全文获取类型
收费全文 | 33497篇 |
免费 | 4152篇 |
国内免费 | 2414篇 |
专业分类
化学 | 20685篇 |
晶体学 | 500篇 |
力学 | 2203篇 |
综合类 | 110篇 |
数学 | 3897篇 |
物理学 | 12668篇 |
出版年
2024年 | 39篇 |
2023年 | 533篇 |
2022年 | 717篇 |
2021年 | 906篇 |
2020年 | 1076篇 |
2019年 | 1076篇 |
2018年 | 923篇 |
2017年 | 798篇 |
2016年 | 1316篇 |
2015年 | 1223篇 |
2014年 | 1515篇 |
2013年 | 2124篇 |
2012年 | 2865篇 |
2011年 | 3033篇 |
2010年 | 2067篇 |
2009年 | 1982篇 |
2008年 | 2142篇 |
2007年 | 1956篇 |
2006年 | 1831篇 |
2005年 | 1488篇 |
2004年 | 1162篇 |
2003年 | 911篇 |
2002年 | 827篇 |
2001年 | 873篇 |
2000年 | 778篇 |
1999年 | 736篇 |
1998年 | 593篇 |
1997年 | 591篇 |
1996年 | 611篇 |
1995年 | 482篇 |
1994年 | 421篇 |
1993年 | 312篇 |
1992年 | 319篇 |
1991年 | 295篇 |
1990年 | 256篇 |
1989年 | 213篇 |
1988年 | 147篇 |
1987年 | 143篇 |
1986年 | 119篇 |
1985年 | 124篇 |
1984年 | 82篇 |
1983年 | 64篇 |
1982年 | 66篇 |
1981年 | 48篇 |
1980年 | 36篇 |
1979年 | 29篇 |
1978年 | 31篇 |
1977年 | 22篇 |
1976年 | 26篇 |
1975年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 953 毫秒
61.
Q. B. Li 《Optics and Lasers in Engineering》1989,11(2)
The smoothing spline function has been used for differentiation of photomechanical data in experimental stress analysis. However, since the available software packages use the algorithm with the so-called natural boundary conditions which are not necessarily suitable in many circumstances, errors tend to occur in both the first and second derivatives. In this paper we have modified the algorithm so that the user can have more freedom in selecting boundary conditions which suit the problem best and therefore, as a result, improve the accuracy of the analysis. Two examples are given to show the improvement achievable using the new scheme. 相似文献
62.
Singlet-Triplet Transition in Quantum Dots Confined by Triangular and Bowl-Like Potentials: the Effect of Electric Fields
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We theoretically investigate the energy spectra of two-electron two-dimensional (2e 2D) quantum dots (QDs) confined by triangular potentials and bowl-like potentials in a magnetic field by exact diagonalization in the framework of effective mass theory. An in-plane electric field is found to contribute to the singlet-triplet transition of the ground state of the 2e 2D QDs confined by triangular or bowl-like potentials in a perpendicular magnetic field. The stronger the in-plane electric field, the smaller the magnetic field for the total spin of the ground states in the dot systems to change from S = 0 to S = 1. However, the influence of an in-plane electric field on the singlettriplet transition of the ground state of two electrons in a triangular QD modulated by a perpendicular magnetic field is quite small because the triangular potential just deviates from the harmonic potential well slightly. We find that the strength of the perpendicular magnetic field needed for the spin singlet-triplet transition of the ground state of the QD confined by a bowl-like potential is reduced drastically by applying an in-plane electric field. 相似文献
63.
凹整数规划的分枝定界解法 总被引:3,自引:0,他引:3
凹整数规划是一类重要的非线性整数规划问题,也是在经济和管理中有着广泛应用的最优化问题.本文主要研究用分枝定界方法求解凹整数规划问题,这一方法的基本思想是对目标函数进行线性下逼近,然后用乘子搜索法求解连续松弛问题.数值结果表明,用这种分枝定界方法求解凹整数规划是有效的. 相似文献
64.
Due to avoiding the inherent escrow of identity-based cryptography and yet not requiring certificates to guarantee the authenticity of public keys, certificateless public key cryptography has received a significant attention. Due to various applications of bilinear pairings in cryptography, numerous pairing-based encryption schemes, signature schemes, and other cryptographic primitives have been proposed. In this paper, a new certificateless signature scheme based on bilinear pairings is presented. The signing algorithm of the proposed scheme is very simple and does not require any pairing computation. Combining our signature scheme with certificateless public key cryptography yields a complete solution of certificateless public key system. As an application of the proposed signature scheme, a certificateless proxy signature scheme is also presented. We analyze both schemes from security point of view.__________Published in Lietuvos Matematikos Rinkinys, Vol. 45, No. 1, pp. 95–103, January–March, 2005. 相似文献
65.
The inhomogeneous Dirichlet problems concerning divergence form elliptic equations are studied. Optimal regularity requirements on the coefficients and domains for the W1,p theory, 1 < p < ∞, are obtained. The principal coefficients are supposed to be in the John‐Nirenberg space with small BMO seminorms. The domain is a Reifenberg domain. These conditions for the W1,p theory not only weaken the requirements on the coefficients but also lead to a more general geometric condition on the domains. In fact, these domains might have fractal dimensions. © 2004 Wiley Periodicals, Inc. 相似文献
66.
The first α‐diimine nickel(I) complex having a chloro bridge is reported. The centrosymmetric dinuclear structure of {[ArN?C(Me)C(Me)?NAr]NiCl}2[Ar?2,6?C6H3(i‐Pr)2] features two chelating α‐diimine ligands and two bridged chlorine atoms, so that a distorted tetrahedral N2Cl2 coordination geometry for nickel results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
67.
D. Liu N.Q. Ngo X.Y. Dong S.C. Tjin P. Shum 《Applied physics. B, Lasers and optics》2005,81(6):807-811
We propose and experimentally demonstrate a stable dual-wavelength erbium-doped polarization-maintaining (PM) fiber laser
with tunable wavelength spacing using an all-PM linear cavity that makes use of two reflection peaks from the PM fiber Bragg
grating (PM-FBG). Experimental results show stable dual lasing lines with a wavelength separation of ∼0.22 nm and a large
optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. By applying axial strain to the PM-FBG, the center
wavelengths of the two lasing lines can be tuned over several nanometers and the wavelength separation between the lasing
lines can also be tuned to as small as 0.05 nm, which, to our knowledge, is the smallest wavelength spacing ever obtained
from a stable room-temperature dual-wavelength fiber laser. The proposed laser configuration has the advantages of simple
structure, low loss, stable dual-wavelength operation and a very small lasing linewidth of ∼5 kHz .
PACS 42.55.Wd; 42.81.-i; 42.81.Gs 相似文献
68.
69.
Zhang Xinliang Huang Dexiu Sun Junqiang Liu Deming 《Optical and Quantum Electronics》2004,36(7):627-634
A simple scheme for single to multi-channel wavelength conversion based on cross-gain modulation of amplified spontaneous emission (ASE) spectrum in semiconductor optical amplifier (SOA) is described. Single to 16-channel wavelength conversion at 10 Gb/s is first demonstrated without any additional probe lights, the modulation information carried by input signal could be converted into arbitrary many channels if only the demultiplexer with enough channels is exploited. Output performance and pattern effects are investigated experimentally. 相似文献
70.