全文获取类型
收费全文 | 2007篇 |
免费 | 164篇 |
国内免费 | 120篇 |
专业分类
化学 | 294篇 |
晶体学 | 4篇 |
力学 | 93篇 |
综合类 | 55篇 |
数学 | 1354篇 |
物理学 | 491篇 |
出版年
2024年 | 2篇 |
2023年 | 22篇 |
2022年 | 47篇 |
2021年 | 45篇 |
2020年 | 51篇 |
2019年 | 56篇 |
2018年 | 54篇 |
2017年 | 54篇 |
2016年 | 63篇 |
2015年 | 47篇 |
2014年 | 91篇 |
2013年 | 150篇 |
2012年 | 79篇 |
2011年 | 137篇 |
2010年 | 133篇 |
2009年 | 130篇 |
2008年 | 147篇 |
2007年 | 146篇 |
2006年 | 130篇 |
2005年 | 72篇 |
2004年 | 81篇 |
2003年 | 95篇 |
2002年 | 74篇 |
2001年 | 58篇 |
2000年 | 55篇 |
1999年 | 45篇 |
1998年 | 42篇 |
1997年 | 24篇 |
1996年 | 31篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 1篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2291条查询结果,搜索用时 15 毫秒
1.
Thin Ca films were evaporated on Si(1 1 1) under UHV conditions and subsequently annealed in the temperature range 200–650 °C. The interdiffusion of Ca and Si was examined by ex situ Auger depth profiling. In situ monitoring of the Si 2p core-level shift by X-ray photoemission spectroscopy (XPS) was employed to study the silicide formation process. The formation temperature of CaSi2 films on Si(1 1 1) was found to be about 350 °C. Epitaxial growth takes place at T≥400 °C. The morphology of the films, measured by atomic force microscopy (AFM), was correlated with their crystallinity as analyzed by X-ray diffraction (XRD). According to measurements of temperature-dependent I–V characteristics and internal photoemission the Schottky-barrier height of CaSi2 on Si(1 1 1) amounts to qΦBn=0.25 eV on n-type and to qΦBp=0.82 eV on p-type silicon. 相似文献
2.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
3.
A Necessary and Sufficient Condition for the Existence of a Heterochromatic Spanning Tree in a Graph
Kazuhiro Suzuki 《Graphs and Combinatorics》2006,22(2):261-269
We prove the following theorem. An edge-colored (not necessary to be proper) connected graph G of order n has a heterochromatic spanning tree if and only if for any r colors (1≤r≤n−2), the removal of all the edges colored with these r colors from G results in a graph having at most r+1 components, where a heterochromatic spanning tree is a spanning tree whose edges have distinct colors. 相似文献
4.
Given a tree
with leaf set X, there are certain ways of arranging the elements of X in a circular order so that
can be embedded in the plane and ‘preserve’ this ordering. We investigate some new combinatorial properties of these ‘circular orderings.’ We then use these properties to establish two results concerning dissimilarity maps on X that are induced by edge-weighted trees with leaf set X. 相似文献
5.
6.
7.
Searching in trees 总被引:1,自引:0,他引:1
Frank Recker 《Discrete Applied Mathematics》2004,140(1-3):169-183
In (Discrete Math. 17 (1977)181) Rivest introduced the search complexity of binary trees and proved that among all binary trees with a fixed search complexity the smallest ones are the so-called Fibonacci trees. This result is extended for q-trees. The structure of the smallest q-trees is again Fibonacci-like but more complicated than in the binary case. In addition an upper bound for the asymptotic growth of these trees is given. 相似文献
8.
We present an O(min(Kn,n2)) algorithm to solve the maximum integral multiflow and minimum multicut problems in rooted trees, where K is the number of commodities and n is the number of vertices. These problems are NP-hard in undirected trees but polynomial in directed trees. In the algorithm we propose, we first use a greedy procedure to build the multiflow then we use duality properties to obtain the multicut and prove the optimality. 相似文献
9.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
10.
应用七级目测法对浙江中部地区27个夏熟作物田样点的杂草进行了优势等级调查,将所得数据转换成重要值,以杂草在27个样点中的重要值为运算指标,应用主成分分析法和图论聚类中的最小生成树法,对24种杂草的生态学相似性进行了比较,指出了长期使用单一的除草剂导致农田杂草种群迅速更迭的原因:杂草对除草剂的敏感性差异及不同杂草间的生态学特性的差异。 相似文献