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1.
T. V. Ramakrishnan H. R. Krishnamurthy S. R. Hassan G. Venketeswara Pai 《Journal of Chemical Sciences》2003,115(5-6):767-774
Manganites of the LA1−x
Ca
x
MnO3 family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach
recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degeneratee
g
states at the Mn sites dynamically reorganize themselves into localised, JT polaronsl with exponentially small inter-site hopping, and band-like, nonpolaronic statesb, leading to anew 2-band model for manganites which includes strong Coulomb and Hund’s couplings. We also discuss some results from a dynamical mean-field theory treatment
of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and
CMR, in terms of the influence of physical conditions on the relative energies and occupation of thel andb states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and
spatial correlation is the key to manganite physics.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
2.
Cooperative conformational transitions of proteins and nucleic acids are of decisive importance to many processes of molecular biology, and particularly to their regulation. They proceed via numerous interdependent elementary processes, and their kinetics are therefore often complicated. They are frequently also very fast. However, kinetic analyses can be carried out by chemical relaxation methods. The theoretical interpretation is comparatively simple in the case of linear biopolymers. When the linear Ising model extended for kinetics was applied to model peptides and polynucleotides, it provided an insight into the fundamental principles of cooperative transformations. 相似文献
3.
4.
X-ray diffraction experiments onp-dichlorobenzene at high pressures show a transition at ~ 0.3 GPa, to a new phase, the diffraction pattern of which cannot be indexed on the anticipated low temperature monoclinic crystal structure. We have instead found an orthorhombic cell, very closely related to the low temperature monoclinic cell, for this new phase. This structure, which also occurs inp-diiodobenzene at ambient conditions, has cell constantsa =14.02,b = 6.06,c = 7.41Å andZ = 4. The space group is Pbca. This new phase has a non-β herring-bone structure, in contrast with the initialα phase which has aβ-structure with ribbon-like arrangement of molecules, with Cl-Cl contacts of ~ 4A between adjacent molecules. This implies that with pressure the halogen-halogen interaction in this compound plays a less dominant role in crystal engineering. 相似文献
5.
We have computed the exact partition function of the 3D Ising spin glass on lattices of effective size 3×3×Lz, 4×4×Lz, and 5×5×Lz forL
z
up to 9, and several random bond configurations. Studying the distribution of zeros of the associated partition functions, we find further evidence that these systems have a singularity in the thermodynamic limit. 相似文献
6.
7.
Spectral changes induced by moderate electric fields provide detailed insight into the electronic states of organic and inorganic solids. Although the basic effects, Stark effect and Franz–Keldysh effect, are the same in both types of material, the electroabsorption spectra vary strongly in size and spectral lineshape due to competing interactions. The large variance of the effects is demonstrated by representative examples of high mobility semiconductors, quantum wells, π-conjugated polymers, and charge transfer transitions in single crystals, disordered films and a double-quantum well. It is shown that only high-quality samples reveal the quantum mechanics of field-induced effects which are very sensitive to disorder. 相似文献
8.
Łosik M Kubowicz S Smarsly B Schlaad H 《The European physical journal. E, Soft matter》2004,15(4):407-411
This work compares the solid-state structures of films made from a polystyrene-poly(Z-L-lysine) (1) and a polystyrene-poly(-benzyl-L-glutamate) (2) block copolymer, both having virtually the same numbers of repeating units and block length ratios. Small-angle X-ray scattering (SAXS) revealed a hexagonal-in-undulated lamellar morphology for both films. The long-period and the thickness of layers obtained for 2 were by a factor of three smaller as compared to 1, indicating that PBLGlu helices were folded twice, whereas PZLLys helices were fully stretched. Another difference shows up in the packing of helices, the level of ordering being considerably lower in 2. This might be due to spatial restrictions in the proper alignment of back-folded helical segments. 相似文献
9.
G. Schütz 《Journal of statistical physics》1993,71(3-4):471-505
We present a model for a one-dimensional anisotropic exclusion process describing particles moving deterministically on a ring of lengthL with a single defect, across which they move with probability 0 p 1. This model is equivalent to a two-dimensional, six-vertex model in an extreme anisotropic limit with a defect line interpolating between open and periodic boundary conditions. We solve this model with a Bethe ansatz generalized to this kind of boundary condition. We discuss in detail the steady state and derive exact expressions for the currentj, the density profilen(x), and the two-point density correlation function. In the thermodynamic limitL the phase diagram shows three phases, a low-density phase, a coexistence phase, and a high-density phase related to the low-density phase by a particle-hole symmetry. In the low-density phase the density profile decays exponentially with the distance from the boundary to its bulk value on a length scale . On the phase transition line diverges and the currentj approaches its critical valuej
c = p as a power law,j
c – j –1/2. In the coexistence phase the width of the interface between the high-density region and the low-density region is proportional toL
1/2 if the density
f 1/2 and=0 independent ofL if = 1/2. The (connected) two-point correlation function turns out to be of a scaling form with a space-dependent amplitude n(x1, x2) =A(x2)A
Ke–r/ withr = x
2 –x
1 and a critical exponent = 0. 相似文献
10.
Summary We have applied the Tiwary approach to calculate the opticaloscillator strengths, of both the length and velocity forms, for
the inner-shell excitation1s
2
2s
2
2p
6
3s
2
S
e
→1s
2
2s
2
2p
5
3s
2
2
P
0
transition in Ca X, Sc XI, Ti XII, Cu XIX, Zn XX, Br XXV and Kr XXVI ions of the sodium isoelectronic sequence employing
Hartree-Fock (HF) and configuration interaction (CI) wave functions of both the initial and final states involved in the transition.
Our present calculated results demonstrate that the Tiwary approach is capable of yielding encouraging results.
A part of this work was done while the author was Research Director and Professor, CNRS Laboratory, University of Paris-Sud
and Observatoire de Paris, Meudon, Paris, France. 相似文献