全文获取类型
收费全文 | 749篇 |
免费 | 60篇 |
国内免费 | 33篇 |
专业分类
化学 | 33篇 |
晶体学 | 1篇 |
力学 | 4篇 |
综合类 | 10篇 |
数学 | 242篇 |
物理学 | 552篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 19篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 11篇 |
2017年 | 17篇 |
2016年 | 21篇 |
2015年 | 22篇 |
2014年 | 34篇 |
2013年 | 46篇 |
2012年 | 21篇 |
2011年 | 32篇 |
2010年 | 29篇 |
2009年 | 55篇 |
2008年 | 59篇 |
2007年 | 56篇 |
2006年 | 51篇 |
2005年 | 49篇 |
2004年 | 43篇 |
2003年 | 33篇 |
2002年 | 31篇 |
2001年 | 32篇 |
2000年 | 28篇 |
1999年 | 20篇 |
1998年 | 35篇 |
1997年 | 20篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有842条查询结果,搜索用时 31 毫秒
51.
52.
53.
54.
We use the improved Faddeev-Jackiw quantization method to quantize the electromagnetic field and its Lagrange multiplier fields. The method's comparison with the usual Faddeev-Jackiw method and the Dirac method is given. We show that this method is equivalent to the Dirac method and also retains all the merits of the usual Faddeev-Jackiw method. Moreover, it is simpler than the usual one if one needs to obtain new secondary constraints. Therefore, the improved Faddeev-Jackiw method is essential. Meanwhile, we find the new meaning of the Lagrange multipliers and explain the Faddeev-Jackiw generalized brackets concerning the Lagrange multipliers. 相似文献
55.
Wolfgang Kreitmeier 《Mathematische Nachrichten》2008,281(9):1307-1327
For a large class of dyadic homogeneous Cantor distributions in ?, which are not necessarily self‐similar, we determine the optimal quantizers, give a characterization for the existence of the quantization dimension, and show the non‐existence of the quantization coefficient. The class contains all self‐similar dyadic Cantor distributions, with contraction factor less than or equal to 1/3. For these distributions we calculate the quantization errors explicitly. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
56.
In this paper we consider the Bounded Length Median Path Problem which can be defined as the problem of locating a path-shaped facility that departures from a given origin and arrives at a given destination in a network. The length of the path is assumed to be bounded by a given maximum length. At each vertex of the network (customer-point) the demand for the service is given and the cost to reach the closest service-point is computed. The objective is to minimize the sum of these costs over all the customer-points in the network. 相似文献
57.
The paper is devoted to peculiarities of the deformation quantization in the algebro-geometric context. A direct application of the formality theorem to an algebraic Poisson manifold gives a canonical sheaf of categories deforming coherent sheaves. The global category is very degenerate in general. Thus, we introduce a new notion of a semiformal deformation, a replacement in algebraic geometry of an actual deformation (versus a formal one). Deformed algebras obtained by semiformal deformations are Noetherian and have polynomial growth. We propose constructions of semiformal quantizations of projective and affine algebraic Poisson manifolds satisfying certain natural geometric conditions. Projective symplectic manifolds (e.g. K3 surfaces and Abelian varieties) do not satisfy our conditions, but projective spaces with quadratic Poisson brackets and Poisson–Lie groups can be semiformally quantized. 相似文献
58.
We consider the application of semiclassical approximation to relativistic potentials for massless particles where the kinetic
energy is a nontrivial, nonlocal operator. Quantization rules are derived for an arbitrary confining potential and compared
to some exact results forS-waves. These results admit of a partial generalization to smalll values. 相似文献
59.
研究谐振子势与高斯势联合势阱中玻色爱因斯坦凝聚体的基态。发现凝聚体形成巨涡旋时,其涡旋个数等于平均角动量,且凝聚体密度分布和角动量密度分布相同,进而得到凝聚体形成巨涡旋时所处基态是角动量的本征态。发现势阱从各向同性的环形势阱逐渐变为各向异性的环形势阱的过程中,凝聚体的平均角动量与涡旋个数之比先由1平缓下降,然后迅速下降,最后保持在0.5附近。同时给出凝聚体密度分布和角动量分布的特征,并作出相应解释。 相似文献
60.
Quantizers play a critical role in digital signal processing systems. Recent works have shown that the performance of acquiring multiple analog signals using scalar analog-to-digital converters (ADCs) can be significantly improved by processing the signals prior to quantization. However, the design of such hybrid quantizers is quite complex, and their implementation requires complete knowledge of the statistical model of the analog signal. In this work we design data-driven task-oriented quantization systems with scalar ADCs, which determine their analog-to-digital mapping using deep learning tools. These mappings are designed to facilitate the task of recovering underlying information from the quantized signals. By using deep learning, we circumvent the need to explicitly recover the system model and to find the proper quantization rule for it. Our main target application is multiple-input multiple-output (MIMO) communication receivers, which simultaneously acquire a set of analog signals, and are commonly subject to constraints on the number of bits. Our results indicate that, in a MIMO channel estimation setup, the proposed deep task-bask quantizer is capable of approaching the optimal performance limits dictated by indirect rate-distortion theory, achievable using vector quantizers and requiring complete knowledge of the underlying statistical model. Furthermore, for a symbol detection scenario, it is demonstrated that the proposed approach can realize reliable bit-efficient hybrid MIMO receivers capable of setting their quantization rule in light of the task. 相似文献