全文获取类型
收费全文 | 3175篇 |
免费 | 492篇 |
国内免费 | 307篇 |
专业分类
电工技术 | 102篇 |
综合类 | 302篇 |
化学工业 | 160篇 |
金属工艺 | 67篇 |
机械仪表 | 300篇 |
建筑科学 | 145篇 |
矿业工程 | 31篇 |
能源动力 | 43篇 |
轻工业 | 38篇 |
水利工程 | 52篇 |
石油天然气 | 24篇 |
武器工业 | 109篇 |
无线电 | 742篇 |
一般工业技术 | 427篇 |
冶金工业 | 137篇 |
原子能技术 | 13篇 |
自动化技术 | 1282篇 |
出版年
2024年 | 5篇 |
2023年 | 65篇 |
2022年 | 76篇 |
2021年 | 114篇 |
2020年 | 122篇 |
2019年 | 107篇 |
2018年 | 105篇 |
2017年 | 146篇 |
2016年 | 135篇 |
2015年 | 198篇 |
2014年 | 251篇 |
2013年 | 233篇 |
2012年 | 246篇 |
2011年 | 255篇 |
2010年 | 211篇 |
2009年 | 240篇 |
2008年 | 232篇 |
2007年 | 226篇 |
2006年 | 182篇 |
2005年 | 181篇 |
2004年 | 119篇 |
2003年 | 112篇 |
2002年 | 91篇 |
2001年 | 52篇 |
2000年 | 46篇 |
1999年 | 32篇 |
1998年 | 26篇 |
1997年 | 28篇 |
1996年 | 18篇 |
1995年 | 12篇 |
1994年 | 25篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1965年 | 1篇 |
1964年 | 3篇 |
1959年 | 1篇 |
1955年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有3974条查询结果,搜索用时 31 毫秒
1.
针对图像拼接存在色差过渡不均匀、图像倾斜扭曲及拼接效率低的现象,提出一种基于拼接缝自适应消除和全景图矫直的快速图像拼接算法。首先,用尺度不变特征变换(SIFT)提取图像指定区域特征点并用双向K近邻(KNN)算法进行图像配准,有效提高算法效率;其次,利用动态规划思想提出自适应公式找到最优拼接缝并用图像融合算法对其自适应消除,解决拼接缝色差过渡不均匀问题;最后,针对累积拼接误差形成全景图倾斜的现象,利用边缘检测算法提出自适应拟合四边形矫直模型,把原始全景图矫直为一个全新的全景图。所提算法与分块图像拼接和二叉树图像拼接算法相比,图像质量提升了5.84%~7.83%,拼接时间仅为原来的50%~70%。实验结果表明,该算法不仅通过自适应更新机制减少不同图像背景下拼接缝色差过渡不均匀的现象,从而提高了图像质量;而且提高了拼接效率,降低了全景图倾斜扭曲程度。 相似文献
2.
In this research work, a 40-km2 SPOT-5 High-Resolution Imagery (HRI) of the Warsak locality in district Peshawar, Pakistan, was utilized to approximate the quantity of cultivated land lost to urbanization, due to the construction of new homes and buildings. The imagery from a period of 2005 to 2015 for wheat crop was taken, specifically during the months of March and June when the crop is rich green and golden ripe respectively. eCognition ® program’s Object-Oriented Classification Method (OOCM) was employed for recognition of land versus buildings. Nearest Neighbour (NN), Support Vector Machine (SVM), Decision Trees (DT) and Random Forests (RF) were utilized for the classification process. The results demonstrated that the urbanized area had increased by approximately 28 per cent in the area considered. Moreover, the efficacy of the proposed method is depicted by an accuracy of 97.9 per cent and a Kappa Statistics of 0.975 for the SVM classifier. 相似文献
3.
针对目前运动想象脑电(EEG)信号识别率较低的问题,考虑到脑电信号蕴含着丰富的时频信息,提出一种基于时频域的卷积神经网络(CNN)运动想象脑电信号识别方法。首先,利用短时傅里叶变换(STFT)对脑电信号的相关频带进行预处理,并将多个电极的时频图组合构造出一种二维时频图;然后,针对二维时频图的时频特性,通过一维卷积的方法设计了一种新颖的CNN结构;最后,通过支持向量机(SVM)对CNN提取的特征进行分类。基于BCI数据集的实验结果表明,所提方法的平均识别率为86.5%,优于其他传统运动想象脑电信号识别方法;同时将该方法应用在智能轮椅上,验证了其有效性。 相似文献
4.
针对人脸识别系统中出现的通过照片或视频“欺诈”解锁问题,提出一种活体检测方法,通过随机指令判断被检测对象是否为真人。利用HOG特征和随机森林算法对摄像头采集的图像进行人脸检测,预测脸部68个特征点位置,把68个特征点位置和脸部位置的相对位置归一化后作为姿态的特征,提取的姿态特征与SVM分类器相结合,训练出分类效果较好的头部姿态估计分类器。通过多次实验,对特征提取方法进行优化,进一步提高检测准确率。最后,使用随机互动式命令序列对被检测人发出指令,实现活体检测。该方法对头部姿态估计具有较高的鲁棒性,并且可以有效地防范照片和视频认证攻击。 相似文献
5.
《International Journal of Hydrogen Energy》2020,45(28):14470-14479
High-temperature operation of solid oxide fuel cells causes several degradation and material issues. Lowering the operating temperature results in reduced fuel cell performance primarily due to the limited ionic conductivity of the electrolyte. Here we introduce the Fe-doped SrTiO3-δ (SFT) pure perovskite material as an electrolyte, which shows good ionic conduction even at lower temperatures, but has low electronic conduction avoiding short-circuiting. Fuel cell fabricated using this electrolyte exhibits a maximum power density of 540 mW/cm2 at 520 °C with Ni-NCAL electrodes. It was found that the Fe-doping into the SrTiO3-δ facilitates the creation of oxygen vacancies enhancing ionic conductivity and transport of oxygen ions. Such high performance can be attributed to band-bending at the interface of electrolyte/electrode, which suppresses electron flow, but enhances ionic flow. 相似文献
6.
Zhigang Yang Zhijia Zhao Jianbo Yu Zhongming Ren 《International Journal of Applied Ceramic Technology》2019,16(4):1381-1389
Textured porous Si3N4-TiB2 composites were prepared by gel-casting–assisted magnetic field alignment technology and subsequent pressureless sintering in the N2 atmosphere. The effects of TiB2 content on grain orientation and properties of composites were studied. Results showed that using the magnetic field of 6T, Si3N4 grains exhibited a high a- or b-axis orientation and TiB2 grains exhibited a high c-axis orientation. In textured green bodies, the increase in TiB2 content from 0 to 20 wt%, the degree of texture of Si3N4 grains showed a slight decrease from 0.78 to 0.71. However, the degree of texture of TiB2 grains was maintained at about 0.98 regardless of TiB2 content. After sintering, except for the Si3N4 and TiB2 phases, new TiN and BN phases also appeared in the samples. Additionally, the sintering process promotes grain orientation of Si3N4 and TiB2. Herein, the degree of texture of TiB2 reached to about 1 regardless of TiB2 content, meaning that the complete grain orientation formed for TiB2. Owing to the reconstruction reaction between TiB2 and N2, new TiN and BN phases did not form the orientation. The increase in TiB2 contents gradually increased the apparent porosity of the textured samples from 27.9% to 39.4%, thereby leading to the decrease in bending strength from 126.8 ± 18.8 MPa to 60.3 ± 11.2 MPa and from 105.3 ± 19.8 MPa to 53.6 ± 13.0 MPa in two directions, respectively. 相似文献
7.
Nathan M. Wilbur Antin M. O'Sullivan Kerry T. B. MacQuarrie Tommi Linnansaari R. Allen Curry 《河流研究与利用》2020,36(5):769-783
Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems. 相似文献
8.
9.
Yubing Guo Hamed Shahsavan Metin Sitti 《Advanced materials (Deerfield Beach, Fla.)》2020,32(38):2002753
The shape-shifting behavior of liquid crystal networks (LCNs) and elastomers (LCEs) is a result of an interplay between their initial geometrical shape and their molecular alignment. For years, reliance on either one-step in situ or two-step film processing techniques has limited the shape-change transformations from 2D to 3D geometries. The combination of various fabrication techniques, alignment methods, and chemical formulations developed in recent years has introduced new opportunities to achieve 3D-to-3D shape-transformations in large scales, albeit the precise control of local molecular alignment in microscale 3D constructs remains a challenge. Here, the voxel-by-voxel encoding of nematic alignment in 3D microstructures of LCNs produced by two-photon polymerization using high-resolution topographical features is demonstrated. 3D LCN microstructures (suspended films, coils, and rings) with designable 2D and 3D director fields with a resolution of 5 µm are achieved. Different shape transformations of LCN microstructures with the same geometry but dissimilar molecular alignments upon actuation are elicited. This strategy offers higher freedom in the shape-change programming of 3D LCN microstructures and expands their applicability in emerging technologies, such as small-scale soft robots and devices and responsive surfaces. 相似文献
10.
The proposed work involves the multiobjective PSO based adaption of optimal neural network topology for the classification of multispectral satellite images. It is per pixel supervised classification using spectral bands (original feature space). This paper also presents a thorough experimental analysis to investigate the behavior of neural network classifier for given problem. Based on 1050 number of experiments, we conclude that following two critical issues needs to be addressed: (1) selection of most discriminative spectral bands and (2) determination of optimal number of nodes in hidden layer. We propose new methodology based on multiobjective particle swarm optimization (MOPSO) technique to determine discriminative spectral bands and the number of hidden layer node simultaneously. The accuracy with neural network structure thus obtained is compared with that of traditional classifiers like MLC and Euclidean classifier. The performance of proposed classifier is evaluated quantitatively using Xie-Beni and β indexes. The result shows the superiority of the proposed method to the conventional one. 相似文献