全文获取类型
收费全文 | 15905篇 |
免费 | 500篇 |
国内免费 | 1913篇 |
专业分类
化学 | 9385篇 |
晶体学 | 121篇 |
力学 | 585篇 |
综合类 | 197篇 |
数学 | 4191篇 |
物理学 | 3839篇 |
出版年
2023年 | 242篇 |
2022年 | 195篇 |
2021年 | 181篇 |
2020年 | 233篇 |
2019年 | 303篇 |
2018年 | 211篇 |
2017年 | 261篇 |
2016年 | 267篇 |
2015年 | 293篇 |
2014年 | 511篇 |
2013年 | 1234篇 |
2012年 | 780篇 |
2011年 | 805篇 |
2010年 | 709篇 |
2009年 | 928篇 |
2008年 | 958篇 |
2007年 | 1028篇 |
2006年 | 898篇 |
2005年 | 785篇 |
2004年 | 739篇 |
2003年 | 572篇 |
2002年 | 498篇 |
2001年 | 450篇 |
2000年 | 1236篇 |
1999年 | 929篇 |
1998年 | 863篇 |
1997年 | 320篇 |
1996年 | 275篇 |
1995年 | 260篇 |
1994年 | 229篇 |
1993年 | 199篇 |
1992年 | 175篇 |
1991年 | 119篇 |
1990年 | 85篇 |
1989年 | 62篇 |
1988年 | 49篇 |
1987年 | 54篇 |
1986年 | 35篇 |
1985年 | 52篇 |
1984年 | 42篇 |
1983年 | 29篇 |
1982年 | 30篇 |
1981年 | 46篇 |
1980年 | 21篇 |
1979年 | 28篇 |
1978年 | 25篇 |
1977年 | 16篇 |
1976年 | 12篇 |
1974年 | 9篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 527 毫秒
61.
Shunsuke Inenaga Ayumi Shinohara Masayuki Takeda Setsuo Arikawa 《Journal of Discrete Algorithms》2004,2(1):33
Suffix trees are a well-known and widely-studied data structure highly useful for string matching. The suffix tree of a string w can be constructed in O(n) time and space, where n denotes the length of w. Larsson achieved an efficient algorithm to maintain suffix trees for a sliding window. It contributes to prediction by partial matching (PPM) style statistical data compression scheme. Compact directed acyclic word graphs (CDAWGs) are a more space-economical data structure for indexing strings. In this paper we propose a linear-time algorithm to maintain CDAWGs for a sliding window. 相似文献
62.
Nikolaos S. PAPAGEORGIOU Nikolaos YANNAKAKIS 《数学学报(英文版)》2005,21(5):977-996
This is the first part of a work on second order nonlinear, nonmonotone evolution inclusions defined in the framework of an evolution triple of spaces and with a multivalued nonlinearity depending on both x(t) and x(t). In this first part we prove existence and relaxation theorems. We consider the case of an usc, convex valued nonlinearity and we show that for this problem the solution set is nonempty and compact in C^1 (T, H). Also we examine the Isc, nonconvex case and again we prove the existence of solutions. In addition we establish the existence of extremal solutions and by strengthening our hypotheses, we show that the extremal solutions are dense in C^1 (T, H) to the solutions of the original convex problem (strong relaxation). An example of a nonlinear hyperbolic optimal control problem is also discussed. 相似文献
63.
64.
变系数计量经济学联立模型的局部线性工具向量估计及其性质 总被引:3,自引:1,他引:2
联立方程计量经济学模型在经济政策制定、经济结构分析和经济预测方面起着重要作用。本文首次提出了我国宏观经济的一类变系数联立模型,并建立了函数系数的局部线性工具向量估计,同时在时间点列固定设计、经济变量随机设计条件下,研究了估计量的大样本性质。与我国宏观经济经典线性联立模型相比,变系数联立模型拟合效果更优。另外它也有助于克服我国宏观经济数据不多而造成的非参数方法应用困难的现实情况。 相似文献
65.
Noureddine Igbida 《Journal of Mathematical Analysis and Applications》2007,335(2):1061-1078
In this paper, we study the nonlinear evolution equation of Hele-Shaw type with dynamical boundary conditions. That is, the equation ut=Δw+f where u∈H(w) and H is the Heaviside function, with boundary condition μ(x,w)t∂w+k∇w⋅ν=g, where ν denotes the outward normal vector of the fixed boundary of the domain. We prove existence, uniqueness and some qualitative properties of the solution. 相似文献
66.
Shawn Shih 《中国化学会会志》2003,50(4):815-822
A large class of stereochemcial and related interactions in organic chemistry are repulsive and others are attractive, but the relative orientation of two methyl groups and the amount of energy required to twist one relative to the other (the hindered rotation energy barriers), or the alignment of such a group with respect to a conjugated ring to which it is attached (widely attributed to a mechanism called “hyperconjugation”) are estimated to be small in compared with the total energy of the molecule. We used theories of both isotropic and anisotropic proton hyperfine interactions in the π‐electron systems developed in the early sixties. They are approximated by the magnetic dipole nteractions between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals center on carbon atoms. We have extended these theories to the non‐planar olefinic cation radicals, which are very important in biochemistry as well as in petroleum catalysis. A three dimensional electron spin density equation has been developed in this paper to handle some Jahn‐Teller vibronic molecules. The new electron spin density equation related the observed proton hyperfine splittings to the non‐planar structures of the open‐chain alkene cation radicals generated by radiolysis and various chemical oxidation methods. The spin densities and the conformational calculations based on valence bond theory and symmetry principles are compared with some more elaborated molecular orbital calculations in the literature. The localized valence bond approaches are better in accord with our experimental results. The anomalous line‐width effect of the four methyl groups observed in the 2,3‐dimethyl‐2‐butene cation radicals also confirmed the positive sign of the electron‐proton hyperfine constant of hyper‐conjugation mechanism. A methyl substituent attached to a conjugated molecule often behaves as if it formed part of the region of conjugation; the charge appears to flow from the methyl group into the π electron system and it may also give rise to an appreciable dipole moment. Methylation also gives rise to an appreciable dipole moment, and the resultant red shift of electronic absorption bands is of some importance in the design of dye molecules. 相似文献
67.
The effect of an applied magnetic field on an inhomogeneous superconductor is studied and the value of the upper critical magnetic field Hc3 at which superconductivity can nucleate is estimated. In addition, the authors locate the concentration of the order parameter, which depends on the inhomogeneous term a(x). Unlikely to the homogeneous case, the order parameter may concentrate in the interior of the superconducting material, due to the influence of the inhomogeneous term a(x). 相似文献
68.
戴滨林 《数学物理学报(A辑)》2007,27(5):935-940
该文对高维非初等Mò'bius变换群进行了研究,得到了一些重要性质,给出了几个关于离散准则和代数收敛性的定理. 相似文献
69.
70.
We discuss differential equations with nonlinear boundary conditions. We formulate sufficient conditions under which problems
with deviating arguments have quasisolutions or solutions. To obtain the results, we apply the method of monotone iterations. 相似文献