全文获取类型
收费全文 | 4368篇 |
免费 | 892篇 |
国内免费 | 409篇 |
专业分类
化学 | 812篇 |
晶体学 | 18篇 |
力学 | 295篇 |
综合类 | 148篇 |
数学 | 2266篇 |
物理学 | 2130篇 |
出版年
2024年 | 6篇 |
2023年 | 58篇 |
2022年 | 69篇 |
2021年 | 118篇 |
2020年 | 126篇 |
2019年 | 102篇 |
2018年 | 142篇 |
2017年 | 178篇 |
2016年 | 192篇 |
2015年 | 209篇 |
2014年 | 272篇 |
2013年 | 315篇 |
2012年 | 266篇 |
2011年 | 277篇 |
2010年 | 215篇 |
2009年 | 248篇 |
2008年 | 294篇 |
2007年 | 261篇 |
2006年 | 249篇 |
2005年 | 256篇 |
2004年 | 215篇 |
2003年 | 225篇 |
2002年 | 195篇 |
2001年 | 199篇 |
2000年 | 158篇 |
1999年 | 126篇 |
1998年 | 102篇 |
1997年 | 80篇 |
1996年 | 98篇 |
1995年 | 52篇 |
1994年 | 40篇 |
1993年 | 30篇 |
1992年 | 30篇 |
1991年 | 30篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 25篇 |
1987年 | 23篇 |
1986年 | 14篇 |
1985年 | 21篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1974年 | 4篇 |
排序方式: 共有5669条查询结果,搜索用时 750 毫秒
31.
I.IntroductionThepcrformanccsofAcousto-optic(AO)dcviccareoftenlimitcdbythepropertiesofAOmcdiawhenitisusedinAOsigna1processingsystems.Thespectrumanalyzersandcorre1ationreceivers,forinstancc,areexpcctcdtoimprovcthereso1utionanddynamicrangcwhilereducingtheproccssorvolume.Rccent1y,ancwclassofmateria1s,themercurousha1ides,promiscstocontributeimportantsolutionstosuchnccdsandisrefincdtopractica1uti1izations.Themecurousha1ideweconsidcrinthispapcrismecurouschloride(Hg,C1,).Thesing1ecrystalofHg,Cl… 相似文献
32.
This paper describes the performance and simulation of a compact integrated optical processor for the real-time reconstruction of two-dimensional images in airborne stripmap synthetic aperture radar applications. The functional behavior of the processor is explained in some detail. The design criteria are briefly given. The simulation step allowed the main processor characteristics and properties to be identified. A number of comparisons were obtained in airborne SAR mission scenarios between the predictions of the optical device and those achieved by the modern electronic digital approach, based on the wavefront reconstruction method by matched filtering. 相似文献
33.
关于PFI-代数与剩余格 总被引:10,自引:0,他引:10
本文提出了一种强FI代数-PFI代数,并且深入研究了它的性质,借此进一步揭示了FI-代数和剩余格之间更加密切的联系,进而以FI-代数为基本框架建立了R0-代数、正则剩余格等逻辑系统的结构特征(包括对隅结构)及其相互关系.这种以FI-代数为基础来统一处理剩余格和R0-代数的方法,同样适合于格蕴涵代数和MV代数等代数结构,而且从中更能清楚地看出它们之间的密切联系,也将有助于对相应形式逻辑系统与模糊推理的研究. 相似文献
34.
The mass spectrum ofcb meson is investigated with an effective quark-antiquark potential of the form -αc/r +Ar
νwith ν varying from 0.5 to 2.0. TheS andP-wave masses, pseudoscalar decay constant, weak decay partial widths in spectator model and the lifetime ofB
cmeson are computed. The properties calculated here are found to be in good agreement with other theoretical and experimental
values at potential index,ν = 1 相似文献
35.
E. Liénard G. Ban J. Blieck D. Durand F. Duval X. Fléchard M. Herbane M. Labalme Y. Lemière F. Mauger A. Méry O. Naviliat-Cuncic D. Rodríguez J. C. Thomas 《Hyperfine Interactions》2006,172(1-3):29-33
We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller
decay of 6He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The
6He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to
deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this
experiment. Up to 105 coincidences were recorded during a second run in 2006. 相似文献
36.
We prove equivalence of the definitions by the author and by Korevaar and Schoen of the Sobolev classes of mappings of a domain of an arithmetic n-dimensional space to a metric space. 相似文献
37.
38.
Nguyen Minh Chuong Bui Kien Cuong 《Proceedings of the American Mathematical Society》2004,132(12):3589-3597
A class of Cauchy problems for interesting complicated periodic pseudodifferential equations is considered. By the Galerkin-wavelet method and with weak solutions one can find sufficient conditions to establish convergence estimates of weak Galerkin-wavelet solutions to a Cauchy problem for this class of equations.
39.
The signals of a single-pulse echo (SE) generated on nonresonant excitation of an inhomogeneously broadened two-level system by a radio-frequency pulse (RFP), against the background of which a magnetic video pulse (MVP) of certain length has been switched on, have been described analytically. It is established that under the conditions of such excitation several SE signals are formed whose generation moments are determined by the duration and amplitudes of the RFP and MVP. The amplitudes of some of these signals depend on the Rabi frequency according to a quadratic law, and the amplitudes of others depend on this frequency according to a biquadratic law. It has been established that the mechanism underlying the appearance of these signals is associated with zero beats arising as a result of superposition of the magnetization fluctuations at variable frequencies and at a frequency of detuning from resonance. It is shown that in the limiting case, where the RFP duration considerably exceeds the duration of the MVP or is comparable with it, the number of SE signals decreases to two. Theoretical results on the formation of SE and the dependence of the amplitude of these signals on the MVP amplitude agree with the experimental data on NMR pulsed signals in ferromagnetic materials. 相似文献
40.
Employing positive-definiteness arguments we analyse Boson field states, which combine classical and quantum mechanical features (signal and noise), in a constructive manner. Mathematically, they constitute Bauer simplexes within the convex, weak-*-compact state space of the C*-Weyl algebra, defined by a presymplectic test function space (smooth one-Boson wave functions) and are affinely homeomorphic to a state space of a classical field. The regular elements are expressed in terms of weak distributions (probability premeasures) on the dual test function space. The Bauer simplex arising from the bare vacuum is shown to generalize the quantum optical photon field states with positive P-functions. 相似文献