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101.
In order to overcome the deficiency in classical method of low order spectral model, a new method for low order spectral model was advanced. Through calculating the multiple correlation coefficients between combinations of different functions and the recorded data under the least square criterion, the truncated functions which can mostly reflect the studied physical phenomenon were objectively distilled from these data. The new method overcomes the deficiency of artificially selecting the truncated functions in the classical low order spectral model. The new method being applied to study the inter-annual variation of summer atmospheric circulation over Northern Hemisphere, the truncated functions were obtained with the atmospheric circulation data of June 1994 and June 1998. The mechanisms for the two-summer atmospheric circulation variations over Northern Hemisphere were obtained with two-layer quasi-geostrophic baroclinic equation. 相似文献
102.
大气运动非线性稳定性研究中的能量-Casimir方法 总被引:6,自引:0,他引:6
介绍使用能量-Casimir方法(Arnol'd方法)研究大气与海洋运动非线性稳定性所取得的若干新进展,建立了适用于有限振幅、任意空间结构扰动的非线性稳定性判据.用初始状态给出了扰动场在任意时刻的上界与下界估计,提供了关于扰动变化性态的有关信息.对该领域理论研究与应用的深化与发展问题也作了讨论. 相似文献
103.
104.
Zhenjun Yang 《Acta Mechanica Sinica》2006,22(3):243-256
The scaled boundary finite element method (SBFEM) is a recently developed numerical method combining advantages of both finite element methods (FEM) and boundary element methods (BEM) and with its own special features as well. One of the most prominent advantages is its capability of calculating stress intensity factors (SIFs) directly from the stress solutions whose singularities at crack tips are analytically represented. This advantage is taken in this study to model static and dynamic fracture problems. For static problems, a remeshing algorithm as simple as used in the BEM is developed while retaining the generality and flexibility of the FEM. Fully-automatic modelling of the mixed-mode crack propagation is then realised by combining the remeshing algorithm with a propagation criterion. For dynamic fracture problems, a newly developed series-increasing solution to the SBFEM governing equations in the frequency domain is applied to calculate dynamic SIFs. Three plane problems are modelled.
The numerical results show that the SBFEM can accurately predict static and dynamic SIFs, cracking paths and load-displacement curves, using only a fraction of degrees of freedom generally needed by the traditional finite element methods.The project supported by the National Natural Science Foundation of China (50579081) and the Australian Research Council (DP0452681)The English text was polished by Keren Wang. 相似文献
105.
An elastic-viscoplastic constitutive model was adopted to analyze asymptotically the tip-field of moving crack in linear-hardening materials under plane strain condition. Under the assumption that the artificial viscosity coefficient was in inverse proportion to power law of the rate of effective plastic strain, it is obtained that stress and strain both possess power law singularity and the singularity exponent is uniquely determined by the power law exponent of the rate of effective plastic strain. Variations of zoning structure according to each material parameter were discussed by means of numerical computation for the tip-field of mode Ⅱ dynamic propagating crack, which show that the structure of crack tip field is dominated by hardening coefficient rather than viscosity coefficient. The secondary plastic zone can be ignored for weak hardening materials while the secondary plastic zone and the secondary elastic zone both have important influence on crack tip field for strong hardening materials. The dynamic solution approaches to the corresponding quasi-static solution when the crack moving speed goes to zero, and further approaches to the HR (Hui-Riedel) solution when the hardening coefficient is equal to zero. 相似文献
106.
Poisson-Boltzrnann equation for EDL (electric double layer) and Navier-Stokes equation for liquid flows were numerically solved to investigate resistance effect of electric double layer on liquid flow in microchannel. The dimension analysis indicates that the resistance effect of electric double layer can be estimated by an electric resistance number, which is proportional to the square of the liquid dielectric constant and the solid surface zeta potential, and inverse-proportional to the liquid dynamic viscosity, electric conductivity and the square of the channel width. An "electric current density balancing" (ECDB) condition was proposed to evaluate the flow-induced streaming potential, instead of conventional "electric current balancing" (ECB) condition which may induce spurious local backflow in neighborhood of the solid wall of the microchannel. The numerical results of the flow rate loss ratio and velocity profile are also given to demonstrate the resistance effect of electric double layer in microchannel. 相似文献
107.
求解二维结构-声耦合问题的一种半数值半解析方法 总被引:2,自引:1,他引:2
基于传递矩阵法和虚拟源强模拟技术提出了一种求解在谐激励作用下二维结构-声相互作用问题的半数值半解析法.在足够小的积分步长内,文中对任意形状弹性环沿周向曲线坐标的非齐次状态微分方程组,建立了一种齐次扩容方法.对于外声场,采用多圆形虚拟源强配置方案。并在每一条圆形配置曲线上将源强密度函数用Fourier级数展开,同时结合快速Fourier变换法,提出了一种高精度、高效率求解任意形状二维孔穴Helmholtz外问题的快速算法.在耦合方程的求解方面,根据叠加原理,将外激励和虚拟源强的Fourier级数展开项作为广义力分别作用在弹性环上,借助齐次扩容方法和精细积分法求得弹性环的状态向量,再利用流固交接条件和最小二乘法直接建立了耦合系统的求解方程.文中给出了二个典型弹性环在集中谐激励力作用下声辐射算例,计算结果表明该文方法较通常采用的混合FE-BE法更为有效. 相似文献
108.
109.
Antonio Castellanos Xiaoping Jia Carlos Soria-Hoyo Jose Manuel Valverde 《Particuology》2011,9(6):659-662
The propagation velocity (vs) of an ultrasonic signal through a granular material depends on the type of interparticle contact. For noncohesive glass beads, a power law behavior for consolidation stresses applied (σc) above 1 MPa has been measured in previous work. This equation is compatible with Hertz's interaction law between elastic solids. In the present work, we have tested the propagation velocity of ultrasound signals through a sample of fine powder. The tensile strength and compactivity of the powder were previously measured by means of the Seville powder tester (SPT), indicating plastic deformation of the surface asperities in contact for small to moderate consolidation stresses. However, the measurements of ultrasound propagation at high consolidations presented here are compatible with Hertz's law. This finding suggests that for high consolidation stresses, surface asperities are flattened, and it is therefore the elastic deformation of the bulk of the particles that determines the transmission of ultrasonic pulses. 相似文献
110.