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981.
The microstructural properties of gelatin samples derived from the bovine bone as well as skin of fish which inhabit in the cold sea were examined at molecular scale by using the positron annihilation lifetime spectroscopy(PALS). The longest-lived component of PALS provides information about the free-volume holes in gelatin macromolecules. The results show that both average size and number of free-volume holes in the fish gelatin macromolecules are lower than those in the bovine gelatin macromolecules. Silver halide emulsions were also precipitated by using the balanced double-jet technique,for which two types of media containing fish gelatin and bone gelatin were used in the stage of nucleus formation,respectively. The monodispersibility of silver halide crystallites can be improved and the growth and coalescence of nucleus grains can be restricted when the fish gelatino-peptizer was used as dispersion medium at the nucleus formation. It thus suggested that the function of gelatino-peptizers as protective colloid is correlated with the microstructure character of gelatin macromolecules established by PALS. The gelatino-peptizer derived from the fish skin possesses stronger power governing nucleation and growth of silver halide grains compared with that made from the bovine bone. 相似文献
982.
Akira Kaito Nobutaka Tanigaki Momoyo Wada Mikiko Yoshida 《Journal of Polymer Science.Polymer Physics》2000,38(5):698-706
Tractable polysilanes were prepared by the copolymerization of a methyl‐n‐propylsilylene (MP) unit into poly(dimethylsilylene), which neither dissolves in common solvents nor melts before decomposition. Although poly(dimethylsilylene‐co‐methyl‐n‐propylsilylene) has poor solubility in the composition range of the dimethylsilylene (DM) unit to the MP unit (DM/MP = 7/3 ∼ 9/1), the copolymers form the columnar mesophase at elevated temperatures. Highly oriented rods were prepared via the extrusion of the copolymers with a circular tube die in a temperature range in which the transition to the columnar mesophase began to occur (70°C when DM/MP = 7/3 and 8/2 and 120°C when DM/MP = 9/1). The extruded rods were characterized in detail by dynamic viscoelasticity and wide‐angle X‐ray diffraction (WAXD) to clarify the structure–mechanical‐property relationship. The orientation functions of the extruded rods were determined by the azimuthal intensity distribution of the WAXD reflection. The orientation function and dynamic storage modulus increased with an increasing extrusion ratio. The dynamic storage modulus at −150°C was 8 ∼ 10 GPa at the highest extrusion ratio and correlated well with the crystal orientation function. The dynamic storage modulus at room temperature was lowered by the structural relaxations at −100 ∼ +30°C, which corresponded to the molecular motion of the rigid molecular chains of the copolymer and the local molecular motion of the MP unit. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 698–706, 2000 相似文献
983.
I-Wei Chen 《Interface Science》2000,8(2-3):147-156
Kinetics of grain boundaries in oxides with the cubic fluorite structure and its derivatives has been investigated using fine grain ceramics that are fully dense. Grain growth measurements in these materials have provided information on grain boundary diffusivity over a diffusion distance of the order of the initial grain size. With the addition of solute cations, grain boundary mobility can be varied over many orders of magnitude, often with very different activation energies. This is caused by the variation of defect population and the defect-solute association. Definitive evidence for solute drag has also been observed in some cases, but solute drag can not be confirmed as a general mechanism in solid solutions. Lastly, while grain boundary at low temperature may continue to serve as a fast diffusion path, it may not be able to migrate because of additional pinning mechanisms such as those exerted by grain boundary nodal points or lines. This means that sintering without grain growth is possible, opening up an avenue for obtaining ultrafine ceramics by pressureless sintering. 相似文献
984.
郑振华 《宁波大学学报(理工版)》1994,(1)
本文由受主缺陷扩散层模型详细计算了扩散极限下晶界附近的准费米能级的空间变化。对n型半导体费米能级的变化几乎全部落在负偏向的晶界附近的较小的范围内。在受主缺陷扩散层中费未能级的变化是线性的。晶界和正偏向晶粒的费未能级只差一个kT数量级的值,受主缺陷扩散层存在并不改变该值和外加电压的关系但系数增大。 相似文献
985.
986.
W. G. Kim B. A. Garetz M. C. Newstein N. P. Balsara 《Journal of Polymer Science.Polymer Physics》2001,39(19):2231-2242
The factors controlling grain growth during the disorder‐to‐order transition in a polystyrene‐block‐polyisoprene copolymer melt were studied with time‐resolved depolarized light scattering. The ordered phase consisted of hexagonally packed polyisoprene cylinders, and the order–disorder‐transition temperature of the block copolymer (TODT) was 132 ± 1 °C. Our objective was to identify the temperature at which the grain growth rate was maximized (Tmax) and compare it with theoretical predictions. We conducted seeded grain growth experiments, which comprised two steps. In the first step, which lasted for 43 min, the sample was cooled from the disordered state to 124 °C. This resulted in the formation of a small number of ordered grains or seeds. This was followed by a second step in which the sample was heated to temperatures between 124 and 132 °C and the seeds grew with time. Our objective was to study grain growth at different temperatures starting from the same initial condition. The value of Tmax obtained experimentally was 128 °C. The theoretically predicted value of Tmax, based entirely on the rheological properties of the disordered sample and TODT, was also 128 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2231–2242, 2001 相似文献
987.
Perturbed γγ-angular correlation spectroscopy (PAC) was used to investigate nanocrystalline Ni and NiCu alloys, which are
prepared by pulsed electrodeposition (PED). Using diffusion for doping nanocrystalline Ni with 111In four different ordered grain boundary structures are observed, which are characterized by unique electric field gradients.
The incorporation of 111In on substitutional bulk sites of Ni is caused by moving grain boundaries below 1000 K and by volume diffusion above 1000
K. The nanocrystalline NiCu alloys prepared by PED are microscopically inhomogeneous as observed by PAC. In contrast, this
inhomogeneity cannot be detected by X-ray diffraction. The influence of the temperature of the electrolyte, the current density
during deposition, and the optional addition of saccharin to the electrolyte on the homogeneity of nanocrystalline NiCu alloys
was investigated.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
988.
Arkady Vilenkin 《Interface Science》2001,9(3-4):323-329
An equation of grain boundary motion in a binary polycrystal is derived. The derivation is based on minimization of free energy of the total systems. The equation takes into account an impurity segregation at the grain boundary, grain boundary curvature and energy.As an example, we apply this equation to the analysis of the impurity drag effect problem. It is shown, that the sign of the impurity effect on grain boundary velocity (delay or acceleration) does not depend on kinetic coefficients. The sign of the effect is determined by a thermodynamic function which combines the grain boundary segregation coefficient, the derivative of grain boundary energy with respect to absorbed impurity concentration, and the derivative of bulk free energy with respect to bulk impurity concentration. 相似文献
989.
The compensation effect or Meyer-Neldel rule has been observed in a wide range of phenomena. It seems to be a fundamental property of the many families of activated processes following an Arrhenius dependence on temperature. The kinetic properties of grain boundaries and triple junctions depend strongly on their crystallographic parameters and obey the Arrhenius law. The data on the Meyer-Neldel rule for grain boundaries and triple junctions in Al and Zn and the values of the compensation temperature for the migration of grain boundaries and triple junctions are presented in this paper. 相似文献
990.
Research on factors influencing on the microwave permeability of nanocrystalline FeB alloys
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Nanocrystalline FeB alloys have been prepared with optimized grain
size and internal stress. Samples prepared under different annealing
conditions are analysed by x-ray diffraction, and the permeability
$\mu(\omega)$ is measured by HP8510B Vector Network Analyser in the
frequency range 2--18GHz. The results show that annealing leads to
the growth of the grain size and reduces the internal stress, and
smaller grain size and larger internal stress favours the magnetic
dissipation. 相似文献