全文获取类型
收费全文 | 1981篇 |
免费 | 70篇 |
国内免费 | 9篇 |
专业分类
化学 | 1441篇 |
晶体学 | 9篇 |
力学 | 44篇 |
数学 | 232篇 |
物理学 | 334篇 |
出版年
2023年 | 25篇 |
2022年 | 66篇 |
2021年 | 76篇 |
2020年 | 50篇 |
2019年 | 43篇 |
2018年 | 30篇 |
2017年 | 39篇 |
2016年 | 82篇 |
2015年 | 71篇 |
2014年 | 76篇 |
2013年 | 136篇 |
2012年 | 146篇 |
2011年 | 132篇 |
2010年 | 96篇 |
2009年 | 103篇 |
2008年 | 148篇 |
2007年 | 121篇 |
2006年 | 98篇 |
2005年 | 82篇 |
2004年 | 71篇 |
2003年 | 47篇 |
2002年 | 59篇 |
2001年 | 27篇 |
2000年 | 23篇 |
1999年 | 15篇 |
1998年 | 8篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1974年 | 4篇 |
1962年 | 2篇 |
1937年 | 2篇 |
排序方式: 共有2060条查询结果,搜索用时 31 毫秒
931.
932.
933.
Mateus F. Venâncio Clebio S. Nascimento Jr. Cleber P. A. Anconi Juliana Fedoce Lopes Willian R. Rocha Hélio F. Dos Santos Wagner B. De Almeida 《Journal of Polymer Science.Polymer Physics》2011,49(15):1101-1111
The inclusion compound formed between cross‐linked α‐cyclodextrin dimer and substituted oligothiophene, was investigated using density functional theory (DFT). Energy gap, spectroscopy (IR, UV–vis, 13C NMR, and 1H NMR) and first hyperpolarizability data were analyzed for the free species and inclusion compound, pp‐PT@(αCD–αCD). The semiconducting property of the included pp‐PT was not substantially affected on inclusion, with the energy gap increasing by only 10% after interaction with αCD–αCD. On the other hand, the nonlinear optical (NLO) response was significantly decreased, with the first hyperpolarizability, β, predicted to be just more than 60% lower for the [2]rotaxane than for free pp‐PT, but still having considerable magnitude. This was explained by the two‐state model based on the charge‐transfer contribution to the electronic transitions. The sensitivity of electronic spectra might also be useful for the inclusion complex characterization. The IR spectrum was slightly sensitive to the host–guest interaction and the calculated 13C NMR and 1H NMR chemical shifts for the pp‐PT guest showed appreciable variations of 5–10 and 1–1.5 ppm, respectively, and so can be used for the characterization of inclusion compounds. We concluded that the formation of inclusion complexes with CDs, seems indeed very promising and the use of encapsulating conducting material should be experimentally pursued. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
934.
Boundary-transmission problems of first order for the Helmholtz equation are considered within the context of wave diffraction by a periodic strip grating and formulated as convolution type operators acting on a Bessel potential periodic space setting. Two boundary-value problems are studied for an arbitrary geometry of the grating: the oblique derivative and the classic Neumann boundary-value problems. The convolution type operators on the grating which correspond to the given boundary-transmission problems are associated with Toeplitz operators acting on spaces of matrix functions defined on composed contours. A Fredholm theory for periodic boundary-value problems of first order is established independently of the grating period and the Fredholm indices for the oblique derivative and the classic Neumann boundary-value problems are given. 相似文献
935.
C. Lopes Gil A. P. De Lima N. Ayres De Campos P. Sperr G. Kögel W. Triftshäuser 《辐射效应与固体损伤》2013,168(4):111-118
Abstract Deuteron-irradiated and deformed stainless steel specimens were investigated by positron lifetime and Doppler broadening measurements. The evolution of the defect structures was studied as a function of the isochronal annealing temperature and for various degrees of deformation. A different behaviour was observed for deformed and irradiated stainless steel specimens. Evidence for vacancy clusters was found in the deuteron-irradiated steel. These clusters disappear after annealing around 900 K. 相似文献
936.
Piotr Badzia̧g Ingemar Bengtsson Adán Cabello Helena Granström Jan-Åke Larsson 《Foundations of Physics》2011,41(3):414-423
Klyachko and coworkers consider an orthogonality graph in the form of a pentagram, and in this way derive a Kochen-Specker
inequality for spin 1 systems. In some low-dimensional situations Hilbert spaces are naturally organised, by a magical choice
of basis, into SO(N) orbits. Combining these ideas some very elegant results emerge. We give a careful discussion of the pentagram operator,
and then show how the pentagram underlies a number of other quantum “paradoxes”, such as that of Hardy. 相似文献
937.
Paul Doukhan Adam Jakubowski Silvia R.C. Lopes Donatas Surgailis 《Stochastic Processes and their Applications》2019,129(4):1326-1348
We introduce a class of discrete time stationary trawl processes taking real or integer values and written as sums of past values of independent ‘seed’ processes on shrinking intervals (‘trawl heights’). Related trawl processes in continuous time were studied in Barndorff-Nielsen et al. (2011, 2014).In the case when the trawl function decays as a power function of the lag with exponent , the trawl process exhibits long memory and its covariance function is non-summable. We show that under general conditions on generic seed process, the normalized partial sums of such trawl process may tend either to a fractional Brownian motion or to an -stable Lévy process. Moreover if the trawl function admits a faster decay rate, then the classical Donsker’s invariance principle holds true. 相似文献
938.
Annica Tevell Åberg Helena Löfgren Ulf Bondesson Mikael Hedeland 《Rapid communications in mass spectrometry : RCM》2010,24(10):1447-1456
Cunninghamella elegans is a filamentous fungus that has been shown to biotransform drugs into the same metabolites as mammals. In this paper we describe the use of C. elegans to aid the identification of clemastine metabolites since high concentrations of the metabolites were produced and MSn experiments were facilitated. The combination of liquid chromatography and tandem mass spectrometry with two different ionization techniques and hydrogen/deuterium exchange were used for structural elucidation of the clemastine metabolites. Norclemastine, four isomers of hydroxylated clemastine, and two N‐oxide metabolites were described for the first time in C. elegans incubations. The N‐oxidations were confirmed by hydrogen/deuterium exchange and deoxygenation (?16 Da) upon atmospheric pressure chemical ionization mass spectrometry. By MSn fragmentation it was concluded that two of the hydroxylated metabolites were oxidized on the methylpyrridyl moiety, one on the aromatic ring with the chloro substituent, and one on the aromatic ring without the chlorine. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
939.
940.
Juan Límaco Haroldo Rodrigues Clark Cicero Lopes Frota Luis Adauto Medeiros 《Mathematical Methods in the Applied Sciences》2011,34(16):2047-2059
In this paper, we analyze from the mathematical point of view a model for small vertical vibrations of an elastic string with weak internal damping and quadratic term, coupled with mixed boundary conditions of Dirichlet type and acoustic type. Our goal is to extend some of the results of Frota‐Goldstein work in the sense of considering a weaker internal damping and one more quadratic nonlinearity in the elastic string equation. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献