全文获取类型
收费全文 | 8588篇 |
免费 | 1486篇 |
国内免费 | 755篇 |
专业分类
化学 | 5888篇 |
晶体学 | 89篇 |
力学 | 504篇 |
综合类 | 36篇 |
数学 | 999篇 |
物理学 | 3313篇 |
出版年
2024年 | 25篇 |
2023年 | 168篇 |
2022年 | 299篇 |
2021年 | 300篇 |
2020年 | 369篇 |
2019年 | 306篇 |
2018年 | 289篇 |
2017年 | 267篇 |
2016年 | 434篇 |
2015年 | 443篇 |
2014年 | 489篇 |
2013年 | 617篇 |
2012年 | 803篇 |
2011年 | 768篇 |
2010年 | 546篇 |
2009年 | 504篇 |
2008年 | 567篇 |
2007年 | 436篇 |
2006年 | 479篇 |
2005年 | 351篇 |
2004年 | 276篇 |
2003年 | 224篇 |
2002年 | 178篇 |
2001年 | 145篇 |
2000年 | 148篇 |
1999年 | 175篇 |
1998年 | 155篇 |
1997年 | 127篇 |
1996年 | 131篇 |
1995年 | 112篇 |
1994年 | 96篇 |
1993年 | 80篇 |
1992年 | 78篇 |
1991年 | 76篇 |
1990年 | 44篇 |
1989年 | 38篇 |
1988年 | 40篇 |
1987年 | 35篇 |
1986年 | 28篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In this paper we develop a numerical method for computing higher order local approximations of center manifolds near steady states in Hamiltonian systems. The underlying system is assumed to be large in the sense that a large sparse Jacobian at the equilibrium occurs, for which only a linear solver and a low-dimensional invariant subspace is available. Our method combines this restriction from linear algebra with the requirement that the center manifold is parametrized by a symplectic mapping and that the reduced equation preserves the Hamiltonian form. Our approach can be considered as a special adaptation of a general method from Numer. Math. 80 (1998) 1-38 to the Hamiltonian case such that approximations of the reduced Hamiltonian are obtained simultaneously. As an application we treat a finite difference system for an elliptic problem on an infinite strip. 相似文献
52.
53.
54.
A diffusive predator-prey model in heterogeneous environment 总被引:1,自引:0,他引:1
In this paper, we demonstrate some special behavior of steady-state solutions to a predator-prey model due to the introduction of spatial heterogeneity. We show that positive steady-state solutions with certain prescribed spatial patterns can be obtained when the spatial environment is designed suitably. Moreover, we observe some essential differences of the behavior of our model from that of the classical Lotka-Volterra model that seem to arise only in the heterogeneous case. 相似文献
55.
Wenping Deng Gang Xu Lei Wan Anwen Liu Bo Gao Junhe Du Shuiming Hu Yang Chen 《Acta Physico》2008,24(8):1329-1334
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser spectrometer was built for the study of the matrix isolation spectrum in solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar, and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (ν=0←0, J=6←0) line around 2410 cm−1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-helium temperature was studied. 相似文献
56.
An exfoliated poly(4,4′-oxybis(benzene)disulfide) (POBDS)/vermiculite (VMT) nanocomposite was prepared by using cyclo(4,4′-oxybis(benzene)disulfide) (COBDS) oligomers and cetyltrimethyl ammonium bromide exchanged VMT. The POBDS/VMT nanocomposites were fabricated in two steps. First, the COBDS oligomers were used to swell and exfoliate organo VMT to afford COBDS-VMT nanocomposite precursor. Subsequently, the exfoliated POBDS-VMT nanocomposite can be made via in situ and instant melt ring-opening polymerization of the COBDS-VMT nanocomposite precursor. High molecular weight POBDS polymer can be formed in a few minutes. The nano scale dispersion of VMT layers within POBDS polymer was confirmed by both the X-ray diffraction patterns and TEM examinations. This methodology provides a potential approach to synthesize high performance polymer nanocomposite. 相似文献
57.
当地震信号通过复杂地球介质时,地层除了表现为各向异性,还表现为内在的黏弹性特征 因此,为准确描述地震波在地球介质中的传播特征,理想的地球介质模型应该能够模拟岩石 的各向异性特征和衰减特征.给出了各向异性黏弹性介质模型的波动方程,推导了伪谱法波场正演模拟的递推公式,并利用伪谱法实现了地震波波场数值模拟.表明了该介质模型中地 震波场特征与各向异性主轴方位和介质的黏滞性参数之间的关系.
关键词:
黏弹性
各向异性
伪谱法 相似文献
58.
本文针对空间光学系统轻型特点,设计了一个二元光学折/衍混合红外反射式望远系统。采用了离轴式格里高利(Gregorian)结构形式,消除了望远系统中的中心遮拦问题。用衍射光学元件校正系统象差,使反射面为球面,二元光学表面尺寸比施密特(Schmidt)校正板(位于入瞳处)缩小于3~4倍,光学设计运用OSLO软件,光学系统的通光孔径φ=120mm,焦距f=-1000mm,波长λ=4.3μm,视场2ω=2°×6°(子午×弧矢),分辨率Res=0.05mm,MTF≥0.4(空间频率fre≤10cl/mm). 相似文献
59.
60.
缺失功能性p35基因的苜蓿尺蠖核形多角体病毒(AcNPV)突变体(vΔP35K/pol+)感染草地夜蛾细胞(Sf9和Sf21)[1]及海灰翅夜蛾细胞(SL2)[2]时,引起细胞凋亡,从而使病毒的感染流产.我们发现海灰翅夜蛾核形多角体病毒(SlNPV)... 相似文献