全文获取类型
收费全文 | 6064篇 |
免费 | 1202篇 |
国内免费 | 466篇 |
专业分类
电工技术 | 897篇 |
综合类 | 672篇 |
化学工业 | 435篇 |
金属工艺 | 396篇 |
机械仪表 | 378篇 |
建筑科学 | 280篇 |
矿业工程 | 108篇 |
能源动力 | 271篇 |
轻工业 | 132篇 |
水利工程 | 80篇 |
石油天然气 | 351篇 |
武器工业 | 83篇 |
无线电 | 1222篇 |
一般工业技术 | 814篇 |
冶金工业 | 335篇 |
原子能技术 | 45篇 |
自动化技术 | 1233篇 |
出版年
2024年 | 22篇 |
2023年 | 161篇 |
2022年 | 227篇 |
2021年 | 256篇 |
2020年 | 339篇 |
2019年 | 336篇 |
2018年 | 252篇 |
2017年 | 285篇 |
2016年 | 330篇 |
2015年 | 323篇 |
2014年 | 452篇 |
2013年 | 449篇 |
2012年 | 483篇 |
2011年 | 431篇 |
2010年 | 348篇 |
2009年 | 372篇 |
2008年 | 345篇 |
2007年 | 364篇 |
2006年 | 297篇 |
2005年 | 250篇 |
2004年 | 209篇 |
2003年 | 189篇 |
2002年 | 170篇 |
2001年 | 171篇 |
2000年 | 133篇 |
1999年 | 104篇 |
1998年 | 74篇 |
1997年 | 66篇 |
1996年 | 50篇 |
1995年 | 47篇 |
1994年 | 51篇 |
1993年 | 35篇 |
1992年 | 26篇 |
1991年 | 6篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1961年 | 1篇 |
1956年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有7732条查询结果,搜索用时 15 毫秒
131.
This paper presents a class of dual–primal proximal point algorithms (PPAs) for extended convex programming with linear constraints. By choosing appropriate proximal regularization matrices, the application of the general PPA to the equivalent variational inequality of the extended convex programming with linear constraints can result in easy proximal subproblems. In theory, the sequence generated by the general PPA may fail to converge since the proximal regularization matrix is asymmetric sometimes. So we construct descent directions derived from the solution obtained by the general PPA. Different step lengths and descent directions are chosen with the negligible additional computational load. The global convergence of the new algorithms is proved easily based on the fact that the sequences generated are Fejér monotone. Furthermore, we provide a simple proof for the O(1/t) convergence rate of these algorithms. 相似文献
132.
分层内积加密方案为内积加密体制提供了私钥分发功能,可有效降低系统根节点的任务量。针对现有分层内积加密方案密文长度过长的问题,首先提出一个完全安全且固定密文长度的内积加密方案,并以该方案为基础,构造了一个新的分层内积加密方案,利用对偶系统加密的新技术,在标准模型下证明了该分层内积加密方案是完全安全的。新方案密文长度达到了固定值,并且解密时只需要7个双线性对运算。与现有方案比,新方案计算效率高,且易于实现,占用通信带宽低,具有一定的优势。 相似文献
133.
134.
135.
虚拟网映射竞争算法设计与分析 总被引:1,自引:0,他引:1
对网络虚拟化技术中的虚拟网映射问题及其研究现状进行了介绍,针对虚拟节点映射已知且物理网不支持路径分割的虚拟网映射问题,提出以物理网提供商收益最大化为目标的虚拟网映射竞争算法,并给出了算法的竞争比分析。实验表明,所提出的算法能提高物理网资源的负载均衡度和利用率,从而提高了虚拟网构建请求的接受率和物理网提供商的收益。 相似文献
136.
Independently controllable dual‐band microstrip bandpass filter using quadruple‐mode stub‐loaded resonator 下载免费PDF全文
In this article, a quadruple‐mode stub‐loaded resonator (QM‐SLR) is introduced and its four modes are excited using a simple approach, which can provide a dual‐band behavior. By changing the length of the loaded stubs, independently tunable transmission characteristics of the proposed quadruple‐mode stub‐loaded resonator were extensively described for filter design. Moreover, microwave varactors were adopted to represent the length variation of the loaded stubs for the dual‐band tunability. The equivalent circuit modeling of the open stub with microwave varactor was given and discussed. Then, adopting the compact quadruple‐mode stub‐loaded resonator with three varactors, an independently controllable dual‐band bandpass filter (BPF) was designed, analyzed, and fabricated. Its separated bandwidths and transmission zeros can be tuned independently by changing the applying voltage of the microwave varactors. A good agreement between simulated and measured results verified the design methodology. The proposed filter possesses compact size, simple structure, and excellent dual‐band performances. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:602–608, 2016. 相似文献
137.
为了检测回流焊接之后SMT( Surface Mount Technology)封装电路板是否存在缺陷,设计并搭建了基于线结构光传感器的SMT封装电路板三维在线检测系统,通过线结构光扫描测量,获取SMT封装电路板表面三维数据。采用双传感器测量技术,有效减少数据丢失;研究了双传感器统一标定技术,可同时实现两个传感器的参数标定和坐标系统一。提出了自适应光条中心提取算法,对反射或散射影响而形成的光条图像噪声具有很好的抑制效果,能够提取准确的光条中心。实验表明系统测量精度可达到0.02 mm。系统测量得到的三维数据,可以为在线检测SMT封装电路板缺陷提供可靠的三维信息。 相似文献
138.
A novel planar ultrawideband monopole antenna with dual notched bands is presented. The antenna mainly consists of a radiation patch and a modified ground plane. To realize dual band‐notched characteristics, a U‐shaped stub embedded in the rectangular slot of the radiation patch and a novel coupled open‐/shorted‐circuit stub resonator are used on the backside of the substrate. The bandwidth of the dual notched bands can be controllable by adjusting some key parameters. The simulated and measured results indicate that the proposed antenna offers a very wide bandwidth from 2.6 to 18 GHz with Voltage Standing Wave Ratio (VSWR) < 2, except the dual notched bands of 3.3–3.7 GHz (World Interoperability for Microwave Access [WiMAX]) and 5.15–5.825 GHz (Wireless Local Area Network [WLAN]). Furthermore, good group delay and stable gains can be achieved over the operating frequencies. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:48–55, 2015. 相似文献
139.
Design of a compact dual‐band folded‐waveguide bandpass filter using multilayer waveguide resonators 下载免费PDF全文
A novel compact dual‐band bandpass filter based on multilayer folded‐waveguide (FWG) structure is presented in this article.In this design, slots are used to realize direct coupling between adjacent resonators and apertures are adopted to implement cross coupling between non‐adjacent resonators.A new technique of external quality factor of FWG resonator and coupling coefficients between different resonators are studied using full‐wave simulator. In order to demonstrate the proposed technique, a four‐pole dual‐band bandpass filter is designed, fabricated and measured using vector network analyzer. Measurement results which are well agreed with simulation results are presented. Moreover, four‐pole substrate integrated folded waveguide SIFW dual‐band bandpass filter, using two layers of slotted folded waveguide resonators, is demonstrated. The proposed filter has a compact size and it is excellent candidate for the application of wireless communication systems. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:780–788, 2015. 相似文献
140.
A compact slot antenna with an overall dimension of 30 × 30 × 1.6 mm3 is proposed for dual band applications. The radiating element is a hexagonal shape patch which protrudes from a Co‐Planar Waveguide (CPW) feed into a step shape slot. The slot is basically rectangular in shape and is extended by inserting rectangular cuts of different sizes on the ground plane around it. The ultrawide impedance bandwidth is achieved using asymmetric feed line along with extended rectangular cuts around the slot. For realizing the second band for personal communication system applications (near 1.9 GHz), a metallic stub of quarter wave length is attached at the top of the slot. The measured impedance bandwidth (for S11 < ?10 dB) is 110 MHz (1.86–1.97 GHz) for the first band and 9 GHz (3.0–12.0 GHz) for the second band. The antenna is further characterized by omnidirectional radiation patterns in the H‐plane, dumb‐bell shape radiation patterns in the E‐plane and a peak gain of 3–5 dBi over the ultrawideband. All the measured results are found to be in good agreement with the simulated results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:243–254, 2015. 相似文献