全文获取类型
收费全文 | 12968篇 |
免费 | 1191篇 |
国内免费 | 412篇 |
专业分类
电工技术 | 585篇 |
综合类 | 595篇 |
化学工业 | 2708篇 |
金属工艺 | 503篇 |
机械仪表 | 561篇 |
建筑科学 | 706篇 |
矿业工程 | 236篇 |
能源动力 | 487篇 |
轻工业 | 1868篇 |
水利工程 | 189篇 |
石油天然气 | 313篇 |
武器工业 | 39篇 |
无线电 | 1107篇 |
一般工业技术 | 1808篇 |
冶金工业 | 964篇 |
原子能技术 | 167篇 |
自动化技术 | 1735篇 |
出版年
2024年 | 42篇 |
2023年 | 154篇 |
2022年 | 390篇 |
2021年 | 597篇 |
2020年 | 411篇 |
2019年 | 478篇 |
2018年 | 483篇 |
2017年 | 527篇 |
2016年 | 456篇 |
2015年 | 483篇 |
2014年 | 569篇 |
2013年 | 875篇 |
2012年 | 801篇 |
2011年 | 862篇 |
2010年 | 732篇 |
2009年 | 661篇 |
2008年 | 661篇 |
2007年 | 617篇 |
2006年 | 507篇 |
2005年 | 354篇 |
2004年 | 382篇 |
2003年 | 520篇 |
2002年 | 619篇 |
2001年 | 544篇 |
2000年 | 270篇 |
1999年 | 204篇 |
1998年 | 282篇 |
1997年 | 218篇 |
1996年 | 157篇 |
1995年 | 115篇 |
1994年 | 84篇 |
1993年 | 92篇 |
1992年 | 51篇 |
1991年 | 29篇 |
1990年 | 59篇 |
1989年 | 36篇 |
1988年 | 31篇 |
1987年 | 21篇 |
1986年 | 22篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 26篇 |
1975年 | 11篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Silvio Frosini De Barros Ferraz Luis Miguel Silva Almeida Canteiro Capão Carlos Alberto Vettorazzi 《International journal of remote sensing》2013,34(3):459-472
The Amazon has been under an intense deforestation process for the last 30 years, causing landscape fragmentation in many different regions and at distinct stages. The fragmentation process is commonly assessed by land‐use maps derived from satellite sensor data and analysed at a landscape context. The analysis of fragmentation depends on an adequate choice of spatial resolution of land‐use maps, and temporal scale in landscape dynamics studies. In this study, spatial–temporal resolution variation effects on fragmentation assessment were analysed in the Quatro Cachoeiras watershed, located at central Rondônia, Brazilian Amazon. Land‐use maps derived from 1984 to 2002 satellite sensor data at 2‐year intervals were used for landscape structure analysis on 12 samples randomly distributed along the watershed. In the spatial resolution variation analysis, landscape metrics obtained at 30 m resolution were compared with those obtained at coarser spatial resolutions. Effects of temporal scale variation were tested by comparison of landscape metrics calculated at 2‐, 4‐ and 6‐year intervals in the studied period. Results show that fragmentation stage influences sensitivity of landscape metrics for spatial resolution and at initial stages of fragmentation finer spatial resolution is required. Also, coarser resolutions up to 100 m could be used to assess landscape fragmentation at regions and the adequate time interval for landscape dynamics studies should be between 3 and 4 years. 相似文献
992.
Yusuke Tokuyoshi Takashi Sekine Tiago da Silva Takashi Kanai 《Computer Graphics Forum》2013,32(7):315-324
This paper proposes an adaptive rendering technique for ray‐bundle tracing. Ray‐bundle tracing can be done by per‐pixel linked‐list construction on a GPU rasterization pipeline. This rasterization based approach offers significant benefits for the efficient generation of light maps (e.g., hardware acceleration, tessellation, and recycling of shaders used in real‐time graphics). However, it is inapplicable to large and complex scenes due to the limited capacity of the GPU memory because it requires a high‐resolution frame buffer and high‐capacity node buffer for the linked‐lists. In addition, memory overflow can potentially occur on the per‐pixel linked‐list since the memory usage of the lists is usually unknown before the rendering process. We introduce an adaptive tiling technique with memory usage prediction. Our method uses an appropriately tiled frame buffer, thus eliminating almost all of the overflow risks thanks to our adaptive tile subdivision scheme. Using this technique, we are able to render high‐quality light maps of large and complex scenes which cannot be computed using previous ray‐bundle based methods. 相似文献
993.
David Bommes Bruno Lévy Nico Pietroni Enrico Puppo Claudio Silva Marco Tarini Denis Zorin 《Computer Graphics Forum》2013,32(6):51-76
Triangle meshes have been nearly ubiquitous in computer graphics, and a large body of data structures and geometry processing algorithms based on them has been developed in the literature. At the same time, quadrilateral meshes, especially semi‐regular ones, have advantages for many applications, and significant progress was made in quadrilateral mesh generation and processing during the last several years. In this survey we discuss the advantages and problems of techniques operating on quadrilateral meshes, including surface analysis and mesh quality, simplification, adaptive refinement, alignment with features, parametrisation and remeshing. 相似文献
994.
In this paper, performance limitations in the linear control of general linear discrete-time scalar systems are considered. The performance is measured with the 2-norm of an error function which, at the same time, ensures that the closed loop poles lie in a prescribed region. The deleterious effect of this constraint on a classical performance measurement is also quantified, in such a way, that the interplay between the size of the desired region and structural features of the plant is revealed. 相似文献
995.
In this paper, the generation of time signals in a network node based on the weighting of phases from two master signals is studied. A discussion about the stability of such a system is conducted with techniques of multi-variable robust control. Designing compensators by using multi-variable linear quadratic gaussian (LQG) and loop transfer recovery (LTR) robust control techniques seems to improve the response of the whole clock generation process, even in the presence of parasitic poles. 相似文献
996.
997.
Nadia Segura Roberta Claro da Silva Fabiana A. Schäfer de M. Soares Luiz Antonio Gioielli Iván Jachmanián 《Journal of the American Oil Chemists' Society》2011,88(12):1945-1954
Although beef tallow (BT) has been considered a hard low-trans fat convenient to be used in several bakery applications, it has some undesirable characteristics like fatty acid composition,
crystallization behavior, graininess formation and poor plastic range. This work studied the modification of BT by blending
at different percentages with high oleic sunflower oil (HOSFO) followed by the enzyme-catalyzed interesterification of the
blends. The reduction in the solid fat content achieved by the simple blending was enhanced by the interesterification process,
as a result of the increase in the concentration of the diunsaturated monosaturated type triacylglycerols. Interesterification
strongly impacted too on the crystallization behavior of the blends, since products showed more homogeneous and regular crystals
than the starting mixture. Results show that lipase catalyzed interesterification of BT with HOSFO offers a useful tool for
the design of fats with adjustable physicochemical properties, improved with respect to that of the starting fats. 相似文献
998.
999.
The purpose of the laser in laser assisted jet ECM (LAJECM) is to localise machining to specified areas so that precision and the productivity is improved. Temperature is a predominant determinant of this localisation effect and must be carefully monitored to avoid any heat affected zones or spark damage due to electrolyte boiling. This paper investigates the thermal effects in LAJECM on several alloys by temperature distribution modelling and experimental analysis. The laser influence on material micro removal has led to 25 μm deeper cavities with a reflective surface of roughness 20 nm Ra, without any detectable heat affected zone. 相似文献
1000.
Leite da Silva A.M. Da Fonseca Manso L.A. De Oliveira Mello J.C. Billinton R. 《Power Systems, IEEE Transactions on》2000,15(1):73-80
This paper presents a new methodology to evaluate loss of load indices, with particular emphasis on LOLC (loss of load cost) assessment, for composite generation and transmission systems considering time varying loads for different areas or buses. The proposed approach, named pseudo-chronological simulation, retains the computational efficiency of nonsequential Monte Carlo simulation and the ability to model chronological load curves in sequential simulation. It considers the actual blocks of unsupplied energy per consumer class, per bus, and the respective duration, to accurately characterize the interruption process. Case studies on the IEEE-MRTS (Modified Reliability Test System) and the BSS (Brazilian South-Southeastern System) are presented and discussed 相似文献