全文获取类型
收费全文 | 12946篇 |
免费 | 2368篇 |
国内免费 | 1199篇 |
专业分类
电工技术 | 641篇 |
技术理论 | 1篇 |
综合类 | 696篇 |
化学工业 | 1173篇 |
金属工艺 | 288篇 |
机械仪表 | 1509篇 |
建筑科学 | 162篇 |
矿业工程 | 122篇 |
能源动力 | 139篇 |
轻工业 | 544篇 |
水利工程 | 55篇 |
石油天然气 | 693篇 |
武器工业 | 193篇 |
无线电 | 5478篇 |
一般工业技术 | 2047篇 |
冶金工业 | 113篇 |
原子能技术 | 513篇 |
自动化技术 | 2146篇 |
出版年
2024年 | 75篇 |
2023年 | 338篇 |
2022年 | 510篇 |
2021年 | 587篇 |
2020年 | 600篇 |
2019年 | 536篇 |
2018年 | 590篇 |
2017年 | 654篇 |
2016年 | 741篇 |
2015年 | 732篇 |
2014年 | 882篇 |
2013年 | 839篇 |
2012年 | 1037篇 |
2011年 | 1051篇 |
2010年 | 796篇 |
2009年 | 791篇 |
2008年 | 787篇 |
2007年 | 822篇 |
2006年 | 683篇 |
2005年 | 547篇 |
2004年 | 516篇 |
2003年 | 409篇 |
2002年 | 331篇 |
2001年 | 242篇 |
2000年 | 240篇 |
1999年 | 198篇 |
1998年 | 164篇 |
1997年 | 158篇 |
1996年 | 149篇 |
1995年 | 83篇 |
1994年 | 95篇 |
1993年 | 73篇 |
1992年 | 55篇 |
1991年 | 43篇 |
1990年 | 38篇 |
1989年 | 30篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 20篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
提出了一种基于红外图像的建筑物墙体空鼓检测方法,不但可以远距离、无损地对建筑物空鼓等缺陷进行定性检测,还能对建筑物热工缺陷进行定量分析;采用一种红外图像处理方法来消除墙体温度分布中梯度干扰的影响;通过自适应地调整参数对红外图像进行图像增强处理,有效地排除了环境干扰;通过基于空鼓缺陷边缘轮廓的连通域计算,可直接得到空鼓面积的大小数据;建筑物缺陷现场检测实验结果表明,提出的检测方法既能快速定位出建筑物空鼓等缺陷位置又能以78.3%的精度检测出空鼓面积大小,具有较高的工程应用性。 相似文献
102.
103.
104.
关于雷达图像优化,提高分辨率的问题,场景较为复杂的图像,固有噪声图像效果不够理想,对具有不同统计特性的像素点缺乏精确的区分。由于传统参数估计方法降噪效果不足,为解决上述问题,提出了一种基于纹理特征分类的参数估计方法。首先计算极化总功率图像的灰度共生矩阵,并提取纹理特征矢量,用K均值聚类的方法进行分类。然后根据分类结果,在滑动邻域窗内选取与中心像素同类别的像素用于参数估计。实验结果表明,改进的纹理分类的滤波方法具有更好的降噪效果,对于复杂场景的极化SAR图像表现了较大的优越性。 相似文献
105.
万振杰 《计算机光盘软件与应用》2012,(2):163+168
SAR图像处理主要包括相干斑抑制、特征提取等,如果在使用Photoshop插件SAR图像处理图片,将主要精力集中于算法的设计和优化方面,可以尽量减少在用户界面、内存管理和基本的图像操作方面的编程,既可以实现多种图像处理,又容易实现功能的充分扩大与填充,从而在最短的时间内做做多的事。 相似文献
106.
Irving Kaufman Pan-Tze Chang Hsueh-Shun Hsu Wen-Yuan Huang Daw-Yang Shyong 《Journal of Nondestructive Evaluation》1987,6(2):87-100
This paper discusses surface crack detection by photothermal radiometric imaging (PRI). In PRI, also called dynamic infrared scanning, a surface is scanned with a spot of heat. Imperfections are detected by radiometrically sensing changes in the surface temperature of a small area in the vicinity of this spot. In the work described, cracks narrower than 25 µm (0.001 in.) in a lightly rusted steel surface have been detected. Indiscrete scanning an amplitude modulated heating beam is moved in steps, remaining at each location long enough to measure amplitude and phase of the AC temperature. Incontinuous scanning a constant intensity heating beam is moved continuously while the temperature deviations are measured. This paper presents methods of calculating amplitude and phase of surface temperature for discrete scanning and instantaneous temperature for continuous scanning across a surface crack. For a steel surface scanned by a watt-level laser beam, predicted surface temperature deviations when crossing the crack are several degrees Celsius, with expected radiometrically detected power several orders of magnitude above the detector noise. In experiments performed, both techniques easily detected narrow cracks in a smooth, clean surface. Discolorations and pits, on the other hand, generate a disturbing type of surface noise. This noise was minimized by differential detection. Based on results obtained, continuously scanned PRI with a fan-type heating beam and array detection could become a viable way of mapping surface cracks at practical scanning speeds. 相似文献
107.
Yeonsil Moon Changmok Lim Yeahoon Kim Won-Jin Moon 《International journal of molecular sciences》2021,22(6)
The role of the blood–brain barrier (BBB) breakdown has been recognized as being important in Alzheimer’s disease pathogenesis. We aimed to evaluate whether regional BBB integrity differed according to sex and whether differences in BBB integrity changed as a consequence of aging or cognitive decline, using dynamic contrast-enhanced (DCE)-magnetic resonance imaging (MRI). In total, 75 participants with normal cognition (NC) or mild cognitive impairment (MCI) underwent cognitive assessments and MRI examination including DCE-MRI. Regional Ktrans was calculated in cortical regions and the Patlak permeability model was used to calculate BBB permeability (Ktrans, min−1). Females had a lower median Ktrans in the cingulate and occipital cortices. In the “older old” group, sex differences in Ktrans were only observed in the occipital cortex. In the MCI group, sex differences in Ktrans were only observed in the occipital cortex. Age was the only predictor of cognitive assessment scores in the male MCI group; however, educational years and Ktrans in the occipital cortex could predict cognitive scores in the female MCI group. Our study revealed that females may have better BBB integrity in cingulate and occipital cortices. We also found that sex-related differences in BBB integrity are attenuated with aging or cognitive decline. 相似文献
108.
Bianca Stoean Dumitrita Rugina Monica Focsan Ana-Maria Craciun MÎdÎlina Nistor Tamas Lovasz Alexandru Turza Ioan-Dan Porumb Emese Gl Castelia Cristea Luminita Silaghi-Dumitrescu Simion Astilean Luiza Ioana Gaina 《International journal of molecular sciences》2021,22(6)
We report here the synthesis and structural characterization of novel cationic (phenothiazinyl)vinyl-pyridinium (PVP) dyes, together with optical (absorption/emission) properties and their potential applicability as fluorescent labels. Convective heating, ultrasound irradiation and mechanochemical synthesis were considered as alternative synthetic methodologies proficient for overcoming drawbacks such as long reaction time, nonsatisfactory yields or solvent requirements in the synthesis of novel dye (E)-1-(3-chloropropyl)-4-(2-(10-methyl-10H-phenothiazin-3-yl)vinyl)pyridin-1-ium bromide 3d and its N-alkyl-2-methylpyridinium precursor 1c. The trans geometry of the newly synthesized (E)-4-(2-(7-bromo-10-ethyl-10H-phenothiazin-3-yl)vinyl)-1-methylpyridin-1-ium iodide 3b and (E)-1-methyl-4-(2-(10-methyl-10H-phenothiazin-3-yl)vinyl)pyridin-1-ium tetrafluoroborate 3a′ was confirmed by single crystal X-ray diffraction. A negative solvatochromism of the dyes in polar solvents was highlighted by UV-Vis spectroscopy and explanatory insights were supported by molecular modeling which suggested a better stabilization of the lowest unoccupied molecular orbitals (LUMO). The photostability of the dye 3b was investigated by irradiation at 365 nm in different solvents, while the steady-state and time-resolved fluorescence properties of dye 3b and 3a′ in solid state were evaluated under one-photon excitation at 485 nm. The in vitro cytotoxicity of the new PVP dyes on B16-F10 melanoma cells was evaluated by WST-1 assay, while their intracellular localization was assessed by epi-fluorescence conventional microscopy imaging as well as one- and two-photon excited confocal fluorescence lifetime imaging microscopy (FLIM). PVP dyes displayed low cytotoxicity, good internalization inside melanoma cells and intense fluorescence emission inside the B16-F10 murine melanoma cells, making them suitable staining agents for imaging applications. 相似文献
109.
Aiming at the requirements of high-resolution imaging and high integration of the blast furnace radar,this paper presents a method for designing a wideband microstrip array antenna,which broadens the antenna bandwidth through the design of parasitic patches and air layers.By combining multi-input multi-output (MIMO) radar and synthetic aperture radar (SAR) imaging principles,a linear MIMO array is designed,and a near-field simulation imaging experiment is performed on the simulated feed line through the wave number domain imaging algorithm.Simulation results show that the gain of the main lobe of the antenna can reach 14.05 dBi,the reflection coefficient is less than -10 dB,the absolute bandwidth is 5.25 GHz,the operating frequency is 20.67~25.92 GHz,and the range resolution is increased to 3 cm compared with the existing blast furnace radar.The average error of the azimuth direction of the simulated material line imaging is 0.008 m,and the range direction is 0.0011 m.Compared with the traditional microstrip array antenna,this antenna effectively widens the bandwidth,and the range resolution is higher than that of the traditional blast furnace radar.It can accurately obtain the shape information on the simulated material line,and has an engineering application value for blast furnace surface monitoring. 相似文献
110.
针对密集观测场景下敏捷成像卫星任务规划问题求解空间大、输入任务序列较长的特点,综合考虑时间窗口约束、任务转移时卫星姿态调整时间、存储约束和电量约束,对敏捷成像卫星任务规划问题进行建模. 提出融合IndRNN和Pointer Networks的算法模型(Ind-PN)对敏捷成像卫星任务规划问题进行求解,使用多层的IndRNN结构作为算法模型的解码器. 基于Pointer Networks机制对输入任务序列进行选择,使用Mask向量考虑敏捷成像卫星任务规划问题中的各类约束. 基于Actor Critic强化学习算法对算法模型进行训练,以获得最大的观测收益率. 实验结果表明,对于密集观测场景下的任务规划,Ind-PN算法的收敛速度更快,可以获得更高的观测收益率. 相似文献