全文获取类型
收费全文 | 77563篇 |
免费 | 558篇 |
国内免费 | 111篇 |
专业分类
化学 | 41188篇 |
晶体学 | 1260篇 |
力学 | 3277篇 |
综合类 | 1篇 |
数学 | 7827篇 |
物理学 | 24679篇 |
出版年
2022年 | 568篇 |
2021年 | 869篇 |
2020年 | 965篇 |
2019年 | 1103篇 |
2018年 | 1596篇 |
2017年 | 1685篇 |
2016年 | 2148篇 |
2015年 | 1022篇 |
2014年 | 1718篇 |
2013年 | 3268篇 |
2012年 | 2896篇 |
2011年 | 3274篇 |
2010年 | 2636篇 |
2009年 | 2634篇 |
2008年 | 2996篇 |
2007年 | 2872篇 |
2006年 | 2767篇 |
2005年 | 2432篇 |
2004年 | 2237篇 |
2003年 | 2071篇 |
2002年 | 2133篇 |
2001年 | 2233篇 |
2000年 | 1623篇 |
1999年 | 1252篇 |
1998年 | 1125篇 |
1997年 | 1036篇 |
1996年 | 891篇 |
1995年 | 831篇 |
1994年 | 811篇 |
1993年 | 811篇 |
1992年 | 864篇 |
1991年 | 933篇 |
1990年 | 877篇 |
1989年 | 905篇 |
1988年 | 816篇 |
1987年 | 767篇 |
1986年 | 739篇 |
1985年 | 864篇 |
1984年 | 961篇 |
1983年 | 818篇 |
1982年 | 834篇 |
1981年 | 746篇 |
1980年 | 701篇 |
1979年 | 768篇 |
1978年 | 890篇 |
1977年 | 913篇 |
1976年 | 808篇 |
1975年 | 774篇 |
1974年 | 790篇 |
1973年 | 760篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
251.
Y. Oner O. Kamer Joseph H. Ross Jr. 《Journal of magnetism and magnetic materials》2006,300(2):373-381
We report resistivity and magnetization measurements on an amorphous Ni74Mn24Pt2 thin film in the temperature range of 3–300 K. Two significant features are apparent in both the magnetic susceptibility and electrical resistivity. A low-temperature (low-T) anomaly is observed at about 40 K, where a cusp appears in the resistivity, while a concomitant step-like increase in zero-field-cooled (ZFC) magnetization (M) appears with increasing temperature. The low-T anomaly is attributed to a crossover from a pure re-entrant spin-glass within individual domains to a mixed ferro-spin-glass regime at lower temperatures. By contrast, the high-temperature (high-T) anomaly, signaled by the appearance of hysteresis below 250 K, corresponds to the freezing of transverse spins in individual domains acting independently. Between the low-T and high-T anomalies a small but discernable magnetic hysteresis is observed for warming vs. cooling in the field-cooled (FC) case. This behavior clearly indicates the presence of domain structure in the sample, while the disappearance of this hysteresis at lower temperatures indicates the complete freezing of the spin orientation of these domains. According to these results, we have divided the magnetic state of this sample into three regions: at temperatures above 250 K, the sample behaves like a soft ferromagnet, exhibiting M vs. H loops with very small hysteresis (less than 5 Oe). As the temperature is lowered into the intermediate region (the range 40–250 K), spins become frozen randomly and progressively within the individual domains. These domains behave independently, rather than as a cooperative behavior of the sample. Weak irreversibility sets in, indicating the onset of transverse spin freezing within the domains. At temperatures below 40 K, the M vs. H loops exhibit larger hysteresis, for both the ZFC and FC cases, as in a pure spin-glass. We have also demonstrated giant noise in the resistivity at temperatures just below 250 K. Such noise can originate from fluctuations of the domains near the film surface because of competing effective bulk and surface anisotropy fields. The large observed amplitude may be explained by means of a large ferromagnetic anisotropy in the resistivity due to the large spin–orbit effect seen in NiMn systems. Finally, the low-T peak in the resistivity has been analyzed using Fisher and Langer's expression based on the Friedel Model proposed for critical transitions in transition metals (s–d systems). The fitted results are in satisfactory agreement with the predictions of this model. 相似文献
252.
In this paper we prove existence results for semilinear neutral functional differential inclusions with finite or infinite
delay in Banach spaces. Our theory makes use of analytic semigroups and fractional powers of closed operators, integrated
semigroups and cosine families.
相似文献
253.
E. Chikoidze Y. Dumont H.J. von Bardeleben J. Gleize F. Jomard E. Rzepka G. Berrerar D. Ferrand O. Gorochov 《Applied Physics A: Materials Science & Processing》2007,88(1):167-171
ZnO:Mn thin films are grown by the metal organic chemical vapor deposition technique. Mn (x) varies in the 0<x<0.44 range.
Vegard’s law has been verified for the lattice parameters. Electron paramagnetic resonance (EPR) measurements prove the substitutional
incorporation of Mn2+ on zinc sites. The behavior of the EPR line width regarding temperature is discussed. All ZnO:Mn layers show antiferromagnetic
interaction and a J1/kB=-15 K effective exchange constant. The optical band gap of ZnO:Mn increases with the manganese concentration. Raman spectroscopy
reveals a Mn-related scattering band.
PACS 71.55.Gs; 75.50.Pp; 61.10.Nz; 76.30.Fc; 75.30.Et; 78.40.-q 相似文献
254.
J.O. Andersen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):389-396
We consider an interacting homogeneous Bose gas at zero temperature in two spatial dimensions. The properties of the system
can be calculated as an expansion in powers of g, where g is the coupling constant. We calculate the ground state pressure and the ground state energy density to second order in the
quantum loop expansion. The renormalization group is used to sum up leading and subleading logarithms from all orders in perturbation
theory. In the dilute limit, the renormalization group improved pressure and energy density are expansions in powers of the
T
2B and T
2Bln(T
2B), respectively, where T
2B is the two-body T-matrix.
Received 19 April 2002 Published online 13 August 2002 相似文献
255.
A. P. Solov’ev M. I. Perchenko Yu. P. Sinichkin O. V. Zyuryukina 《Technical Physics》2002,47(8):996-1001
An expression for a signal at the ultrasonic frequency from a photodetector arising when diffraction waves at the cathode
mix is obtained for the case when the optical and acoustic beams are space-limited and Bragg angles are small. The alternating
current generated when the scattering medium is crossed by a focused 3-MHz ultrasonic beam and illuminated by a cw He-Ne laser
is measured. Satisfactory agreement between experimental results and those calculated from the formulas obtained indicates
that our model treating acoustooptical interaction in the medium in terms of Raman-Nath diffraction is valid. Conditions for
measuring the alternating current (which is a parameter of acoustooptical imaging) that are optimal from the viewpoint of
maximizing the signal and signal-to-noise ratio are predicted theoretically and corroborated experimentally. 相似文献
256.
A new method for the characterization of partially covered electrodes is proposed. It is based on the formal analogy between such electrodes and those having a first-order chemical reaction associated with the charge transfer. It consists in making use of the two linear segments in Z(s? appearing on some specified conditions on the operational impedance spectrum obtained for semi-infinite diffusion. To avoid confusion between these two types of electrode, an identification method is proposed, involving the measurements of diffusion-limiting currents on a RDE. Analysis of the limits of validity of these methods leads to the conclusion that most inhibiting coverages fulfilling the conditions necessary for their characterization should not be mistaken for a chemical reaction. 相似文献
257.
The long-range sound propagation from a deep ocean to a receiving system located on the shelf is modeled. The waveguide model is constructed on the basis of the data of an acoustic-oceanographic experiment carried out in the northwestern Pacific. The sensitivity and the frequency dependence of the difference in the sound field levels at the crossing of the frontal zone on the geoacoustic characteristics of the bottom of the shelf and the continental slope are investigated. It is shown that the level difference decreases by 8.2 dB as the velocity of longitudinal waves increases by 100 m/s in the range within 1490–1820 m/s. 相似文献
258.
Results of acoustic measurements in skeletal muscle are generalized. It is shown that assessment of the pathologies and functional condition of the muscular system is possible with the use of shear waves. The velocity of these waves in muscles is much smaller than the velocity of sound; therefore, a higher symmetry type is formed for them. In the presence of a preferential direction (along muscle fibers), it is characterized by only two rather than five (as in usual media with the same anisotropy) moduli of elasticity. A covariant form of the corresponding wave equation is presented. It is shown that dissipation properties of skeletal muscles can be controlled by contracting them isometrically. Pulsed loads (shocks) and vibrations are damped differently, depending on their frequency spectrum. Characteristic frequencies on the order of tens and hundreds of hertz are attenuated due to actin-myosin bridges association/dissociation dynamics in the contracted muscle. At higher (kilohertz) frequencies, when the muscle is tensed, viscosity of the tissue increases by a factor of several tens because of the increase in friction experienced by fibrillar structures as they move relative to the surrounding liquid; the tension of the fibers changes the hydrodynamic conditions of the flow around them. Finally, at higher frequencies, the attenuation is associated with the rheological properties of biological molecules, in particular, with their conformational dynamics in the wave field. Models that describe the controlled shock dissipation mechanisms are proposed. Corresponding solutions are found, including those that allow for nonlinear effects. 相似文献
259.
O. A. Pshenitsyna 《Journal of Mathematical Sciences》2006,135(5):3384-3399
We consider the arithmetic properties of the factor-rank and term-rank functions for matrices over semirings. In particular,
we investigate the sets of matrices that satisfy the extremes of inequalities for these rank functions of matrix union. The
classification of the linear transformations that keep these sets invariant is obtained.
__________
Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 9, No. 3, pp. 175–197, 2003. 相似文献
260.
N. O. Maksimova 《Journal of Mathematical Sciences》2006,135(1):2675-2679
In the article, it is proved that any nonnegative solution of an elliptic quasilinear inequality that vanishes on a subset
of positive measure is trivial.
__________
Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 25, pp. 112–118, 2005. 相似文献