全文获取类型
收费全文 | 2877篇 |
免费 | 96篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 13篇 |
综合类 | 2篇 |
化学工业 | 456篇 |
金属工艺 | 31篇 |
机械仪表 | 53篇 |
建筑科学 | 39篇 |
矿业工程 | 3篇 |
能源动力 | 78篇 |
轻工业 | 261篇 |
水利工程 | 19篇 |
石油天然气 | 17篇 |
无线电 | 66篇 |
一般工业技术 | 225篇 |
冶金工业 | 1438篇 |
原子能技术 | 8篇 |
自动化技术 | 266篇 |
出版年
2024年 | 14篇 |
2023年 | 21篇 |
2022年 | 37篇 |
2021年 | 86篇 |
2020年 | 64篇 |
2019年 | 76篇 |
2018年 | 72篇 |
2017年 | 60篇 |
2016年 | 74篇 |
2015年 | 47篇 |
2014年 | 68篇 |
2013年 | 132篇 |
2012年 | 87篇 |
2011年 | 105篇 |
2010年 | 106篇 |
2009年 | 108篇 |
2008年 | 61篇 |
2007年 | 68篇 |
2006年 | 37篇 |
2005年 | 27篇 |
2004年 | 32篇 |
2003年 | 30篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1999年 | 45篇 |
1998年 | 464篇 |
1997年 | 270篇 |
1996年 | 152篇 |
1995年 | 90篇 |
1994年 | 85篇 |
1993年 | 86篇 |
1992年 | 21篇 |
1991年 | 22篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 31篇 |
1976年 | 95篇 |
1975年 | 3篇 |
排序方式: 共有2975条查询结果,搜索用时 15 毫秒
11.
A DSS integrating empty and full containers transshipment operations is presented, addressing the typically unbalanced export/import containers trading problem. The problem is modeled as a network, where nodes represent customers, leasing companies, harbors and warehouses, while arcs represent transportation routes. The underlying mathematical model operates in stages, first prioritizing and adjusting full containers demands considering available empty containers supplies, and then statically optimizing costs. Transportation routes are registered and dynamically controlled, cyclically, for a given time horizon. The DSS is flexible, allowing several parameters to be configured. Experimental examples using randomly generated parameters were conducted to evaluate the effectiveness of the system. 相似文献
12.
Luiz A. Canalle Sander S. van Berkel Laurens T. de Haan Jan C. M. van Hest 《Advanced functional materials》2009,19(21):3464-3470
The copper‐catalyzed azide–alkyne 1,3‐dipolar cycloaddition (CuAAC) is extensively used for the functionalization of well‐defined polymeric materials. However, the necessity for copper, which is inherently toxic, limits the potential applications of these materials in the area of biology and biomedicine. Therefore, the first entirely copper‐free procedure for the synthesis of clickable coatings for the immobilization of functional molecules is reported. In the first step, azide‐functional coatings are prepared by thermal crosslinking of side‐chain azide‐functional polymers and dialkyne linkers. In a second step, three copper‐free click reactions (i.e., the Staudinger ligation, the dibenzocyclooctyne‐based strain‐promoted azide–alkyne [3+2] cycloaddition, and the methyl‐oxanorbornadiene‐based tandem cycloaddition?retro‐Diels?Alder (crDA) reaction) are used to functionalize the azide‐containing surfaces with fluorescent probes, allowing qualitative comparison with the traditional CuAAC. 相似文献
13.
Antonio Luiz P. S.?CamposEmail author Adaildo Gomes?d’Assun??oEmail author Milton Luciano C.?Gomes Neto 《Journal of Infrared, Millimeter and Terahertz Waves》2005,26(6):843-854
In this work, the Hertz vector potential method was used to obtain the dyadic Green’s function components for frequency selective surfaces (FSS) on an anisotropic layer. The considered structures are composed by periodic arrays of conducting crossed dipole and rectangular patch elements. Results of reflected power were obtained by using the moment method. Curves for the reflected power versus frequency are presented as function of the structural parameters, assuming x, y, and z orientation for the optical axis in the anisotropic substrate. 相似文献
14.
Wilson De Carvalho Jr. Mario Tosi Furtado Aryton André Bernussi Angelo Luiz Gobbi Mônica Alonso Cotta 《Journal of Electronic Materials》2000,29(1):62-68
We investigated the influence of the growth rate on the quality of zero-net-strained InGaAsP/InGaAsP/InP multiquantum well
structures for 1.55 μm emission grown by low pressure metalorganic vapor phase epitaxy. The samples consisted of fixed compressive
strained wells (ɛ=+1%) and tensile strained barriers (ɛ=−0.5%) grown with different quaternary bandgap wavelengths (λB=1.1–1.4 μm). Using higher growth rates, we obtained for the first time high quality zero net strained multi quantum well
structures, regardless having constant group V composition in the well and barriers. The samples were analyzed by x-ray diffraction,
photoluminescence and atomic force microscopy techniques. The amplitude of surface modulation roughness along [011] direction
decreased from 20 nm to 0.53 nm with increasing growth rate and/or quaternary compositions grown outside the miscibility gap.
A new deep PL broad emission band strongly correlated with the onset of wavy layer growth is also reported. Broad area and
ridge waveguide lasers with 10 wells exhibited low losses (34 cm−1) and low threshold current densities at infinite cavity length (1020 A·cm−2 and 1190 A·cm−2, respectively). 相似文献
15.
Mario Lemes Proença Jr. Gilberto Fernandes Jr. Luiz F. Carvalho Marcos V. O. de Assis Joel J. P. C. Rodrigues 《International Journal of Network Management》2016,26(2):76-94
Because of constant growth in proportion and complexity of networks, flow analysis has become an indispensable tool for network management mechanisms. Through this resource, a traffic characterization, called digital signature of network segment using flow analysis (DSNSF), is accomplished. The models used for this purpose are the ant colony optimization metaheuristic, the Holt–Winters forecasting method and the statistical procedure, principal component analysis. The obtained DSNSF by each model is compared with the actual traffic of packets and bits and then subjected to specific evaluations in order to measure its accuracy. The experimental results show that the three methods could achieve good correlation indices and low normalized mean square error values between the DSNSF curve and the real traffic movement, indicating a good adaptability and efficiency in characterizing a network traffic segment. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
16.
In this paper, we propose a policy-based framework for the management of wireless ad hoc networks and briefly describe a characteristics-based taxonomy that provides a platform to analyze and compare different architectural choices. We develop a solution suite that helps achieve our goal of a self-organizing, robust and efficient management system. One of the main contributions of this work is the prototype implementation and testing of the mechanisms and protocols comprising our framework in a multi-hop ad hoc network environment. Experiments are conducted using both an emulated ad hoc network testbed and a true wireless testbed. Degradation in management system performance is observed as the number of hops between a policy server and client increases. Our proposed k-hop clustering algorithm alleviates this problem by limiting the number of hops between a server and client. We demonstrate the operation of our prototype implementation, illustrating QoS management in a multi-domain ad hoc network environment using the proposed cluster management, redirection, and policy negotiation mechanisms. 相似文献
17.
Trends in Hydrological Parameters of a Southern Brazilian Watershed and its Relation to Human Induced Changes 总被引:4,自引:1,他引:4
Moraes Jorge M. Pellegrino Giampaolo Q. Ballester Maria V. Martinelli Luiz A. Victoria Reynaldo L. Krusche Alex V. 《Water Resources Management》1998,12(4):295-311
The Piracicaba river basin is a subtropical watershed located in the southeastern region of Brazil. With an area of 12 400 km2, the basin is a typical example of new landscape resulting from development in tropical and sub-tropical regions: establishment of intensive industrial and agricultural processes were followed by significant population growth and water management. This scenario has led to significant increase in water demand and decrease in water quality. The main objective of this study is the detection of changes in the patterns of flow and precipitation in the basin, and its possible relation to man-induced changes. Statistical analyses were performed on records of precipitation, evapotranspiration and streamflow, from 1947 to 1991. Precipitation and evapotranspiration totals showed significant increasing trends for the entire basin. From eight streamflow gauge stations, half showed significant decreasing trend. The most probable cause of such trends is the export of water from the basin to the metropolitan region of São Paulo city. 相似文献
18.
Antônio Alisson Alencar Freitas Fernando Lessa Tofoli Edilson Mineiro Sá Junior Sergio Daher Fernando Luiz Marcelo Antunes 《International Journal of Electronics》2016,103(5):898-912
A high voltage step-up nonisolated DC–DC converter based on coupled inductors suitable to photovoltaic (PV) systems applications is proposed in this paper. Considering that numerous approaches exist to extend the voltage conversion ratio of DC–DC converters that do not use transformers, a detailed comparison is also presented among the proposed converter and other popular topologies such as the conventional boost converter and the quadratic boost converter. The qualitative analysis of the coupled-inductor-based topology is developed so that a design procedure can be obtained, from which an experimental prototype is implemented to validate the theoretical assumptions. 相似文献
19.
Affonso Felipe Dias Thiago Magela Rodrigues Pinto Adilson Luiz 《Mobile Networks and Applications》2021,26(1):256-265
Mobile Networks and Applications - Predicting the stock market is a widely studied field, either due to the curiosity in finding an explanation for the behavior of financial assets or for financial... 相似文献
20.
Antonio Luiz Pereira de Siqueira Campos Robson Hebraico Cipriano Maniçoba Adaildo Gomes d’Assunção 《Journal of Infrared, Millimeter and Terahertz Waves》2010,31(12):1503-1511
Numerical and theoretical investigations are presented for a double screen frequency selective surface (DSFSS) with perfectly
conducting Koch fractal patch elements. The work was developed in two steps, in the first step two Koch fractal FSS screens
were designed using the commercial software Ansoft DesignerTM. In the second these FSS were cascaded and separated by an air gap layer, forming the so-called DSFSS, to improve the bandwidth
behavior. Thereafter, a numerical cascading technique is used to analyze the effect of the air gap on the DSFSS. The results
were compared and a good agreement was observed. 相似文献