全文获取类型
收费全文 | 93篇 |
免费 | 5篇 |
专业分类
化学 | 30篇 |
力学 | 2篇 |
数学 | 15篇 |
物理学 | 51篇 |
出版年
2022年 | 1篇 |
2021年 | 4篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2013年 | 2篇 |
2012年 | 5篇 |
2011年 | 6篇 |
2009年 | 3篇 |
2008年 | 2篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1952年 | 1篇 |
1933年 | 3篇 |
1916年 | 2篇 |
1905年 | 1篇 |
排序方式: 共有98条查询结果,搜索用时 15 毫秒
1.
Renewal systems are symbolic dynamical systems originally introduced by Adler. IfW is a finite set of words over a finite alphabetA, then the renewal system generated byW is the subshiftX
W ⊂A
Z formed by bi-infinite concatenations of words fromW. Motivated by Adler’s question of whether every irreducible shift of finite type is conjugate to a renewal system, we prove
that for every shift of finite type there is a renewal system having the same entropy. We also show that every shift of finite
type can be approximated from above by renewal systems, and that by placing finite-type constraints on possible concatenations,
we obtain all sofic systems.
The authors were supported in part by NFS grants DMS-8706284, DMS-8814159 and DMS-8820716. 相似文献
2.
3.
4.
Stanley HE Buldyrev SV Goldberger AL Hausdorff JM Havlin S Mietus J Peng C-K Sciortino F Simons M 《Physica A》1992,191(1-4):1-12
Here we discuss recent advances in applying ideas of fractals and disordered systems to two topics of biological interest, both topics having common the appearance of scale-free phenomena, i.e., correlations that have no characteristic length scale, typically exhibited by physical systems near a critical point and dynamical systems far from equilibrium. (i) DNA nucleotide sequences have traditionally been analyzed using models which incorporate the possibility of short-range nucleotide correlations. We found, instead, a remarkably long-range power law correlation. We found such long-range correlations in intron-containing genes and in non-transcribed regulatory DNA sequences as well as intragenomic DNA, but not in cDNA sequences or intron-less genes. We also found that the myosin heavy chain family gene evolution increases the fractal complexity of the DNA landscapes, consistent with the intron-late hypothesis of gene evolution. (ii) The healthy heartbeat is traditionally thought to be regulated according to the classical principle of homeostasis, whereby physiologic systems operate to reduce variability and achieve an equilibrium-like state. We found, however, that under normal conditions, beat-to-beat fluctuations in heart rate display long-range power law correlations. 相似文献
5.
In this paper,we study the surface instability of a cylindrical pore in the absence of stress. This instability is called the Rayleigh-Plateau instabilty. We consider the model developed by Spencer et ... 相似文献
6.
Ebraheem Abdu Musad Saleh Abdullah Mohammed AL Dawsari Kakul Husain Ismail Hassan Kutty K.M.Lokanatha Rai 《Molecules (Basel, Switzerland)》2021,26(2)
A novel synthesis of thiazolo[2,3-b]quinazolines 4(a–e), pyrido[2′,3′:4,5]thiazolo[2,3-b]quinazolines {5(a–e), 6(a–e), and 7(a–e)}, pyrano[2′,3′:4,5]thiazolo[2,3-b]quinazolines 8(a–e), and benzo[4,5]thiazolo[2,3-b]quinazoloine9(a–e) derivatives starting from 2-(Bis-methylsulfanyl-methylene)-5,5-dimethyl-cyclohexane-1,3-dione 2 as efficient α,α dioxoketen dithioacetal is reported and the synthetic approaches of these types of compounds will provide an innovative molecular framework to the designing of new active heterocyclic compounds. In our study, we also present optimization of the synthetic method along with a biological evaluation of these newly synthesized compounds as antioxidants and antibacterial agents against the bacterial strains, like S. aureus, E. coli, and P. aeruginosa. Among all the evaluated compounds, it was found that some showed significant antioxidant activity at 10 μg/mL while the others exhibited better antibacterial activity at 100 μg/mL. The results of this study showed that compound 6(c) possessed remarkable antibacterial activity, whereas compound 9(c) exhibited the highest efficacy as an antioxidant. The structures of the new synthetic compounds were elucidated by elemental analysis, IR, 1H-NMR, and 13C-NMR. 相似文献
7.
Ivanov PC Nunes Amaral LA Goldberger AL Havlin S Rosenblum MG Stanley HE Struzik ZR 《Chaos (Woodbury, N.Y.)》2001,11(3):641-652
We explore the degree to which concepts developed in statistical physics can be usefully applied to physiological signals. We illustrate the problems related to physiologic signal analysis with representative examples of human heartbeat dynamics under healthy and pathologic conditions. We first review recent progress based on two analysis methods, power spectrum and detrended fluctuation analysis, used to quantify long-range power-law correlations in noisy heartbeat fluctuations. The finding of power-law correlations indicates presence of scale-invariant, fractal structures in the human heartbeat. These fractal structures are represented by self-affine cascades of beat-to-beat fluctuations revealed by wavelet decomposition at different time scales. We then describe very recent work that quantifies multifractal features in these cascades, and the discovery that the multifractal structure of healthy dynamics is lost with congestive heart failure. The analytic tools we discuss may be used on a wide range of physiologic signals. (c) 2001 American Institute of Physics. 相似文献
8.
Gomez L Slutzky C Ferron J de La Figuera J Camarero J Vazquez De Parga AL de Miguel JJ Miranda R 《Physical review letters》2000,84(19):4397-4400
Generic computer simulations using empiric interatomic potentials suggest a new, collective mechanism that could be responsible for mixing at heteroepitaxial interfaces. Even if single adsorbate atoms diffuse by hopping on the substrate surface and do not mix at the terraces, two-dimensional islands formed by nucleation may become unstable above a certain critical size and explode upwards forming clusters of several atomic layers. This process is accompanied by strong distortions of the underlying atomic layers, and on soft materials it can result in surface etching and incorporation of substrate atoms into the islands. 相似文献
9.
10.
We model the forming process as a fluid flow. A finite element program, FIDAP, which analyses flow problems, was used to calculate velocity and strain rates at points throughout the material during the deformation process. This allows predictions to be made on the shape and quality of the resulting part. The stress-strain relation we used models the plastic flow of metals (Bingham fluids). The FEM approximation of such a fluid is tested by comparing results for a simple analytical example. In forming processes provision must be made for friction between dye and workpiece, and the program was modified accordingly. Two classical ring forming simulations are compared to published results. 相似文献