全文获取类型
收费全文 | 19787篇 |
免费 | 1788篇 |
国内免费 | 1034篇 |
专业分类
电工技术 | 843篇 |
综合类 | 2080篇 |
化学工业 | 3179篇 |
金属工艺 | 2733篇 |
机械仪表 | 1384篇 |
建筑科学 | 2053篇 |
矿业工程 | 741篇 |
能源动力 | 365篇 |
轻工业 | 520篇 |
水利工程 | 379篇 |
石油天然气 | 1494篇 |
武器工业 | 100篇 |
无线电 | 1636篇 |
一般工业技术 | 1436篇 |
冶金工业 | 1145篇 |
原子能技术 | 65篇 |
自动化技术 | 2456篇 |
出版年
2024年 | 61篇 |
2023年 | 188篇 |
2022年 | 412篇 |
2021年 | 512篇 |
2020年 | 507篇 |
2019年 | 425篇 |
2018年 | 354篇 |
2017年 | 506篇 |
2016年 | 567篇 |
2015年 | 617篇 |
2014年 | 1248篇 |
2013年 | 1162篇 |
2012年 | 1569篇 |
2011年 | 1555篇 |
2010年 | 1199篇 |
2009年 | 1330篇 |
2008年 | 1152篇 |
2007年 | 1435篇 |
2006年 | 1263篇 |
2005年 | 1031篇 |
2004年 | 825篇 |
2003年 | 864篇 |
2002年 | 732篇 |
2001年 | 629篇 |
2000年 | 494篇 |
1999年 | 416篇 |
1998年 | 305篇 |
1997年 | 247篇 |
1996年 | 201篇 |
1995年 | 170篇 |
1994年 | 160篇 |
1993年 | 105篇 |
1992年 | 82篇 |
1991年 | 65篇 |
1990年 | 56篇 |
1989年 | 44篇 |
1988年 | 34篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1964年 | 1篇 |
1961年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
William M. Pitts Martin Werrel Marco Fernandez Mary A. Long Evan A. Eisenberg James Filliben Cory D. Runyon 《火与材料》2021,45(1):127-154
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF. 相似文献
2.
为解决定距螺旋桨与船用主机在船舶运行工况的机桨匹配问题,结合船舶系泊和航行试验的相关标准,分析和归纳船舶运行数据,将实船测试与船机桨匹配理论计算相结合,得出运输船和拖轮在常用工况及特殊工况下定距螺旋桨对主机外特性的定量要求,为配套不同细分市场时船用主机的优化和开发提供参考依据。 相似文献
3.
4.
Facial Expression Recognition (FER) is an important subject of human–computer interaction and has long been a research area of great interest. Accurate Facial Expression Sequence Interception (FESI) and discriminative expression feature extraction are two enormous challenges for the video-based FER. This paper proposes a framework of FER for the intercepted video sequences by using feature point movement trend and feature block texture variation. Firstly, the feature points are marked by Active Appearance Model (AAM) and the most representative 24 of them are selected. Secondly, facial expression sequence is intercepted from the face video by determining two key frames whose emotional intensities are minimum and maximum, respectively. Thirdly, the trend curve which represents the Euclidean distance variations between any two selected feature points is fitted, and the slopes of specific points on the trend curve are calculated. Finally, combining Slope Set which is composed by the calculated slopes with the proposed Feature Block Texture Difference (FBTD) which refers to the texture variation of facial patch, the final expressional feature are formed and inputted to One-dimensional Convolution Neural Network (1DCNN) for FER. Five experiments are conducted in this research, and three average FER rates 95.2%, 96.5%, and 97% for Beihang University (BHU) facial expression database, MMI facial expression database, and the combination of two databases, respectively, have shown the significant advantages of the proposed method over the existing ones. 相似文献
5.
6.
Bahram Rashidi 《International Journal of Circuit Theory and Applications》2020,48(8):1227-1243
In this paper, low-cost and two-cycle hardware structures of the PRINCE lightweight block cipher are presented. In the first structure, we proposed an area-constrained structure, and in the second structure, a high-speed implementation of the PRINCE cipher is presented. The substitution box (S-box) and the inverse of S-box (S-box−1) blocks are the most complex blocks in the PRINCE cipher. These blocks are designed by an efficient structure with low critical path delay. In the low-cost structure, the S-boxes and S-boxes−1 are shared between the round computations and the intermediate step of PRINCE cipher. Therefore, the proposed architecture is implemented based on the lowest number of computation resources. The two-cycle implementation of PRINCE cipher is designed by a processing element (PE), which is a general and reconfigurable element. This structure has a regular form with the minimum number of the control signal. Implementation results of the proposed structures in 180-nm CMOS technology and Virtex-4 and Virtex-6 FPGA families are achieved. The proposed structures, based on the results, have better critical path delay and throughput compared with other's related works. 相似文献
7.
8.
介绍了世界上第1套上流式反应器技术(UFR)在胜利炼油厂渣油加氢脱硫(VRDS)装置的生产运行情况。结果表明:UFR技术可以极大地优化VRDS装置的运转,减少装置运转的苛刻度,有效地延长装置运转周期,提高装置的经济效益。 相似文献
9.
10.