全文获取类型
收费全文 | 23703篇 |
免费 | 916篇 |
国内免费 | 391篇 |
专业分类
化学 | 5892篇 |
晶体学 | 323篇 |
力学 | 638篇 |
综合类 | 53篇 |
数学 | 9514篇 |
物理学 | 8590篇 |
出版年
2023年 | 102篇 |
2022年 | 185篇 |
2021年 | 121篇 |
2020年 | 167篇 |
2019年 | 493篇 |
2018年 | 317篇 |
2017年 | 317篇 |
2016年 | 215篇 |
2015年 | 189篇 |
2014年 | 251篇 |
2013年 | 1037篇 |
2012年 | 489篇 |
2011年 | 1020篇 |
2010年 | 559篇 |
2009年 | 855篇 |
2008年 | 979篇 |
2007年 | 973篇 |
2006年 | 939篇 |
2005年 | 641篇 |
2004年 | 1047篇 |
2003年 | 1181篇 |
2002年 | 1763篇 |
2001年 | 1791篇 |
2000年 | 1634篇 |
1999年 | 1799篇 |
1998年 | 1537篇 |
1997年 | 919篇 |
1996年 | 453篇 |
1995年 | 231篇 |
1994年 | 197篇 |
1993年 | 88篇 |
1992年 | 89篇 |
1991年 | 73篇 |
1990年 | 162篇 |
1989年 | 145篇 |
1988年 | 96篇 |
1987年 | 83篇 |
1986年 | 125篇 |
1985年 | 188篇 |
1984年 | 178篇 |
1983年 | 74篇 |
1982年 | 137篇 |
1981年 | 237篇 |
1980年 | 229篇 |
1979年 | 106篇 |
1978年 | 168篇 |
1977年 | 103篇 |
1976年 | 71篇 |
1975年 | 80篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
P. Kavouras Th. Kehagias K. Chrissafis Ph. Komninou Th. Karakostas 《Journal of Thermal Analysis and Calorimetry》2006,86(3):715-719
Three batch compositions of pure oxides (SiO2,
Fe2O3, PbO, Na2O)
with equivalent SiO2, Fe2O3
and PbO contents and a gradually increased Na2O content
were vitrified through heating in a high temperature electric furnace and
subsequent quenching. The resulting vitreous products were thermally treated
in order to study the devitrification behaviour, under conditions designated
from differential thermal analysis experiments. Depending on the Na2O
content, crystal phase separation gave rise to the growth of acmite and hematite
or maghemite. A uniformly phase separated glass-ceramic material, with crystallites
of similar size and population density, was produced from devitrification
of the vitreous product with the higher Na2O content. 相似文献
132.
On the third largest Laplacian eigenvalue of a graph 总被引:1,自引:0,他引:1
Ji-Ming Guo 《Linear and Multilinear Algebra》2007,55(1):93-102
In this article, a sharp lower bound for the third largest Laplacian eigenvalue of a graph is given in terms of the third largest degree of the graph. 相似文献
133.
134.
The notion of balanced bipartitions of the vertices in a tree T was introduced and studied by Reid (Networks 34 (1999) 264). Reid proved that the set of balance vertices of a tree T consists of a single vertex or two adjacent vertices. In this note, we give a simple proof of that result. 相似文献
135.
136.
Eckhard Steffen 《Discrete Mathematics》2004,280(1-3):191-214
Cubic bridgeless graphs with chromatic index four are called uncolorable. We introduce parameters measuring the uncolorability of those graphs and relate them to each other. For k=2,3, let ck be the maximum size of a k-colorable subgraph of a cubic graph G=(V,E). We consider r3=|E|−c3 and
. We show that on one side r3 and r2 bound each other, but on the other side that the difference between them can be arbitrarily large. We also compare them to the oddness ω of G, the smallest possible number of odd circuits in a 2-factor of G. We construct cyclically 5-edge connected cubic graphs where r3 and ω are arbitrarily far apart, and show that for each 1c<2 there is a cubic graph such that ωcr3. For k=2,3, let ζk denote the largest fraction of edges that can be k-colored. We give best possible bounds for these parameters, and relate them to each other. 相似文献
137.
Hongrui Zhang Mingju Chao Mingyi Gao Liwen Zhang Jianquan Yao 《Optics & Laser Technology》2003,35(6):573-449
A fiber-coupled diode-single-end-pumped Nd:YVO4 laser with an Nd:YVO4 crystal of 0.3 at% doping concentration and 3×3×10 mm3 dimensions was reported. 14.850 W of continuous-wave output power in an M2 factor of 1.12 was obtained under pump power of 27.365 W, with an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%. 相似文献
138.
Annalisa Baldi Bruno Franchi 《Calculus of Variations and Partial Differential Equations》2003,16(3):283-298
Abstract. In this paper we study the notion of perimeter associated with doubling metric measures or strongly weights. We prove that the metric perimeter in the sense of L. Ambrosio and M. Miranda jr. coincides with the metric Minkowski
content and can be obtained also as a -limit of Modica-Mortola type degenerate integral functionals.
Received: 27 August 2001 / Accepted: 29 November 2001 / Published online: 10 June 2002
Investigation supported by University of Bologna, funds for selected research topics and by GNAMPA of INdAM, Italy. The authors
are very grateful to Luigi Ambrosio and Francesco Serra Cassano for making their preprints available to them, for listening
with patience and for many unvaluable suggestions. 相似文献
139.
Muhammet Yürüsoy 《Applied mathematics and computation》2004,150(3):775-783
Two dimensional unsteady boundary layer equations of a general model of non-Newtonian fluids were investigated in this study. In this model, the shear stress is taken as an arbitrary function of the velocity gradient. Group classification of the equations with respect to shear stress is done using two different approaches: (1) classical theory (2) equivalence transformations. Both approaches yield identical results. It is found that the principle Lie Algebra extends only for cases of Newtonian and Power-Law flows. 相似文献
140.
Shunsuke Inenaga Ayumi Shinohara Masayuki Takeda Setsuo Arikawa 《Journal of Discrete Algorithms》2004,2(1):33
Suffix trees are a well-known and widely-studied data structure highly useful for string matching. The suffix tree of a string w can be constructed in O(n) time and space, where n denotes the length of w. Larsson achieved an efficient algorithm to maintain suffix trees for a sliding window. It contributes to prediction by partial matching (PPM) style statistical data compression scheme. Compact directed acyclic word graphs (CDAWGs) are a more space-economical data structure for indexing strings. In this paper we propose a linear-time algorithm to maintain CDAWGs for a sliding window. 相似文献