全文获取类型
收费全文 | 7728篇 |
免费 | 700篇 |
国内免费 | 616篇 |
专业分类
化学 | 613篇 |
晶体学 | 5篇 |
力学 | 156篇 |
综合类 | 201篇 |
数学 | 7385篇 |
物理学 | 684篇 |
出版年
2024年 | 26篇 |
2023年 | 126篇 |
2022年 | 207篇 |
2021年 | 164篇 |
2020年 | 260篇 |
2019年 | 278篇 |
2018年 | 279篇 |
2017年 | 274篇 |
2016年 | 191篇 |
2015年 | 170篇 |
2014年 | 263篇 |
2013年 | 671篇 |
2012年 | 293篇 |
2011年 | 401篇 |
2010年 | 405篇 |
2009年 | 562篇 |
2008年 | 525篇 |
2007年 | 410篇 |
2006年 | 473篇 |
2005年 | 355篇 |
2004年 | 322篇 |
2003年 | 293篇 |
2002年 | 290篇 |
2001年 | 259篇 |
2000年 | 252篇 |
1999年 | 231篇 |
1998年 | 194篇 |
1997年 | 142篇 |
1996年 | 108篇 |
1995年 | 81篇 |
1994年 | 76篇 |
1993年 | 53篇 |
1992年 | 39篇 |
1991年 | 32篇 |
1990年 | 22篇 |
1989年 | 29篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1985年 | 31篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 29篇 |
1981年 | 12篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1977年 | 24篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1974年 | 14篇 |
1973年 | 19篇 |
排序方式: 共有9044条查询结果,搜索用时 15 毫秒
131.
132.
133.
134.
《Discrete Mathematics》2022,345(12):113173
For a graph G, the unraveled ball of radius r centered at a vertex v is the ball of radius r centered at v in the universal cover of G. We obtain a lower bound on the weighted spectral radius of unraveled balls of fixed radius in a graph with positive weights on edges, which is used to present an upper bound on the (where ) smallest normalized Laplacian eigenvalue of irregular graphs under minor assumptions. Moreover, when , the result may be regarded as an Alon–Boppana type bound for a class of irregular graphs. 相似文献
135.
XU ShangJin WU ZhengFei & DENG YunPing College of Mathematics Information Science Guangxi University Nanning 《中国科学A辑(英文版)》2009,(2)
A graph is said to be s-arc-regular if its full automorphism group acts regularly on the set of its s-arcs. In this paper, we investigate connected cubic s-arc-regular Cayley graphs of finite nonabelian simple groups. Two suffcient and necessary conditions for such graphs to be 1- or 2-arc-regular are given and based on the conditions, several infinite families of 1-or 2-arc-regular cubic Cayley graphs of alternating groups are constructed. 相似文献
136.
Khodakhast Bibak 《International journal of quantum chemistry》2013,113(8):1209-1212
For a graph G, a “spanning tree” in G is a tree that has the same vertex set as G. The number of spanning trees in a graph (network) G, denoted by t(G), is an important invariant of the graph (network) with lots of decisive applications in many disciplines. In the article by Sato (Discrete Math. 2007, 307, 237), the number of spanning trees in an (r, s)‐semiregular graph and its line graph are obtained. In this article, we give short proofs for the formulas without using zeta functions. Furthermore, by applying the formula that enumerates the number of spanning trees in the line graph of an (r, s)‐semiregular graph, we give a new proof of Cayley's Theorem. © 2013 Wiley Periodicals, Inc. 相似文献
137.
Let (W,S) be a Coxeter system with a strictly complete Coxeter graph. The present paper concerns the set Red(z) of all reduced expressions for any z∈W. By associating each bc-expression to a certain symbol, we describe the set Red(z) and compute its cardinal |Red(z)| in terms of symbols. An explicit formula for |Red(z)| is deduced, where the Fibonacci numbers play a crucial role. 相似文献
138.
Gutman and Wagner proposed the concept of matching energy (ME) and pointed out that the chemical applications of ME go back to the 1970s. Let G be a simple graph of order n and be the roots of its matching polynomial. The ME of G is defined to be the sum of the absolute values of . In this article, we characterize the graphs with minimal ME among all unicyclic and bicyclic graphs with a given diameter d. © 2014 Wiley Periodicals, Inc. Complexity 21: 224–238, 2015 相似文献
139.
Grooming uniform all‐to‐all traffic in optical (SONET) rings with grooming ratio C requires the determination of a decomposition of the complete graph into subgraphs each having at most C edges. The drop cost of such a grooming is the total number of vertices of nonzero degree in these subgraphs, and the grooming is optimal when the drop cost is minimum. The determination of optimal C‐groomings has been considered for , and completely solved for . For , it has been shown that the lower bound for the drop cost of an optimal C‐grooming can be attained for almost all orders with 5 exceptions and 308 possible exceptions. For , there are infinitely many unsettled orders; especially the case is far from complete. In this paper, we show that the lower bound for the drop cost of a 6‐grooming can be attained for almost all orders by reducing the 308 possible exceptions to 3, and that the lower bound for the drop cost of a 7‐grooming can be attained for almost all orders with seven exceptions and 16 possible exceptions. Moreover, for the unsettled orders, we give upper bounds for the minimum drop costs. 相似文献
140.
Christian Neis Thomas Kradolfer Kaspar Hegetschweiler 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(6):632-637
Single crystals of (1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol‐κ3O2,O4,O6)(1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol‐κ3O2,O4,O6)lithium(I) diiodide dihydrate, [Li(C6H16N3O3)(C6H15N3O3)]I2·2H2O or [Li(Htaci)(taci)]I2·2H2O (taci is 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol), (I), bis(1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol‐κ3O2,O4,O6)sodium(I) iodide, [Na(C6H15N3O3)2]I or [Na(taci)2]I, (II), and bis(1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol‐κ3O2,O4,O6)potassium(I) iodide, [K(C6H15N3O3)2]I or [K(taci)2]I, (III), were grown by diffusion of MeOH into aqueous solutions of the complexes. The structures of the Na and K complexes are isotypic. In all three complexes, the taci ligands adopt a chair conformation with axial hydroxy groups, and the metal cations exhibit exclusive O‐atom coordination. The six O atoms of the resulting MO6 unit define a centrosymmetric trigonal antiprism with approximate D3d symmetry. The interligand O...O distances increase significantly in the order Li < Na < K. The structure of (I) exhibits a complex three‐dimensional network of R—NH2—H...NH2—R, R—O—H...NH2—R and R—O—H...O(H)—H...NH2—R hydrogen bonds. The structures of the Na and K complexes consist of a stack of layers, in which each taci ligand is bonded to three neighbours via pairwise O—H...NH2 interactions between vicinal HO—CH—CH—NH2 groups. 相似文献