全文获取类型
收费全文 | 611篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
化学 | 218篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 109篇 |
物理学 | 285篇 |
出版年
2019年 | 7篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 18篇 |
2012年 | 13篇 |
2011年 | 29篇 |
2010年 | 15篇 |
2009年 | 18篇 |
2008年 | 30篇 |
2007年 | 20篇 |
2006年 | 21篇 |
2005年 | 25篇 |
2004年 | 24篇 |
2003年 | 23篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 17篇 |
1999年 | 13篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 12篇 |
1973年 | 13篇 |
1972年 | 4篇 |
1971年 | 10篇 |
1969年 | 4篇 |
1928年 | 4篇 |
排序方式: 共有624条查询结果,搜索用时 15 毫秒
91.
92.
Nathan Rosen 《General Relativity and Gravitation》1973,4(6):435-447
A bi-metric theory of gravitation is proposed, satisfying the covariance and equivalence principles. It is based on a simple form of Lagrangian and has a simpler mathematical structure than that of the general theory of relativity. The theory agrees with general relativity up to the accuracy of the observations made up to now. The static spherically symmetric solution of the present field equations does not involve any 'black hole'. 相似文献
93.
Let μ be the measure onI′ (? d ) corresponding to the Gaussian process with mean zero and covariance (f,(?Δ+1)?1 g) onI (? d ). It is proven that the set $$( - \Delta _{d - 1} + 1)^{d/4 - \tfrac{1}{2} + \alpha } (1 + x^2 )^{d/4} [\log (2 + x^2 )]^\beta L^2 (\mathbb{R}^d )$$ has μ measure one if α>0 and β>1/2 and μ measure zero if α>0 and β<1/2; here Δ d?1 is the Laplacian in anyd?1 dimensions whend>1 and Δ0=Δ. 相似文献
94.
We explore the possibility of using neutral weak interactions to see whether neutrinos may flip their helicity. Experiments ranging from low-energy neutrino-nucleus scattering to high-energy inclusive reactions are discussed as tests for the presence of helicity-flipping scalar, pseudoscalar and tensor interactions. 相似文献
95.
I.G Rosen 《Journal of Differential Equations》1981,40(3):377-449
A discrete approximation framework for initial-value problems involving certain classes of linear functional differential equations (FDE) of the retarded type is constructed. An equivalence between the FDE and abstract evolution equations (AEE) in an appropriately chosen Hilbert space is established. This equivalence is then employed in the development of discrete approximation schemes in which the infinite-dimensional AEE is replaced by a finite-dimensional system of difference equations. Convergence and rates of convergence are demonstrated via the properties of rational functions with operator arguments and both classical and recent results from linear semigroup theory. Two examples of families of approximation schemes which are included in the general framework and which may be implemented directly on high-speed computing machines are developed. A numerical study of examples which illustrates the application and feasibility of the approximation techniques in a variety of problems together with a summary and analysis of the numerical results are also included. 相似文献
96.
Einstein's principle of general relativity is a dynamical-group approach in that all dynamics is implied by the invariance and no force is introduced (as an external, symmetry-breaking factor). In this spirit we take a Poincaré-invariant free wave equation and, deforming the Poincaré group to the de Sitter group, obtain interaction. This illustrates our algebraic approach to gauge invariance, whereby the (generalized) Maxwell tensor of the Yang-Mills field appears as structure constants of the homogeneous algebra obtained as a deformation of an inhomogeneous one, with interaction appearing via the same tensor, which plays a role corresponding to the curvature tensor in Einstein's general relativity. 相似文献
97.
G. Rosen 《Physics letters. A》1973,45(3):263-264
It is shown that within the manifold of exact solutions a system of reaction-diffusion equations admits only travelling waves with planar symmetry. A derivation of the generic form of approximate (asymptotic) cylindrical and spiral travelling periodic wave solutions is given. If an exact solution homogeneous in space and periodic in time is admitted by the system of reaction-diffusion equations, then travelling periodic spiral waves are admissble as approximate solutions. This is the theoretical explanation for the travelling periodic waves of chemical activity observed in recent experiments. 相似文献
98.
We study the higher Legendre transforms Γ(r) {A } of the generating functional G for connected Green's functions in Euclidean boson field theories. To analyze Γ(r) {A } rigorously even when it does not make sense as an ordinary functional, we develop the framework of formal power series in A. For r = 1, 2 we isolate regularity conditions on G that ensure the existence of Γ(r) as a formal power series and we verify these conditions for the weakly coupled P(φ)2 model. We also establish the improved regularity of the functional Φ(r) obtained by subtracting from Γ(r) its trivial singular part. 相似文献
99.
A concave function defined on a polytope may have many local minima (in fact every extreme point may be a local minimum). Sufficient conditions are given such that if they are satisfied at a point, this point is known to be a global minimum. It is only required to solve a single linear program to test whether the sufficient conditions are satisfied. This test has been incorporated into an earlier algorithm to give improved performance. Computational results presented show that these sufficient conditions are satisfied for certain types of problems and may substantially reduce the effort needed to find and recognize a global minimum. 相似文献
100.
The problem of approximating m data points (x
i
, y
i
) in , with a quadratic function q(x, p) with s parameters, m ≥ s, is considered. The parameter vector is to be determined so as to satisfy three conditions: (1) q(x, p) must underestimate all m data points, i.e. q(x
i
, p) ≤ y
i
, i=1,...,m. (2) The error of the approximation is to be minimized in the L1 norm. (3) The eigenvalues of H are to satisfy specified lower and upper bounds, where H is the Hessian of q(x, p) with respect to x. This is called the Quadratic Underestimator with Bounds on Eigenvalues (QUBE) problem. An algorithm for its solution (QUBE algorithm) is given and justified, and computational results presented. The QUBE algorithm has application to finding the global minimum of a basin (or funnel) shaped function with a large number of local minima. Such problems arise in computational biology where it is desired to find the global minimum of an energy surface, in order to predict native protein-ligand docking geometry (drug design) or protein structure. Computational results for a simulated docking energy surface, with n=15, are presented. It is shown that specifying a small condition number for H improves the ability of the underestimator to correctly predict the global minimum point. 相似文献