全文获取类型
收费全文 | 4900篇 |
免费 | 235篇 |
国内免费 | 170篇 |
专业分类
化学 | 1017篇 |
晶体学 | 9篇 |
力学 | 164篇 |
综合类 | 22篇 |
数学 | 3638篇 |
物理学 | 455篇 |
出版年
2024年 | 3篇 |
2023年 | 15篇 |
2022年 | 77篇 |
2021年 | 74篇 |
2020年 | 63篇 |
2019年 | 214篇 |
2018年 | 232篇 |
2017年 | 59篇 |
2016年 | 67篇 |
2015年 | 117篇 |
2014年 | 243篇 |
2013年 | 298篇 |
2012年 | 229篇 |
2011年 | 438篇 |
2010年 | 355篇 |
2009年 | 415篇 |
2008年 | 411篇 |
2007年 | 463篇 |
2006年 | 349篇 |
2005年 | 196篇 |
2004年 | 163篇 |
2003年 | 167篇 |
2002年 | 80篇 |
2001年 | 39篇 |
2000年 | 49篇 |
1999年 | 64篇 |
1998年 | 49篇 |
1997年 | 39篇 |
1996年 | 45篇 |
1995年 | 30篇 |
1994年 | 42篇 |
1993年 | 36篇 |
1992年 | 30篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有5305条查询结果,搜索用时 15 毫秒
951.
We show the existence of a continuous solution to a nonlinear parabolic obstacle problem with a continuous time-dependent obstacle. The solution is constructed by an adaptation of the Schwarz alternating method. Moreover, if the obstacle is Hölder continuous, we prove that the solution inherits the same property. 相似文献
952.
Peter Hegarty 《Journal of Number Theory》2009,129(12):3052-3058
Let A be an asymptotic basis for N and X a finite subset of A such that A?X is still an asymptotic basis. Farhi recently proved a new batch of upper bounds for the order of A?X in terms of the order of A and a variety of parameters related to the set X. He posed two questions concerning possible improvements to his bounds. In this note, we answer both questions. 相似文献
953.
Stéphane R. Louboutin 《Journal of Number Theory》2009,129(10):2289-2294
J. Cohen, J. Sonn, F. Sairaiji and K. Shimizu proved that there are only finitely many imaginary quadratic number fields K whose Ono invariants OnoK are equal to their class numbers hK. Assuming a Restricted Riemann Hypothesis, namely that the Dedekind zeta functions of imaginary quadratic number fields K have no Siegel zeros, we determine all these K's. There are 114 such K's. We also prove that we are missing at most one such K. M. Ishibashi proved that if OnoK is large enough compared with hK, then the ideal class groups of K is cyclic. We give a short proof and a precision of Ishibashi's result. We prove that there are only finitely many imaginary quadratic number fields K satisfying Ishibashi's sufficient condition. Assuming our Restricted Riemann Hypothesis, we prove that the absolute values dK of their discriminants are less than 2.3⋅109. We determine all these K's with dK?106. There are 76 such K's. We prove that there is at most one such K with dK?1.8⋅1011. 相似文献
954.
Daniel Carando 《Journal of multivariate analysis》2009,100(5):981-992
We consider a problem of nonparametric density estimation under shape restrictions. We deal with the case where the density belongs to a class of Lipschitz functions. Devroye [L. Devroye, A Course in Density Estimation, in: Progress in Probability and Statistics, vol. 14, Birkhäuser Boston Inc., Boston, MA, 1987] considered these classes of estimates as tailor-made estimates, in contrast in some way to universally consistent estimates. In our framework we get the existence and uniqueness of the maximum likelihood estimate as well as strong consistency. This NPMLE can be easily characterized but it is not easy to compute. Some simpler approximations are also considered. 相似文献
955.
This paper examines asymptotic distributions of the canonical correlations between and with q≤p, based on a sample of size of N=n+1. The asymptotic distributions of the canonical correlations have been studied extensively when the dimensions q and p are fixed and the sample size N tends toward infinity. However, these approximations worsen when q or p is large in comparison to N. To overcome this weakness, this paper first derives asymptotic distributions of the canonical correlations under a high-dimensional framework such that q is fixed, m=n−p→∞ and c=p/n→c0∈[0,1), assuming that and have a joint (q+p)-variate normal distribution. An extended Fisher’s z-transformation is proposed. Then, the asymptotic distributions are improved further by deriving their asymptotic expansions. Numerical simulations revealed that our approximations are more accurate than the classical approximations for a large range of p,q, and n and the population canonical correlations. 相似文献
956.
A general depth measure, based on the use of one-dimensional linear continuous projections, is proposed. The applicability of this idea in different statistical setups (including inference in functional data analysis, image analysis and classification) is discussed. A special emphasis is made on the possible usefulness of this method in some statistical problems where the data are elements of a Banach space.The asymptotic properties of the empirical approximation of the proposed depth measure are investigated. In particular, its asymptotic distribution is obtained through U-statistics techniques. The practical aspects of these ideas are discussed through a small simulation study and a real-data example. 相似文献
957.
Robert Willenbring 《Discrete Applied Mathematics》2009,157(7):1607-1614
We construct a permutation representation for RNA secondary structure. We also introduce some basic combinatorial statistics for RNA secondary structure and relate them to permutation statistics when appropriate. These statistics allow us to quantify some structural phenomena in RNA secondary structure. 相似文献
958.
Santi Spadaro 《Topology and its Applications》2009,156(4):721-727
Say that a cardinal number κ is small relative to the space X if κ<Δ(X), where Δ(X) is the least cardinality of a non-empty open set in X. We prove that no Baire metric space can be covered by a small number of discrete sets, and give some generalizations. We show a ZFC example of a regular Baire σ-space and a consistent example of a normal Baire Moore space which can be covered by a small number of discrete sets. We finish with some remarks on linearly ordered spaces. 相似文献
959.
Chuan Liu 《Topology and its Applications》2009,156(5):849-854
In this paper, we consider the following question: when does a topological group G have a Hausdorff compactification bG with a remainder belonging to a given class of spaces? We extend the results of A.V. Arhangel'skii by showing that if a remainder of a non-locally compact topological group G has a countable open point-network or a locally Gδ-diagonal, then G and the compactification bG of G are separable and metrizable. 相似文献
960.
Samson Saneblidze 《Topology and its Applications》2009,156(5):897-910
Using the notion of truncating twisting function from a simplicial set to a cubical set a special, bitwisted, Cartesian product of these sets is defined. For the universal truncating twisting function, the (co)chain complex of the corresponding bitwisted Cartesian product agrees with the standard Cartier (Hochschild) chain complex of the simplicial (co)chains. The modelling polytopes Fn are constructed. An explicit diagonal on Fn is defined and a multiplicative model for the free loop fibration ΩY→ΛY→Y is obtained. As an application we establish an algebra isomorphism H∗(ΛY;Z)≈S(U)⊗Λ(s−1U) for the polynomial cohomology algebra H∗(Y;Z)=S(U). 相似文献