全文获取类型
收费全文 | 19979篇 |
免费 | 3521篇 |
国内免费 | 1898篇 |
专业分类
化学 | 7206篇 |
晶体学 | 353篇 |
力学 | 2817篇 |
综合类 | 239篇 |
数学 | 5541篇 |
物理学 | 9242篇 |
出版年
2024年 | 27篇 |
2023年 | 174篇 |
2022年 | 325篇 |
2021年 | 411篇 |
2020年 | 579篇 |
2019年 | 538篇 |
2018年 | 512篇 |
2017年 | 632篇 |
2016年 | 763篇 |
2015年 | 611篇 |
2014年 | 839篇 |
2013年 | 1940篇 |
2012年 | 1085篇 |
2011年 | 1151篇 |
2010年 | 984篇 |
2009年 | 1170篇 |
2008年 | 1203篇 |
2007年 | 1266篇 |
2006年 | 1220篇 |
2005年 | 1191篇 |
2004年 | 1040篇 |
2003年 | 1075篇 |
2002年 | 894篇 |
2001年 | 704篇 |
2000年 | 712篇 |
1999年 | 598篇 |
1998年 | 459篇 |
1997年 | 437篇 |
1996年 | 347篇 |
1995年 | 314篇 |
1994年 | 296篇 |
1993年 | 275篇 |
1992年 | 222篇 |
1991年 | 195篇 |
1990年 | 157篇 |
1989年 | 113篇 |
1988年 | 110篇 |
1987年 | 88篇 |
1986年 | 90篇 |
1985年 | 105篇 |
1984年 | 98篇 |
1983年 | 36篇 |
1982年 | 59篇 |
1981年 | 67篇 |
1980年 | 40篇 |
1979年 | 48篇 |
1978年 | 50篇 |
1977年 | 41篇 |
1976年 | 27篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
1.
针对考虑几何和材料非线性的石英晶体板厚度剪切振动和弯曲振动的方程组,利用扩展伽辽金法对该方程组进行转化和求解,分别获得了强烈耦合的厚度剪切振动模态和弯曲振动模态的频率响应关系,绘制了不同振幅比和不同驱动电压影响下的频率响应曲线图。数值计算结果表明可以选取石英晶片的最佳长厚比尺寸来避免两种模态的强烈耦合。驱动电压的变化将引起石英晶体谐振器厚度剪切振动频率的明显改变,必须将振动频率的漂移值控制在常用压电声波器件的允许值之内。扩展伽辽金法对石英晶体板非线性振动方程组的求解为非线性有限元分析和偏场效应分析奠定了基础。 相似文献
2.
二维材料MXene纳米片由于具有较大的比表面积和较高的电子迁移率而受到广泛的关注。本文采用基于密度泛函理论的第一性原理计算,对单层MXene纳米片Ti2N电磁特性的过渡金属(Sc、V、Zr)掺杂效应进行了系统研究。结果表明,所有过渡金属掺杂体系结合能均为负值,结构均稳定;其中Ti2N-Sc体系的形成能为-2.242 eV,结构更易形成,且保持稳定;掺杂后Ti2N-Sc、Ti2N-Zr体系磁矩增大;此外,Ti2N-Sc体系中保留了较高的自旋极化率,达到84.9%,可预测该体系在自旋电子学中具有潜在的应用价值。 相似文献
3.
Baoquan Zhou Daqing Jiang Bingtao Han Tasawar Hayat 《Mathematical Methods in the Applied Sciences》2022,45(1):423-455
Considering the effect of stochasticity including white noise and colored noise, this paper aims to study a hybrid stochastic cholera epidemic model with waning vaccine-induced immunity and nonlinear telegraph perturbations. First, we derive a critical value related to the basic reproduction number of the deterministic model. The key aim of this paper is to generalize the θ-stochastic criterion method proposed by the recent work (Han et al. in Chaos Solit Fract 140:110238, 2020) to eliminate nonlinear telegraph perturbations. Next, via constructing several θ-stochastic Lyapunov functions and using the generalized method, we further prove that the stochastic model have a unique ergodic stationary distribution under . Results show that the prevention and control of cholera epidemic depend on low transmission rate and small telegraph perturbations. Finally, the corresponding numerical simulations are performed to illustrate our analytical results and a practical application on the Somalia cholera outbreak is shown at the end of this paper. 相似文献
4.
5.
6.
7.
Asymmetric mode transformation in waveguide is of great significance for on-chip integrated devices with one-way effect, while it is challenging to achieve asymmetric nonlinear-mode-conversion (NMC) due to the limitations imposed by phase-matching. In this work, we theoretically proposed a new scheme for realizing asymmetric NMC by combining frequency-doubling process and periodic PT symmetric modulation in an optical waveguide. By engineering the one-way momentum from PT symmetric modulation, we have demonstrated the unidirectional conversion from pump to second harmonic with desired guided modes. Our findings offer new opportunities for manipulating nonlinear optical fields with PT symmetry, which could further boost more exploration on on-chip nonlinear devices assisted by non-Hermitian optics. 相似文献
8.
9.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results. 相似文献
10.
Perdew-Burke-Ernzerhof (PBE) and PBE adapted for solids (PBEsol) are exchange-correlation (xc) functionals widely used in density functional theory simulations. Their differences are the exchange, μ, and correlation, β, coefficients, causing PBEsol to lose the Local Spin Density (LSD) response. Here, the μ/β two-dimensional (2D) accuracy landscape is analyzed between PBE and PBEsol xc functional limits for 27 transition metal (TM) bulks, as well as for 81 TM surfaces. Several properties are analyzed, including the shortest interatomic distances, cohesive energies, and bulk moduli for TM bulks, and surface relaxation degree, surface energies, and work functions for TM surfaces. The exploration, comparing the accuracy degree with respect experimental values, reveals that the found xc minimum, called VV, being a PBE variant, represents an improvement of 5% in mean absolute percentage error terms, whereas this improvement reaches ~11% for VVsol, a xc resulting from the restoration of LSD response in PBEsol, and so regarded as its variant. 相似文献