全文获取类型
收费全文 | 2084篇 |
免费 | 86篇 |
国内免费 | 13篇 |
专业分类
化学 | 1207篇 |
晶体学 | 12篇 |
力学 | 50篇 |
数学 | 222篇 |
物理学 | 414篇 |
无线电 | 278篇 |
出版年
2023年 | 14篇 |
2022年 | 26篇 |
2021年 | 22篇 |
2020年 | 44篇 |
2019年 | 36篇 |
2018年 | 44篇 |
2017年 | 19篇 |
2016年 | 60篇 |
2015年 | 46篇 |
2014年 | 78篇 |
2013年 | 111篇 |
2012年 | 127篇 |
2011年 | 120篇 |
2010年 | 78篇 |
2009年 | 60篇 |
2008年 | 113篇 |
2007年 | 123篇 |
2006年 | 115篇 |
2005年 | 149篇 |
2004年 | 88篇 |
2003年 | 91篇 |
2002年 | 65篇 |
2001年 | 36篇 |
2000年 | 24篇 |
1998年 | 30篇 |
1997年 | 29篇 |
1996年 | 22篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 16篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 21篇 |
1984年 | 22篇 |
1983年 | 20篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 24篇 |
1979年 | 11篇 |
1978年 | 16篇 |
1977年 | 21篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1974年 | 9篇 |
1973年 | 11篇 |
排序方式: 共有2183条查询结果,搜索用时 15 毫秒
1.
2.
Shanchieh Jay Yang Gustavo de Veciana 《Networking, IEEE/ACM Transactions on》2004,12(2):349-360
With a view on improving user-perceived performance on networks supporting best effort flows, e.g., multimedia/data file transfers, we propose a family of bandwidth allocation criteria that depends on the residual work of on-going transfers. Analysis and simulations show that allocating bandwidth in this fashion can significantly improve the user-perceived delay, bit transmission delay, and throughput over traditional approaches, e.g., by 58% on an 80% loaded linear network. A simple implementation based on TCP Reno, exemplifies how one might approach practically realizing such gains. We discuss several other advantages of incorporating such differentiation at the transport level. In particular we make the case that favoring small transfers combined with user impatience or peak rate constraints, both of which are natural mechanisms for users to express the utility of completing transfers, offers a lightweight approach to achieving good overall network goodput and/or utility for best effort networks. 相似文献
3.
J. -Ph. Jay J. Ben Youssef H. Le Gall 《Journal of magnetism and magnetic materials》2002,240(1-3):287-290
The dynamic response of trilayer magnetoresistive permalloy/Cu/Co films was studied by high-frequency permeability spectra measurements. The resonance frequency is shown to depend on the interlayer copper thickness. This dependence is related to exchange coupling between permalloy and cobalt and the interaction field is estimated using the Landau–Lifschitz–Gilbert model. 相似文献
4.
In this article we use classical formulas involving the K–Bessel function in two variables to express the Poisson kernel on a Riemannian manifold in terms of the heat kernel. We then use the small time asymptotics of the heat kernel on certain Riemannian manifolds to obtain a meromorphic continuation of the associated Poisson kernel to all values of complex time with identifiable singularities. This result reproves in a different setting by different means a well–known theorem due to Duistermaat and Guillemin [DG 75]. Also, we develop analytic expressions for the heat kernel beyond asymptotic expansions. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
6.
The purpose of the present study was to describe the effects ofacute laryngitis on some aerodynamic, acoustic, and perceptual measures. Eleven subjects with diagnosed acute laryngitis due to upper respiratory infection were recorded during a laryngitic episode and 1 week to 10 days after amelioration of the laryngitic condition. Fundamental frequency values, collapsed across the five vowels, were significantly reduced in the laryngitic compared with the normal speaking condition. The decrease in fundamental frequency associated with acute laryngitis suggests an increase in the mass of the vocal folds. In addition, aerodynamic values differed significantly for the laryngitic condition compared with the normal speaking condition, suggesting the presence of laryngeal hypofunction. Perceptual data indicated that speakers in the laryngitic condition were judged to have a hoarse voice when compared with the normal speaking condition. 相似文献
7.
The basic structural units of the genome are nucleotides. A single nucleotide polymorphism (SNP) is a mutation at a single nucleotide position. This paper discusses several major problems in SNP data analysis and review some existing solutions in this work. Generally speaking, a rich set of SNP analysis problems are cast in the signal processing framework. Our objective is to offer a state-of-the art review on this topic from a signal processing viewpoint so that researchers in the signal processing field can grasp the important domain knowledge to overcome the barrier between the two fields 相似文献
8.
9.
10.
Sergiy V. Rosokha Jian Jiang Lu Sergey M. Dibrov Jay K. Kochi 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):o464-o466
The title compound, C6H2N6O10·2C2H4Cl2, forms layered stacks of pentanitroaniline molecules, which possess twofold symmetry. The voids between these stacks are occupied by dichloroethane molecules, which reside near a 2/m symmetry element and display pseudo‐inversion symmetry. The C atoms in one of the two solvent molecules are threefold disordered. In the pentanitroaniline molecule, considerable distortion of the benzenoid ring, coupled with the short C—N(H2) bond and out‐of‐plane NO2 twistings, point to significant intramolecular `push–pull' charge transfer at the amino‐ and nitro‐substituted (ortho and para) positions, as theoretically quantified by natural bond orbital analysis of the π‐electron density. 相似文献