全文获取类型
收费全文 | 852篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
化学 | 510篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 146篇 |
物理学 | 218篇 |
出版年
2023年 | 12篇 |
2022年 | 14篇 |
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 28篇 |
2018年 | 20篇 |
2017年 | 11篇 |
2016年 | 29篇 |
2015年 | 26篇 |
2014年 | 24篇 |
2013年 | 26篇 |
2012年 | 55篇 |
2011年 | 46篇 |
2010年 | 43篇 |
2009年 | 34篇 |
2008年 | 27篇 |
2007年 | 32篇 |
2006年 | 32篇 |
2005年 | 26篇 |
2004年 | 21篇 |
2003年 | 21篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 18篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1988年 | 8篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1971年 | 5篇 |
1928年 | 6篇 |
排序方式: 共有884条查询结果,搜索用时 15 毫秒
31.
32.
Jakob Heller Tobias F. Pascher Dr. Christian van der Linde Dr. Milan Ončák Prof. Dr. Martin K. Beyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(66):16367-16376
Hydrated aluminium cations have been investigated as a photochemical model system with up to ten water molecules by UV action spectroscopy in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Intense photodissociation was observed starting at 4.5 eV for two to eight water molecules with loss of atomic hydrogen, molecular hydrogen and water molecules. Quantum chemical calculations for n=2 reveal that solvation shifts the intense 3s–3p excitations of Al+ into the investigated photon energy range below 5.5 eV. During the photochemical relaxation, internal conversion from S1 to T2 takes place, and photochemical hydrogen formation starts on the T2 surface, which passes through a conical intersection, changing to T1. On this triplet surface, the electron that was excited to the Al 3p orbital is transferred to a coordinated water molecule, which dissociates into a hydroxide ion and a hydrogen atom. If the system remains in the triplet state, this hydrogen radical is lost directly. If the system returns to singlet multiplicity, the reaction may be reversed, with recombination with the hydroxide moiety and electron transfer back to aluminium, resulting in water evaporation. Alternatively, the hydrogen radical can attack the intact water molecule, forming molecular hydrogen and aluminium dihydroxide. Photodissociation is observed for up to n=8. Clusters with n=9 or 10 occur exclusively as HAlOH+(H2O)n-1 and are transparent in the investigated energy range. For n=4–8, a mixture of Al+(H2O)n and HAlOH+(H2O)n-1 is present in the experiment. 相似文献
33.
Gerhard Bieri Edgar Heilbronner Else Kloster-Jensen Andreas Schmelzer Jakob Wirz 《Helvetica chimica acta》1974,57(5):1265-1283
The photoelectron spectra of 1,5-cyclooctadiyne ( 2 ) and of 1,6-dithiacyclodeca-3,8-diyne ( 3 ) have been recorded. The first four ( 2 ) or six ( 3 ) PE. bands have been assigned as follows; in increasing order of ionization potentials: The relative sequence and the positions of the PE. bands are explained in terms of through-bond and through-space interactions between the basis π-orbitals and σ-orbitals of appropriate symmetry behaviour. An analysis of the PE. spectroscopic data for cyclooctyne ( 1 ) and for ( 2 ) indicates that a cis-bend of the acetylene moiety by θ < 20° leads to a split in energy of the in-plane and out-of-plane basis π-orbitals which is smaller than ∽ 0.2 eV. This is in agreement with the predictions derived from semiempirical models (MINDO/2, SPINDO) and qualitative orbital arguments. However, it is shown by using orbital localization procedures, that the rationales underlying the two semiempirical models differ significantly. 相似文献
34.
Robert Fugmann Herbert Nickelsen Ingeborg Nickelsen Jakob H. Winter 《Angewandte Chemie (International ed. in English)》1970,9(8):589-595
In mechanized systems used for searching in literature stores there is a steadily growing necessity not only to be able to formulate concepts as a search condition but also the characteristic connections under which these concepts appear in the inquiry. In this way the precision of the mechanized literature search is considerably increased. TOSAR has been developed in order to improve computerized literature searching in this respect. 相似文献
35.
Given a precompact subset of a type Banach space , where , we prove that for every and all
holds, where is the absolutely convex hull of and denotes the dyadic entropy number. With this inequality we show in particular that for given and with for all the inequality holds true for all . We also prove that this estimate is asymptotically optimal whenever has no better type than . For this answers a question raised by Carl, Kyrezi, and Pajor which has been solved up to now only for the Hilbert space case by F. Gao.
holds, where is the absolutely convex hull of and denotes the dyadic entropy number. With this inequality we show in particular that for given and with for all the inequality holds true for all . We also prove that this estimate is asymptotically optimal whenever has no better type than . For this answers a question raised by Carl, Kyrezi, and Pajor which has been solved up to now only for the Hilbert space case by F. Gao.
36.
Jakob J. Keller 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1996,47(6):821-836
Introducing a vector potential, that is based on a pair of stream functions, and a velocity potential, antisymmetric equations for the stream functions are derived with the help of a variational principle. It is found that the equations are in a suitable form to investigate flows with helical symmetry, and, for example, to connect upstream axisymmetric flows with downstream helical flows. The special case of a transition from an upstream solid-body vortex to a downstream helical flow is investigated in detail. Furthermore, the stream-function equations are particularly useful to investigate general small-amplitude inertia waves on vortex flows. Time-dependent helical flows that are time-independent in a suitably rotating frame of reference can also be discussed with the proposed method. 相似文献
37.
We derive constraints on the asymptotic behaviour of total cross sections which follow from dispersion relations and measured real parts of the forward scattering amplitudes. For πN and pp scattering, these constraints are calculated using recent results from FNAL and Serpukhov. The relation to other methods is discussed. 相似文献
38.
Jakob Yngvason 《Communications in Mathematical Physics》1973,34(4):315-333
It is shown that every continuous linear functional on the field algebra can be defined by a vector in the Hilbert space of some representation of the algebra. The functionals which can be written as a difference of positive ones are characterized. By an example it is shown that a positive functional on a subalgebra does not always have an extension to a positive functional on the whole algebra. 相似文献
39.
40.
M. Diehl Th Feldmann R. Jakob P. Kroll 《The European Physical Journal C - Particles and Fields》2005,39(1):1-39
We present a simple empirical parameterization of the x- and t-dependence of generalized parton distributions at zero skewness, using forward parton distributions as input. A fit to experimental data for the Dirac, Pauli and axial form factors of the nucleon allows us to discuss quantitatively the interplay between longitudinal and transverse partonic degrees of freedom in the nucleon (nucleon tomography). In particular we obtain the transverse distribution of valence quarks at given momentum fraction x. We calculate various moments of the distributions, including the form factors that appear in the handbag approximation to wide-angle Compton scattering. This allows us to estimate the minimal momentum transfer required for reliable predictions in that approach to be around
. We also evaluate the valence contributions to the energy-momentum form factors entering Jis sum rule.Received: 16 September 2004, Revised: 15 October 2004, Published online: 17 December 2004 相似文献