全文获取类型
收费全文 | 9213篇 |
免费 | 510篇 |
国内免费 | 65篇 |
专业分类
电工技术 | 255篇 |
综合类 | 31篇 |
化学工业 | 1883篇 |
金属工艺 | 204篇 |
机械仪表 | 241篇 |
建筑科学 | 316篇 |
矿业工程 | 12篇 |
能源动力 | 617篇 |
轻工业 | 983篇 |
水利工程 | 119篇 |
石油天然气 | 207篇 |
武器工业 | 6篇 |
无线电 | 1117篇 |
一般工业技术 | 1639篇 |
冶金工业 | 561篇 |
原子能技术 | 82篇 |
自动化技术 | 1515篇 |
出版年
2023年 | 198篇 |
2022年 | 366篇 |
2021年 | 628篇 |
2020年 | 478篇 |
2019年 | 484篇 |
2018年 | 612篇 |
2017年 | 437篇 |
2016年 | 502篇 |
2015年 | 301篇 |
2014年 | 456篇 |
2013年 | 755篇 |
2012年 | 518篇 |
2011年 | 541篇 |
2010年 | 365篇 |
2009年 | 307篇 |
2008年 | 270篇 |
2007年 | 250篇 |
2006年 | 207篇 |
2005年 | 180篇 |
2004年 | 144篇 |
2003年 | 111篇 |
2002年 | 128篇 |
2001年 | 72篇 |
2000年 | 79篇 |
1999年 | 94篇 |
1998年 | 164篇 |
1997年 | 133篇 |
1996年 | 74篇 |
1995年 | 96篇 |
1994年 | 61篇 |
1993年 | 59篇 |
1992年 | 44篇 |
1991年 | 28篇 |
1990年 | 33篇 |
1989年 | 53篇 |
1988年 | 49篇 |
1987年 | 31篇 |
1986年 | 33篇 |
1985年 | 53篇 |
1984年 | 48篇 |
1983年 | 39篇 |
1982年 | 32篇 |
1981年 | 24篇 |
1980年 | 32篇 |
1979年 | 22篇 |
1978年 | 19篇 |
1977年 | 22篇 |
1976年 | 34篇 |
1975年 | 17篇 |
1973年 | 18篇 |
排序方式: 共有9788条查询结果,搜索用时 156 毫秒
991.
A subclass of Cohen's class of time-frequency (TF) distributions is introduced in which the TF distribution kernels are provided via the frequency transformation method (FTM), used in two dimensional (2-D) filter design. The FTM kernels have finite extent in time and frequency and allow the TF distribution to be efficiently implemented in all four domains 相似文献
992.
Phosphatic materials of agronomic interest were synthesised. These materials of good mechanical quality and of significant porosity show high P2O5 contents (up to 28%). They have been prepared by treatment of volcanic pumices with a solution of phosphoric acid (1N, 5N or 10N) at 200°C in a closed system for 72h using a mass solid/liquid ratio of 1:3.After reaction, the precipitation of amorphous phosphates and crystalline aluminium phosphates has been detected by XRD both outside and inside of the material. The morphological study by SEM reveals several crystalline forms of aluminium phosphates: crystals of small size migrate into the internal porosity of the pumices and crystals of berlinite appear (AlPO4) well developed in a matrix of amorphous phosphate overlapping the initial material.Normal tests of reactivity in water and in 2% citric acid show that the percentages of released P2O5 in solution are greater after treatment with weak concentrations of phosphoric acid. Lixiviation of treated materials with citric acid reagent shows that, after three days of reaction, losses in weight are considerable and the kinetic curves of phosphorus liberation present a linear evolution.The fertilizing value of these materials did not decrease during the leaching; so phosphorus will be solubilized with time thus allowing these materials to gain a good agronomical availability and to propose their use as delayed fertilizer types for tropical agricultural soils. 相似文献
993.
Protective coatings for carbon bonded carbon fibre composites 总被引:1,自引:0,他引:1
F. Smeacetto M. Ferraris M. Salvo S.D. Ellacott A. Ahmed R.D. Rawlings A.R. Boccaccini 《Ceramics International》2008
Carbon bonded carbon fibre composites (CBCF) were modified by direct reaction with molten silicon in order to obtain a silicon carbide layer on the composite surface. Subsequently, the Si-infiltrated CBCF material was coated with a silica-based glass containing yttria and alumina by means of a slurry-dipping technique. On heat treatment the glass yielded a glass-ceramic layer thus giving a multi-layered oxidation and erosion protection system. The microstructural characterisation of the coating was conducted by standard microscopy techniques and by X-ray diffraction. The controlled crystallization of the glass-produced cristobalite, yttrium silicate (Y2Si2O7, keiviite, β-form) and mullite as main crystalline phases. These are excellent ceramic materials for oxidation and erosion protection of SiC-coated carbon-based composites since their coefficients of thermal expansion (CTE) closely match that of SiC. The possibility of healing (closure) of micro cracks by a thermal treatment at 1375 °C, thus exploiting the viscous flow of the residual glass in the glass-ceramic, was explored in order to extend the service life of the protection system. 相似文献
994.
Maxime Wack Ahmed Nait-Sidi-Moh Sid Lamrous Nathanael Cottin 《Artificial Intelligence and Law》2006,14(3):161-175
Legal information certification and secured storage combined with documents electronic signature are of great interest when
digital documents security and conservation are in concern. Therefore, these new and evolving technologies offer powerful
abilities, such as identification, authentication and certification. The latter contribute to increase the global security
of legal digital archives conservation and access. However, currently used cryptographic and hash coding concepts cannot intrinsically
enclose cognitive information about both the signer and the signed content. Indeed, an evolution of these technologies may
be necessary to achieve full text researches within hundreds or thousands of electronically signed documents. This article
aims at describing a possible model along with associated processes to create and make use of these new electronic signatures
called “meaningful electronic signatures” as opposed to traditional electronic signatures based on bit per bit computation. 相似文献
995.
T Essam E Tamer M A Amin O El Tayeb B Mattiasson B Guieysse E T Ossama M Bo G Benoit 《Water science and technology》2006,53(11):117-125
An algal-bacterial consortium was tested for the treatment from a coke factory. A Chlorella vulgaris strain and a phenol-degrading Alcaligenes sp. were first isolated from the wastewater treatment plant to serve as inocula in the subsequent biodegradation tests. Batch tests were then conducted with samples from the real wastewater or using a synthetic wastewater containing 325 mg phenol/l and 500 mg NH4+/l as target pollutants. Direct biological treatment of the real wastewater was not possible due to the toxicity of organic compounds. Activated carbon adsorption and UV(A-B)-irradiation were efficient in detoxifying the effluent for subsequent biological treatment as inoculation of pretreated samples with the algal-bacterial consortium was followed by complete phenol removal and NH4+ removal of 45%. Complete phenol removal and 33% NH4+ removal were achieved during the fed-batch treatment of artificial wastewater at 6 d hydraulic retention time (HRT). Under continuous feeding at 3.6 d HRT, phenol and NH4+ removal dropped to 58 and 18%, respectively. However, complete phenol removal and 29% NH4+ removal were achieved when 8 g NaHCO3/l was added to the artificial wastewater to enhance algal growth. This study confirms the potential of solar-based industrial wastewater treatment based on solar-based UV pretreatment followed by algal-bacterial biodegradation. 相似文献
996.
A set of physical constants for In0.53Ga0.47As as required for transport calculations is obtained by reviewing the literature. Velocities for fields up to 100 kV/cm, calculated by the Monte Carlo method using these constants, are presented for the temperatures of 95 and 300 K. The calculated values are found to be in good agreement with the available experimental results. 相似文献
997.
998.
Photo-oxidative degradation reactions are mainly responsible for reduced lifetime in polymers. These reactions are responsible for the decay in useful physical and chemical properties of polymers. In addition to high ultraviolet radiation doses, hostile environments have increased temperature, high humidity, and air-borne sand. In this work white pigmented polyvinyl chloride (PVC) pipe sections were exposed to natural weather at seven different locations. Characterization studies were made on exposed samples using Fourier transform infrared (FTIR) spectroscopic, gel permeation chromatographic (GPC), and scanning electron microscopic (SEM) studies. Performance characteristics were determined by testing changes in the mechanical properties. Functional groups introduced during the processing of PVC and irregularities in the polymer chain can be held responsible for the initiation and propagation of photo-oxidative degradation reactions catalyzed by high surface temperature and increased humidity. 相似文献
999.
Amin M.G. Feng K.D. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1988,76(3):289-290
The use of a multiple-pole filter in the time-average estimation of the autocorrelation allows the power spectrum estimates to be recursive in the order of multiplicity of the filter pole. The recursive generation of the estimates from various filter orders provides the flexibility to select the estimator of interest in terms of the variance and spectral and temporal resolution 相似文献
1000.
Ahmed El Oualkadi Jean-Marie Paillot Herv Guegnaud Rachid Allam 《AEUE-International Journal of Electronics and Communications》2005,59(6):352-358
A new RF switched capacitor bandpass filter and its command circuit made up of a ring voltage controlled oscillator with ‘XOR’ gates are proposed. Implemented in a standard CMOS technology, this circuit is intended to be used in a subset of professional mobile phone applications [380–520 MHz]. Experiments carried out on a prototype show a tunable center frequency range of 260 MHz [240–500 MHz], with a quality factor that can be as high as 300. 相似文献