全文获取类型
收费全文 | 23174篇 |
免费 | 2920篇 |
国内免费 | 1855篇 |
专业分类
电工技术 | 2180篇 |
技术理论 | 1篇 |
综合类 | 2308篇 |
化学工业 | 3033篇 |
金属工艺 | 1432篇 |
机械仪表 | 1573篇 |
建筑科学 | 1712篇 |
矿业工程 | 940篇 |
能源动力 | 682篇 |
轻工业 | 2590篇 |
水利工程 | 676篇 |
石油天然气 | 931篇 |
武器工业 | 444篇 |
无线电 | 2518篇 |
一般工业技术 | 2101篇 |
冶金工业 | 907篇 |
原子能技术 | 422篇 |
自动化技术 | 3499篇 |
出版年
2024年 | 183篇 |
2023年 | 539篇 |
2022年 | 1104篇 |
2021年 | 1437篇 |
2020年 | 1050篇 |
2019年 | 798篇 |
2018年 | 821篇 |
2017年 | 888篇 |
2016年 | 803篇 |
2015年 | 1126篇 |
2014年 | 1419篇 |
2013年 | 1667篇 |
2012年 | 1907篇 |
2011年 | 1961篇 |
2010年 | 1754篇 |
2009年 | 1568篇 |
2008年 | 1515篇 |
2007年 | 1557篇 |
2006年 | 1338篇 |
2005年 | 984篇 |
2004年 | 700篇 |
2003年 | 579篇 |
2002年 | 489篇 |
2001年 | 472篇 |
2000年 | 359篇 |
1999年 | 162篇 |
1998年 | 98篇 |
1997年 | 91篇 |
1996年 | 73篇 |
1995年 | 61篇 |
1994年 | 55篇 |
1993年 | 43篇 |
1992年 | 36篇 |
1991年 | 24篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1977年 | 12篇 |
1973年 | 9篇 |
1965年 | 16篇 |
1964年 | 7篇 |
1959年 | 18篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
低轨互联网星座是当前全球研究和发展的热点,互联网星座支持随遇接入遥感卫星和信息在轨直接处理的应用前景备受期待,但由于轨道高度不同会产生双向高动态异构星座的接入互联问题。首先,通过设定低轨卫星互联网星座在不同轨道特性、不同卫星数量情况下的随遇接入仿真场景,重点探讨了时空非连续可视性和多普勒频移问题对遥感卫星接入性能的影响;其次,基于遥感卫星随遇接入互联网星座场景的特点,分析了不同时延性在轨处理任务的流程及其星地功能分配;最后,对当前在轨智能处理算法存在的问题和未来研究重点进行阐述,为未来低轨互联网星座及遥感卫星的发展和联合组网应用提供可靠的理论支撑。 相似文献
2.
目前管道泄漏检测方法可有效检测突发泄漏,对于缓慢泄漏则存在检测灵敏度低、定位不准确等问题。基于此,提出了一种基于信号增强的缓慢泄漏检测方法。通过信号压缩(抽取及移位)克服缓慢泄漏压力信号下降平缓的缺点;根据声波信号具有波形尖锐突出、对突发泄漏敏感的优点,通过建立以压力为输入、虚拟声波为输出的声波信号变送器模型,将压力信号转换为声波信号,克服了泄漏压力信号容易被淹没在管道压力波动及背景噪声中的缺点,实现了缓慢泄漏信号的增强;利用临近插值方法重构虚拟声波信号,基于延时互相关分析实现了缓慢泄漏的准确定位。实验结果表明,该方法具有显著的信号增强效果和定位精度,实现了缓慢泄漏的准确检测。 相似文献
3.
4.
不同折流板结构螺旋折流板换热器传热性能的比较(英文) 总被引:1,自引:0,他引:1
Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers, the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as wel as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20° (20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overal heat transfer coefficient K, shel-side heat transfer coefficient ho and shel-side average comprehensive index ho/Δpo. 相似文献
5.
6.
Study on the relationship between the particle size distribution and the effectiveness of the K‐powder fire extinguishing agent 下载免费PDF全文
The relationship between the particle size distribution and the extinguishing effectiveness of the new K‐powder fire extinguishing agent has been studied experimentally, to explore the reason of the great extinguishing efficiency exhibited by the new K‐powder fire extinguishing agent on Class B fire (liquid fuel fire). The results of the experiment showed that the extinguishing effectiveness increased along with the decrease of the particle size distribution. In addition, a sharp discontinuity appeared around the limiting size, about 40 μm. The powder with the particle size below 40 μm exhibited highly effective extinguishing with the minimum effective extinguishing concentration Cxr = 23 g·m?3, while the powder with the particle size above 40 μm exhibited little fire extinguishing efficiency. Compared with other fire extinguishing agents produced by different substances, the new K‐powder fire extinguishing has the bigger limiting size. That means, in the same particle size distribution, the new K‐powder fire extinguishing agent contains more highly effective powder than others contain, and is more effective. 相似文献
7.
8.
Simulating the psychological experience of human vision,a road extraction model based on the format tower is proposed to extract the road in the high resolution remote sensing image from the perspective of morphology.Firstly,based on the spectral and texture information,the suspected road targets are extracted by using segmentation technology.Then these targets are classified according to their reliability and extract the road targets for each category.Finally,three types of identified road information are verified and merged,and the continuous smooth road extraction results are obtained.Experiments on real high resolution images show that the results are consistent with the visual perception of the human eye,and the overall classification accuracy is higher,indicating that the algorithm is effective and feasible and has good use value. 相似文献
9.
Effect of Supports and Promoters on the Performance of Ni-Based Catalysts in Ethanol Steam Reforming
Thanh Khoa Phung Thong Le Minh Pham Anh-Nga T. Nguyen Khanh B. Vu Ha Ngoc Giang Tuan-Anh Nguyen Thanh Cong Huynh Hong Duc Pham 《化学工程与技术》2020,43(4):672-688
Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni-based catalysts on the ESR process. 相似文献
10.