全文获取类型
收费全文 | 73624篇 |
免费 | 12080篇 |
国内免费 | 2915篇 |
学科分类
数理化 | 88619篇 |
出版年
2024年 | 15篇 |
2023年 | 149篇 |
2022年 | 404篇 |
2021年 | 618篇 |
2020年 | 982篇 |
2019年 | 2739篇 |
2018年 | 2586篇 |
2017年 | 3189篇 |
2016年 | 3484篇 |
2015年 | 5657篇 |
2014年 | 5667篇 |
2013年 | 7938篇 |
2012年 | 6161篇 |
2011年 | 5898篇 |
2010年 | 4899篇 |
2009年 | 4715篇 |
2008年 | 5118篇 |
2007年 | 4359篇 |
2006年 | 4032篇 |
2005年 | 3780篇 |
2004年 | 3125篇 |
2003年 | 2947篇 |
2002年 | 3524篇 |
2001年 | 1928篇 |
2000年 | 1740篇 |
1999年 | 923篇 |
1998年 | 298篇 |
1997年 | 280篇 |
1996年 | 231篇 |
1995年 | 196篇 |
1994年 | 148篇 |
1993年 | 108篇 |
1992年 | 101篇 |
1991年 | 75篇 |
1990年 | 69篇 |
1989年 | 56篇 |
1988年 | 46篇 |
1987年 | 41篇 |
1986年 | 45篇 |
1985年 | 79篇 |
1984年 | 40篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 38篇 |
1980年 | 13篇 |
1979年 | 26篇 |
1978年 | 18篇 |
1977年 | 22篇 |
1976年 | 16篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
关于一类二次哈密尔顿系统在二次扰动下的极限环个数问题 总被引:2,自引:0,他引:2
本文研究了一类具有两个鞍点和一个中心的通用二次哈密尔顿向量场在二次扰动下的三参数开折,证明极限环的最小上界为2。 相似文献
5.
6.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
7.
Claudio Simeone 《General Relativity and Gravitation》2002,34(11):1887-1893
A consistent quantization with a clear notion of time and evolution is given for the anisotropic Kantowski–Sachs cosmological model. It is shown that a suitable coordinate choice allows to obtain a solution of the Wheeler–DeWitt equation in the form of definite energy states, and that the results can be associated to two disjoint equivalent theories, one for each sheet of the constraint surface. 相似文献
8.
Let G=(V(G),E(G)) be a graph. A (n,G, λ)‐GD is a partition of the edges of λKn into subgraphs (G‐blocks), each of which is isomorphic to G. The (n,G,λ)‐GD is named as graph design for G or G‐decomposition. The large set of (n,G,λ)‐GD is denoted by (n,G,λ)‐LGD. In this work, we obtain the existence spectrum of (n,P3,λ)‐LGD. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 151–159, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10008 相似文献
9.
A Dirac picture perturbation theory is developed for the time evolution operator in classical dynamics in the spirit of the Schwinger–Feynman–Dyson perturbation expansion and detailed rules are derived for computations. Complexification formalisms are given for the time evolution operator suitable for phase space analyses, and then extended to a two-dimensional setting for a study of the geometrical Berry phase as an example. Finally a direct integration of Hamilton's equations is shown to lead naturally to a path integral expression, as a resolution of the identity, as applied to arbitrary functions of generalized coordinates and momenta. 相似文献
10.
Several new families of c‐Bhaskar Rao designs with block size 4 are constructed. The necessary conditions for the existence of a c‐BRD (υ,4,λ) are that: (1)λmin=?λ/3 ≤ c ≤ λ and (2a) c≡λ (mod 2), if υ > 4 or (2b) c≡ λ (mod 4), if υ = 4 or (2c) c≠ λ ? 2, if υ = 5. It is proved that these conditions are necessary, and are sufficient for most pairs of c and λ; in particular, they are sufficient whenever λ?c ≠ 2 for c > 0 and whenever c ? λmin≠ 2 for c < 0. For c < 0, the necessary conditions are sufficient for υ> 101; for the classic Bhaskar Rao designs, i.e., c = 0, we show the necessary conditions are sufficient with the possible exception of 0‐BRD (υ,4,2)'s for υ≡ 4 (mod 6). © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 361–386, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10009 相似文献