全文获取类型
收费全文 | 13257篇 |
免费 | 1610篇 |
国内免费 | 1099篇 |
专业分类
化学 | 3079篇 |
晶体学 | 69篇 |
力学 | 1023篇 |
综合类 | 289篇 |
数学 | 6298篇 |
物理学 | 5208篇 |
出版年
2024年 | 16篇 |
2023年 | 104篇 |
2022年 | 297篇 |
2021年 | 323篇 |
2020年 | 281篇 |
2019年 | 273篇 |
2018年 | 301篇 |
2017年 | 382篇 |
2016年 | 422篇 |
2015年 | 349篇 |
2014年 | 677篇 |
2013年 | 967篇 |
2012年 | 657篇 |
2011年 | 791篇 |
2010年 | 679篇 |
2009年 | 800篇 |
2008年 | 909篇 |
2007年 | 888篇 |
2006年 | 769篇 |
2005年 | 713篇 |
2004年 | 589篇 |
2003年 | 557篇 |
2002年 | 556篇 |
2001年 | 401篇 |
2000年 | 399篇 |
1999年 | 384篇 |
1998年 | 355篇 |
1997年 | 290篇 |
1996年 | 234篇 |
1995年 | 220篇 |
1994年 | 214篇 |
1993年 | 131篇 |
1992年 | 138篇 |
1991年 | 104篇 |
1990年 | 81篇 |
1989年 | 86篇 |
1988年 | 82篇 |
1987年 | 68篇 |
1986年 | 50篇 |
1985年 | 77篇 |
1984年 | 52篇 |
1983年 | 38篇 |
1982年 | 50篇 |
1981年 | 28篇 |
1980年 | 27篇 |
1979年 | 29篇 |
1978年 | 33篇 |
1977年 | 23篇 |
1976年 | 21篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Yao Ping HOU 《数学学报(英文版)》2005,21(4):955-960
A signed graph is a graph with a sign attached to each edge. This paper extends some fundamental concepts of the Laplacian matrices from graphs to signed graphs. In particular, the relationships between the least Laplacian eigenvalue and the unbalancedness of a signed graph are investigated. 相似文献
22.
Matrix extensions and eigenvalue completions, the generic case 总被引:2,自引:0,他引:2
William Helton Joachim Rosenthal Xiaochang Wang 《Transactions of the American Mathematical Society》1997,349(8):3401-3408
In this paper we provide new necessary and sufficient conditions for the so-called eigenvalue completion problem.
23.
Space time-index plots for probing dynamical nonstationarity 总被引:3,自引:0,他引:3
We propose a simple method to efficiently probe dynamical nonstationarity in observed time series. In a space time-index plot, the density distributions as a function of normalized time-index are V-shaped due to nonstationarity. We show that this method is workable for short data sets and typical examples are illustrated. 相似文献
24.
Yoshikazu Takada 《Annals of the Institute of Statistical Mathematics》1998,50(2):325-335
This paper gives a condition which implies the nonexistence of parametric statistical procedures with bounded risk or error performance characteristics. Many examples for which such a condition is satisfied are considered. 相似文献
25.
引入了随机环境中双移民生灭过程的概念,定义了过程的模态指示函数,在此基础上研究了其转移矩阵的平稳分布,给出了平稳分布众数的位置与模态指示函数之间的关系.研究了平稳分布的众数与边界关系. 相似文献
26.
Longlan Cui Hong Xu Ping He Keiko Sumitomo Yoshinori Yamaguchi Hongchen Gu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5285-5295
A hybrid emulsion polymerization was formulated for synthesizing Fe3O4/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe3O4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe3O4/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007 相似文献
27.
Tensile impact experiments of EC8.0−24×7 glass fiber bundles at different low temperaturesT(14°C, −40°C and −10°C) and strain rates ɛ were carried out, and complete stress-strain curves were obtained. Within the range
of the experiment temperatures and strain rates, it is found that the initial modulusE, the ultimate strength σmax and the unstable strain ɛ
b
of the glass fiber bundles all increase with ɛ at an identicalT. At an identical ɛ, with the decrease ofT, E and σmax increase; but ɛ
b
increases when 10°C>T>−40°C and decreases when −40°C>T>−100°C. The strain-rate- and temperature-dependent bimodal Weibull statistical constitutive theory was adopted for the statistical
analysis of the experimental results, and the Weibull parameters of single fiber were obtained. The results show that the
bimodal Weibull distribution function is suitable to represent the strength distribution of the glass fiber at low temperature
and different strain rates. The differences in the mechanical properties between EC8.0−24×7 and EC5.5−12 ×14 glass fiber bundles
were also discussed.
Project supported by the National Natural Science Foundation of China (No. 19772058). 相似文献
28.
Robert J. Rubin 《Journal of statistical physics》1991,65(5-6):1207-1216
A one-dimensional lattice random walk in the presence ofm equally spaced traps is considered. The step length distribution is a symmetric exponential. An explicit analytic expression is obtained for the probability that the random walk will be trapped at thejth trapping site. 相似文献
29.
The decay process J/ψ→p X X→p P,where p,p and P are the proton,antiproton and pseudoscalar states,respectively,has been studied in terms of the angular distribution and the generalized moment analysis methods.The result shows that we can identify the spin,but cannot determine the parity of the baryon resonance state X produced in the process J/ψ→p X X→p P. 相似文献
30.
对于任意秩有限总体,在二次损失下,有关文献已给出了线性可预测变量在齐次线性预测类中的唯一线性Minimax预测.本文在正态假设下,证明了这个线性Minimax预测也是线性可预测变量在一切预测类中的唯一Minimax预测. 相似文献