全文获取类型
收费全文 | 1109篇 |
免费 | 59篇 |
国内免费 | 61篇 |
专业分类
化学 | 207篇 |
晶体学 | 3篇 |
力学 | 57篇 |
综合类 | 31篇 |
数学 | 591篇 |
物理学 | 340篇 |
出版年
2024年 | 3篇 |
2023年 | 17篇 |
2022年 | 23篇 |
2021年 | 22篇 |
2020年 | 41篇 |
2019年 | 40篇 |
2018年 | 31篇 |
2017年 | 26篇 |
2016年 | 32篇 |
2015年 | 31篇 |
2014年 | 54篇 |
2013年 | 96篇 |
2012年 | 46篇 |
2011年 | 63篇 |
2010年 | 64篇 |
2009年 | 94篇 |
2008年 | 98篇 |
2007年 | 75篇 |
2006年 | 56篇 |
2005年 | 55篇 |
2004年 | 40篇 |
2003年 | 40篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 21篇 |
1999年 | 21篇 |
1998年 | 25篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 10篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有1229条查询结果,搜索用时 15 毫秒
91.
Given two Banach spaces E,F, let B(E,F) be the set of all bounded linear operators from E into F, Σ
r
the set of all operators of finite rank r in B(E,F), and Σ
r
# the number of path connected components of Σ
r
. It is known that Σ
r
is a smooth Banach submanifold in B(E,F) with given expression of its tangent space at each A ∈ Σ
r
. In this paper,the equality Σ
r
# = 1 is proved. Consequently, the following theorem is obtained: for any nonnegative integer r, Σ
r
is a smooth and path connected Banach submanifold in B(E,F) with the tangent space T
A
Σ
r
= {B ∈ B(E,F): BN(A) ⊂ R(A)} at each A ∈ Σ
r
if dim F = ∞. Note that the routine method can hardly be applied here. So in addition to the nice topological and geometric property
of Σ
r
the method presented in this paper is also interesting. As an application of this result, it is proved that if E = ℝ
n
and F = ℝ
m
, then Σ
r
is a smooth and path connected submanifold of B(ℝ
n
, ℝ
m
) and its dimension is dimΣ
r
= (m+n)r−r
2 for each r, 0 <- r < min {n,m}.
Supported by the National Science Foundation of China (Grant No.10671049 and 10771101). 相似文献
92.
We give new bounds on the star arboricity and the caterpillar arboricity of planar graphs with given girth. One of them answers an open problem of Gyárfás and West: there exist planar graphs with track number 4. We also provide new NP-complete problems. 相似文献
93.
Direct numerical simulations with a C3-chemistry model have been performed to investigate the transient behavior and internal structure of flames propagating in an axisymmetric fuel jet of methane, ethane, ethylene, acetylene, or propane in normal earth gravity (1g) and zero gravity (0g). The fuel issued from a 3-mm-i.d. tube into quasi-quiescent air for a fixed mixing time of 0.3 s before it was ignited along the centerline where the fuel–air mixture was at stoichiometry. The edge of the flame formed a vigorously burning peak reactivity spot, i.e., reaction kernel, and propagated through a flammable mixture layer, leaving behind a trailing diffusion flame. The reaction kernel broadened laterally across the flammable mixture layer and possessed characteristics of premixed flames in the direction of propagation and unique flame structure in the transverse direction. The reaction kernel grew wings on both fuel and air sides to form a triple-flame-like structure, particularly for ethylene and acetylene, whereas for alkanes, the fuel-rich wing tended to merge with the main diffusion flame zone, particularly methane. The topology of edge diffusion flames depend on the properties of fuels, particularly the rich flammability limit, and the mechanistic oxidation pathways. The transit velocity of edge diffusion flames, determined from a time series of calculated temperature field, equaled to the measured laminar flame speed of the stoichiometric fuel–air mixtures, available in the literature, independent of the gravity level. 相似文献
94.
95.
广义笛卡尔积图的连通度 总被引:1,自引:0,他引:1
黄琼湘 《新疆大学学报(理工版)》1991,8(2):5-10
本文定义了图G_1、G_2的广义笛卡尔积图G=G_1∫G_2,并且证明了它们的连通度具有关系k(G)≥k(G_1)+k(G_2)。这一结果是对文[1]中关于G_1与G_2直积的结果的推广。此外,本文还讨论了G=G_1∫G_2的直径及Hamilton性。最后,利用G=G_1∫G_2的结果对循环图的连通度进行了讨论。 相似文献
96.
97.
We consider the effects on the algebraic connectivity of various graphs when vertices and graphs are appended to the original graph. We begin by considering weighted trees and appending a single isolated vertex to it by adding an edge from the isolated vertex to some vertex in the tree. We then determine the possible set vertices in the tree that can yield the maximum change in algebraic connectivity under such an operation. We then discuss the changes in algebraic connectivity of a star when various graphs such as trees and complete graphs are appended to its pendant vertices. 相似文献
98.
In this paper, by using the Discharging Method, we show that any graph with maximum degree Δ 8 that is embeddable in a surface Σ of characteristic χ(Σ) 0 is class one and any graph with maximum degree Δ 9 that is embeddable in a surface Σ of characteristic χ(Σ) = − 1 is class one. For surfaces of characteristic 0 or −1, these results improve earlier results of Mel'nikov. 相似文献
99.
The main result of this paper establishes that the irregularity strength of any tree with no vertices of degree two is its number of pendant vertices. 相似文献
100.
为了提高镀层的表面质量,提出了一种超声辅助电镀的方法。超声的空化与搅拌作用可以影响电镀的电沉积过程。设计了合理的换能器结构,并搭建了超声辅助电镀装置。通过对模型进行压电声学场与电镀场耦合仿真分析,结果表明:在硫酸铜电解液,镀铜时间60s,电压300V条件下,进行超声辅助电镀,镀层厚度分布均匀,镀层中部电流密度分布均匀,边缘最大电流密度是未加超声的2倍左右 。基于仿真结果,进行相同的实验测试,结果表明:超声辅助电镀可以提高镀层的均匀性,减少铜颗粒表面的杂质,提高表面的光洁度。阴极样品距离换能器头部位置在60mm左右,镀层质量良好。 相似文献