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11.
M. Dubiel S. Brunsch W. Seifert H. Hofmeister G.L. Tan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):229-232
Ag particles of 3.9 and 5.1 nm mean size in silicate glasses were produced by ion exchange and subsequent annealing at 480
and 600 °C. These thermal treatments may induce stresses in matrix and particles in addition to the well known effect of surface atoms
because of the thermal expansion mismatch of both materials. Structural characterisation of the particles by high-resolution
electron microscopy revealed a size-dependent lattice dilatation quite opposite to the so far observed lattice contraction
of similar metal/glass composites. This result, confirmed by X-ray absorption spectroscopy at the Ag K-edge, is discussed
in terms of an Ag-Ag bond length increase near the particle surface. The temperature-dependent EXAFS spectra (10-300 K) indicate
an increased thermal expansion coefficient of the particles with an increased mean particle size calculated on the basis of
an anharmonic Einstein model. With that the bond length increase can be explained. The results can be interpreted by a combination
of both the particle size effects and the influence of the surrounding matrix.
Received 30 November 2000 相似文献
12.
S. Pleutin A. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):521-531
The static polarizability of cylindrical systems is shown to have a strong dependence on a uniform magnetic field applied
parallel to the tube axis. This dependence is demonstrated by performing exact numerical diagonalizations of simple cylinders
(rolled square lattices), armchair and zig-zag carbon nanotubes (rolled honeycomb lattices) for different electron-fillings.
At low temperature, the polarizability as function of the magnetic field has a discontinuous character where plateau-like
region are separated by sudden jumps or peaks. A one to one correspondence is pointed out between each discontinuity of the
polarizability and the magnetic-field induced cross-over between the ground state and the first excited state. Our results
suggest the possibility to use measurements of the static polarizability under magnetic field to get important informations
about excited states of cylindrical systems such as carbon nanotubes.
Received 29 March 2001 and Received in final form 8 August 2001 相似文献
13.
D. Serero G. Reydellet P. Claudin É. Clément D. Levine 《The European physical journal. E, Soft matter》2001,6(2):169-179
We measured the vertical pressure response function of a layer of sand submitted to a localized normal force at its surface.
We found that this response profile depends on the way the layer has been prepared: all profiles show a single centered peak
whose width scales with the thickness of the layer, but a dense packing gives a wider peak than a loose one. We calculate
the prediction of isotropic elastic theory in the presence of a bottom boundary and compare it to the data. We found that
the theory gives the right scaling and the correct qualitative shape, but fails to really fit the data.
Received 3 August 2001 相似文献
14.
S.G. Mishra P.A. Sreeram 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):287-291
Specific heat versus temperature curves for various pressures, or magnetic fields (or some other external control parameter) have been seen to
cross at a point or in a very small range of temperatures in many correlated fermion systems. We show that this behavior is
related to the possibility of existence of a quantum critical point. Vicinity to a quantum critical point in these systems
leads to a crossover from quantum to classical fluctuation regime at some temperature . The temperature at which the curves cross turns out to be near this crossover temperature. We have discussed the case of
the normal phase of liquid Helium three and the heavy fermion systems CeAl3 and UBe13 in detail within the spin fluctuation theory, a theory which inherently contains a low energy scale which can be identified
with . When the crossover scale is a homogeneous function of these control parameters there is always crossing at a point. We also
mention other theories exhibiting a low energy scale near a quantum critical point and discuss this phenomenon in those theories.
Received 25 June 1999 相似文献
15.
A general theory of critical sound propagation, including phonon-spin-energy coupling, is studied in anisotropic magnets above
their transition temperature. The Kawasaki weak singularity in the ultrasonic attenuation is found as a nonasymptotic effect.
A new nonasymptotic regime similar to the one in the binary mixture is also determined. The role of coupling constants and
the bare relaxation times in establishing the dominance region of particular terms, is discussed.
Received: 9 December 1997 / Accepted: 24 February 1998 相似文献
16.
A method for independent control of the particle size and distance is presented for rhodium epitaxy on TiO2(110)-(1×2) surface. The real space imaging of the surface morphology was performed by scanning tunneling microscopy. The amount of the deposited rhodium was checked by Auger electron spectrometry. The method consists of two steps: (i) evaporation of 0.001–0.050 ML equivalent of rhodium at room temperature with a post-annealing at 1100 K (“seeding”); (ii) post-deposition of rhodium for growing of the Rh nanoparticles formed in step (i) (“growing”). The mechanism of this procedure is based on the large difference of the surface diffusion coefficient between Rh adatoms and Rh nanocrystallites larger than 1–2 nm. In the first step the average distance between the metal particles is controlled in the range 5–200 nm, the second step determines the particles size (2–50 nm). This work demonstrates that the diffusion processes of metal nanoparticles of different sizes and the growing modes of the crystallites can be studied in detail by application of seeded surfaces. 相似文献
17.
The electrical resistivity of bulk Ge20Te80 has been measured as a function of pressure and temperature. At 5 GPa, an amorphous semiconductor-to-crystalline metal transition
has been observed. The sample recovered from the high pressure cell, after the application of 7 GPa, has a face-centred cubic
structure with a lattice constant of 6·42 A. In crystalline sample, the semiconductor-to-metal transition occurs at 7 GPa.
The thermoelectric power has also been measured for glassy samples in the temperature range 300–240 K. 相似文献
18.
High resolution solid state NMR techniques(such as MAS,CP/MAS andCRAMPS)were employed to study the nature of organic molecules adsorbed onporous solids. A magic angle spinning system was achieved for sealed samples with a spinning speed from 2KHz to 4.2KHz.Using this technique,high resolution ~1HMAS spectra of organic molecules and H_2S adsorbed on charcoal were obtained.EXperimental results suggest that for high coverage of adsorbed organic molecules,the spectral lines were resolved very well.But for low coverage,the spectrallines could not be separated completely.As the organic molecules condensed in 相似文献
19.
Murat Durandurdu 《哲学杂志》2020,100(14):1818-1833
ABSTRACT We investigate the pressure-induced structural phase transformation of amorphous silicon hexaboride (a-SiB6) using a constant pressure first principles approach. a-SiB6 is found to undergo a gradual phase transformation to a high-density amorphous phase (HDA) in which the average coordination number of both B and Si atoms is about 6. The HDA phase consists of differently coordinated motifs ranging from 4 to 8. B12 icosahedra are found to persist during compression of a-SiB6 and the structural modifications primarily occur around Si atoms and in the regions linking pentagonal pyramid-like configurations to each other. Upon pressure release, an amorphous structure, similar to the uncompressed one, is recovered, indicating a reversible amorphous-to-amorphous phase change in a-SiB6. When the electronic structure is considered, the HDA phase is perceived to have a wider forbidden band gap than the uncompressed one. 相似文献
20.
This paper studies the force network properties of marginally and deeply jammed packings of frictionless soft particlesfrom the perspective of complex network theory. We generate zero-temperature granular packings at different pressures by minimizing the inter-particle potential energy. The force networks are constructed as nodes representing particles and links representing normal forces between the particles. Deeply jammed solids show remarkably different behavior from marginally jammed solids in their degree distribution, strength distribution, degree correlation, and clustering coefficient. Bimodal and multi-modal distributions emerge when the system enters the deep jamming region. The results also show that small and large particles can show different correlation behavior in this simple system. 相似文献