全文获取类型
收费全文 | 2875篇 |
免费 | 237篇 |
国内免费 | 240篇 |
专业分类
化学 | 382篇 |
晶体学 | 13篇 |
力学 | 1487篇 |
综合类 | 40篇 |
数学 | 442篇 |
物理学 | 988篇 |
出版年
2024年 | 5篇 |
2023年 | 19篇 |
2022年 | 35篇 |
2021年 | 37篇 |
2020年 | 75篇 |
2019年 | 59篇 |
2018年 | 72篇 |
2017年 | 80篇 |
2016年 | 109篇 |
2015年 | 99篇 |
2014年 | 128篇 |
2013年 | 262篇 |
2012年 | 97篇 |
2011年 | 140篇 |
2010年 | 106篇 |
2009年 | 142篇 |
2008年 | 139篇 |
2007年 | 163篇 |
2006年 | 167篇 |
2005年 | 134篇 |
2004年 | 168篇 |
2003年 | 123篇 |
2002年 | 121篇 |
2001年 | 90篇 |
2000年 | 93篇 |
1999年 | 92篇 |
1998年 | 97篇 |
1997年 | 84篇 |
1996年 | 63篇 |
1995年 | 59篇 |
1994年 | 44篇 |
1993年 | 38篇 |
1992年 | 49篇 |
1991年 | 49篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有3352条查询结果,搜索用时 15 毫秒
71.
72.
Sergio Conti Matteo Focardi Flaviana Iurlano 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2019,36(2):455-474
We consider the Griffith fracture model in two spatial dimensions, and prove existence of strong minimizers, with closed jump set and continuously differentiable deformation fields. One key ingredient, which is the object of the present paper, is a generalization to the vectorial situation of the decay estimate by De Giorgi, Carriero, and Leaci. This is based on replacing the coarea formula by a method to approximate functions with small jump set by Sobolev functions, and is restricted to two dimensions. The other two ingredients will appear in companion papers and consist respectively in regularity results for vectorial elliptic problems of the elasticity type and in a method to approximate in energy functions by ones. 相似文献
73.
We develop a variational optimization method for crystal analysis in atomic resolution images, which uses information from a 2D synchrosqueezed transform (SST) as input. The synchrosqueezed transform is applied to extract initial information from atomic crystal images: crystal defects, rotations and the gradient of elastic deformation. The deformation gradient estimate is then improved outside the identified defect region via a variational approach, to obtain more robust results agreeing better with the physical constraints. The variational model is optimized by a nonlinear projected conjugate gradient method. Both examples of images from computer simulations and imaging experiments are analyzed, with results demonstrating the effectiveness of the proposed method. 相似文献
74.
In this paper we are interested in developing constitutive equations for fiber-reinforced nonlinearly viscoelastic solids. It has been shown that constitutive equations for such bodies can be expressed in terms of a complete minimal set of 18 classical invariants associated with deformation and fiber orientation. In this paper, we give an alternative formulation using a set of spectral invariants. It is shown via the use of spectral invariants that only 11 of the 18 classical invariants are independent. We analyze the spectral invariants for two illustrative deformation gradients: (i) simple tension, and (ii) simple shear. 相似文献
75.
We report the mechanical response of a model nanocomposite system of poly(styrene) (PS)-silica to large-amplitude oscillatory shear deformations. Nonlinear behavior of PS nanocomposites is discussed with the changes in particle dispersion upon deformation to provide a complete physical picture of their mechanical properties. The elastic stresses for the particle and polymer are resolved by decomposing the total stress into its purely elastic and viscous components for composites at different strain levels within a cycle of deformation. We propose a mechanistic model which captures the deformation of particles and polymer networks at small and large strains, respectively. We show, for the first time, that chain stretching in a polymer nanocomposite obtained in large amplitude oscillatory deformation is in good agreement with the nonlinear chain deformation theory of polymeric networks. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
76.
Numerical simulation of the red blood cell aggregation and deformation behaviors in ultrasonic field
The objective of this paper is to propose an immersed boundary lattice Boltzmann method (IB-LBM) considering the ultrasonic effect to simulate red blood cell (RBC) aggregation and deformation in ultrasonic field. Numerical examples involving the typical streamline, normalized out-of-plane vorticity contours and vector fields in pure plasma under three different ultrasound intensities are presented. Meanwhile, the corresponding transient aggregation behavior of RBCs, with special emphasis on the detailed process of RBC deformation, is shown. The numerical results reveal that the ultrasound wave acted on the pure plasma can lead to recirculation flow, which contributes to the RBCs aggregation and deformation in microvessel. Furthermore, increasing the intensity of the ultrasound wave can significantly enhance the aggregation and deformation of the RBCs. And the formation of the RBCs aggregation leads to the fluctuated and dropped vorticity value of plasma in return. 相似文献
77.
Of interest here is the influence of loading rate on the stability of structures where inertia is taken into account, with particular attention to the comparison between static and dynamic buckling. This work shows the importance of studying stability via perturbations of the initial conditions, since a finite velocity governs the propagation of disturbances. The method of modal analysis that determines the fastest growing wavelength, currently used in the literature to analyze dynamic stability problems, is meaningful only for cases where the velocity of the perfect structure is significantly lower than the associated wave propagation speeds. 相似文献
78.
In this paper, we introduced a method to measure grain rotation of nanomaterials under external stress using a high pressure diamond anvil cell and the Laue microdiffraction technique at a synchrotron facility. We used tungsten carbide marker crystals to investigate grain rotation activities of 3 and 500?nm nickel media. Our results show that the grain rotation of 3 and 500?nm nickel nanocrystals increase with pressure and finally rotation of 500?nm nickel tends to stop at a lower pressure/stress level than 3?nm nickel. 3?nm nickel nanocrystals show a higher rotation magnitude than 500?nm nickel nanocrystals. Our measurements show an effective method to study the grain rotation of nanomaterials especially in ultrafine nanocrystals. 相似文献
79.
A mathematical theory of time-dependent dislocation mechanics of
unrestricted geometric and material nonlinearity is reviewed. Within
a ``small deformation" setting, a suite of simplified and
interesting models consisting of a nonlocal Ginzburg Landau
equation, a nonlocal level set equation, and a nonlocal generalized
Burgers equation is derived. In the finite deformation setting, it
is shown that an additive decomposition of the total velocity
gradient into elastic and plastic parts emerges naturally from a
micromechanical starting point that involves no notion of plastic
deformation but only the elastic distortion, material velocity,
dislocation density and the dislocation velocity. Moreover, a
plastic spin tensor emerges naturally as well. 相似文献
80.
以120种煤样为数据基础,采用布谷鸟算法(CS)优化BP(Back Propagation)神经网络,建立了CSBP模型对单煤、煤掺添加剂和配煤等3类样本的煤灰变形温度(DT)样本进行预测。模型以煤灰化学成分及其组合参数等13个变量作为输入量,以变形温度(DT)作为输出量。CSBP模型预测结果与BP神经网络模型预测结果进行对比发现,无论是单煤、煤掺添加剂还是配煤,CSBP模型较BP模型对煤灰变形温度(DT)的预测都更加精准,平均相对误差分别达到了3.11%、4.08%和4.22%。另外,对比3类样本预测结果发现,无论是CSBP模型还是BP模型,相比单煤预测而言,煤掺添加剂及配煤的预测误差都有明显的增加。 相似文献