全文获取类型
收费全文 | 301篇 |
免费 | 10篇 |
国内免费 | 4篇 |
专业分类
化学 | 204篇 |
晶体学 | 3篇 |
力学 | 18篇 |
数学 | 46篇 |
物理学 | 44篇 |
出版年
2022年 | 3篇 |
2021年 | 14篇 |
2020年 | 3篇 |
2019年 | 12篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 24篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 21篇 |
2009年 | 16篇 |
2008年 | 21篇 |
2007年 | 23篇 |
2006年 | 19篇 |
2005年 | 15篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 1篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有315条查询结果,搜索用时 15 毫秒
21.
We continue our investigation of massive gravity in the massless limit of vanishing graviton mass. From gauge invariance we
derive the most general coupling between scalar matter and gravity. We get further couplings beside the standard coupling
to the energy–momentum tensor. On the classical level this leads to a further modification of general relativity. 相似文献
22.
A complete local ring of embedding codepth 3 has a minimal free resolution of length 3 over a regular local ring. Such resolutions carry a differential graded algebra structure, based on which one can classify local rings of embedding codepth 3. We give examples of algebra structures that have been conjectured not to occur. 相似文献
23.
24.
Anna Polishchuk Tatyna Emelina Emilya Karaseva Oana Cramariuc Vladimir Chukharev Vladimir Karasev 《Photochemistry and photobiology》2014,90(1):79-84
The effect of intermolecular proton transfer on the spectral properties of levofloxacin in the ground and excited electronic states was studied. The preferred direction of possible protolytic reactions induced by UV irradiation in this compound was studied. It was found that the proton transfer processes have a considerable effect on the capability of the compound to emit light and occur on the nanosecond timescale. The photochemical reactions of the tree forms of levofloxacin (pH: 4.0, 7.0, 10.0) were studied by laser flash photolysis and product studies. Irradiation at pH 4 yielded a pulse and transient (λmax = 395, 515, 575 nm) assigned to the protonated triplet. Irradiation at pH 7 yielded a transient species (λmax = 525, 610 nm) assigned to the neutral form. Protonation of the anionic singlet excited state was also observed (λmax = 440, 570, 680 nm). 相似文献
25.
This paper deals with a scalar conservation law in 1-D space
dimension, and in particular, the focus is on the stability analysis
for such an equation. The problem of feedback stabilization under
proportional-integral-derivative (PID for short) boundary control is
addressed. In the proportional-integral (PI for short) controller
case, by spectral analysis, the authors provide a complete
characterization of the set of stabilizing feedback parameters, and
determine the corresponding time delay stability interval. Moreover,
the stability of the equilibrium is discussed by Lyapunov function
techniques, and by this approach the exponential stability when a
damping term is added to the classical PI controller scheme is
proved. Also, based on Pontryagin results on stability for
quasipolynomials, it is shown that the closed-loop system subject to
PID control is always unstable. 相似文献
26.
Baker ML Piligkos S Bianchi A Carretta S Collison D McDouall JJ McInnes EJ Mutka H Timco GA Tuna F Vadivelu P Weihe H Güdel HU Winpenny RE 《Dalton transactions (Cambridge, England : 2003)》2011,40(34):8533-8539
An investigation into the physical consequences of including a Jahn-Teller distorted Cu(II) ion within an antiferromagnetically coupled ring, [R(2)NH(2)][Cr(7)CuF(8)((O(2)C(t)Bu)(16))] is reported. Inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) spectroscopic data are simulated using a microscopic spin Hamiltonian, and show that the two Cr-Cu exchange interactions must be inequivalent. One Cr-Cu exchange is found to be antiferromagnetic and the other ferromagnetic. The geometry of the Jahn-Teller elongation is deduced from these results, and shows that a Jahn-Teller elongation axis must lie in the plane of the Cr(7)Cu wheel; the elongation is not observed by X-ray crystallography, due to positional disorder of the Cu site within the wheel. An electronic structure calculation confirms the structural distortion of the Cu site. 相似文献
27.
Baker ML Bianchi A Carretta S Collison D Docherty RJ McLnnes EJ McRobbie A Muryn CA Mutka H Piligkos S Rancan M Santini P Timco GA Tregenna-Piggott PL Tuna F Güdel HU Winpenny RE 《Dalton transactions (Cambridge, England : 2003)》2011,40(12):2725-2734
We report a detailed physical analysis on a family of isolated, antiferro-magnetically (AF) coupled, chromium(III) finite chains, of general formula (Cr(RCO(2))(2)F)(n) where the chain length n = 6 or 7. Additionally, the chains are capped with a selection of possible terminating ligands, including hfac (= l,l,l,5,5,5-hexafluoropentane-2,4-dionate(l-)), acac (= pentane-2,4-dionate(l-)) or (F)(3). Measurements by inelastic neutron scattering (INS), magnetometery and electron paramagnetic resonance (EPR) spectroscopy have been used to study how the electronic properties are affected by n and capping ligand type. These comparisons allowed the subtle electronic effects the choice of capping ligand makes for odd member spin 3/2 ground state and even membered spin 0 ground state chains to be investigated. For this investigation full characterisation of physical properties have been performed with spin Hamiltonian parameterisation, including the determination of Heisenberg exchange coupling constants and single ion axial and rhombic anisotropy. We reveal how the quantum spin energy levels of odd or even membered chains can be modified by the type of capping ligand terminating the chain. Choice of capping ligands enables Cr-Cr exchange coupling to be adjusted by 0, 4 or 24%, relative to Cr-Cr exchange coupling within the body of the chain, by the substitution of hfac, acac or (F)(3) capping ligands to the ends of the chain, respectively. The manipulation of quantum spin levels via ligands which play no role in super-exchange, is of general interest to the practise of spin Hamilton modelling, where such second order effects are generally not considered of relevance to magnetic properties. 相似文献
28.
Stefan T. Ochsenbein Dr. Floriana Tuna Dr. Marzio Rancan Rachel S. G. Davies Christopher A. Muryn Dr. Oliver Waldmann Dr. Roland Bircher Dr. Andreas Sieber Dr. Graham Carver Dr. Hannu Mutka Dr. Felix Fernandez‐Alonso Dr. Andrew Podlesnyak Dr. Larry P. Engelhardt Dr. Grigore A. Timco Dr. Hans U. Güdel Prof. Dr. Richard E. P. Winpenny Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(17):5087-5087
29.
Timco GA Batsanov AS Larsen FK Muryn CA Overgaard J Teat SJ Winpenny RE 《Chemical communications (Cambridge, England)》2005,(29):3649-3651
Heterometallic wheels can be templated about tertiary amines and imidazoles, leading to new octa-, nona- and deca-nuclear rings. 相似文献
30.