全文获取类型
收费全文 | 38825篇 |
免费 | 4950篇 |
国内免费 | 3550篇 |
专业分类
化学 | 20462篇 |
晶体学 | 284篇 |
力学 | 1945篇 |
综合类 | 273篇 |
数学 | 3281篇 |
物理学 | 10617篇 |
无线电 | 10463篇 |
出版年
2024年 | 148篇 |
2023年 | 909篇 |
2022年 | 1001篇 |
2021年 | 1317篇 |
2020年 | 1363篇 |
2019年 | 1279篇 |
2018年 | 1096篇 |
2017年 | 1044篇 |
2016年 | 1508篇 |
2015年 | 1593篇 |
2014年 | 1937篇 |
2013年 | 2553篇 |
2012年 | 3093篇 |
2011年 | 3122篇 |
2010年 | 2116篇 |
2009年 | 2141篇 |
2008年 | 2272篇 |
2007年 | 2152篇 |
2006年 | 1998篇 |
2005年 | 1720篇 |
2004年 | 1246篇 |
2003年 | 1136篇 |
2002年 | 1013篇 |
2001年 | 806篇 |
2000年 | 859篇 |
1999年 | 940篇 |
1998年 | 844篇 |
1997年 | 771篇 |
1996年 | 871篇 |
1995年 | 689篇 |
1994年 | 629篇 |
1993年 | 537篇 |
1992年 | 505篇 |
1991年 | 409篇 |
1990年 | 323篇 |
1989年 | 239篇 |
1988年 | 186篇 |
1987年 | 159篇 |
1986年 | 156篇 |
1985年 | 131篇 |
1984年 | 100篇 |
1983年 | 67篇 |
1982年 | 46篇 |
1981年 | 38篇 |
1980年 | 21篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1976年 | 21篇 |
1975年 | 34篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
将心磁信号从干扰噪声中加以提取并有效地消除噪声干扰是心磁信号处理中尤为重要的环节 .从改进算法的角度出发,提出互补型自适应滤波器结构以实现心磁信号的消噪处理.该滤波器针对心磁这类非平稳信号进行设计,有效地解决了常规自适应滤波器应用于心磁信号处理时收敛速度和稳态误差的矛盾.通过仿真实验和心磁实验结果表明,该算法能有效地消除心磁信号的背景噪声和工频干扰噪声.同时该算法也可用于其他非平稳信号的消噪处理.
关键词:
自适应滤波
心磁图
最小均方误差 相似文献
163.
Huayi Wu Xiaohua Jia Yanxiang He Chuanhe Huang 《International Journal of Communication Systems》2005,18(9):803-816
This paper investigates the issues of QoS routing in CDMA/TDMA ad hoc networks. Since the available bandwidth is very limited in ad hoc networks, a QoS request between two nodes will be blocked if there does not exist a path that can meet the QoS requirements, even though there is enough free bandwidth in the whole system. In this paper, we propose a new scheme of using multiple paths between two nodes as the route for a QoS call. The aggregate bandwidth of the multiple paths can meet the bandwidth requirement of the call and the delays of these paths are within the required bound of the call. We also propose three strategies by which to choose a set of paths as the route, namely, shortest path first (SPF), largest bandwidth first (LBF), and largest hop‐bandwidth first (LHBF). Extensive simulations have been conducted to evaluate the performance of the three strategies in comparison with a traditional single path routing algorithm. The simulation results show that the proposed multiple paths routing scheme significantly reduces the system blocking rates in various network environments, especially when the network load is heavy. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
164.
A new fluorescent chemosensor with imidazole as ionophore was synthesized by the selective derivation of calixarene, which can effectively recognize Cu2+ and Zn2+ leading to different fluoroscopic behaviors in CH3OH-H2O. This system could be considered as a molecular switch. By modulating the pH of the solution, on-off-on fluorescent switching is carried out upon combinatory addition of acid, base and Cu2+. 相似文献
165.
In this paper, we present some counterexamples which show that there is no theory on the spectrum of homogeneous compact operators which parallels the Riesz-Schauder theory on the spectrum of linear compact operators. These counterexamples also illustrate that it is impossible to study in a unified setting the Fucik spectrum of the Laplacian: -△w = au+ - bu- inΩand u = 0 on (?)Ω, as well as the spectrum of the p-Laplacian: -div(|(?)u| p-2(?)u) = λ|u|p-2u and u = 0 on (?)Ω. 相似文献
166.
A Novel Segmentation and Feedback Model for Resolving Contention in Optical Burst Switching 总被引:2,自引:0,他引:2
A novel segmentation and feedback model (SFM) applied to resolve contention is proposed. Simulation and performance analyses show that the SFM effectively avoids contentions in optical burst switching (OBS). The long delay time of deflection routing and the immature technology of wavelength converters and optical buffers are not deployed in the SFM. The SFM does not only realize fast switching but also allows preemption by higher priority bursts. 相似文献
167.
Lin-Ping Shen Wei-Ping Huang Shui-Sheng Jian 《Lightwave Technology, Journal of》2003,21(7):1644-1651
A general procedure for design of photonic crystal fibers (PCFs) with desirable dispersion properties is presented. The design model is based on the combination of a rigorous vector mode solver and a scaling transformation for the dispersion properties of the PCFs. In comparison with the conventional design method, the new design procedure is more efficient and can be readily automated for the purpose of design optimization. Several applications of the design procedure, e.g., the design optimization for dispersion shifted fibers, dispersion flattened fibers, and dispersion compensation fibers, are demonstrated and discussed. 相似文献
168.
Yikun Huang Nehorai A. Friedman G. 《Antennas and Propagation, IEEE Transactions on》2003,51(6):1307-1314
Coupling between two collocated orthogonal circular thin-wire loops is analyzed in this paper. Two coupled integral equations for the loop currents are derived and their solution in general form is found in terms of Fourier series. An analytical expression for currents induced through the mutual coupling is obtained for the case when all loop current harmonics higher than first can be ignored. It is found that strong coupling can exist for all loop current harmonics, except for the fundamental. It is also found that coupling for orthogonal collocated loop antennas depends on the relative locations of the loop terminals. 相似文献
169.
Chenn-Jung Huang Wei-Kuang Lai Sheng-Yu Hsiao Hao-Yu Liu Rui-Lin Luo 《International Journal of Wireless Information Networks》2004,11(3):131-146
In this paper, a routing protocol which utilizes the characteristics of Bluetooth technology is proposed for Bluetooth-based mobile ad hoc networks. The routing tables are maintained in the master devices and the routing zone radius for each table is adjusted dynamically by using evolving fuzzy neural networks. Observing there exists some useless routing packets which are helpless to build the routing path and increase the network loads in the existing ad hoc routing protocols, we selectively use multiple unicasts or one broadcast when the destination device is out of the routing zone radius coverage of the routing table. The simulation results show that the dynamic adjustment of the routing table size in each master device results in much less reply time of routing request, fewer request packets and useless packets compared with two representative protocols, Zone Routing Protocol and Dynamic Source Routing. 相似文献
170.