全文获取类型
收费全文 | 126551篇 |
免费 | 10616篇 |
国内免费 | 5593篇 |
专业分类
电工技术 | 7303篇 |
技术理论 | 7篇 |
综合类 | 8454篇 |
化学工业 | 21131篇 |
金属工艺 | 7793篇 |
机械仪表 | 8696篇 |
建筑科学 | 10331篇 |
矿业工程 | 4171篇 |
能源动力 | 3652篇 |
轻工业 | 8119篇 |
水利工程 | 2228篇 |
石油天然气 | 8644篇 |
武器工业 | 1064篇 |
无线电 | 13640篇 |
一般工业技术 | 14653篇 |
冶金工业 | 6111篇 |
原子能技术 | 1246篇 |
自动化技术 | 15517篇 |
出版年
2024年 | 558篇 |
2023年 | 2122篇 |
2022年 | 3697篇 |
2021年 | 5180篇 |
2020年 | 3979篇 |
2019年 | 3317篇 |
2018年 | 3566篇 |
2017年 | 4001篇 |
2016年 | 3681篇 |
2015年 | 5112篇 |
2014年 | 6070篇 |
2013年 | 7250篇 |
2012年 | 7896篇 |
2011年 | 8466篇 |
2010年 | 7387篇 |
2009年 | 7197篇 |
2008年 | 6942篇 |
2007年 | 6631篇 |
2006年 | 7120篇 |
2005年 | 6110篇 |
2004年 | 4070篇 |
2003年 | 3998篇 |
2002年 | 4062篇 |
2001年 | 3602篇 |
2000年 | 3082篇 |
1999年 | 3411篇 |
1998年 | 2629篇 |
1997年 | 2174篇 |
1996年 | 2126篇 |
1995年 | 1785篇 |
1994年 | 1423篇 |
1993年 | 965篇 |
1992年 | 817篇 |
1991年 | 539篇 |
1990年 | 442篇 |
1989年 | 379篇 |
1988年 | 290篇 |
1987年 | 187篇 |
1986年 | 135篇 |
1985年 | 88篇 |
1984年 | 67篇 |
1983年 | 56篇 |
1982年 | 53篇 |
1981年 | 34篇 |
1980年 | 36篇 |
1979年 | 19篇 |
1978年 | 2篇 |
1965年 | 1篇 |
1959年 | 2篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
通过分析PHS网络中各寻呼区的统计指标,剖析指标劣化的根本原因,采取修改相应的参数配置、移站、调整天线等措施进行网络优化,优化实施后再次收集统计指标做对比分析,总结经验。 相似文献
92.
This paper presents a very efficient algorithm for image denoising based on wavelets and multifractals for singularity detection. A challenge of image denoising is how to preserve the edges of an image when reducing noise. By modeling the intensity surface of a noisy image as statistically self-similar multifractal processes and taking advantage of the multiresolution analysis with wavelet transform to exploit the local statistical self-similarity at different scales, the pointwise singularity strength value characterizing the local singularity at each scale was calculated. By thresholding the singularity strength, wavelet coefficients at each scale were classified into two categories: the edge-related and regular wavelet coefficients and the irregular coefficients. The irregular coefficients were denoised using an approximate minimum mean-squared error (MMSE) estimation method, while the edge-related and regular wavelet coefficients were smoothed using the fuzzy weighted mean (FWM) filter aiming at preserving the edges and details when reducing noise. Furthermore, to make the FWM-based filtering more efficient for noise reduction at the lowest decomposition level, the MMSE-based filtering was performed as the first pass of denoising followed by performing the FWM-based filtering. Experimental results demonstrated that this algorithm could achieve both good visual quality and high PSNR for the denoised images. 相似文献
93.
This paper studies a Kansas Department of Transportation welded plate girder bridge that developed fatigue cracks at small web gaps close to the girder top flange. Repair had been previously performed by softening the connection plate end with a slot retrofit, but cracks were recently found to have reinitiated at some of the repaired details and are again propagating. A comprehensive finite-element method study was performed to investigate the cracking behavior observed in the bridge and to recommend appropriate measures for future bridge retrofit. The analytical results show that stresses developed at the top flange web gaps could exceed yielding under the loading of an HS15 fatigue truck. The current slot repair used in the bridge was found to have introduced higher magnitude fatigue stresses in the web gap. To achieve a permanent repair of the bridge, it is recommended that a welded connection plate to flange attachment be used during future bridge retrofit. The web gap details should be able to withstand unlimited number of load cycles once this additional repair is performed. 相似文献
94.
Qing-Chang Zhong Author Vitae 《Automatica》2003,39(3):499-508
This paper generalizes the frequency-domain results on the delay-type Nehari problem in the stable case to the unstable case. The solvability condition of the delay-type Nehari problem is formulated in terms of the nonsingularity of three matrices. The optimal value γopt is the maximal γ∈(0,∞) such that one of the three matrices becomes singular. All sub-optimal compensators are parameterized in a transparent structure incorporating a modified Smith predictor. 相似文献
95.
自动线性跟踪Butterworth有源滤波器研究 总被引:2,自引:0,他引:2
滤波是通信、测试、数据采集和实时控制等领域至关重要的环节。通常的模拟滤波器,由于截止频率固定,在某些宽频率动态范围且有实时性要求的应用场合,往往达不到预期的滤波效果,有时甚至影响整个系统的正常运行。本文从有源滤波器的机理分析入手,提出了一种由单片机参与的滤波系统,它能自动跟踪输入信号频率,线性地选择合适的滤波器截止频率,弥补了原有滤波器的不足。 相似文献
96.
97.
98.
Miao Wang Xinluo Zhao Masato Ohkohchi Yoshinori Ando 《Fullerenes, Nanotubes and Carbon Nanostructures》1996,4(5):1027-1039
Carbon nanotubes prepared by de arc discharge of graphite electrodes in He and CH4 gas took markedly different morphology. Thick nanotubes embellished with many carbon nanoparticles were obtained by evaporation under high CH4 gas pressure and high arc current. Thin and long carbon nanotubes were obtained under a CH4 gas pressure of 50Torr and an arc current of 20A for the anode with a diameter of 6mm. 相似文献
99.
100.
WC对Cu/WC_P复合材料性能及组织的影响 总被引:8,自引:0,他引:8
通过WC含量对WC/Cu复合材料性能的影响,确定了冷压-烧结法制备Cu/WC材料的适宜WC含量为10vol%左右。并就WC对该材料组织和再结晶行为的影响进行了有益的探讨。 相似文献