全文获取类型
收费全文 | 1031篇 |
免费 | 46篇 |
国内免费 | 3篇 |
专业分类
化学 | 739篇 |
晶体学 | 6篇 |
力学 | 33篇 |
数学 | 174篇 |
物理学 | 128篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 16篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 30篇 |
2015年 | 22篇 |
2014年 | 35篇 |
2013年 | 48篇 |
2012年 | 87篇 |
2011年 | 116篇 |
2010年 | 74篇 |
2009年 | 51篇 |
2008年 | 82篇 |
2007年 | 55篇 |
2006年 | 68篇 |
2005年 | 50篇 |
2004年 | 51篇 |
2003年 | 48篇 |
2002年 | 41篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 14篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1080条查询结果,搜索用时 46 毫秒
201.
Sylvain Fouliard Sonia Benhamida Natacha Lenuzza Franoise Xavier 《Mathematical and Computer Modelling》2009,49(11-12):2104-2108
Regenerative medicine and cell therapy provide great hopes for the use of adult and stem cells. The latter are far less present in tissue than the former and must be expanded using cell culture. Stem cells culture requires the conservation of their proliferation and self-renewal capabilities. Still, the complex interaction between cell populations, for example in primary cell cultures, are not well-known and may account for part of the variability of such cultures. In order to represent and understand the evolution of cultured stem cells, we present here a mathematical model of cell proliferation and differentiation. Based on the formalism of cellular automata, this model simulates the evolution of several cell classes (which may represent either different levels of differentiation or different cell types) in an environment modeling the growth medium. We model the cell cycle as on the one hand a quiescence phase during which a cell rests, and on the other hand a division phase during which the cell starts the division process. In order to represent cell–cell interaction, the transition probability between those phases depends on the local composition of the growth medium depending itself on neighboring cells. An interaction between cellular populations is represented by a quantitative parameter which has a direct impact on cellular proliferation. Differentiation results in a change of the cell class and depends on the biological model studied : it may result from an asymmetric division or be a consequence of the local composition of the growth medium. This mathematical model aims at a better understanding of the interactions between cell populations in a culture. By defining constraints on the potential or the type of the cells at the end of a culture, it will then be possible to find optimal experimental conditions for cell production. 相似文献
202.
203.
Berchadsky Y Bernard-Henriet C Finet JP Lauricella R Marque SR Tordo P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(27):7084-7094
Persistent noncyclic phosphoranyl radicals have been prepared and observed by electron paramagnetic resonance (EPR) for the first time. They were obtained by UV-photolysis of a solution containing a bis(trialkylsilyl) peroxide (R = Me, Et) and a tris(trialkylsilyl) phosphite (R = Me, Et, iPr). EPR parameters (a(P) approximately 100 mT) are typical of phosphoranyl radicals exhibiting a trigonal-bipyramidal structure, with the odd electron in an equatorial site. Analysis of the pseudo-first-order decay shows that these phosphoranyl radicals decay by S(H)2 homolytic substitution on the bis(trialkylsilyl) peroxide and by loss of a trialkylsilyloxyl radical (alpha-scission reaction). Both the S(H)2 and alpha-scission reactions depend on the steric bulk of the alkyl groups, that is, the bulkier the alkyl group, the slower the S(H)2 and alpha-scission reactions. 相似文献
204.
Multifrequency EPR and redox reactivity investigations of a bis(mu-thiolato)-dicopper(II,II) complex
Rammal W Belle C Béguin C Duboc C Philouze C Pierre JL Le Pape L Bertaina S Saint-Aman E Torelli S 《Inorganic chemistry》2006,45(25):10355-10362
From a new tripodal ligand [N2SS'H] with mixed N, S(thioether), and S(thiolate) donor set, the corresponding bis(mu-thiolato)dicopper(II) complex has been prepared and characterized. X-ray crystallographic analysis of the complex [Cu2(N2SS')2](ClO4)2.C4H10O (1) demonstrates that the two five-coordinated Cu atoms are bridged by two thiolates leading to a nearly planar Cu2S2 core with a Cu1...Cu1* distance of 3.418(8) A and a large bridging angle Cu1S1Cu1* of 94.92 degrees. X-band (10 GHz), Q-band (34 GHz), and F-Band (115 GHz) EPR spectra of 1 are consistent with a weakly coupled dicopper(II,II) center attributed to an S = 1 state. Simulations for the three frequencies are obtained with a unique set of electronic parameters. The mean values of the spin Hamiltonian parameters for 1 are D = 0.210(3) cm(-1), E = 0.0295(5) cm(-1), |E/D| = 0.140, gx = 2.030(2), gy = 2.032(2), gz = 2.128(2). The electrochemical one-electron reduction of 1 generates the mixed-valent CuIICuI species. EPR and UV-vis spectra are consistent with a type I localized mixed-valent species, while dinuclear CuA centers of native cytochrome c oxidase (CcO)1-3 or nitrous oxide reductase (N2OR)4 have a delocalized CuIICuI mixed-valent state. After reoxidation of the CuIICuI species, the initial complex 1 is regenerated through a reversible interconversion process. 相似文献
205.
Maribel Arroyo Sylvain Bernès Norma Calixto Carina Gómez 《Journal of fluorine chemistry》2006,127(1):22-28
A series of three new trithioether compounds containing fluorinated phenyl moieties, 1,3,5-(CH2SRf)3-2,4,6-(CH3)3C6, Rf = C6F5 (1), 4-HC6F4 (2), or 2-FC6H4 (3), were prepared by treatment of 1,3,5-(CH2Br)3-2,4,6-(CH3)3C6 with the corresponding Pb(SC6F5)2 or NaSRf. The new structures were verified by elemental analyses, IR, 1H NMR, 19F NMR spectroscopies, and mass spectra. The single crystal X-ray diffraction studies of 1-3 show a similar cis,trans,trans-conformation for the three fluorophenylthiomethyl groups attached to the central benzene ring with all dihedral angles between planes of central ring and external rings close to 0°, giving flat molecules. Comparing, 1-3 with closely related tripodal molecules built-up on 2,4,6-trimethylbenzene, arrangement of one SR group respect to others seems to be defined by the nature of the R substituent. Then in the case of 1-3, a parallel arrangement of rings is favored over an orthogonal one, which would bring the ortho-F atoms close to H atoms of the methylene groups. 相似文献
206.
A 2D, square lattice, vectorial photonic crystal is formed by vectorial holography using an azo-dye-doped liquid-crystal material. Four coherent beams are interfered to generate a highly stable, switchable polarization holography structure. The formation of the vectorial lattice by the liquid-crystal molecular orientation is confirmed by diffraction pattern and polarization microscopy analysis. Simulations of the alignment and diffraction pattern are in good agreement with the experimental results. Polarization sensitive diffraction behavior is also consistent with the Kakichashvili model. 相似文献
207.
We establish a limiting absorption principle for some long range perturbations of the Dirac systems at threshold energies.
We cover multi-center interactions with small coupling constants. The analysis is reduced to studying a family of non-self-adjoint
operators. The technique is based on a positive commutator theory for non-self-adjoint operators, which we develop in the
Appendix. We also discuss some applications to the dispersive Helmholtz model in the quantum regime. 相似文献
208.
Sylvain?Ervedoza Olivier?Glass Sergio?GuerreroEmail author Jean-Pierre?Puel 《Archive for Rational Mechanics and Analysis》2012,206(1):189-238
In this paper we deal with the isentropic (compressible) Navier-Stokes equation in one space dimension and we adress the problem of the boundary controllability for this system. We prove that we can drive initial conditions which are sufficiently close to some constant states to those constant states. This is done under some natural hypotheses on the time of control and on the regularity on the initial conditions. 相似文献
209.
Marie Labat Jean-Blaise Brubach Alessandra Ciavardini Marie-Emmanuelle Couprie Erik Elkaim Pierre Fertey Tom Ferte Philippe Hollander Nicolas Hubert Emmanuelle Jal Claire Laulhé Jan Luning Olivier Marcouillé Thierry Moreno Paul Morin Francois Polack Pascale Prigent Sylvain Ravy Jean-Paul Ricaud Pascale Roy Mathieu Silly Fausto Sirotti Amina Taleb Marie-Agnès Tordeux Amor Nadji 《Journal of synchrotron radiation》2018,25(2):385-398
The investigation of ultrafast dynamics, taking place on the few to sub‐picosecond time scale, is today a very active research area pursued in a variety of scientific domains. With the recent advent of X‐ray free‐electron lasers (XFELs), providing very intense X‐ray pulses of duration as short as a few femtoseconds, this research field has gained further momentum. As a consequence, the demand for access strongly exceeds the capacity of the very few XFEL facilities existing worldwide. This situation motivates the development of alternative sub‐picosecond pulsed X‐ray sources among which femtoslicing facilities at synchrotron radiation storage rings are standing out due to their tunability over an extended photon energy range and their high stability. Following the success of the femtoslicing installations at ALS, BESSY‐II, SLS and UVSOR, SOLEIL decided to implement a femtoslicing facility. Several challenges were faced, including operation at the highest electron beam energy ever, and achievement of slice separation exclusively with the natural dispersion function of the storage ring. SOLEIL's setup also enables, for the first time, delivering sub‐picosecond pulses simultaneously to several beamlines. This last feature enlarges the experimental capabilities of the facility, which covers the soft and hard X‐ray photon energy range. In this paper, the commissioning of this original femtoslicing facility is reported. Furthermore, it is shown that the slicing‐induced THz signal can be used to derive a quantitative estimate for the degree of energy exchange between the femtosecond infrared laser pulse and the circulating electron bunch. 相似文献
210.
Gérard Audran Matisse Bim Batsiandzy Ibanou Paul Brémond Sylvain R. A. Marque Germain Obame Valérie Roubaud Didier Siri 《Journal of Physical Organic Chemistry》2014,27(5):387-391
In a recent work (Org. Lett. 2012, 14, 358–361), we showed that the activation by benzylation of alkoxyamine 1 (diethyl (1‐(tert‐butyl(1‐(pyridin‐4‐yl)ethoxy)amino)‐2,2‐dimethylpropyl)phosphonate) afforded a surprisingly large C–ON bond homolysis rate constant kd. Taking advantage of the easy preparation of para‐X‐benzyl‐activated alkoxyamines 2 and of the presence of a shielding methylene group between the two aromatic moieties, we investigated the long range (10 bonds between the X group and the C–ON bond) polar effect for X = H, F, OMe, CN, NO2, NMe2, +NHMe2,Br?. It was observed that the effect was weak (4‐fold) and mainly due to the zwiterionic mesomeric forms generated by the presence of group X on the para position, i.e. kd increased for CN and NO2 and decreased for OMe, NMe2 and +NMe2H,Br?. DFT calculations at the B3LYP/6‐31G(d,p) level were performed to determine orbital interactions (natural bond orbital (NBO) analysis), Mulliken and NBO charges which support the reactivity described. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献