全文获取类型
收费全文 | 355篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
化学 | 99篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 197篇 |
物理学 | 54篇 |
出版年
2021年 | 3篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 14篇 |
2011年 | 23篇 |
2010年 | 15篇 |
2009年 | 13篇 |
2008年 | 16篇 |
2007年 | 11篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 13篇 |
2003年 | 18篇 |
2002年 | 10篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 9篇 |
1998年 | 2篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1967年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有365条查询结果,搜索用时 15 毫秒
21.
Partha Niyogi Stephen Smale Shmuel Weinberger 《Discrete and Computational Geometry》2008,39(1-3):419-441
Recently there has been a lot of interest in geometrically motivated approaches to data analysis in high-dimensional spaces.
We consider the case where data are drawn from sampling a probability distribution that has support on or near a submanifold
of Euclidean space. We show how to “learn” the homology of the submanifold with high confidence. We discuss an algorithm to
do this and provide learning-theoretic complexity bounds. Our bounds are obtained in terms of a condition number that limits
the curvature and nearness to self-intersection of the submanifold. We are also able to treat the situation where the data
are “noisy” and lie near rather than on the submanifold in question.
The main results of this paper were first presented at a conference in honor of John Franks and Clark Robinson at Northwestern
University in April 2003. These results were formally written as Technical Report No. TR-2004-08, Department of Computer Science,
University of Chicago. 相似文献
22.
Motivated by experimental measurements of the uniaxial response of collagen fibers, a new strain energy-density function for a solid which is finitely extensible along a preferred direction is proposed. Next, by application of a homogenization technique, the macroscopic strain energy-density function of composites with one and two families of fibers of this material embedded in a neo-Hookean matrix are determined. The resulting explicit expressions for the macroscopic strain energy-density functions are given in terms of the behaviors of the individual phases and their volume fractions. The responses of a few specific composites are investigated, revealing the lock-up surfaces of these composites. Finally, we examine the ability of the macroscopic model to capture experimentally measured stress-strain curves for the medial layer of a human abdominal aorta. 相似文献
23.
The multi-transshipment problem is NP-hard already for two commodities over bipartite networks. Nonetheless, using our recent
theory of n-fold integer programming and extensions developed herein, we are able to establish the polynomial time solvability of the
problem in two broad situations. First, for any fixed number of commodities and number of suppliers, we solve the problem
over bipartite networks with variable number of consumers in polynomial time. This is very natural in operations research
applications where few facilities serve many customers. Second, for every fixed network, we solve the problem with variable
number of commodities in polynomial time. 相似文献
24.
Using mutually modulated cross-gain modulation, Stokes optical frequency changes are converted into modulation phase changes with high sensitivity. In the slow-light transition regime, we demonstrate kilohertz sensitivity to the Stokes optical carrier frequency. The sensitivity is inversely proportional to the modulation frequency of the pump and Stokes beams. 相似文献
25.
By varying the absorption coefficient and width of an intralipid-India ink solution in a quasi-one-dimensional experiment, we investigate the transition between the ballistic and the diffusive regimes. The medium's attenuation coefficient changes abruptly between two different values within a single mean free path. This problem is analyzed both experimentally and theoretically, and it is demonstrated that the transition location depends on the scattering coefficient as well as on the measuring solid angle. 相似文献
26.
We provide a complexity classification of four variants of robust integer programming when the underlying Graver basis is given. We discuss applications to robust multicommodity flows and multiway statistical table problems, and describe an effective parametrization of robust integer programming. 相似文献
27.
The effect of thermal aging on three different elastomeric polyurethane adhesives was studied. Consequently, an attempt was made to predict the polyurethanes' service lifetimes from the changes in tensile properties, hardness of bulk specimens and adhesion strength properties (lap shear and butt joints) of polycarbonate bonded joints. Aging temperatures ranged from ambient to 70 °C (at 50% relative humidity) for durations from 20 days to 18 months. Experimental results were analyzed according to a kinetic rate theory and using limit values for the various properties. Consequently, service lifetimes were determined and compared to results from actual service life. Predictions of long-term performance from accelerated tests proved to be reasonable for the properties and materials studied. 相似文献
28.
A new family of copper ligand-exchange selectors, L- or D-β-amino alcohols, is employed for the chiral separation of D,L-dansyl-amino acids, unmodified amino acid racemates, phenylalanine and tryptophan, and β-blocker L,D-propranolol by SDS-micellar electrokinetic chromatography and by electrophoretic chromatography in a low molecular weight organogel (LMOG)-filled capillary. The LMOG comprised a self-assembled fibrillar gel of trans-(1S,2S)-1,2-bis-(dodecylamido) cyclohexane in methanol. The di-L-valinol-copper complex exhibited the best performance on LMOG-CE compared with all other β-amino alcohol-copper selectors. The dependence of chiral resolution on the pH*, the ratio between the copper and the L-valinol ligand and the concentration of added selector complex in the run buffer were investigated revealing a marked difference between the activity of the copper-valinol and the previously studied copper-valine selector. The optimal separation conditions were achieved using a 2:1 valinol/copper ratio, in accordance with the 2:1 structure of the complex, which was proven by single crystal and powder X-ray diffractions and by elemental analysis. Unlike the copper-valine selectors that could be used only under acidic conditions (pH* 3.5), the copper-valinol selectors could be used under near-neutral conditions and even at pH* 9.1. A comparison between SDS-micellar electrokinetic chromatography and LMOG-CE under otherwise identical conditions revealed a significant superior separation on the LMOG-filled capillaries. 相似文献
29.
We continue the works of Gurevich-Shelah and Lifsches-Shelah by showing that it is consistent with ZFC that the first-order
theory of random graphs is not interpretable in the monadic theory of all chains. It is provable from ZFC that the theory
of random graphs is not interpretable in the monadic second order theory of short chains (hence, in the monadic theory of
the real line).
Received: 18 July 1996 相似文献
30.
Fluorescence experiments on (1-butyl-4-(1H-inden-1-ylidene)-1,4-dihydropyridine (BIDP) are reported in liquid and glassy solutions. The data indicate a fast decay in the fluid nonpolar, nonprotic solutions (decay times approximately 10(-12) s) and rapid but considerably slower decay in polar ones. In frozen solutions (polar and nonpolar), the fluorescence quantum yield is much higher (near 0.5 and around 0.1 in polar and nonpolar glasses, respectively). The rapid nonradiative transitions in fluid solutions are assigned to internal conversion in both solvent classes, as intersystem crossing is much slower and no net reaction is observed. These results are in agreement with predictions made for the closely related (in terms of electronic structure) but simpler molecule cyclopentadienyl-1,4-dihydropyridine (CPDHP) for which an S1/S0 conical intersection was recently proposed [Int. J. Quant. Chem. 2005, 102, 961]. The crossing of the two lowest singlet states is calculated to vanish in polar solvents such as methyl cyanide, leading to longer lifetime of S1 of CPDHP. As BIDP has a very similar electronic structure, the model predicts a corresponding change in this larger molecule. The strong fluorescence observed in the glassy environments is rationalized by the hindering of the internal torsion required to reach the geometry of the conical intersection. 相似文献