全文获取类型
收费全文 | 653356篇 |
免费 | 6410篇 |
国内免费 | 2032篇 |
专业分类
化学 | 299613篇 |
晶体学 | 9257篇 |
力学 | 25357篇 |
综合类 | 22篇 |
数学 | 64919篇 |
物理学 | 176438篇 |
无线电 | 86192篇 |
出版年
2021年 | 5041篇 |
2020年 | 5664篇 |
2019年 | 6225篇 |
2018年 | 7849篇 |
2017年 | 7939篇 |
2016年 | 11700篇 |
2015年 | 6835篇 |
2014年 | 11378篇 |
2013年 | 27810篇 |
2012年 | 20453篇 |
2011年 | 24765篇 |
2010年 | 18254篇 |
2009年 | 18973篇 |
2008年 | 23908篇 |
2007年 | 24619篇 |
2006年 | 23335篇 |
2005年 | 21206篇 |
2004年 | 19608篇 |
2003年 | 17779篇 |
2002年 | 17397篇 |
2001年 | 19779篇 |
2000年 | 15718篇 |
1999年 | 12730篇 |
1998年 | 11020篇 |
1997年 | 10829篇 |
1996年 | 10294篇 |
1995年 | 9447篇 |
1994年 | 9069篇 |
1993年 | 8827篇 |
1992年 | 9942篇 |
1991年 | 9885篇 |
1990年 | 9478篇 |
1989年 | 9167篇 |
1988年 | 8731篇 |
1987年 | 8128篇 |
1986年 | 7644篇 |
1985年 | 9741篇 |
1984年 | 9849篇 |
1983年 | 8118篇 |
1982年 | 8423篇 |
1981年 | 8043篇 |
1980年 | 7778篇 |
1979年 | 8174篇 |
1978年 | 8332篇 |
1977年 | 8309篇 |
1976年 | 8186篇 |
1975年 | 7676篇 |
1974年 | 7373篇 |
1973年 | 7641篇 |
1972年 | 5298篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
The theory of characteristic modes for aperture problems is used in this paper to solve the equivalent magnetic current and aperture fields due to a conducting cylinder with multiple slots. It is assumed that these slots are illuminated by either a transverse electric (TE) or a transverse magnetic (TM) plane wave and the media inside and outside the cylinder exhibit different electromagnetic properties. The formulation is given for the general case and numerical results for a limited number of slots are presented 相似文献
22.
Mine K. Kubota N. Morimoto F. Sanada M. Zhang Qi 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(3):253-255
This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance 相似文献
23.
Crosstalk between microstrip transmission lines 总被引:1,自引:0,他引:1
Hill D.A. Cavcey K.H. Johnk R.T. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):314-321
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk 相似文献
24.
Younan N.H. Cox B.I. Taylor C.D. Prather W.D. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):394-398
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz 相似文献
25.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9 相似文献
26.
A general (possibly asymmetric noncausal and/or nonminimum phase) 2D autoregressive moving average random field model driven by an independent and identically distributed 2D nonGaussian sequence is considered. The model is restricted to be invertible, i.e., system zeros are not allowed to lie on the unit bicircle. Three performance criteria are investigated for parameter estimation of the system parameters given only the output measurements (image pixels). The proposed criteria are functions of the higher order cumulant statistics of an inverse filter output. One of these criteria is novel and the others have been considered in past only for moving average inverses and without any analysis of their consistency. In the paper strong consistency of the proposed methods under the assumption that the system order is known is proved. The convergence of the proposed parameter estimators under overparametrization is also analyzed. Experimental results involving synthesized as well as real life textures are presented to illustrate the performance of two of the considered approaches. Experimental results of synthesis of 128x128 textures visually resembling several real life textures in the Brodatz album (and other sources) are presented. 相似文献
27.
A low threshold current density of ~100 A/cm2 has been obtained at 1.55 μm using a graded-index separate-confinement-heterostructure strained InGaAsP single-quantum-well laser. The design of the laser structure is based on results calculated from the viewpoint of effective carrier injection into the well 相似文献
28.
Bouillet E. Mitra D. Ramakrishnan K.G. 《Selected Areas in Communications, IEEE Journal on》2002,20(4):691-699
The paper proposes a structure for quality-of-service (QoS)-centered service level agreements (SLA), and a framework for their real-time management in multiservice packet networks. The SLA is structured to be fair to both parties, the service provider and their customer. The SLA considered here are for QoS assured delivery of aggregate bandwidth from ingress to egress nodes; however, the control and signaling is for the more granular flows or calls. A SLA monitoring scheme is presented in which revenue is generated by the admission of flows into the network, and penalty incurred when flows are lost in periods when the service provider is not SLA compliant. In the SLA management scheme proposed, the results of a prior off-line design are used, in conjunction with measurements taken locally at ingress nodes, to classify the loading status of routes. The routing and resource management are based on virtual partitioning and its supporting mechanism of bandwidth protection. The effectiveness of SLA management is measured by the robustness in performance in the presence of substantial diversity in actual traffic conditions. A simulation testbed called D'ARTAGNAN has been built from which we report numerical results for a case study. The results show that the SLA management scheme is robust, fair and efficient over a broad range of traffic conditions 相似文献
29.
This paper presents a new self-routing packet network called the plane interconnected parallel network (PIPN). In the proposed design, the traffic arriving at the network is shaped and routed through two banyan network based interconnected planes. The interconnections between the planes distribute the incoming load more homogeneously over the network. The throughput of the network under uniform and heterogeneous traffic requirements is studied analytically and by simulation. The results are compared with the results of the baseline network and another banyan network based parallel interconnection network. It is shown that, for the proposed design, a higher degree of heterogeneity results in better performance 相似文献
30.
The effect of high oxide field stress is studied using capacitance-time (C-t) measurements of MOS capacitors. The stress results in parallel shifts of the C-t curve along the time axis. The flatband voltage shift ΔVFB obtained from the initial deep depletion capacitance C(t=0+) follows the same trend as that from the high-frequency C-V characteristics. However, the discrepancy between the two flatband voltages becomes larger as the stress increases due to the effect of interface charges on C-t characteristics. The flatband voltage difference is converted to interface trap density, showing a steady increase of interface trap density with stress, similar to that from low-frequency C-V measurements 相似文献