全文获取类型
收费全文 | 6931篇 |
免费 | 373篇 |
国内免费 | 412篇 |
专业分类
化学 | 1334篇 |
晶体学 | 75篇 |
力学 | 468篇 |
综合类 | 58篇 |
数学 | 3516篇 |
物理学 | 2265篇 |
出版年
2023年 | 37篇 |
2022年 | 90篇 |
2021年 | 79篇 |
2020年 | 93篇 |
2019年 | 96篇 |
2018年 | 76篇 |
2017年 | 112篇 |
2016年 | 102篇 |
2015年 | 96篇 |
2014年 | 148篇 |
2013年 | 401篇 |
2012年 | 212篇 |
2011年 | 298篇 |
2010年 | 316篇 |
2009年 | 769篇 |
2008年 | 766篇 |
2007年 | 639篇 |
2006年 | 598篇 |
2005年 | 351篇 |
2004年 | 262篇 |
2003年 | 282篇 |
2002年 | 283篇 |
2001年 | 227篇 |
2000年 | 181篇 |
1999年 | 186篇 |
1998年 | 194篇 |
1997年 | 129篇 |
1996年 | 94篇 |
1995年 | 68篇 |
1994年 | 85篇 |
1993年 | 44篇 |
1992年 | 44篇 |
1991年 | 45篇 |
1990年 | 32篇 |
1989年 | 24篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 27篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有7716条查询结果,搜索用时 0 毫秒
991.
S. Marques Pinto M. Teresa Oliveira‐Martins M. Cu Pinto 《Mathematical Logic Quarterly》2006,52(2):134-150
The main purpose of this work is to introduce the class of the monadic dynamic algebras (dynamic algebras with one quantifier). Similarly to a theorem of Kozen we establish that every separable monadic dynamic algebra is isomorphic to a monadic (possibly non‐standard) Kripke structure. We also classify the simple (monadic) dynamic algebras. Moreover, in the dynamic duality theory, we analyze the conditions under which a hemimorphism of a dynamic algebra into itself defines a quantifier. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
992.
Xuejun Wang 《Optics Communications》2006,268(1):75-78
The 96GeO-(3-χ)Al2O3-χNa2O-1NaBiO3 (χ = 0, 0.5, 1.5 molar percent designated as A1, A2 and A3) and 96GeO-(3.5-ψ)Al2O3-ψNa2O-0.5Bi2O3 (ψ = 0.5, 1, 2 molar percent designated as B1, B2 and B3) glasses were prepared by conventional melting method with the measurement of their DTA curve, fluorescence decay curve, transmission, absorption and emission spectra. The near infrared superbroadband emission characteristics of the A1, A2, B1 and B2 glasses peak at ∼1220 nm were observed when pumped by an 800 nm laser diode. The stimulated emission cross section (σp) was obtained from the emission spectra. The result indicated that the introduction of Bi5+ in NaBiO3 into raw materials could increase the emission intensity of the obtained glasses by 5.6 times than that of Bi3+ in Bi2O3, and the FWHM (Δλ) and emission lifetime (τ) at 1220 nm increased from 195 nm to 275 nm, and 280 μs to 434 μs. Meanwhile, it was found that the absorption edges were blue-shifted from 486 to 447 nm by comparing those of A1 and B1. The absorption edges were considered to be ascribed to the charge transfer from Bi3+ 6s2 to Bi5+ 6s0. Therefore we could conclude that the content of Bi5+ ions in A1 was more than that in B1 glasses. It could be deduced from the emission and absorption spectra that the stronger emission intensity and wider FWHM were due to the higher concentration of Bi5+ ion in glass. In particular, the increase of Na2O content was in proportion to the thermal stability and the value of σp × τ and σp × Δλ of glasses. 相似文献
993.
Two random-walk related problems which have been studied independently in the past, the expected maximum of a random walker
in one dimension and the flux to a spherical trap of particles undergoing discrete jumps in three dimensions, are shown to
be closely related to each other and are studied using a unified approach as a solution to a Wiener-Hopf problem. For the
flux problem, this work shows that a constant c = 0.29795219 which appeared in the context of the boundary extrapolation length, and was previously found only numerically,
can be derived analytically. The same constant enters in higher-order corrections to the expected-maximum asymptotics. As
a byproduct, we also prove a new universal result in the context of the flux problem which is an analogue of the Sparre Andersen
theorem proved in the context of the random walker's maximum. 相似文献
994.
Laurent Baillet Taoufik Sassi 《Numerical Methods for Partial Differential Equations》2006,22(6):1489-1508
In this article, we propose and study different mixed variational methods in order to approximate the Signorini problem with friction using finite elements. The discretized normal and tangential constraints at the contact interface are expressed by using either continuous piecewise linear or piecewise constant Lagrange multipliers in the saddle?point formulation. A priori error estimates are established and several numerical examples corresponding to the different choices of the discretized normal and tangential constraints are carried out. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006 相似文献
995.
《Magnetic resonance in chemistry : MRC》2002,40(7):480-482
1H, 13C and 15N NMR chemical shifts of 10 substituted pyrazolo[1,5‐a]pyrimidines were assigned based on DQF 1H, 1H COSY, PFG 1H, 13C HMQC and PFG 1H,X (X = 13C and 15N) HMBC experiments and on literature data. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
996.
H. Norström K. Maex J. Vanhellemont G. Brijs W. Vandervorst U. Smith 《Applied Physics A: Materials Science & Processing》1990,51(6):459-466
The formation of (TixW1–x)Si2/(TixW1–x)N, by rapid thermal processing of TixW1–x on Si in an N2 ambient is investigated. An activation energy of 1.7 eV is obtained for silicide formation. A distinct snow-ploughing of As atoms is observed during silicide formation whereas the interfacial B concentration decreases with increasing silicide formation temperature. The diffusion barrier properties of the (TixW1–x)Si2/(TixWi1–x)N stack in contact with Al is investigated upon post-metal annealing. No interaction between the layers is found for temperatures as high as 475°C after 60 min. The improved thermal stability of the (TixW1–x)N layer in contact with Al is attributed to nitrogen blocking of the grain boundaries. 相似文献
997.
M. Hofheinz X. Jehl M. Sanquer G. Molas M. Vinet S. Deleonibus 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(3):299-307
We study anomalies in the Coulomb blockade spectrum of a quantum dot
formed in a silicon nanowire. These anomalies are attributed to electrostatic
interaction with charge traps in the device. A simple model reproduces these
anomalies accurately and we show how the capacitance matrices of the traps can
be obtained from the shape of the anomalies. From these capacitance matrices
we deduce that the traps are located near or inside the wire. Based on the
occurrence of the anomalies in wires with different doping levels we infer
that most of the traps are arsenic dopant states. In some cases the anomalies
are accompanied by a random telegraph signal which allows time resolved
monitoring of the occupation of the trap. The spin of the trap states is
determined via the Zeeman shift. 相似文献
998.
For the first time, the dissipation of laser-radiation energy in the gas surrounding a target is investigated under the conditions
of intense plasma formation near a surface and the existence of large spots of: irradiation. The parameters of different regions
of the heated gas are measured and an energy balance of the process of laser effects is obtained.
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 814–817, November–December, 1998. 相似文献
999.
The Heisenberg spin-S quantum antiferromagnet is studied near the large-spin limit, applying a new continuous unitary transformation which extends the usual Bogoliubov transformation to higher order in the 1/S-expansion of the Hamiltonian. This allows to diagonalize the bosonic Hamiltonian resulting from the Holstein-Primakoff representation
beyond the conventional spin-wave approximation. The zero-temperature flow equations derived from the extension of the Bogoliubov
transformation to order for the ground-state energy, the spin-wave velocity, and the staggered magnetization are solved exactly and yield results
which are in agreement with those obtained by a perturbative treatment of the magnon interactions.
Received: 19 March 1998 / Revised: 2 June 1998 / Accepted: 8 June 1998 相似文献
1000.
Reflection properties of metallic photonic crystals 总被引:1,自引:0,他引:1
B. Temelkuran E. Ozbay M. Sigalas G. Tuttle C.M. Soukoulis K.M. Ho 《Applied Physics A: Materials Science & Processing》1998,66(3):363-365
Received: 10 November 1997/Accepted: 16 November 1997 相似文献