全文获取类型
收费全文 | 51722篇 |
免费 | 4731篇 |
国内免费 | 1853篇 |
专业分类
电工技术 | 16810篇 |
技术理论 | 3篇 |
综合类 | 4371篇 |
化学工业 | 2274篇 |
金属工艺 | 2803篇 |
机械仪表 | 6290篇 |
建筑科学 | 1690篇 |
矿业工程 | 2151篇 |
能源动力 | 2068篇 |
轻工业 | 1610篇 |
水利工程 | 1820篇 |
石油天然气 | 997篇 |
武器工业 | 722篇 |
无线电 | 4162篇 |
一般工业技术 | 2204篇 |
冶金工业 | 2797篇 |
原子能技术 | 201篇 |
自动化技术 | 5333篇 |
出版年
2024年 | 195篇 |
2023年 | 610篇 |
2022年 | 1176篇 |
2021年 | 1460篇 |
2020年 | 1392篇 |
2019年 | 1011篇 |
2018年 | 1013篇 |
2017年 | 1538篇 |
2016年 | 1552篇 |
2015年 | 1716篇 |
2014年 | 3080篇 |
2013年 | 2402篇 |
2012年 | 3749篇 |
2011年 | 4230篇 |
2010年 | 3014篇 |
2009年 | 3059篇 |
2008年 | 2930篇 |
2007年 | 3913篇 |
2006年 | 3432篇 |
2005年 | 3079篇 |
2004年 | 2299篇 |
2003年 | 2192篇 |
2002年 | 1725篇 |
2001年 | 1607篇 |
2000年 | 1321篇 |
1999年 | 1028篇 |
1998年 | 690篇 |
1997年 | 659篇 |
1996年 | 506篇 |
1995年 | 412篇 |
1994年 | 365篇 |
1993年 | 196篇 |
1992年 | 175篇 |
1991年 | 133篇 |
1990年 | 96篇 |
1989年 | 101篇 |
1988年 | 62篇 |
1987年 | 42篇 |
1986年 | 22篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1964年 | 8篇 |
1962年 | 6篇 |
1961年 | 6篇 |
1958年 | 5篇 |
1957年 | 6篇 |
1956年 | 7篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 687 毫秒
1.
Small object detection is challenging and far from satisfactory. Most general object detectors suffer from two critical issues with small objects: (1) Feature extractor based on classification network cannot express the characteristics of small objects reasonably due to insufficient appearance information of targets and a large amount of background interference around them. (2) The detector requires a much higher location accuracy for small objects than for general objects. This paper proposes an effective and efficient small object detector YOLSO to address the above problems. For feature representation, we analyze the drawbacks in previous backbones and present a Half-Space Shortcut(HSSC) module to build a background-aware backbone. Furthermore, a coarse-to-fine Feature Pyramid Enhancement(FPE) module is introduced for layer-wise aggregation at a granular level to enhance the semantic discriminability. For loss function, we propose an exponential L1 loss to promote the convergence of regression, and a focal IOU loss to focus on prime samples with high classification confidence and high IOU. Both of them significantly improves the location accuracy of small objects. The proposed YOLSO sets state-of-the-art results on two typical small object datasets, MOCOD and VeDAI, at a speed of over 200 FPS. In the meantime, it also outperforms the baseline YOLOv3 by a wide margin on the common COCO dataset. 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(2):1306-1318
The effective and efficient utilization of low-calorific value (LCV) gases has gained increasing attention in scientific research and industrial fields. In this study, the combustion characteristics of three LCV gases in practical devices are analyzed by using a nonadiabatic perfectly stirred reactor model. The complete steady-state solution in the temperature-residence time parameter space is obtained with arc-length continuation. The stable operation region is quantified by the eigenvalue analysis. The transition of solution curves is quantified with heat loss coefficient. Five key system parameters are systematically investigated on their effects on stability limits. With the combustion performance being quantified by a combustion state index, a combustion state regulation method is proposed to find the optimal regulation path of system parameters. Active subspace method is further applied to shorten the regulation step by identifying the active direction. The proposed method and findings are useful for optimal regulation of burning LCV gases in industrial burners. 相似文献
3.
《Ceramics International》2022,48(18):25984-25995
Design of architectured composites with layered-ordered structure can solve the strength-toughness mismatch problem of structural materials. In the present study, heterostructure Ti6Al4V/TiAl laminated composite sheets with different thicknesses of interface layer and TiAl composite layer were successfully produced by hot-pressing technology. The effects of interface regulation and laminated structure on their mechanical properties, crack propagation, and fracture behavior were studied. The results indicated that compressive strength of the sheets increased with the decrease in interface thickness. Compressive strength of TiAl composite sheet with thicker composite layer reached 1481.55 MPa at the arrester orientation with sintering holding time of 40 min, which was 25.96% higher than that of the sheet obtained at 120 min. Analysis indicated that the interface area transferred stress through slip bands and through-interface cracks. Compressive strength at the divider orientation reached 1443.06 MPa, which was 45.78% higher than that of the sheet obtained at 120 min. In this case, the interface area transferred stress through slip bands and along-interface cracks. For TiAl composite sheets with thinner composite layer, compressive strength was further improved to 1631.01 MPa and 1594.66 MPa at the arrester and divider orientations with sintering holding time of 40 min, respectively. The ductile metal layer exerted a significant toughening effect. Both interface regulation and laminated structure transformation could enhance the hetero-deformation induced (HDI) strengthening and improve the comprehensive mechanical properties of the composite sheets. 相似文献
4.
《Ceramics International》2022,48(13):18793-18802
The luminescence center energy transfer, crystal field strength, and covalency are limited by the crystal structure of the host and subsequently affect the luminescence efficiency, color, and intensity. Here, we report an excellent red phosphor BaLaLiWO6:0.40Eu3+ and the dependence between symmetry and luminous performance. A model for changing symmetry is drawn by analyzing the Coulomb potential and structure for the application of a double-perovskite phosphor BLLWO: Dy3+, Eu3+ in white light LEDs. The addition of Dy3+/Eu3+ makes the W-O bond formed by the B-site and oxygen ion longer and the Li-O bond shorter, and the difference between the eight octahedral around the A-site is reduced, increasing the symmetry of the A-site. Local symmetry was successfully modulated by changing the Eu3+ concentration to control the Y/B ratio of Dy3+ and the R/O ratio of Eu3+ and smoothly achieved (0.382, 0.373) warm white light color coordinate. The phosphor has excellent thermal stability and still has 92.3% intensity at 475 K. The above results show that the wavelength composition of the luminescence is tunable by changing the symmetry of the environment in which the doped ions are located. It applies to single hosts for the regulation of white light emission. 相似文献
5.
6.
This study proposes that a novel integrated circuit (IC) and system design for renewable energy inverters can harvest renewable energy to power direct current (DC) and alternating current (AC) loads. In addition, an intelligent synthesis and management tool is developed to design the proposed system and to judge the system’s operational maintenance decisions. Finally, a renewable energy inverter’s information is posted to an online system. Users can obtain the proposed system’s information at any time and place. The accurate and superior performance of the proposed IC and system is confirmed by computer simulations and experimental results. 相似文献
7.
Australia's electricity market is rapidly adding renewable energy generation. Utility-scale batteries could have a major role in facilitating these transitions; however, their deployment is still largely state-subsidized. We summarize the current and future roles for batteries from a legal-economic perspective in the context of Australia's electricity market framework. We find that the future of batteries in Australia is not only a function of the large-scale deployment of renewables, their cost development and the comparative future cost of competing gas turbines but also of national electricity market and state policy reforms focusing on reliability. 相似文献
8.
9.
针对目前运动想象脑电(EEG)信号识别率较低的问题,考虑到脑电信号蕴含着丰富的时频信息,提出一种基于时频域的卷积神经网络(CNN)运动想象脑电信号识别方法。首先,利用短时傅里叶变换(STFT)对脑电信号的相关频带进行预处理,并将多个电极的时频图组合构造出一种二维时频图;然后,针对二维时频图的时频特性,通过一维卷积的方法设计了一种新颖的CNN结构;最后,通过支持向量机(SVM)对CNN提取的特征进行分类。基于BCI数据集的实验结果表明,所提方法的平均识别率为86.5%,优于其他传统运动想象脑电信号识别方法;同时将该方法应用在智能轮椅上,验证了其有效性。 相似文献
10.