全文获取类型
收费全文 | 10111篇 |
免费 | 1389篇 |
国内免费 | 690篇 |
专业分类
电工技术 | 892篇 |
技术理论 | 1篇 |
综合类 | 816篇 |
化学工业 | 1580篇 |
金属工艺 | 581篇 |
机械仪表 | 649篇 |
建筑科学 | 801篇 |
矿业工程 | 341篇 |
能源动力 | 314篇 |
轻工业 | 865篇 |
水利工程 | 196篇 |
石油天然气 | 577篇 |
武器工业 | 135篇 |
无线电 | 1222篇 |
一般工业技术 | 1084篇 |
冶金工业 | 378篇 |
原子能技术 | 171篇 |
自动化技术 | 1587篇 |
出版年
2024年 | 108篇 |
2023年 | 317篇 |
2022年 | 599篇 |
2021年 | 821篇 |
2020年 | 595篇 |
2019年 | 448篇 |
2018年 | 498篇 |
2017年 | 536篇 |
2016年 | 417篇 |
2015年 | 566篇 |
2014年 | 665篇 |
2013年 | 715篇 |
2012年 | 795篇 |
2011年 | 718篇 |
2010年 | 603篇 |
2009年 | 527篇 |
2008年 | 497篇 |
2007年 | 471篇 |
2006年 | 442篇 |
2005年 | 308篇 |
2004年 | 223篇 |
2003年 | 213篇 |
2002年 | 202篇 |
2001年 | 175篇 |
2000年 | 157篇 |
1999年 | 114篇 |
1998年 | 83篇 |
1997年 | 69篇 |
1996年 | 63篇 |
1995年 | 56篇 |
1994年 | 47篇 |
1993年 | 37篇 |
1992年 | 26篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
1.
2.
3.
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
4.
5.
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
![点击此处可从《火与材料》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
6.
7.
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
8.
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
9.
10.
求解二维结构-声耦合问题的一种直接方法 总被引:1,自引:1,他引:0
本文基于传递矩阵法(TMM)和虚拟边界元法(VBEM),提出了一种求解在谐激励作用下二维结构-声耦合问题的直接法。文中对任意形状的二维弹性环建立了一阶非齐次运动微分方程组,便于用齐次扩容精细积分法求解,对于含有任意形状孔穴的无穷域流体介质的Helmholtz外问题,采用复数形式的Burton-Miller型组合层势法建立了虚拟边界元方程,保证了声压在全波数域内存在唯一解。根据叠加原理并结合最小二乘法,提出了一种耦合方程的直接解法,由于该方法不存在迭代过程,因而具有较高的计算精度和效率。文中给出了二个典型弹性环在集中谐激励力作用下声辐射算例,计算结果表明本文方法较通常采用的混合FE/BE法更为有效。 相似文献