全文获取类型
收费全文 | 22228篇 |
免费 | 547篇 |
国内免费 | 453篇 |
专业分类
化学 | 3977篇 |
晶体学 | 937篇 |
力学 | 413篇 |
综合类 | 45篇 |
数学 | 14015篇 |
物理学 | 3841篇 |
出版年
2023年 | 56篇 |
2022年 | 150篇 |
2021年 | 151篇 |
2020年 | 168篇 |
2019年 | 418篇 |
2018年 | 455篇 |
2017年 | 303篇 |
2016年 | 354篇 |
2015年 | 356篇 |
2014年 | 659篇 |
2013年 | 1476篇 |
2012年 | 601篇 |
2011年 | 1734篇 |
2010年 | 1535篇 |
2009年 | 1473篇 |
2008年 | 1549篇 |
2007年 | 1563篇 |
2006年 | 1152篇 |
2005年 | 988篇 |
2004年 | 865篇 |
2003年 | 681篇 |
2002年 | 668篇 |
2001年 | 464篇 |
2000年 | 443篇 |
1999年 | 420篇 |
1998年 | 426篇 |
1997年 | 313篇 |
1996年 | 379篇 |
1995年 | 377篇 |
1994年 | 365篇 |
1993年 | 286篇 |
1992年 | 274篇 |
1991年 | 189篇 |
1990年 | 194篇 |
1989年 | 180篇 |
1988年 | 114篇 |
1987年 | 131篇 |
1986年 | 98篇 |
1985年 | 172篇 |
1984年 | 123篇 |
1983年 | 75篇 |
1982年 | 104篇 |
1981年 | 128篇 |
1980年 | 115篇 |
1979年 | 66篇 |
1978年 | 112篇 |
1977年 | 96篇 |
1976年 | 96篇 |
1975年 | 40篇 |
1974年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
111.
In the classical channel assignment problem, transmitters that are sufficiently close together are assigned transmission frequencies that differ by prescribed amounts, with the goal of minimizing the span of frequencies required. This problem can be modeled through the use of an L(2,1)-labeling, which is a function f from the vertex set of a graph G to the non-negative integers such that |f(x)-f(y)|? 2 if xand y are adjacent vertices and |f(x)-f(y)|?1 if xand y are at distance two. The goal is to determine the λ-number of G, which is defined as the minimum span over all L(2,1)-labelings of G, or equivalently, the smallest number k such that G has an L(2,1)-labeling using integers from {0,1,…,k}. Recent work has focused on determining the λ-number of generalized Petersen graphs (GPGs) of order n. This paper provides exact values for the λ-numbers of GPGs of orders 5, 7, and 8, closing all remaining open cases for orders at most 8. It is also shown that there are no GPGs of order 4, 5, 8, or 11 with λ-number exactly equal to the known lower bound of 5, however, a construction is provided to obtain examples of GPGs with λ-number 5 for all other orders. This paper also provides an upper bound for the number of distinct isomorphism classes for GPGs of any given order. Finally, the exact values for the λ-number of n-stars, a subclass of the GPGs inspired by the classical Petersen graph, are also determined. These generalized stars have a useful representation on Möebius strips, which is fundamental in verifying our results. 相似文献
112.
113.
Teruhisa Tsuda 《Letters in Mathematical Physics》2006,77(1):21-30
Starting from certain point sets in the projective plane, we construct a tropical (or subtraction-free birational) representation of Weyl groups over the field of τ-functions. In particular, our construction includes E
8
(1)
, E
7
(1)
, E
6
(1)
and D
5
(1)
as affine cases; each of them gives rise to the q-difference Painlevé equation. 相似文献
114.
We prove a conjecture by F. Ferrari. Let X be the total space of a nonlinear deformation of a rank two holomorphic vector bundle on a smooth rational curve, such that X has trivial canonical bundle and has sections. Then the normal bundle to such sections is computed in terms of the rank of the Hessian of a suitably defined superpotential at its critical points. 相似文献
115.
Fidel Casarrubias-Segura Alejandro Ramírez-Páramo 《Topology and its Applications》2007,154(7):1307-1313
In this paper we make use of the Pol-Šapirovski?'s technique to prove several cardinal inequalities, which generalize other well-known inequalities. 相似文献
116.
Michael Holcomb 《Topology and its Applications》2007,154(1):124-143
One can form a polygonal linkage by identifying initial and terminal points of two free linkages. Likewise, one can form a multipolygonal linkage by identifying initial and terminal points of three free linkages. The geometric and topological properties of moduli spaces of multipolygonal linkages in the plane are studied. These spaces are compact algebraic varieties. Some conditions under which these spaces are smooth manifolds, cross products or disjoint unions of moduli spaces of polygonal linkages, or connected, are determined. Dimensions in smooth manifold cases and some Euler characteristics are computed. A classification of generic multiquadrilateral linkages is also made. 相似文献
117.
The q-Catalan numbers studied by Carlitz and Riordan are polynomials in q with nonnegative coefficients. They evaluate, at q = 1, to the Catalan numbers: 1, 1, 2, 5, 14,…, a log-convex sequence. We use a combinatorial interpretation of these polynomials
to prove a q-log-convexity result. The sequence of q-Catalan numbers is not q-log-convex in the narrow sense used by other authors, so our work suggests a more flexible definition of q-log convex be adopted.
Received January 2, 2007 相似文献
118.
L. Olsen 《Indagationes Mathematicae》2004,15(4):535-547
We give a systematic and detailed account of the Hausdorff dimensions of sets of d-tuples of numbers defined in terms of the asymptotic behaviour of the frequencies of strings of digits in their N-adic expansion. 相似文献
119.
In 1934, Romanoff proved that there are a positive proportion natural numbers which can be expressed as the sum of a prime and a power of 2. In this paper, a quantitative version of this theorem is given. We show that the proportion is larger than 0.0868 and for a positive proportion of odd integers the number of such representations is between 1 and 16. 相似文献
120.
Hirofumi Tsumura 《Journal of Number Theory》2004,106(1):155-168
In this paper, we define the multiple Euler numbers and consider some multiple harmonic series of Mordell-Tornheim's type, which is a partial sum of the Mordell-Tornheim zeta series defined by Matsumoto. Indeed, we prove a certain reducibility of these series as well as the multiple zeta values. 相似文献