全文获取类型
收费全文 | 22543篇 |
免费 | 2688篇 |
国内免费 | 2281篇 |
专业分类
化学 | 3206篇 |
晶体学 | 55篇 |
力学 | 2185篇 |
综合类 | 530篇 |
数学 | 14047篇 |
物理学 | 7489篇 |
出版年
2024年 | 34篇 |
2023年 | 194篇 |
2022年 | 398篇 |
2021年 | 461篇 |
2020年 | 503篇 |
2019年 | 514篇 |
2018年 | 510篇 |
2017年 | 682篇 |
2016年 | 785篇 |
2015年 | 604篇 |
2014年 | 1178篇 |
2013年 | 1508篇 |
2012年 | 1238篇 |
2011年 | 1411篇 |
2010年 | 1276篇 |
2009年 | 1538篇 |
2008年 | 1504篇 |
2007年 | 1590篇 |
2006年 | 1396篇 |
2005年 | 1347篇 |
2004年 | 1127篇 |
2003年 | 1008篇 |
2002年 | 852篇 |
2001年 | 786篇 |
2000年 | 721篇 |
1999年 | 622篇 |
1998年 | 560篇 |
1997年 | 524篇 |
1996年 | 397篇 |
1995年 | 327篇 |
1994年 | 277篇 |
1993年 | 206篇 |
1992年 | 172篇 |
1991年 | 143篇 |
1990年 | 156篇 |
1989年 | 102篇 |
1988年 | 100篇 |
1987年 | 87篇 |
1986年 | 73篇 |
1985年 | 92篇 |
1984年 | 76篇 |
1983年 | 52篇 |
1982年 | 66篇 |
1981年 | 64篇 |
1980年 | 41篇 |
1979年 | 36篇 |
1978年 | 31篇 |
1977年 | 29篇 |
1976年 | 32篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The theoretical investigation of the image states in front of an ultrathin iron film grown on copper has been performed by means of the embedding method and a recently developed procedure for the inclusion of the image potential tail in a first principle calculation. From the electronic response to an applied electric field, the image plane position has been evaluated. This also allows one to obtain useful information about the spin dependent screening properties of the system. Exchange splitting, effective mass, and lifetime of such surface states result in good agreement with recently performed two-photon photoemission experiments [see A.B. Schmidt, M. Pickel, M. Wiemhöfer, M. Donath, M. Weinelt, Phys. Rev. Lett. 95 (2005) 107402]. 相似文献
102.
Yu-hai WU~ 《中国科学A辑(英文版)》2007,50(7):925-940
This paper concerns the number and distributions of limit cycles in a Z_2-equivariant quintic planar vector field.25 limit cycles are found in this special planar polynomial system and four different configurations of these limit cycles are also given by using the methods of the bifurcation theory and the qualitative analysis of the differential equation.It can be concluded that H(5)≥25=5~2, where H(5)is the Hilbert number for quintic polynomial systems.The results obtained are useful to study the weakened 16th Hilbert problem. 相似文献
103.
Morten Nielsen 《Advances in Computational Mathematics》2007,27(2):195-209
Given a dilation matrix A :ℤd→ℤd, and G a complete set of coset representatives of 2π(A
−Tℤd/ℤd), we consider polynomial solutions M to the equation ∑
g∈G
M(ξ+g)=1 with the constraints that M≥0 and M(0)=1. We prove that the full class of such functions can be generated using polynomial convolution kernels. Trigonometric
polynomials of this type play an important role as symbols for interpolatory subdivision schemes. For isotropic dilation matrices,
we use the method introduced to construct symbols for interpolatory subdivision schemes satisfying Strang–Fix conditions of
arbitrary order.
Research partially supported by the Danish Technical Science Foundation, Grant No. 9701481, and by the Danish SNF-PDE network. 相似文献
104.
首先通过集代数得到了Stone代数的表示定理,然后证明了每一个Stone代数均嵌入到某个集合X上的一个Stone映射类S中. 相似文献
105.
薛儒英 《浙江大学学报(理学版)》1991,(2)
本文讨论了半线性椭圆方程△u+f(u)=0在三种边界条件下正解的存在性和唯一性,给出了正解存在和唯一的一些条件. 相似文献
106.
Veli B. Shakhmurov 《Journal of Mathematical Analysis and Applications》2007,327(2):1182-1201
The nonlocal boundary value problems for anisotropic partial differential-operator equations with a dependent coefficients are studied. The principal parts of the appropriate generated differential operators are nonself-adjoint. Several conditions for the maximal regularity and the fredholmness in Banach-valued Lp-spaces of these problems are given. These results permit us to establish that the inverse of corresponding differential operators belongs to Schatten q-class. Some spectral properties of the operators are investigated. In applications, the nonlocal BVP's for quasielliptic partial differential equations and for systems of quasielliptic equations on cylindrical domain are studied. 相似文献
107.
We investigate analytical properties of a measure geometric Laplacian which is given as the second derivative w.r.t. two atomless finite Borel measures μ and ν with compact supports supp μ ? supp ν on the real line. This class of operators includes a generalization of the well‐known Sturm‐Liouville operator as well as of the measure geometric Laplacian given by . We obtain for this differential operator under both Dirichlet and Neumann boundary conditions similar properties as known in the classical Lebesgue case for the euclidean Laplacian like Gauß‐Green‐formula, inversion formula, compactness of the resolvent and its kernel representation w.r.t. the corresponding Green function. Finally we prove nuclearity of the resolvent and give two representations of its trace. 相似文献
108.
Andreas Fischer 《Mathematical Programming》1997,76(3):513-532
The paper deals with complementarity problems CP(F), where the underlying functionF is assumed to be locally Lipschitzian. Based on a special equivalent reformulation of CP(F) as a system of equationsφ(x)=0 or as the problem of minimizing the merit functionΘ=1/2∥Φ∥
2
2
, we extend results which hold for sufficiently smooth functionsF to the nonsmooth case.
In particular, ifF is monotone in a neighbourhood ofx, it is proved that 0 εδθ(x) is necessary and sufficient forx to be a solution of CP(F). Moreover, for monotone functionsF, a simple derivative-free algorithm that reducesΘ is shown to possess global convergence properties. Finally, the local behaviour of a generalized Newton method is analyzed.
To this end, the result by Mifflin that the composition of semismooth functions is again semismooth is extended top-order semismooth functions. Under a suitable regularity condition and ifF isp-order semismooth the generalized Newton method is shown to be locally well defined and superlinearly convergent with the
order of 1+p. 相似文献
109.
In this paper,the concept of the infinitesimal realization factor is extended to the parameter-dependent performance functions in closed queueing networks. Then the concepts of realization matrix (its elements are called realization factors) and performance potential are introduced,and the relations between infinitesimal realization factors and these two quantities are discussed. This provides a united framework for both IPA and non IPA approaches. Finally,another physical meaning of the service rate is given. 相似文献
110.
Fluorescence line narrowing (FLN) spectroscopy was used to study the role of the polypeptide chain in influencing the spectrum of Zn-substituted cytochrome c (Zn cyt c) and metal-free cyt c (porphyrin cyt c). For both derivatives the spectra show characteristics of relaxed fluorescence from an inhomogeneously broadened sample. Zero phonon lines and phonon wings can be clearly distinguished, and vibrational frequencies of the ground and excited states were identified. The inhomogeneous distribution width for porphyrin cyt c is slightly wider than that of Zn cyt c and a second population of molecules was apparent in the porphyrin cyt c. The phonon coupling was greater for Zn cyt c than for porphyrin cyt c, which may be due to the extra coupling to the polypeptide chain by metal ligation.This work has been done in partial fulfillment of the requirements for the Doctor of Philosophy degree. 相似文献