全文获取类型
收费全文 | 62481篇 |
免费 | 6069篇 |
国内免费 | 2634篇 |
专业分类
电工技术 | 3624篇 |
技术理论 | 4篇 |
综合类 | 3638篇 |
化学工业 | 10776篇 |
金属工艺 | 3568篇 |
机械仪表 | 4230篇 |
建筑科学 | 4296篇 |
矿业工程 | 1727篇 |
能源动力 | 2023篇 |
轻工业 | 4723篇 |
水利工程 | 1177篇 |
石油天然气 | 2801篇 |
武器工业 | 553篇 |
无线电 | 7546篇 |
一般工业技术 | 8301篇 |
冶金工业 | 2996篇 |
原子能技术 | 903篇 |
自动化技术 | 8298篇 |
出版年
2024年 | 224篇 |
2023年 | 1016篇 |
2022年 | 1845篇 |
2021年 | 2633篇 |
2020年 | 1957篇 |
2019年 | 1759篇 |
2018年 | 2021篇 |
2017年 | 2117篇 |
2016年 | 2052篇 |
2015年 | 2614篇 |
2014年 | 3313篇 |
2013年 | 3920篇 |
2012年 | 4508篇 |
2011年 | 4833篇 |
2010年 | 4062篇 |
2009年 | 3917篇 |
2008年 | 3660篇 |
2007年 | 3379篇 |
2006年 | 3222篇 |
2005年 | 2695篇 |
2004年 | 2058篇 |
2003年 | 1890篇 |
2002年 | 1936篇 |
2001年 | 1670篇 |
2000年 | 1352篇 |
1999年 | 1312篇 |
1998年 | 1026篇 |
1997年 | 782篇 |
1996年 | 685篇 |
1995年 | 613篇 |
1994年 | 451篇 |
1993年 | 380篇 |
1992年 | 296篇 |
1991年 | 213篇 |
1990年 | 172篇 |
1989年 | 115篇 |
1988年 | 114篇 |
1987年 | 64篇 |
1986年 | 75篇 |
1985年 | 43篇 |
1984年 | 41篇 |
1983年 | 23篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 18篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1970年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
Impurity is one of the main factors that affect the measurement accuracy of an ultrasonic heat meter. To study the effects of different impurity species and concentrations on the accuracy of heat meters, flow tests were carried out for the suspending of calcium carbonate and yellow mud. By analyzing the attenuation characteristics of the ultrasound amplitude in different impurity concentrations and species, the influence of the impurities on the heat meter measurement accuracy is evaluated. In order to avoid the inaccuracy caused by the sediment of the reflective bottom surface, a vortex generator is put ahead of the reflective surface. According to the test, the calcium carbonate suspension with a mass concentration of 1%, which influences the heat meter accuracy severely, is used as the flow media. The influence of the vortex generator on the calcium carbonate suspension flow field in the heat meter body is studied with numerical simulations. The results of this paper provide some theoretical guide on improving the heat meter measurement accuracy when the water contains impurities. 相似文献
994.
995.
Implementation of Envelope Analysis on a Wireless Condition Monitoring System for Bearing Fault Diagnosis 总被引:1,自引:0,他引:1
Guo-Jin Feng James Gu Dong Zhen Mustafa Aliwan Feng-Shou Gu rew D. Ball 《国际自动化与计算杂志》2015,12(1):14-24
Envelope analysis is an effective method for characterizing impulsive vibrations in wired condition monitoring (CM) systems. This paper depicts the implementation of envelope analysis on a wireless sensor node for obtaining a more convenient and reliable CM system. To maintain CM performances under the constraints of resources available in the cost effective Zigbee based wireless sensor network (WSN), a low cost cortex-M4F microcontroller is employed as the core processor to implement the envelope analysis algorithm on the sensor node. The on-chip 12 bit analog-to-digital converter (ADC) working at 10 kHz sampling rate is adopted to acquire vibration signals measured by a wide frequency band piezoelectric accelerometer. The data processing flow inside the processor is optimized to satisfy the large memory usage in implementing fast Fourier transform (FFT) and Hilbert transform (HT). Thus, the envelope spectrum can be computed from a data frame of 2048 points to achieve a frequency resolution acceptable for identifying the characteristic frequencies of different bearing faults. Experimental evaluation results show that the embedded envelope analysis algorithm can successfully diagnose the simulated bearing faults and the data transmission throughput can be reduced by at least 95% per frame compared with that of the raw data, allowing a large number of sensor nodes to be deployed in the network for real time monitoring. 相似文献
996.
Sam Dong Jung Jeong Soo Kim Jung Won Park Jong Hwa Won Moon Kyum Kim 《Multimedia Tools and Applications》2015,74(20):9017-9029
A technique is developed to clearly establish the shear resistance of a cellular structure, retaining wall composed of a steel frame and fill materials with both continuous and discontinuous characteristics. To overcome the limitation of the existing analysis approach based on continuum mechanics, in which the shear behavior and interaction between the frames and fill material of this type of structure are difficult to describe, this paper introduces displacement incremental analysis into the distinct element method. The results obtained by using the proposed approach are compared with experimental results to verify its accuracy. The results show an internal friction angle of fill materials and overburdening load are major factor determining the shear resistance of a retaining wall with a cellular structure type. From the results of the parametric study on the shear behavior of this type of structure, this paper also proposes a shear resistance moment-shear displacement formula for designing a retaining wall with a cellular structure type. 相似文献
997.
998.
999.
建立了激光惯性导航系统的三维有限元模型,对其力学特性进行了模态分析,建立了整个模型B样条小波有限元模型;研究了一类新的有限元空间,它以B样条小波函数作为有限等参元的形状函数;建立了IMU模型的B样条小波有限元序列,利用B样条小波函数的变尺度特性在不改变网格的剖分下提高分辨率,因此在处理局部应力集中,曲率分布突变边界等应用中具有一定的优势,所以它的结果更接近于实际;最后对系统模型进行了仿真,给出了各个阶次模态值,通过与传统有限元比较发现小波有限元具有收敛性好、求解迅速和网格划分灵活优点,离散的单元数减少了13%,计算时间也是原来的35%,这对于激光惯性导航系统的优化设计具有重要参考价值. 相似文献
1000.
摘要:针对光伏并网逆变器电路中故障信号的非线性、非平稳特点,提出一种基于经验模态分解(EMD)和样本熵(SampEn)的故障诊断方法。首先,利用经验模态分解对逆变器的三相输出电压进行分解,得到有限个本征模式分量(IMF),从中选取包含故障主要信息的前几个本征模式分量提取故障信息。然后,计算本征模式分量的样本熵,从而得到用于故障诊断的特征向量;最后,将逆变器开路故障进行分类和编码,将故障特征向量输入BP神经网络进行模式识别,从而达到故障诊断的目的。在Matlab环境下对光伏并网逆变器的故障诊断进行了实验,实验结果证明了文中方法能实现对光伏并网逆变器的故障诊断,且与小波包变换相比,该方法具有诊断效率高和准确度高等特点。 相似文献