全文获取类型
收费全文 | 7942篇 |
免费 | 841篇 |
国内免费 | 497篇 |
专业分类
电工技术 | 882篇 |
综合类 | 1275篇 |
化学工业 | 328篇 |
金属工艺 | 199篇 |
机械仪表 | 440篇 |
建筑科学 | 684篇 |
矿业工程 | 139篇 |
能源动力 | 197篇 |
轻工业 | 122篇 |
水利工程 | 129篇 |
石油天然气 | 169篇 |
武器工业 | 83篇 |
无线电 | 1300篇 |
一般工业技术 | 1112篇 |
冶金工业 | 108篇 |
原子能技术 | 148篇 |
自动化技术 | 1965篇 |
出版年
2024年 | 10篇 |
2023年 | 72篇 |
2022年 | 89篇 |
2021年 | 133篇 |
2020年 | 210篇 |
2019年 | 183篇 |
2018年 | 186篇 |
2017年 | 238篇 |
2016年 | 259篇 |
2015年 | 276篇 |
2014年 | 392篇 |
2013年 | 534篇 |
2012年 | 529篇 |
2011年 | 558篇 |
2010年 | 448篇 |
2009年 | 472篇 |
2008年 | 452篇 |
2007年 | 519篇 |
2006年 | 490篇 |
2005年 | 431篇 |
2004年 | 372篇 |
2003年 | 302篇 |
2002年 | 302篇 |
2001年 | 245篇 |
2000年 | 231篇 |
1999年 | 209篇 |
1998年 | 167篇 |
1997年 | 154篇 |
1996年 | 149篇 |
1995年 | 128篇 |
1994年 | 90篇 |
1993年 | 82篇 |
1992年 | 61篇 |
1991年 | 50篇 |
1990年 | 51篇 |
1989年 | 38篇 |
1988年 | 28篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 2篇 |
排序方式: 共有9280条查询结果,搜索用时 346 毫秒
991.
This paper deals with numerical methods, developed to analyze plane stationary cracks in piezoelectric structures under dynamic
electromechanical loading conditions. In the first part an explicit finite element scheme is presented, which has been developed
to solve the transient coupled electromechanical boundary value problem. A special technique is implemented in the algorithm,
accounting for the limited electrical permeability of the crack. In contrast to well known algorithms for static calculations
it does not require any iteration. In order to calculate dynamic stress and electric displacement intensity factors for arbitrary
crack configurations, the interaction integral is generalized for electromechanical problems. The efficient applicability
and the high accuracy of the implementations are demonstrated by numerical examples, giving insight into several effects occuring
with dynamically loaded cracks in piezoelectrics 相似文献
992.
Unsupervised texture segmentation using Gabor filters 总被引:88,自引:0,他引:88
This paper presents a texture segmentation algorithm inspired by the multi-channel filtering theory for visual information processing in the early stages of human visual system. The channels are characterized by a bank of Gabor filters that nearly uniformly covers the spatial-frequency domain, and a systematic filter selection scheme is proposed, which is based on reconstruction of the input image from the filtered images. Texture features are obtained by subjecting each (selected) filtered image to a nonlinear transformation and computing a measure of “energy” in a window around each pixel. A square-error clustering algorithm is then used to integrate the feature images and produce a segmentation. A simple procedure to incorporate spatial information in the clustering process is proposed. A relative index is used to estimate the “true” number of texture categories. 相似文献
993.
A plane stress finite element analysis was implemented to understand the stress fields for a crack lying at an aluminium/epoxy interface of a compact tension and shear specimen. The interaction integral method was used to separate the mixed-mode stress intensity factors at the interfacial crack-tip under different loading modes, which can have important implications for characterisation of interfacial crack growth. 相似文献
994.
基于四端口谐振腔滤波理论,采用时域有限差分法(2D—FDTD)对环行谐振腔的滤波特性进行数值仿真,仿真结果给出多模干涉(MMI)耦合长度与滤波特性的关系.所制作的两种GaAlAs/GaAs平面波导环形谐振腔窄带滤波器的测试结果与仿真结果符合较好. 相似文献
995.
A powerful numerical solution is presented for bandpass filters in rectangular waveguides. The filters are composed of cascading of perfectly conducting inductive obstacles with zero thickness: asymmetrical windows, symmetrical windows, or symmetrical strips. The problem is reduced to a set of singular integral equations, which is solved by an extension of Lewin's quasi‐static procedure. After the accuracy of the classical formulas for the equivalent reactance is investigated, the simple inverse formulas are constructed to yield proper window widths for desired equivalent parameters. Their effectiveness is demonstrated by designing practical filters having maximally flat or equal‐ripple characteristics. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(4): 17–25, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10251 相似文献
996.
应用于掺铒超荧光光纤光源的滤波器研究 总被引:1,自引:0,他引:1
介绍了应用于掺铒光纤光源的几种滤波器的研究状况,阐述了它们的优缺点,简述了长周期光纤光栅滤波器的设计过程。指出现阶段使用均匀长周期光纤光栅作为掺铒光纤光源滤波器是比较理想的选择。 相似文献
997.
在小型波导缝隙阵设计中,采用匹配缝隙是减少终端损失、提高天线效率的关键技术之一。本文给出了矩形波导终端匹配缝隙对的分析。该缝隙对是由波导宽壁上的纵缝和横缝构成的。基于等效原理和并矢格林函数建立了缝隙对的耦合积分方程组,然后作数值求解。计算了缝隙对的反射特性与辐射特性,给出了缝隙对口面电场的幅值和相位以及波导驻波比随缝隙长度和频率的变化曲线。本文的计算结果可用于圆极化波导缝隙阵的设计 相似文献
998.
数值积分法计算受损伤圆钢管轴压杆件极限承载力 总被引:5,自引:1,他引:4
以电力构架中常用的圆钢管构件为研究对象,采用数值积分方法研究其在一般受损条件下的轴压极限承载力的变化情况.在迭代条件中采用混合迭代的方法,避免了在截面M-P-φ关系计算中迭代不收敛的问题.并分别讨论了不同损伤区域长度、损伤凹口弹度、损伤位置等对杆件极限承载能力的影响,了解了多杆件极限承载能力的特点,所得结论可供设计人员参考. 相似文献
999.
1000.
Automatic Voltage Regulator Design by Modified Discrete Integral Variable Structure Model Following Control 总被引:2,自引:0,他引:2
In power systems, the automatic voltage regulator (AVR) is designed to make the terminal voltage to accurately track the deviation of the reference voltage. To achieve the desired requirements, this paper proposes the modified discrete integral variable structure model following control (MDIVSMFC) approach. The MDIVSMFC approach comprises a reference model part for specifying the design requirements and a MDIVSC part for minimizing the errors between the plant and model. The non-ideal sliding motion is introduced to take the place of the ideal sliding motion in discrete-time systems. Its existence conditions are used to adapt the proposed approach to the discrete systems. The application of MDIVSMFC to an AVR design is developed. Procedures for determining the control function, the coefficients of the sliding surface and the integral control gain are also proposed in detail. Simulation results are compared with the IEEE type-I voltage regulator to demonstrate that the proposed scheme can achieve fast and robust responses. 相似文献