全文获取类型
收费全文 | 25311篇 |
免费 | 4051篇 |
国内免费 | 2430篇 |
专业分类
化学 | 17784篇 |
晶体学 | 313篇 |
力学 | 1544篇 |
综合类 | 112篇 |
数学 | 2948篇 |
物理学 | 9091篇 |
出版年
2024年 | 39篇 |
2023年 | 502篇 |
2022年 | 637篇 |
2021年 | 823篇 |
2020年 | 1022篇 |
2019年 | 991篇 |
2018年 | 808篇 |
2017年 | 725篇 |
2016年 | 1182篇 |
2015年 | 1119篇 |
2014年 | 1326篇 |
2013年 | 1772篇 |
2012年 | 2387篇 |
2011年 | 2455篇 |
2010年 | 1612篇 |
2009年 | 1526篇 |
2008年 | 1671篇 |
2007年 | 1523篇 |
2006年 | 1376篇 |
2005年 | 1164篇 |
2004年 | 848篇 |
2003年 | 656篇 |
2002年 | 619篇 |
2001年 | 446篇 |
2000年 | 443篇 |
1999年 | 526篇 |
1998年 | 431篇 |
1997年 | 445篇 |
1996年 | 460篇 |
1995年 | 363篇 |
1994年 | 313篇 |
1993年 | 237篇 |
1992年 | 236篇 |
1991年 | 201篇 |
1990年 | 171篇 |
1989年 | 145篇 |
1988年 | 100篇 |
1987年 | 110篇 |
1986年 | 87篇 |
1985年 | 83篇 |
1984年 | 47篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
51.
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
52.
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
53.
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
54.
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
55.
56.
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
57.
58.
Mid-infrared generation based on a periodically poled LiNbO3 optical parametric oscillator 下载免费PDF全文
We report a nanosecond Nd:YVO_4-pumped optical parametric oscillator (OPO) based on periodically poled LiNbO_3 (PPLN). Tuning is achieved in this experiment by varying the temperature and period of the PPLN. The design of double-pass singly resonant oscillator (DSRO) and confocal cavity enables the OPO threshold to be lowered considerably, resulting in a simple, compact, all-solid-state configuration with the mid-infrared idler powers of up to 466mW at 3.41μm. 相似文献
59.
Nickel complexes 1–4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and characterized by FT-IR spectra and elemental analysis.
The molecular structure of complex 2 was confirmed by X-ray crystal diffraction analysis. Activated with methylaluminoxane (MAO), those complexes showed moderate
activities for ethylene oligomerization.
Published in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 710–714.
This article was submitted by the authors in English. 相似文献
60.