全文获取类型
收费全文 | 42691篇 |
免费 | 8934篇 |
国内免费 | 6322篇 |
专业分类
电工技术 | 2012篇 |
综合类 | 6013篇 |
化学工业 | 1039篇 |
金属工艺 | 879篇 |
机械仪表 | 3626篇 |
建筑科学 | 1677篇 |
矿业工程 | 609篇 |
能源动力 | 423篇 |
轻工业 | 1108篇 |
水利工程 | 392篇 |
石油天然气 | 574篇 |
武器工业 | 588篇 |
无线电 | 10860篇 |
一般工业技术 | 4357篇 |
冶金工业 | 454篇 |
原子能技术 | 340篇 |
自动化技术 | 22996篇 |
出版年
2024年 | 367篇 |
2023年 | 908篇 |
2022年 | 1493篇 |
2021年 | 1816篇 |
2020年 | 1804篇 |
2019年 | 1469篇 |
2018年 | 1343篇 |
2017年 | 1751篇 |
2016年 | 1856篇 |
2015年 | 2214篇 |
2014年 | 2943篇 |
2013年 | 2886篇 |
2012年 | 3732篇 |
2011年 | 3714篇 |
2010年 | 3230篇 |
2009年 | 3195篇 |
2008年 | 3327篇 |
2007年 | 3557篇 |
2006年 | 2923篇 |
2005年 | 2564篇 |
2004年 | 2071篇 |
2003年 | 1631篇 |
2002年 | 1326篇 |
2001年 | 1045篇 |
2000年 | 837篇 |
1999年 | 675篇 |
1998年 | 545篇 |
1997年 | 501篇 |
1996年 | 404篇 |
1995年 | 323篇 |
1994年 | 272篇 |
1993年 | 226篇 |
1992年 | 186篇 |
1991年 | 142篇 |
1990年 | 146篇 |
1989年 | 106篇 |
1988年 | 87篇 |
1987年 | 51篇 |
1986年 | 50篇 |
1985年 | 48篇 |
1984年 | 36篇 |
1983年 | 37篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1965年 | 4篇 |
1960年 | 4篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
如何在复杂背景下持续有效地检测目标位置,一直是研究者们需要面对的主要挑战。本文在研究红外点状移动目标特征的基础上,根据目标无纹理,无形状的特性,提出一种改进的形态学目标增强算法,并利用目标连续时空不变性检测目标。首先,建立多尺度的图像金字塔,在每层上采用改进的形态学算法快速、粗糙定位小目标。然后进一步的根据目标在时空上的位置相关性,提出基于目标运动特征分析的精确检测方法。得到精确稳定的检测结果。最后实验结果表明与经典的形态学检测算法及其他算法相比,该技术能更有效地检测弱小目标,具有更高的鲁棒性。 相似文献
2.
A new matching cost computation method based on nonsubsampled contourlet transform (NSCT) for stereo image matching is proposed in this paper. Firstly, stereo image is decomposed into high frequency sub-band images at different scales and along different directions by NSCT. Secondly, by utilizing coefficients in high frequency domain and grayscales in RGB color space, the computation model of weighted matching cost between two pixels is designed based on the gestalt laws. Lastly, two types of experiments are carried out with standard stereopairs in the Middlebury benchmark. One of the experiments is to confirm optimum values of NSCT scale and direction parameters, and the other is to compare proposed matching cost with nine known matching costs. Experimental results show that the optimum values of scale and direction parameters are respectively 2 and 3, and the matching accuracy of the proposed matching cost is twice higher than that of traditional NCC cost. 相似文献
3.
Ali Mohamed 《Journal of Modern Optics》2019,66(13):1392-1407
Anisoplanatic electromagnetic (EM) propagation across a turbulent atmosphere has been recently examined for an unmodulated carrier propagating over an image-bearing transparency through optical lensing, and for the embedded information inside a carrier recovered using heterodyning and digital demodulation. Carrier modulation yielded better recovery than simple lens-based imaging. A possible mitigation strategy is proposed whereby the image information is encrypted on an RF chaotic carrier, thereafter secondarily embedded onto an optical carrier. Results based on the modified von Karman (MVKS) and the Hufnagel-Valley (H-V) models showed that the signal/image recovery under turbulence is improved compared with non-chaotic propagation. The case of time-varying/dynamic images is also taken up; it is demonstrated via cross-correlation products that turbulence is mitigated by the use of chaotic carrier encryption. Overall, transmission via chaos offers mitigation against distortions due to turbulence along with the security feature inherent via the chaos keys which prevent signal recovery without key-matching. 相似文献
4.
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
5.
Haibo Zhang Guohua Geng Kang Li Cheng Liu Yuqing Hou 《Journal of Modern Optics》2018,65(20):2278-2289
Cone-beam X-ray luminescence computed tomography (CB-XLCT) is an attractive hybrid imaging modality, and it has the potential of monitoring the metabolic processes of nanophosphors-based drugs in vivo. However, the XLCT imaging suffers from a severe ill-posed problem. In this work, a sparse nonconvex Lp (0?p?1) regularization was utilized for the efficient reconstruction for early detection of small tumour in CB-XLCT imaging. Specifically, we transformed the non-convex optimization problem into an iteratively reweighted scheme based on the L1 regularization. Further, an iteratively reweighted split augmented lagrangian shrinkage algorithm (IRW_SALSA-Lp) was proposed to efficiently solve the non-convex Lp (0?p?1) model. We studied eight different non-convex p-values (1/16, 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8) in both 3D digital mouse experiments and in vivo experiments. The results demonstrate that the proposed non-convex methods outperform L2 and L1 regularization in accurately recovering sparse targets in CB-XLCT. And among all the non-convex p-values, our Lp(1/4?p?1/2) methods give the best performance. 相似文献
6.
刑事图像技术是刑事科学的重要组成部分:是检验、固定痕迹物证的一种方法。刑事图像的重大应用在于扩大人类的视野,显示肉眼看不到或看不清的重要细节,以便揭露和证实犯罪。 相似文献
7.
首先分析了BMP图像文件格式,然后根据传统LSB算法在BMP图像文件中应用,提出一种改进的LSB隐藏算法,提高了伪装图像质量。最后通过仿真验证了该算法的优越性。 相似文献
8.
介绍如何利用AutoCAD开发适合电气专业使用的CAD系统,通过编制电气CAD的功能菜单,构造电气元件库,增强CAD的专业性能。编制电气CAD可以有效地统一本单位电气制图标准,方便电气工程师使用CAD进行专业设计。 相似文献
9.
A note on the Gauss-Jacobi quadrature formulae for singular integral equations of the second kind 总被引:1,自引:0,他引:1
A fast and efficient numerical method based on the Gauss-Jacobi quadrature is described that is suitable for solving Fredholm
singular integral equations of the second kind that are frequently encountered in fracture and contact mechanics. Here we
concentrate on the case when the unknown function is singular at both ends of the interval. Quadrature formulae involve fixed
nodal points and provide exact results for polynomials of degree 2n − 1, where n is the number of nodes. Finally, an application of the method to a plane problem involving complete contact is presented. 相似文献
10.
在实际应用中常常需要将人像从照片的背景中有效地分割出来,通常的做法是通过提取照片中人像各部分特征来实现分割,其缺陷是计算复杂度较大,分割效果受各种干扰因素影响很大。现提出了一种基于主体外部轮廓信息的照片分割算法,通过梯度锐化、边缘保护、临近像素点相似度比较来确定图像的边界,该算法对于具有相对均匀背景的照片具有较高的计算效率。 相似文献