation. We show that the problem of IF estimation using LC information can be cast in the framework of estimation from irregularly sampled data. The formulation has the generality of estimating different types of IF without the need for a quasistationary assumption. We consider two types of IF-polynomial and bandlimited; we use polynomial interpolating functions for the former, and for the latter, we propose a novel "line plus sum of sines" model. The model parameters are estimated by linear regression. Considering the noisy case, LC data for different levels is analyzed, and methods for combining different estimators from LCs are discussed. Theoretical and extensive simulation results show that the performance of the zero-crossing (ZC) based IF estimator and the level-crossing based IF estimator with smaller level values is better than those obtained with higher level values or their combinations. The new technique reaches the Crame/spl acute/r-Rao bound (CRB) roughly above 4 dB signal-to-noise ratio (SNR), and its performance does not deteriorate rapidly with mismatch in the IF order compared with the other techniques in the literature. 相似文献
974.
The application of micro- and nanofabrication processes to the development of hybrid synthetic and biological systems may enable the production of new devices such as controllable transporters, gears, levers, micropumps, or microgenerators powered by biological molecular motors. However, engineering these hybrid devices requires fabrication processes that are compatible with biological materials such as kinesin motor proteins and microtubules. In this paper, the effects of micro- and nanofabrication processing chemicals and resists on the functionality of casein, kinesin, and microtubule proteins are systematically examined to address the important missing link of the biocompatibility of micro- and nanofabrication processes needed to realize hybrid system fabrication. It is found that both casein, which is used to prevent motor denaturation on surfaces, and kinesin motors are surprisingly tolerant of most of the processing chemicals examined. Microtubules, however, are much more sensitive. Exposure to the processing chemicals leads to depolymerization, which is partially attributed to the pH of the solutions examined. When the chemicals were diluted in aqueous buffers, a subset of them no longer depolymerized microtubules and in their diluted forms still worked as resist removers. This approach broadens the application of micro- and nanofabrication processes to hybrid synthetic and biological system fabrication. 相似文献
975.
Hasan M.K. Hossain N.M. Naylor P.A. 《Vision, Image and Signal Processing, IEE Proceedings -》2005,152(5):520-526
A novel method for parameter estimation of minimum-phase autoregressive moving average (ARMA) systems in noise is presented. The ARMA parameters are estimated using a damped sinusoidal model representation of the autocorrelation function of the noise-free ARMA signal. The AR parameters are obtained directly from the estimates of the damped sinusoidal model parameters with guaranteed stability. The MA parameters are estimated using a correlation matching technique. Simulation results show that the proposed method can estimate the ARMA parameters with better accuracy as compared to other reported methods, in particular for low SNRs. 相似文献
976.
Telecommunications operators are undergoing massive transformations in order to metamorphose themselves into the ICT world and compete with agile, lean IT organisations. The main challenges facing telecommunications operators, such as BT, are to reduce costs and increase agility in deploying software systems for provisioning ICT services. Despite using reusable capabilities and COTS packages, the major source of increased cost lies in the heavy integration tax we incur for integrating diverse systems implemented on diverse platforms and middleware, with heterogeneous data and process models. This paper looks at cost implications of lengthy and often manual migration to-and-from systems and platforms, and shows the clear business benefits of model-driven development (MDD) as defined by the Object Management Group (OMG). It is clearly demonstrated that model-driven development has matured into a practical, industrialised, scalable and evolvable technology, culminating from decades of R&D on specification and design languages, executable formalisms and domainspecific languages and language transformations. 相似文献
977.
The effect of low-power laser radiation on the formation of oriented cadmium sulfide layers from a vapor phase on a substrate cooled with liquid nitrogen (highly nonequilibrium conditions) is studied. The results of technological experiments, the results of a study of electron diffraction (electron diffraction patterns), and condensation diagram data are reported. It is found that, depending on the substrate temperature, laser radiation can both improve and worsen the crystal quality of films. It is shown that a condensation diagram of cadmium sulfide layers formed on a substrate exposed to low-power laser radiation is shifted to higher temperatures relative to a condensation diagram obtained without laser radiation. The experimental results are interpreted in the context of a solitonic heteroepitaxy model. 相似文献
978.
Hadjem A. Lautru D. Dale C. Man Fai Wong Hanna V.F. Wiart J. 《Microwave Theory and Techniques》2005,53(1):4-11
This paper gives a first comparison of specific absorption rate (SAR) induced in a child-sized (CS) head and an adult head using a dual-band mobile phone. In the second study, the visible human head is considered and comparison of SAR induced in a CS or child-like (CL) head and an adult head using a dual-band mobile phone is given. All the peaks of average SAR over a mass of 10 and 1 g in the head and the power budget are determined in the two comparisons using the finite-difference time-domain method. The differences between the results for adult and CS or CL heads are given at 900 and 1800 MHz. No important differences are noted for the peak SAR averaged over 10 g (SAR10 g), between the two adult head models, as well as between the two child head models. The peak SAR10 g in the brain of the CS or CL head is slightly more significant than that for the adult one. 相似文献
979.
O Bernard B Chachuat A Hélias B Le Dantec B Sialve J-P Steyer L Lardon P Neveu S Lambert J Gallop M Dixon P Ratini A Quintabà S Frattesi J M Lema E Roca G Ruiz J Rodriguez A Franco P Vanrolleghem U Zaher D J W De Pauw K De Neve K Lievens D Dochaine O Schoefs H Fibrianto R Farina V Alcaraz Gonzalez V Gonzalez Alvarez P Lemaire J A Martinez F Esandi O Duclaud J F Lavigne 《Water science and technology》2005,52(1-2):457-464
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem. 相似文献
980.
Practical limitations of subwavelength resolution using negative-refractive-index transmission-line lenses 总被引:3,自引:0,他引:3
Previously, we have demonstrated both analytically and experimentally subwavelength imaging using a negative-refractive-index lens made of a periodically L, C loaded transmission line (TL) network. This loaded transmission line network has been referred to as the dual TL lens. Here, we consider the limitations on subwavelength imaging imposed by impedance mismatches and the component losses of a practical dual TL lens. Simple expressions for estimating the resolving capability of a dual TL lens are given. It is found that the resolution enhancement of the dual lens is proportional to the quality factor of the series loading capacitors divided by the electrical thickness of the lens. The effective material parameters of the dual TL lens are also derived so that these expressions can be directly related to those of previous studies considering uniform and isotropic left-handed lenses. Finally, the resolving capability of an experimental lens that achieves subwavelength imaging is theoretically predicted. These theoretical predictions are then directly compared to previously reported experimental results. 相似文献