全文获取类型
收费全文 | 94967篇 |
免费 | 6507篇 |
国内免费 | 3533篇 |
专业分类
电工技术 | 9820篇 |
技术理论 | 28篇 |
综合类 | 7200篇 |
化学工业 | 10326篇 |
金属工艺 | 3886篇 |
机械仪表 | 5327篇 |
建筑科学 | 10116篇 |
矿业工程 | 5030篇 |
能源动力 | 4713篇 |
轻工业 | 7610篇 |
水利工程 | 2311篇 |
石油天然气 | 4416篇 |
武器工业 | 2177篇 |
无线电 | 9806篇 |
一般工业技术 | 4937篇 |
冶金工业 | 4063篇 |
原子能技术 | 393篇 |
自动化技术 | 12848篇 |
出版年
2024年 | 216篇 |
2023年 | 1044篇 |
2022年 | 2181篇 |
2021年 | 2835篇 |
2020年 | 2827篇 |
2019年 | 1829篇 |
2018年 | 1569篇 |
2017年 | 2468篇 |
2016年 | 2792篇 |
2015年 | 3102篇 |
2014年 | 7398篇 |
2013年 | 5260篇 |
2012年 | 7210篇 |
2011年 | 7746篇 |
2010年 | 5792篇 |
2009年 | 6005篇 |
2008年 | 5382篇 |
2007年 | 6382篇 |
2006年 | 5742篇 |
2005年 | 4980篇 |
2004年 | 4229篇 |
2003年 | 3799篇 |
2002年 | 3118篇 |
2001年 | 2638篇 |
2000年 | 2035篇 |
1999年 | 1553篇 |
1998年 | 1059篇 |
1997年 | 806篇 |
1996年 | 684篇 |
1995年 | 564篇 |
1994年 | 416篇 |
1993年 | 304篇 |
1992年 | 240篇 |
1991年 | 178篇 |
1990年 | 144篇 |
1989年 | 102篇 |
1988年 | 71篇 |
1987年 | 47篇 |
1986年 | 51篇 |
1985年 | 43篇 |
1984年 | 40篇 |
1983年 | 20篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
11.
12.
《Ceramics International》2022,48(12):16877-16884
Oxygen selective membrane on the base of cermet δ-Bi2O3/Ag with an interpenetrating structure has the maximum potential efficiency of air separation. However, the degradation processes, including the phase degradation of fluorite δ-Bi2O3, do not make it possible to create a membrane with the required perfection and durability. In this work, the ordering of oxygen vacancies with the transformation of fluorite into the rhombohedral phase (S.G. R-3) was studied by powder HT XRD in situ at 600 °C on dense Bi0.78Er0.2Hf0.02O1.51 ceramics. Fast regeneration of disordered fluorite occurs at T = 640–700 °C. The phase degradation of fluorite due to the segregation of dopants at the second stage leads into stable phases - sillenite, tetragonal or rhombohedral phase (S.G. R-3m), depending on the composition of δ-Bi2O3. Fast regeneration of fluorite occurs when heated to 820 °C, which is unacceptable for membranes. Analysis of all available data allows us to propose approaches to optimize the composition of δ-Bi2O3 and technical solutions for creating durable oxygen selective membranes with promising use in distributed multigeneration. As a result of the analysis, a new solid electrolyte with better parameters was obtained. 相似文献
13.
《Ceramics International》2022,48(8):10921-10931
Coatings were obtained by vacuum electro-spark alloying (VESA), pulsed cathodic arc evaporation (PCAE), magnetron sputtering (MS) techniques and VESA-PCAE-MS hybrid technology using Cr3C2–NiAl electrodes. The structure of the coatings was analyzed using scanning and transmission electron microscopy, X-ray diffraction and energy-dispersive spectroscopy. Mechanical properties were determined by nanoindentation, while tribological properties were assessed using pin-on-disk tribometer. Corrosion resistance was estimated by voltammetry in 1 N H2SO4 and 3.5%NaCl solutions. Oxidation resistance tests were performed at 800°С in air. The VESA coating had the highest thickness, low friction coefficient and high wear resistance. PCAE coating demonstrated the highest hardness (24 GPa) and elastic recovery (59%), oxidation resistance and superior corrosion resistance both in 1 N H2SO4 (icorr = 70 μА/cm2) and 3.5%NaCl (icorr = 0.74 μА/cm2) solutions. The MS coating had average mechanical properties and low corrosion current density (71 μА/cm2) in 1 N H2SO4. Deposition of coatings using VESA-PCAE-MS hybrid technology led to an increase in corrosion and oxidation resistance at least by 1.5 times in comparison with the VESA coating. 相似文献
14.
15.
华治国 《混凝土与水泥制品》2020,(6):70-72
选择了几份典型的外墙外保温系统标准,通过对这几份标准中胶粘剂和抹面胶浆的成型和检测方法的比较,分析了现有检测技术的优劣,并结合工作实践提出了建议。 相似文献
16.
构建工程咨询机构BIM技术应用能力评价的指标体系,提出改进的熵权TOPSIS评价模型,以4个典型的工程咨询单位为例,进行BIM技术运用能力评价。研究表明,BIM行业的整体水平已经有了明显的提升,但是区域间的发展还存在一定差距。 相似文献
17.
Traditionally, in supervised machine learning, (a significant) part of the available data (usually 50%-80%) is used for training and the rest—for validation. In many problems, however, the data are highly imbalanced in regard to different classes or does not have good coverage of the feasible data space which, in turn, creates problems in validation and usage phase. In this paper, we propose a technique for synthesizing feasible and likely data to help balance the classes as well as to boost the performance in terms of confusion matrix as well as overall. The idea, in a nutshell, is to synthesize data samples in close vicinity to the actual data samples specifically for the less represented (minority) classes. This has also implications to the so-called fairness of machine learning. In this paper, we propose a specific method for synthesizing data in a way to balance the classes and boost the performance, especially of the minority classes. It is generic and can be applied to different base algorithms, for example, support vector machines, k-nearest neighbour classifiers deep neural, rule-based classifiers, decision trees, and so forth. The results demonstrated that (a) a significantly more balanced (and fair) classification results can be achieved and (b) that the overall performance as well as the performance per class measured by confusion matrix can be boosted. In addition, this approach can be very valuable for the cases when the number of actual available labelled data is small which itself is one of the problems of the contemporary machine learning. 相似文献
18.
19.
Competition forces manufacturing systems to be flexible and to increase product variety and process complexity. These tasks depend on the flexible design of a bill of materials (BOM), one of the most important inputs in manufacturing planning and control systems. Product variety forces systems to generate BOMs with regard to product properties through a BOM pattern. A variant bill of materials provides a structure to manage product variability. In this study, an algorithm is designed to build a BOM pattern using computer-aided design and computer-aided manufacturing (CAD/CAM) data, and another algorithm is designed to generate variants with regard to product specifications. Genetic algorithm is used to generate new products to provide high product variability for testing algorithms. After the test, both algorithms are applied to a real industry problem. The BOM pattern is built automatically using CAD/CAM data, and variants are generated with regard to the pattern, and the results are discussed. 相似文献
20.
《International Journal of Hydrogen Energy》2021,46(69):34449-34462
Three-dimensional Bödewadt flow (fluid rotates at a large enough distance from the stationary plate) of carbon nanomaterial is examined. Single walled and multi walled CNTs are dissolved in water and gasoline oil baseliquids. Darcy-Forchheimer porous medium is considered. Stationary disk is further stretched linearly in radial direction. Heat transfer effect is examined in presence of radiation and convection. Effect of viscous dissipation is accounted. Entropy generation rate is studied. By using adequate transformation (von Kármán relations), the flow field equations (PDEs) are transmitted into ODEs. Solutions to these ODEs are constructed via implementation of shooting method (bvp4c). In addition to Entropy generation rate, Bejan number, heat transfer rate (Nusselt number), skin friction and temperature of fluid are examined through involved physical parameters. Axial component of velocity intensifies with increment in nanoparticles volume fraction and ratio of stretching rate to angular velocity parameter while it decays with higher porosity parameter. Higher nanoparticles volume fraction and porosity parameter lead to decay in radial as well as tangential component of velocity. However it enhances with higher ratio of stretching rate to angular velocity parameter. Temperature of fluid directly varies with higher ratio of stretching rate to angular velocity parameter, radiation parameter, Eckert number, Biot number and nanoparticles volume fraction. Rate of Entropy generation is reduced with higher estimations of porosity parameter, nanoparticles volume fraction and radiation parameter. Skin friction coefficient decays with higher porosity parameter and ratio of stretching rate to angular velocity parameter. Intensification in porosity parameter, nanoparticles volume fraction and Biot number leads to higher Nusselt number. Prominent impact is shown by multiple-walled CNTs with gasoline oil basefluid than single-walled CNTs with water basefluid. 相似文献