全文获取类型
收费全文 | 91032篇 |
免费 | 10715篇 |
国内免费 | 6326篇 |
专业分类
电工技术 | 7618篇 |
技术理论 | 6篇 |
综合类 | 7456篇 |
化学工业 | 12698篇 |
金属工艺 | 5359篇 |
机械仪表 | 6059篇 |
建筑科学 | 7742篇 |
矿业工程 | 3006篇 |
能源动力 | 2682篇 |
轻工业 | 6982篇 |
水利工程 | 2262篇 |
石油天然气 | 4280篇 |
武器工业 | 1157篇 |
无线电 | 11790篇 |
一般工业技术 | 9795篇 |
冶金工业 | 3365篇 |
原子能技术 | 1260篇 |
自动化技术 | 14556篇 |
出版年
2024年 | 627篇 |
2023年 | 1839篇 |
2022年 | 3712篇 |
2021年 | 5005篇 |
2020年 | 3793篇 |
2019年 | 2899篇 |
2018年 | 3183篇 |
2017年 | 3535篇 |
2016年 | 3116篇 |
2015年 | 4636篇 |
2014年 | 5699篇 |
2013年 | 6593篇 |
2012年 | 7706篇 |
2011年 | 7927篇 |
2010年 | 7100篇 |
2009年 | 6539篇 |
2008年 | 6162篇 |
2007年 | 5561篇 |
2006年 | 4857篇 |
2005年 | 3825篇 |
2004年 | 2574篇 |
2003年 | 1895篇 |
2002年 | 1931篇 |
2001年 | 1560篇 |
2000年 | 1167篇 |
1999年 | 1056篇 |
1998年 | 658篇 |
1997年 | 573篇 |
1996年 | 498篇 |
1995年 | 414篇 |
1994年 | 323篇 |
1993年 | 258篇 |
1992年 | 207篇 |
1991年 | 152篇 |
1990年 | 105篇 |
1989年 | 81篇 |
1988年 | 69篇 |
1987年 | 46篇 |
1986年 | 36篇 |
1985年 | 19篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 24篇 |
1979年 | 17篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1959年 | 16篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Tang Y.Y. Hong Ma Jiming Liu Bing Fa Li Dihua Xi 《IEEE transactions on pattern analysis and machine intelligence》1997,19(8):921-926
Based on wavelets, a theoretical method has been developed to process multi-gray level documents. In this method, two-dimensional multiresolution analysis, a wavelet decomposition algorithm, and compactly supported orthonormal wavelets are used to transform a document image into sub-images. According to these sub-images, the reference lines of a multi-gray level document can be extracted, and knowledge about the geometric structure of the document can be acquired. Particularly, this approach is more efficient to process form documents with gray level background. Experiments indicate that this new method can be applied to process documents with promising results 相似文献
72.
用614.3nm染料激光照射以Ne为缓冲气体的Ca空心阴极灯,观察到了Ca原子的Pen-ning离化效应。对比在Li空心阴极灯中获得的光电流信号,解释了Ca原子的彭宁离化。 相似文献
73.
在本试验中,采用智能同步广播激励器和CCTV传输的1MHz标频,实现了中波同步广播同频保护率趋于0dB.并提出了自适应相位跟踪同步的概念。 相似文献
74.
用于重离子核反应实验测量的纵向电场气体电离室 总被引:1,自引:0,他引:1
本文报道了一种新型的大动态范围,多叠层探测器系统组件之一的纵向电场气体电离室的构造,性能和在中能得离子核反应实验中的应用。 相似文献
75.
Shye Lin Wu Chung Len Lee Tan Fu Lei Chen C.F. Chen L.J. Ho K.Z. Ling Y.C. 《Electron Device Letters, IEEE》1994,15(4):120-122
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device 相似文献
76.
Performance analysis of adaptive interleaving for OFDM systems 总被引:7,自引:0,他引:7
We proposed a novel interleaving technique for orthogonal frequency division multiplexing (OFDM), namely adaptive interleaving, which can break the bursty channel errors more effectively than traditional block interleaving. The technique rearranges the symbols according to instantaneous channel state information of the OFDM subcarriers so as to reduce or minimize the bit error rate (BER) of each OFDM frame. It is well suited to OFDM systems because the channel state information (CSI) values of the whole frame could be estimated at once when transmitted symbols are framed in the frequency dimension. Extensive simulations show that the proposed scheme can greatly improve the performance of the coded modulation systems utilizing block interleaving. Furthermore, we show that the adaptive interleaving out performs any other static interleaving schemes, even in the fast fading channel (with independent fading between symbols). We derived a semi-analytical bound for the BER of the adaptive interleaving scheme under correlated Rayleigh fading channels. Furthermore, we discussed the transmitter-receiver (interleaving pattern) synchronization problem 相似文献
77.
Pd-Ge based ohmic contact to n-GaAs with a TiW diffusion barrier was investigated. Electrical analysis as well as Auger electron
spectroscopy and the scanning electron microscopy were used to study the contact after it was subjected to different furnace
and rapid thermal annealing and different aging steps. All analyses show that TiW can act as a good barrier metal for the
Au/Ge/Pd/n-GaAs contact system. A value of 1.45 × 10−6 Ω-cm2 for the specific contact resistance was obtained for the Au/TiW/Ge/Pd/n-GaAs contact after it was rapid thermally annealed
at 425°C for 90 s. It can withstand a thermal aging at 350°C for 40 h with its ρc increasing to 2.94 × 10−6Ω-cm2 and for an aging at 410°C for 40 h with its ρc increasing to 1.38 × 10−5 Ω-cm2. 相似文献
78.
砖烟囱集团装药定向爆破拆除 总被引:1,自引:1,他引:0
对一座 40 m 高的砖烟囱,采用TNT集团装药实施定向倒塌拆除爆破.介绍了该烟囱拆除爆破工艺技术,爆破参数和施工方法. 相似文献
79.
In this paper, the CdxHg1-xTe (x=1-0.7) doped silica glass was prepared through two step sol-gel process and in-situ growth technique from tetraethoxysilane (TEOS), cadmium acetate, mercury acetate and telluric acid. The influence of various factors on the glass was studied. The structure of the microcrystals was investigated by XRD. The absorption and transmittance spectrum of the composite showed that the shift of absorption edge was in conformity with the quantum size effect. The third-order nonlinear optical susceptibility χ(3) was measured by the degenerate four wave mixing (DFWM). The values of χ(3) was in the range of 10-11-10-12 MO esu at wavelength of 1.06 μm. 相似文献
80.
主动阻尼控制中的扩展加速度输出反馈法 总被引:2,自引:2,他引:0
正位置反馈(PPF)是一种能够显著提高结构模态阻尼的控制策略,但是这种策略在原理和应用中具有一定的局限性。本文在指出了传统的PPF控制器的优缺点基础上,提出一种扩展的加速度输出反馈控制方法AOEF,同时给出了最优AOEF控制器的设计计算方法。仿真计算和实验表明,在传感器/作动器同相的情况下,采用这种控制器的闭环系统具有无条件的稳定性,在非同相的情况下也能达到优良的控制性能。 相似文献