全文获取类型
收费全文 | 61726篇 |
免费 | 6791篇 |
国内免费 | 3447篇 |
专业分类
电工技术 | 4603篇 |
技术理论 | 3篇 |
综合类 | 5677篇 |
化学工业 | 4524篇 |
金属工艺 | 2931篇 |
机械仪表 | 4998篇 |
建筑科学 | 1039篇 |
矿业工程 | 1833篇 |
能源动力 | 632篇 |
轻工业 | 5647篇 |
水利工程 | 453篇 |
石油天然气 | 1899篇 |
武器工业 | 1295篇 |
无线电 | 13508篇 |
一般工业技术 | 4660篇 |
冶金工业 | 2191篇 |
原子能技术 | 506篇 |
自动化技术 | 15565篇 |
出版年
2024年 | 194篇 |
2023年 | 825篇 |
2022年 | 1320篇 |
2021年 | 1729篇 |
2020年 | 1737篇 |
2019年 | 1312篇 |
2018年 | 1281篇 |
2017年 | 1827篇 |
2016年 | 2018篇 |
2015年 | 2504篇 |
2014年 | 3541篇 |
2013年 | 3404篇 |
2012年 | 4508篇 |
2011年 | 4873篇 |
2010年 | 3558篇 |
2009年 | 3568篇 |
2008年 | 3702篇 |
2007年 | 4550篇 |
2006年 | 3975篇 |
2005年 | 3500篇 |
2004年 | 2891篇 |
2003年 | 2526篇 |
2002年 | 2035篇 |
2001年 | 1682篇 |
2000年 | 1503篇 |
1999年 | 1163篇 |
1998年 | 978篇 |
1997年 | 895篇 |
1996年 | 762篇 |
1995年 | 600篇 |
1994年 | 565篇 |
1993年 | 475篇 |
1992年 | 356篇 |
1991年 | 282篇 |
1990年 | 264篇 |
1989年 | 227篇 |
1988年 | 156篇 |
1987年 | 91篇 |
1986年 | 73篇 |
1985年 | 91篇 |
1984年 | 66篇 |
1983年 | 84篇 |
1982年 | 59篇 |
1981年 | 45篇 |
1980年 | 35篇 |
1979年 | 31篇 |
1978年 | 19篇 |
1977年 | 25篇 |
1976年 | 12篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
We present a data-driven method for monitoring machine status in manufacturing processes. Audio and vibration data from precision machining are used for inference in two operating scenarios: (a) variable machine health states (anomaly detection); and (b) settings of machine operation (state estimation). Audio and vibration signals are first processed through Fast Fourier Transform and Principal Component Analysis to extract transformed and informative features. These features are then used in the training of classification and regression models for machine state monitoring. Specifically, three classifiers (K-nearest neighbors, convolutional neural networks and support vector machines) and two regressors (support vector regression and neural network regression) were explored, in terms of their accuracy in machine state prediction. It is shown that the audio and vibration signals are sufficiently rich in information about the machine that 100% state classification accuracy could be accomplished. Data fusion was also explored, showing overall superior accuracy of data-driven regression models. 相似文献
42.
This paper summarizes the basics of pulsed thermal nondestructive testing (TNDT) including theoretical solutions, data processing algorithms and practical implementation. Typical defects are discussed along with 1D analytical and multi-dimensional numerical solutions. Special emphasis is focused on defect characterization by the use of inverse solutions. A list of TNDT terms is provided. Applications of active TNDT, mainly in the aerospace industry, are discussed briefly, and some trends in the further development of this technique are described. 相似文献
43.
Qiang Xia Tao Feng Xiaowei Lou Ying Wang Yangying Sun Daodong Pan Jinxuan Cao 《International Journal of Food Science & Technology》2020,55(2):669-680
As a decisive attribute, flavour could be influenced by HP treatments through multiple physical and chemical pathways within the high pressure (HP)-assisted meat curing process. This investigation aimed to identify the major pathway influencing volatile flavour patterns of two representative vinasse-cured duck (VCD) products with HP treatments (150–300 MPa/15 min), including wet and dry types, by employing headspace fingerprinting as an untargeted approach. Results suggested that HP treatments greatly lowered moisture contents and increased Warner-Bratzler shear force and thiobarbituric acid reactive substances of the cured samples. According to multivariate models, the volatile flavour patterns of the HP-processed VCD could be clearly separated from the unprocessed samples, but the VCD pressurised at different intensities represented similar volatile fingerprinting, which was validated by e-nose analysis. The discriminant analysis (OPLS-DA) model outlined vinasse-derived ethanol, acetic acid, 3-methyl-1-butanol, 2-methyl-1-butanol, phenethyl alcohol and 2-methyl-3-octanone as the major discriminant aromas across the unpressurised and pressurised samples. 相似文献
44.
Modern refractory castables contain between 3.5 and 5?wt.-% water that is necessary for sufficient flow during emplacement and for the formation of hydrate phases, necessary for the green strength of the material. Prior to the high temperature use of this material, it must be dried very carefully to avoid explosive spalling.This paper will demonstrate that beside conventional drying of pre-shaped materials in resistance furnaces microwave radiation is an energy saving and rapid method to remove pore water as well as hydrate bond water from the castable. In comparison to resistance furnaces, the use of microwave radiation does not affect the castable properties as there are mechanical strength (MOR, CCS), open porosity and pore size distribution. This study proved microwave radiation as valuable alternative with a series of tabular alumina based low cement castables (LLC) in which the water-to-cement-ratio (wcr = 0.64, 0.75, 0.82 and 1.13) was systematically altered by changing the cement concentration at constant mixing water concentration of 4.5%. 相似文献
45.
针对行星齿轮箱中各部件所激起的振动成分混叠、早期故障特征经常被较强的各级齿轮谐波成分以及环境噪声所湮没的问题,提出一种多共振分量融合卷积神经网络(multi-resonance component fusion based convolutional neural network,简称MRCF-CNN)的行星齿轮箱故障诊断方法。首先,对振动信号进行共振稀疏分解,得到包含齿轮谐波成分的高共振分量和可能包含轴承故障冲击成分的低共振分量;其次,构建多共振分量融合卷积神经网络,将得到的高、低共振分量和原始振动信号进行自适应的特征级融合,通过有监督的方式训练模型并进行行星齿轮箱故障诊断。对行星齿轮箱实验数据的分析结果表明,该方法能够有效分类行星齿轮箱中滚动轴承和齿轮的故障,成功对行星齿轮箱故障进行诊断,同时能够进一步增强卷积神经网络对振动信号所蕴含的故障信息的辨识能力。 相似文献
46.
1-read/1-write (1R1W) register file (RF) is a popular memory configuration in modern feature rich SoCs requiring significant amount of embedded memory. A memory compiler is constructed using the 8T RF bitcell spanning a range of instances from 32 b to 72 Kb. An 8T low-leakage bitcell of 0.106 μm2 is used in a 14 nm FinFET technology with a 70 nm contacted gate pitch for high-density (HD) two-port (TP) RF memory compiler which achieves 5.66 Mb/mm2 array density for a 72 Kb array which is the highest reported density in 14 nm FinFET technology. The density improvement is achieved by using techniques such as leaf-cell optimization (eliminating transistors), better architectural planning, top level connectivity through leaf-cell abutment and minimizing the number of unique leaf-cells. These techniques are fully compatible with memory compiler usage over the required span. Leakage power is minimized by using power-switches without degrading the density mentioned above. Self-induced supply voltage collapse technique is applied for write and a four stack static keeper is used for read Vmin improvement. Fabricated test chips using 14 nm process have demonstrated 2.33 GHz performance at 1.1 V/25 °C operation. Overall Vmin of 550 mV is achieved with this design at 25 °C. The inbuilt power-switch improves leakage power by 12x in simulation. Approximately 8% die area of a leading 14 nm SoC in commercialization is occupied by these compiled RF instances. 相似文献
47.
GIS在深圳市三防指挥信息系统中的应用 总被引:1,自引:0,他引:1
深圳市三防指挥信息系统利用GIS技术,结合水利(水务)、防汛、抗旱的具体业务,建立了水情遥测数据处 理分系统、工况监测数据处理分系统、水务行业三防信息管理分系统、决策支持分系统、水源优化调度分 系统,提高了现代化管理水平。 相似文献
48.
49.
以子块直方图彩色图像检索算法为基础, 分析了进一步利用图像空间相似信息的颜色匹配对检索算法的性能。在子块直方图的构成、直方图距离值的归类等方面提出了行之有效的改进方法;给出了子块大小、相似度阈值等参数选择的优化原则,使查准率、查全率等检索性能指标得到了较大的提高,得出了几个有用的结论并形成了实验系统。 相似文献
50.