全文获取类型
收费全文 | 20743篇 |
免费 | 2282篇 |
国内免费 | 2183篇 |
专业分类
化学 | 2242篇 |
晶体学 | 30篇 |
力学 | 1762篇 |
综合类 | 537篇 |
数学 | 14710篇 |
物理学 | 5927篇 |
出版年
2024年 | 23篇 |
2023年 | 167篇 |
2022年 | 290篇 |
2021年 | 356篇 |
2020年 | 433篇 |
2019年 | 437篇 |
2018年 | 458篇 |
2017年 | 604篇 |
2016年 | 677篇 |
2015年 | 511篇 |
2014年 | 1039篇 |
2013年 | 1342篇 |
2012年 | 1083篇 |
2011年 | 1294篇 |
2010年 | 1162篇 |
2009年 | 1437篇 |
2008年 | 1409篇 |
2007年 | 1507篇 |
2006年 | 1344篇 |
2005年 | 1287篇 |
2004年 | 1029篇 |
2003年 | 983篇 |
2002年 | 809篇 |
2001年 | 747篇 |
2000年 | 699篇 |
1999年 | 606篇 |
1998年 | 526篇 |
1997年 | 510篇 |
1996年 | 366篇 |
1995年 | 296篇 |
1994年 | 247篇 |
1993年 | 187篇 |
1992年 | 160篇 |
1991年 | 130篇 |
1990年 | 140篇 |
1989年 | 96篇 |
1988年 | 88篇 |
1987年 | 75篇 |
1986年 | 70篇 |
1985年 | 85篇 |
1984年 | 71篇 |
1983年 | 51篇 |
1982年 | 67篇 |
1981年 | 63篇 |
1980年 | 40篇 |
1979年 | 35篇 |
1978年 | 31篇 |
1977年 | 30篇 |
1976年 | 30篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
在考虑自由体积和局部临界扩散势能的基础上,提出一种新的计算自扩散系数模型,并给出新模型中各个因子物理含义.同时还提出一种计算局部临界扩散势能的新方法,并应用于新模型.另外将衍生van der Waals状态方程应用于求解自由体积,式中所需径向分布函数由Morsali-Goharshadi方程得到.在相同条件下,新模型比原自由体积模型更准确. 相似文献
242.
CuX(X=Al, Ga, In)分子的势能函数与稳定性的密度泛函研究 总被引:5,自引:3,他引:2
刘风丽 《原子与分子物理学报》2006,23(5):838-842
根据原子分子反应静力学原理导出了CuX(X=Al,Ga,In) 分子基态电子状态及其离解极限,并在B3LYP/LANL2DZ水平上计算了平衡几何、振动频率和解离能.利用Murrell-Sorbie 函数拟合出了解析势能函数,并计算出光谱参数和力常数.计算结果表明该分子体系是稳定存在的,其稳定性排序为 CuAl>CuGa>CuIn. 相似文献
243.
Feng-Yu Wang 《Stochastic Processes and their Applications》2002,100(1-2):27-39
By using probabilistic approaches, Liouville theorems are proved for a class of Riemannian manifolds with Ricci curvatures bounded below by a negative function. Indeed, for these manifolds we prove that all harmonic functions (maps) with certain growth are constant. In particular, the well-known Liouville theorem due to Cheng for sublinear harmonic functions (maps) is generalized. Moreover, our results imply the Brownian coupling property for a class of negatively curved Riemannian manifolds. This leads to a negative answer to a question of Kendall concerning the Brownian coupling property. 相似文献
244.
D. Schütz 《K-Theory》2002,25(1):59-97
We use the one-parameter fixed-point theory of Geoghegan and Nicas to get information about the closed orbit structure of transverse gradient flows of closed 1-forms on a closed manifold M. We define a noncommutative zeta function in an object related to the first Hochschild homology group of the Novikov ring associated to the 1-form and relate it to the torsion of a natural chain homotopy equivalence between the Novikov complex and a completed simplicial chain complex of the universal cover of M. 相似文献
246.
关于Ramsey数下界的部分结果 总被引:3,自引:1,他引:2
刘富贵 《数学的实践与认识》2002,32(1):97-99
本文得到 Ramsey数下界的一个计算公式 :R( l,s+ t-2 )≥ R( l,s) + R( l,t) -1 ,(式中 l、s、t≥ 3) .用此公式算得的 Ramsey数的下界比用其它公式算得的下界好 . 相似文献
247.
E. Alper Yildirim Xiaofei Fan-Orzechowski 《Computational Optimization and Applications》2006,33(2-3):229-247
We study the maximum stable set problem. For a given graph, we establish several transformations among feasible solutions
of different formulations of Lovász's theta function. We propose reductions from feasible solutions corresponding to a graph
to those corresponding to its induced subgraphs. We develop an efficient, polynomial-time algorithm to extract a maximum stable
set in a perfect graph using the theta function. Our algorithm iteratively transforms an approximate solution of the semidefinite
formulation of the theta function into an approximate solution of another formulation, which is then used to identify a vertex
that belongs to a maximum stable set. The subgraph induced by that vertex and its neighbors is removed and the same procedure
is repeated on successively smaller graphs. We establish that solving the theta problem up to an adaptively chosen, fairly
rough accuracy suffices in order for the algorithm to work properly. Furthermore, our algorithm successfully employs a warm-start
strategy to recompute the theta function on smaller subgraphs. Computational results demonstrate that our algorithm can efficiently
extract maximum stable sets in comparable time it takes to solve the theta problem on the original graph to optimality.
This work was supported in part by NSF through CAREER Grant DMI-0237415. Part of this work was performed while the first author
was at the Department of Applied Mathematics and Statisticsat Stony Brook University, Stony Brook, NY, USA. 相似文献
248.
潘继斌 《数学的实践与认识》2006,36(2):182-185
研究了基于支持向量机的后验概率的应用,提出了对样本集进行分解,以产生局部后验概率,根据模式的稳健性对局部后验概率进行凸组合融合的方法. 相似文献
249.
Dirk P. Kroese Sergey Porotsky Reuven Y. Rubinstein 《Methodology and Computing in Applied Probability》2006,8(3):383-407
In recent years, the cross-entropy method has been successfully applied to a wide range of discrete optimization tasks. In
this paper we consider the cross-entropy method in the context of continuous optimization. We demonstrate the effectiveness
of the cross-entropy method for solving difficult continuous multi-extremal optimization problems, including those with non-linear
constraints.
相似文献
250.
M. Le Vassor D’yerville D. Monge D. Cassagne J. P. Albert 《Optical and Quantum Electronics》2002,34(5-6):445-454
We present here a tight-binding-like modelling of two-dimensional (2D) photonic crystals (PCs). Adopted from solid-state physics,
the concept of generalized Wannier functions is used to construct a localized state basis that allows a parameter-free ab
initio study of defects in PCs. We demonstrate here for a 2D triangular lattice of dielectric rods in air, the existence of
this localized basis and the possibility to study large scale complex dielectric structures deviating from periodicity. Specific
numerical simulations on a split waveguide embedded in this triangular lattice are performed, and they demonstrate the superiority
of this method over plane wave based techniques. 相似文献