全文获取类型
收费全文 | 19798篇 |
免费 | 3002篇 |
国内免费 | 2472篇 |
专业分类
化学 | 15103篇 |
晶体学 | 181篇 |
力学 | 296篇 |
综合类 | 218篇 |
数学 | 5344篇 |
物理学 | 4130篇 |
出版年
2024年 | 61篇 |
2023年 | 265篇 |
2022年 | 845篇 |
2021年 | 890篇 |
2020年 | 1008篇 |
2019年 | 836篇 |
2018年 | 700篇 |
2017年 | 710篇 |
2016年 | 875篇 |
2015年 | 763篇 |
2014年 | 919篇 |
2013年 | 1798篇 |
2012年 | 1117篇 |
2011年 | 1086篇 |
2010年 | 1014篇 |
2009年 | 1227篇 |
2008年 | 1237篇 |
2007年 | 1177篇 |
2006年 | 1141篇 |
2005年 | 976篇 |
2004年 | 947篇 |
2003年 | 866篇 |
2002年 | 647篇 |
2001年 | 583篇 |
2000年 | 573篇 |
1999年 | 532篇 |
1998年 | 479篇 |
1997年 | 343篇 |
1996年 | 270篇 |
1995年 | 276篇 |
1994年 | 227篇 |
1993年 | 144篇 |
1992年 | 147篇 |
1991年 | 80篇 |
1990年 | 62篇 |
1989年 | 75篇 |
1988年 | 58篇 |
1987年 | 42篇 |
1986年 | 37篇 |
1985年 | 54篇 |
1984年 | 37篇 |
1983年 | 11篇 |
1982年 | 22篇 |
1981年 | 25篇 |
1980年 | 25篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A graph is called supereulerian if it has a spanning closed trail. Let G be a 2-edge-connected graph of order n such that each minimal edge cut SE(G) with |S|3 satisfies the property that each component of G−S has order at least (n−2)/5. We prove that either G is supereulerian or G belongs to one of two classes of exceptional graphs. Our results slightly improve earlier results of Catlin and Li. Furthermore, our main result implies the following strengthening of a theorem of Lai within the class of graphs with minimum degree δ4: If G is a 2-edge-connected graph of order n with δ(G)4 such that for every edge xyE(G) , we have max{d(x),d(y)}(n−2)/5−1, then either G is supereulerian or G belongs to one of two classes of exceptional graphs. We show that the condition δ(G)4 cannot be relaxed. 相似文献
42.
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
43.
44.
Annegret K. Wagler 《Mathematical Methods of Operations Research》2002,56(1):127-149
An edge e of a perfect graph G is critical if G−e is imperfect. We would like to decide whether G−e is still “almost perfect” or already “very imperfect”. Via relaxations of the stable set polytope of a graph, we define two
superclasses of perfect graphs: rank-perfect and weakly rank-perfect graphs. Membership in those two classes indicates how
far an imperfect graph is away from being perfect. We study the cases, when a critical edge is removed from the line graph
of a bipartite graph or from the complement of such a graph. 相似文献
45.
本文利用聚集型状态方程,克拉贝龙方程以及临界条件推出聚集活性参量方程.分析结果表明,医药的药理活性是可以用聚集活性参量予以定量表征.本文给出了某些医药的主要的药物成分,如氧化亚氮 乙醚、氯仿和水杨酸甲酯等嘛醉剂),一氧化氮(硝酸甘油)、乙醇胺(医药活性剂)和多巴胺(神经递质)的生物活性数据.实践经验表明,这些化学品分别在生命体的心血管系统、神经系统和免疫系统中起着重要的药理功能作用.这表明,本文研究的内容在医药学研究领域有其重要意义. 相似文献
46.
47.
用分子动力学方法对5%负失配条件下面心立方晶体铝薄膜的原子沉积外延生长进行了三维模拟.铝原子间的相互作用采用嵌入原子法(EAM)多体势计算.模拟结果再现了失配位错的形成现象.分析表明,失配位错在形成之初即呈现为Shockley扩展位错,即由两个伯格斯矢量为〈211〉/6的部分位错和其间的堆垛层错组成,两个部分位错的间距、即层错宽度为1.8 nm,与理论计算结果一致;外延晶体薄膜沉积生长中,位错对会发生滑移,但其间距保持稳定.进一步观察发现,该扩展位错产生于一种类似于“局部熔融-重结晶”的表层局部无序紊乱-
关键词:
失配位错
外延生长
薄膜
分子动力学
铝 相似文献
48.
Signed graphs for portfolio analysis in risk management 总被引:1,自引:0,他引:1
Harary Frank; Lim Meng-Hiot; Wunsch Donald C. 《IMA Journal of Management Mathematics》2002,13(3):201-210
We introduce the notion of structural balance for signed graphsin the context of portfolio analysis. A portfolio of securitiescan be represented as a signed graph with the nodes denotingthe securities and the edges representing the correlation betweenthe securities. With signed graphs, the characteristics of aportfolio from a risk management perspective can be uncoveredfor analysis purposes. It is shown that a portfolio characterizedby a signed graph of positive and negative edges that is structurallybalanced is characteristically more predictable. Investors whoundertake a portfolio position with all positively correlatedsecurities do so with the intention to speculate on the upside(or downside). If the portfolio consists of negative edges andis balanced, then it is likely that the position has a hedgingdisposition within it. On the other hand, an unbalanced signedgraph is representative of an investment portfolio which ischaracteristically unpredictable. 相似文献
49.
本文给出了一个关联图为圈的非负、半正定矩阵A为完全正的一个充要条件.我们还证明了这样的矩阵A(当A为完全正时)的分解指数即为A的阶数. 相似文献
50.
We investigate the conjecture that every circulant graph X admits a k‐isofactorization for every k dividing |E(X)|. We obtain partial results with an emphasis on small values of k. © 2006 Wiley Periodicals, Inc. J Combin Designs 14: 406–414, 2006 相似文献