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891.
The generalized Stokes parameters, which are two-point extensions of conventional Stokes parameters, are determined for a pair of points in the cross-section of a partially coherent broadband light beam. For this purpose, using a two-mirror and two-beam-splitter assembly, unpolarized, linearly polarized and partially polarized electromagnetic beams are generated. This simple experimental method for determining generalized Stokes parameters establishes an analogy with the experimental scheme of determining conventional Stokes parameters, which in succession contributes to appreciable reduction in uncertainty in the measurements. 相似文献
892.
In this work, we report the effect of substrate, film thickness and sputter pressure on the phase transformation and electrical resistivity in tantalum (Ta) films. The films were grown on Si(1 0 0) substrates with native oxides in place and glass substrates by varying the film thickness (t) and pressure of the working gas (pAr). X-ray diffraction (XRD) analysis showed that the formation of α and β phases in Ta films strongly depend on the choice of substrate, film thickness t and sputter pressure pAr. A stable α-phase was observed on Si(1 0 0) substrates for t ≤ 200 nm. Both α and β phases were found to grow on glass substrates at all thicknesses except t = 100 nm. All the films grown on Si(1 0 0) substrates for pAr ≤ 6.5 mTorr had α-phase with strong (1 1 0) texture normal to the film plane. The glass substrates promoted the formation of β-phase in all pAr except pAr = 5.5 mTorr. The resistivity ρ was observed to decrease with t, whereas ρ was increased with pAr on Si(1 0 0) substrates. In all films, the measured resistivity ρ was greater than the bulk resistivity. The resistivity ρ was influenced by the effects of surface roughness and grain size. 相似文献
893.
Clustering provides an effective method for prolonging the lifetime of a wireless sensor network. Current clustering algorithms
usually utilize two techniques; selecting cluster heads with more residual energy, and rotating cluster heads periodically
to distribute the energy consumption among nodes in each cluster and extend the network lifetime. However, they rarely consider
the hot spot problem in multihop sensor networks. When cluster heads cooperate with each other to forward their data to the
base station, the cluster heads closer to the base station are burdened with heavier relay traffic and tend to die much faster,
leaving areas of the network uncovered and causing network partitions. To mitigate the hot spot problem, we propose an Unequal
Cluster-based Routing (UCR) protocol. It groups the nodes into clusters of unequal sizes. Cluster heads closer to the base
station have smaller cluster sizes than those farther from the base station, thus they can preserve some energy for the inter-cluster
data forwarding. A greedy geographic and energy-aware routing protocol is designed for the inter-cluster communication, which
considers the tradeoff between the energy cost of relay paths and the residual energy of relay nodes. Simulation results show
that UCR mitigates the hot spot problem and achieves an obvious improvement on the network lifetime.
Guihai Chen obtained his B.S. degree from Nanjing University, M. Engineering from Southeast University, and PhD from University of Hong
Kong. He visited Kyushu Institute of Technology, Japan in 1998 as a research fellow, and University of Queensland, Australia
in 2000 as a visiting professor. During September 2001 to August 2003, he was a visiting professor at Wayne State University.
He is now a full professor and deputy chair of Department of Computer Science, Nanjing University. Prof. Chen has published
more than 100 papers in peer-reviewed journals and refereed conference proceedings in the areas of wireless sensor networks,
high-performance computer architecture, peer-to-peer computing and performance evaluation. He has also served on technical
program committees of numerous international conferences. He is a member of the IEEE Computer Society.
Chengfa Li was born 1981 and obtained his Bachelor’s Degree in mathematics in 2003 and his Masters Degree in computer science in 2006,
both from Nanjing University, China. He is now a system programmer at Lucent Technologies Nanjing Telecommunication Corporation.
His research interests include wireless ad hoc and sensor networks.
Mao Ye was born in 1981 and obtained his Bachelor’s Degree in computer science from Nanjing University, China, in 2004. He served
as a research assistant At City University of Hong Kong from September 2005 to August 2006. He is now a PhD candidate with
research interests in wireless networks, mobile computing, and distributed systems.
Jie Wu is a professor in the Department of Computer Science and Engineering at Florida Atlantic University. He has published more
than 300 papers in various journal and conference proceedings. His research interests are in the areas of mobile computing,
routing protocols, fault-tolerant computing, and interconnection networks. Dr. Wu serves as an associate editor for the IEEE
Transactions on Parallel and Distributed Systems and several other international journals. He served as an IEEE Computer Society
Distinguished Visitor and is currently the chair of the IEEE Technical Committee on Distributed Processing (TCDP). He is a
member of the ACM, a senior member of the IEEE, and a member of the IEEE Computer Society. 相似文献
894.
895.
896.
给出了一种边缘粗糙度(LER)三维参数评估的方法。采用原子力显微镜(AFM)测量了刻线单侧边缘形貌,根据AFM的工作机理和测量特点重构边缘表面,采用回归分析方法确定了边缘表面的评价基准面。结合集成电路中光刻工艺的具体需求,提出了能够反映边缘表面形貌特征的三维LER表征参数。结合实例,计算了所提出的部分LER参数,分析了LER标准差参数的测量精度。 相似文献
897.
激光焊接技术广泛应用于光电子封装领域,它能形成很强的结合力,显示出无可比拟的优越性.但激光脉冲形状设置仍存在一定缺陷.研究了用于CATV的DFB激光器同轴封装激光焊接技术,利用Nd:YAG激光焊接系统,在两种不同的激光脉冲形式下,对DFB激光器和光纤进行焊接,分析了焊点宽度、深度与激光脉冲的关系.通过推力实验,测得DFB激光器输出先功率的变化大小,验证焊点质量,得出实际生产中脉宽为5 ms和2 ms、电压为310 V和360 V的激光脉冲,从而提高了焊接质量和工艺水平. 相似文献
898.
Jung-Kyun Kim Wataru Nakayama Yoshimi Ito Sang-mo Shin Sun-Kyu Lee 《Mechatronics》2009,19(6):1034-1040
A methodology for modeling and simulating the electro-thermal behavior of an enclosed electronic package is presented and validated. The electro-thermal model is constructed using system dynamics. The system model, in which the electrical and the thermal domain are combined, is presented. The developed model describes the dynamic thermal behavior system that was an electronic device in the test enclosure. An effective way to identify the thermal parameters of the system, especially the thermal contact resistance, is suggested. In detail, the new method for thermal resistance identification is based on the temperature difference behavior between the component and the air temperature inside the enclosure. Based on the proposed model, either the variation of the heat source or the ambient temperature can be estimated. Simulated results were in good agreement with the measured temperature in the transient state accompanying with the variation of the environment. 相似文献
899.
900.
扫频法精确测量高速光调制器频率响应 总被引:1,自引:0,他引:1
同微波网络一样,可以用S参数来精确描述光电子器件的性能.根据微波网络的S参数,详细推导了光电子器件的S参数.搭建了40 GHz高速测试系统,利用矢量网络分析仪(带宽40 GHz)和作为参考的标准高速光探测器(带宽45 GHz),测量了宽带光强度调制器(实测带宽35 GHz)的频率响应.理论上,通过S参数和T参数的互相转换,扣除了微波放大器对测试结果的影响.在120 MHz~35 GHz范围内,测得的结果与出厂数据取得了很好的一致性.文中通过合理的简化,得到了光调制器频率响应的简明表达式,从而降低了数据处理的复杂度. 相似文献