全文获取类型
收费全文 | 103818篇 |
免费 | 9969篇 |
国内免费 | 8901篇 |
专业分类
化学 | 30990篇 |
晶体学 | 397篇 |
力学 | 15592篇 |
综合类 | 1815篇 |
数学 | 39980篇 |
物理学 | 33914篇 |
出版年
2023年 | 899篇 |
2022年 | 1487篇 |
2021年 | 1968篇 |
2020年 | 2412篇 |
2019年 | 2446篇 |
2018年 | 2212篇 |
2017年 | 2820篇 |
2016年 | 3220篇 |
2015年 | 2694篇 |
2014年 | 4174篇 |
2013年 | 7166篇 |
2012年 | 4580篇 |
2011年 | 5372篇 |
2010年 | 4602篇 |
2009年 | 6091篇 |
2008年 | 6401篇 |
2007年 | 6639篇 |
2006年 | 6048篇 |
2005年 | 5271篇 |
2004年 | 4852篇 |
2003年 | 4693篇 |
2002年 | 4201篇 |
2001年 | 3621篇 |
2000年 | 3333篇 |
1999年 | 3004篇 |
1998年 | 2760篇 |
1997年 | 2261篇 |
1996年 | 2006篇 |
1995年 | 1975篇 |
1994年 | 1757篇 |
1993年 | 1463篇 |
1992年 | 1437篇 |
1991年 | 1119篇 |
1990年 | 948篇 |
1989年 | 768篇 |
1988年 | 693篇 |
1987年 | 587篇 |
1986年 | 484篇 |
1985年 | 568篇 |
1984年 | 570篇 |
1983年 | 298篇 |
1982年 | 441篇 |
1981年 | 462篇 |
1980年 | 333篇 |
1979年 | 335篇 |
1978年 | 248篇 |
1977年 | 231篇 |
1976年 | 166篇 |
1974年 | 115篇 |
1973年 | 120篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
This paper deals with a variable diffusion predator–prey model with additive Allee effect. A good understanding of the existence of steady states is gained for the case . The result shows that the reduce problem has multiple solutions. Moreover, by applying the singular perturbation method, we give a proof of existence of large amplitude solutions when is sufficiently small. 相似文献
102.
103.
External electric field(EEF) has shown its advantages in tuning chemical reaction as an efficient and feasible-to-control tool. In this paper, we explored the mechanisms of three EEF-regulated Diels-Alder reactions including two traditional-DA reactions to form two C-C single bonds and a hetero-DA reaction to form both a C-C and a C-O bond, respectively, and introduced an EEF contribution decomposition(ECD) model to understand how the EEF coupled with the intrinsic nuclear and electronic redistributions so as to affect chemical reaction. The ECD model, by decomposing the overall EEF effects into geometry re-equilibrium and static induction parts, can give a clear and quantitative picture of a physical quantity change upon EEF, as demonstrated on relative energies, activation barriers, charge distribution and dipole moments. The ECD analyses will shed light on the effective tuning of chemical reactions by the electric field. 相似文献
104.
105.
106.
《Wave Motion》2020
We review work of Jordan on a hyperbolic variant of the Fisher–KPP equation, where a shock solution is found and the amplitude is calculated exactly. The Jordan procedure is extended to a hyperbolic variant of the Chafee–Infante equation. Extension of Jordan’s ideas to a model for traffic flow are also mentioned. We also examine a diffusive susceptible–infected (SI) model, and generalizations of diffusive Lotka–Volterra equations, including a Lotka–Volterra–Bass competition model with diffusion. For all cases we show how a Jordan–Cattaneo wave may be analysed and we indicate how to find the wavespeeds and the amplitudes. Finally we present details of a fully nonlinear analysis of acceleration waves in a Cattaneo–Christov poroacoustic model. 相似文献
107.
In order to investigate the effect of density ratio of fluid and solid on the convergence behavior of partitioned FSI algorithm, three strong-coupling partitioned algorithms (fixed-point method with a constant under-relaxation parameter, Aitken’s method and Quasi-Newton inverse least squares (QN-ILS) method) have been considered in the context of finite element method. We have employed the incompressible Navier–Stokes equations for a Newtonian fluid domain and the total Lagrangian formulation for a non-linear motion of solid domain. Linear-elastic (hyper-elastic) model has been employed for solid material with small (large) deformation. A pulsatile inlet-flow interacting with a 2D circular channel of linear-elastic material and a pressure wave propagation in a 3D flexible vessel have been simulated. Both linear-elastic and hyper-elastic (Mooney–Rivlin) models have been adopted for the 3D flexible vessel. From the present numerical experiments, we have found that QN-ILS outperforms the others leading to a robust convergence regardless of the density ratio for both linear-elastic and hyper-elastic models. On the other hand, the performances of the fixed-point method with a constant under-relaxation parameter and the Aitken’s method depend strongly on the density ratio, relaxation parameter selected for coupling iteration, and degree of deformation. Although the QN-ILS of this work is still slower than a monolithic method for serial computation, it has an advantage of easier parallelization due to the modularity of the partitioned FSI algorithm. 相似文献
108.
针对现有成像系统因数据冗余而无法兼顾大视场、高分辨、高效性的问题,结合人眼视网膜变分辨成像和并列式复眼成像原理,设计一种多分辨率成像的复合仿生成像系统.该成像系统按照球面和平面兼顾的曲面布局方式,利用11个相机镜头构建相机阵列,组成了四个等级分辨率的子眼拍摄模块.通过物距100 m的远景实验和物距10 m的近景实验发现,该系统在实现高分辨成像的同时,获得总视场达150.8°×37.8°.多分辨率成像实验结果表明,该系统获取的图像的分辨率从中心视场到边缘视场逐渐降低,并且相较于中心清晰全视场成像,四级分辨率成像的拼接图像数据量减少了17.2倍的数据冗余. 相似文献
109.
采用逐次阶散射法求解矢量辐射传输方程来研究气溶胶在不同地表反射模型下的散射偏振特性.首先,选取单一地表反射模型和耦合地表反射模型两种地表反射模型.然后,根据地表反射模型计算得到相应的地表反射率,进而采用逐次阶散射法对矢量辐射传输方程进行求解,得到散射光的Stokes矢量.最后,由Stokes矢量计算得出散射光的偏振度.仿真结果表明,两种地表反射模型下气溶胶单次散射的散射辐射强度和线偏振度均相等;耦合地表反射模型的总散射辐射强度和线偏振度总是大于单一地表反射模型;单一地表反射模型的气溶胶单次散射相对总散射的贡献总是大于耦合地表反射模型.研究结果对气溶胶光学特性的反演具有一定意义. 相似文献
110.
In this paper, the aeroelastic analyses of a rectangular cantilever plate of varying aspect ratio is presented. The classical plate theory has been selected as the structural model. The main point that distinguishes this study from previously reported research is employing Peters’ theory to model aerodynamic effect which is not straightforward. The Peters’ aerodynamic model was originally developed to provide lift and moment, which is only applicable to the structural model based on the beam theories. In this study, using the basic concept of the Peters’ aerodynamic model in addition to utilizing the Fourier series, the pressure distribution is derived, which makes Peters’ model applicable to structural models based on plate theory. This combination provides a much simpler state–space aeroelastic model for plates in comparison to the prevalent panel methods, which could lead to a significant reduction in computational time. In addition, the aeroelastic response of the plate with respect to changes in the structural model from the beam theory to the plate theory is evaluated. By using data from an experiment carried out at Duke University, the theoretical results are evaluated. Furthermore, the differences in structural models obtained from the plate and beam theories can be divided into two distinct parts, which are responsible for differences in bending and torsional behaviors of the structure, separately. This approach enables us to measure the effects of differences of each behavior separately, which could provide with a new insight into the problem. It has been determined that the flutter speeds obtained from the beam and plate aeroelastic models are little affected by the difference in bending behavior, but rather is mainly caused by the difference in torsional frequencies. 相似文献