全文获取类型
收费全文 | 15902篇 |
免费 | 2617篇 |
国内免费 | 2055篇 |
专业分类
化学 | 5996篇 |
晶体学 | 47篇 |
力学 | 775篇 |
综合类 | 132篇 |
数学 | 1614篇 |
物理学 | 4211篇 |
无线电 | 7799篇 |
出版年
2024年 | 110篇 |
2023年 | 316篇 |
2022年 | 485篇 |
2021年 | 612篇 |
2020年 | 815篇 |
2019年 | 580篇 |
2018年 | 547篇 |
2017年 | 626篇 |
2016年 | 794篇 |
2015年 | 759篇 |
2014年 | 1167篇 |
2013年 | 1267篇 |
2012年 | 1132篇 |
2011年 | 1179篇 |
2010年 | 852篇 |
2009年 | 962篇 |
2008年 | 1020篇 |
2007年 | 1001篇 |
2006年 | 960篇 |
2005年 | 767篇 |
2004年 | 660篇 |
2003年 | 718篇 |
2002年 | 611篇 |
2001年 | 434篇 |
2000年 | 409篇 |
1999年 | 285篇 |
1998年 | 241篇 |
1997年 | 197篇 |
1996年 | 177篇 |
1995年 | 151篇 |
1994年 | 116篇 |
1993年 | 110篇 |
1992年 | 100篇 |
1991年 | 47篇 |
1990年 | 48篇 |
1989年 | 55篇 |
1988年 | 41篇 |
1987年 | 34篇 |
1986年 | 29篇 |
1985年 | 45篇 |
1984年 | 33篇 |
1983年 | 11篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Σ-ΔA/D转换技术及仿真 总被引:1,自引:0,他引:1
Σ-ΔA/D转换技术近年来颇受重视,因为基于该技术的A/D转换器能达到很高的分辨率(16bit以上),并另具一系列优点。本文对Σ-ΔA/D转换器的基本原理,包括过采样(Oversampling),噪声成形(NoiseShaping),以及数字抽取滤波(DigitalDecimationFiltering)等内容,均作了叙述。作者还对一个20bitΣ-Δ转换器的算法进行了计算机仿真。该转换器采用了高阶MASH噪声成形技术,而其数字抽取滤波部分则由梳状滤波器与级联的半带滤波器构成。文章中给出了仿真结果。 相似文献
12.
Jong Uhn Kim 《Transactions of the American Mathematical Society》2002,354(3):1117-1135
In this paper we discuss an initial-boundary value problem for a stochastic nonlinear equation arising in one-dimensional viscoelasticity. We propose to use a new direct method to obtain a solution. This method is expected to be applicable to a broad class of nonlinear stochastic partial differential equations.
13.
This paper proposes a software pipelining framework, CALiBeR (ClusterAware Load Balancing Retiming Algorithm), suitable for compilers targetingclustered embedded VLIW processors. CALiBeR can be used by embedded systemdesigners to explore different code optimization alternatives, that is, high-qualitycustomized retiming solutions for desired throughput and program memory sizerequirements, while minimizing register pressure. An extensive set of experimentalresults is presented, demonstrating that our algorithm compares favorablywith one of the best state-of-the-art algorithms, achieving up to 50% improvementin performance and up to 47% improvement in register requirements. In orderto empirically assess the effectiveness of clustering for high ILP applications,additional experiments are presented contrasting the performance achievedby software pipelined kernels executing on clustered and on centralized machines. 相似文献
14.
Daisuke Matsuura 《Tetrahedron letters》2006,47(9):1371-1374
An efficient and stereodefined strategy is described for the asymmetric synthesis of a new styryllactone from the stem bark of Goniothalamus cardiopetalus, cardiobutanolide. The synthetic process is based on requisite manipulation of the functionalized bicyclic lactol-lactone intermediate incorporating the glucuronolactone-derived skeleton in a complete stereoselective manner. 相似文献
15.
16.
Gregorio Falqui 《Reports on Mathematical Physics》2002,50(3):395
We formulate and discuss a reduction theorem for Poisson pencils associated with a class of integrable systems, defined on bi-Hamiltonian manifolds, recently studied by Gel'fand and Zakharevich. The reduction procedure is suggested by the bi-Hamiltonian approach to the separation of variables problem. 相似文献
17.
陈泽乾 《数学物理学报(B辑英文版)》2002,22(3)
A new framework of Gaussian white noise calculus is established, in line with generalized expansion in [3, 4, 7]. A suitable frame of Fock expansion is presented on Gaussian generalized expansion functionals being introduced here, which provides the integral kernel operator decomposition of the second quantization of Koopman operators for chaotic dynamical systems, in terms of annihilation operators dt and its dual, creation operators t*. 相似文献
18.
Under idealized conditions, electroconvection in a nematic liquid crystal sets in at a well-defined threshold of the driving ac voltage. Fluctuating convection rolls of a small amplitude below that threshold have been observed recently. The measurement of the amplitude of these fluctuations is described in detail in this paper. It is based on averaging the light intensity signals using the structure function and a quantitative analysis of the light deflection. 相似文献
19.
L. T. Ashchepkov 《Computational Mathematics and Mathematical Physics》2006,46(7):1168-1175
A general nonlinear programming problem with interval functions is considered. Two reductions of this problem to the deterministic nonlinear programming problem are proposed, and illustrative examples are discussed. 相似文献
20.
Murray Hodgson 《Applied Acoustics》2004,65(1):69-89
The acoustical characteristics of 14 university classrooms at the University of British Columbia were measured before and after renovation—seven of these are discussed in detail here. From these measurements, and theoretical considerations, values of quantities used to assess each classroom configuration were predicted, and used to evaluate renovation quality. Information on each renovation was determined with the help of the university campus-planning office and/or the project acoustical consultant. These were related to the evaluation results in order to determine the relationship between design and acoustical quality. The criteria focused on the quality of verbal communication in the classrooms. Room-average Speech Intelligibility (SI) and its physical correlate, Speech Transmission Index (STI), were used to quantify verbal-communication quality. A simplified STI-calculation procedure was applied. The results indicate that some renovations were beneficial, others were not. Verbal-communication quality varied from ‘poor’ to ‘good’. The effect of a renovation depends on a complex interplay between changes in the reverberation and changes in the signal-to-noise level difference, as affected by sound absorption and the source outputs. Renovations which reduce noise are beneficial unless signal-to-noise level differences remain optimal. Renovations often put too much emphasis on adding sound absorption to control reverberation, at the expense of lower speech levels, particularly at the backs of classrooms. The absorption and noise contributed by room occupants has apparently often been neglected. 相似文献