全文获取类型
收费全文 | 214769篇 |
免费 | 2048篇 |
国内免费 | 653篇 |
专业分类
化学 | 110022篇 |
晶体学 | 3409篇 |
力学 | 9502篇 |
综合类 | 5篇 |
数学 | 23926篇 |
物理学 | 70606篇 |
出版年
2021年 | 1765篇 |
2020年 | 1981篇 |
2019年 | 2149篇 |
2018年 | 2819篇 |
2017年 | 2707篇 |
2016年 | 4033篇 |
2015年 | 2541篇 |
2014年 | 3892篇 |
2013年 | 9600篇 |
2012年 | 7879篇 |
2011年 | 9558篇 |
2010年 | 6435篇 |
2009年 | 6185篇 |
2008年 | 8516篇 |
2007年 | 8727篇 |
2006年 | 8379篇 |
2005年 | 7547篇 |
2004年 | 6941篇 |
2003年 | 6085篇 |
2002年 | 5869篇 |
2001年 | 6548篇 |
2000年 | 5081篇 |
1999年 | 3906篇 |
1998年 | 3144篇 |
1997年 | 3136篇 |
1996年 | 2942篇 |
1995年 | 2733篇 |
1994年 | 2564篇 |
1993年 | 2442篇 |
1992年 | 2786篇 |
1991年 | 2755篇 |
1990年 | 2682篇 |
1989年 | 2459篇 |
1988年 | 2508篇 |
1987年 | 2506篇 |
1986年 | 2324篇 |
1985年 | 3054篇 |
1984年 | 3290篇 |
1983年 | 2683篇 |
1982年 | 2885篇 |
1981年 | 2865篇 |
1980年 | 2707篇 |
1979年 | 2805篇 |
1978年 | 2882篇 |
1977年 | 2882篇 |
1976年 | 2943篇 |
1975年 | 2730篇 |
1974年 | 2701篇 |
1973年 | 2823篇 |
1972年 | 1790篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Considering a system ofN identical interacting particles, which obey Fermi-Dirac or Bose-Einstein statistics, we derive new formulas for correlation functions of the type
(whereB
j is diagonal in the free-particle states) in the thermodynamic limit. Thereby we apply and extend a superoperator formalism, recently developed for the derivation of long-time tails in semiclassical systems. As an illustrative application, the Boltzmann equation value of the time-integrated correlation functionC(t) is derived in a straightforward manner. Due to exchange effects, the obtained t-matrix and the resulting scattering cross section, which occurs in the Boltzmann collision operator, are now functionals of the Fermi-Dirac or Bose-Einstein distribution. 相似文献
912.
Consider the Schrödinger equation –u+V(x)u=u on the intervalI, whereV(x)0 forxI and where Dirichlet boundary conditions are imposed at the endpoints ofI. We prove the optimal bound
相似文献
913.
914.
915.
An approximate method for the analysis of planar-waveguide distributed-feedback lasers is extended to include a nonvanishing reflectivity at the ends of the structure. An index grating structure with parasitic losses is investigated. An expression for the small-signal gain coefficient 0MN as a function of the output power P
MNout normalized to the saturation power P
s
, coupling coefficient K, complex reflectivity R of end reflectors, and waveguide parameters is presented. 相似文献
916.
Semi-insulating electrical properties of undoped inp after heat treatment in a phosphorus atmosphere 总被引:1,自引:0,他引:1
D. Hofmann G. Müller N. Streckfuß 《Applied Physics A: Materials Science & Processing》1989,48(4):315-319
Nominally undoped InP wafers have been annealed in a phosphorus atmosphere under a pressure of about 5 bar at temperatures of 900 °C for about 80 h. It was found that the electrical properties of the samples changed considerably after this treatment. A room temperature resistivity of up to 2×107cm (semi-insulating behaviour) was obtained in the bulk of the samples. The resistivity finally obtained depends on the starting carrier concentration of the untreated samples. The Hall coefficient and Hall mobility have been measured up to 600 °C. The results can be interpreted in terms of a deep electronic level (E
A=0.63 ... 0.65 eV below the conduction band). The Hall coefficient was always found to be negative resulting in a Hall mobility of 1.4 to 4.9×103 cm2/Vs. The highest resistivity in nominally undoped bulk InP so far reported in the literature [1] was =3.6 × 105cm. Therefore, this paper demonstrates for the first time that a really semi-insulating behaviour of >107 cm can be achieved for bulk InP with the purity of nominally undoped material (1015 to 1016cm–3). 相似文献
917.
D. Mauri D. Scholl H. C. Siegmann E. Kay 《Applied Physics A: Materials Science & Processing》1989,49(5):439-447
The spin polarizationP of the low energy cascade electrons excited with a primary unpolarized electron beam is measured with ultrathin films of permalloy (Ni80Fe20) as a function of film thickness, external magnetic field, and temperatureT. Surface adsorbates of small concentrations of less than 10% of a monolayer can change the Curie point and the saturation value ofP
0(T0) by as much as 30%. The Ta-substrate induces a magnetically dead region in permalloy. Conventional spin wave theory cannot account for the observed smallT-dependence of the magnetizationM. Films on a nonmagnetic substrate are compared to similar films coupled to bulk permalloy over an interface of Ta. TheT-dependence ofM with the coupled films can be explained by spin wave theory. At lowT, the films coupled to the bulk exhibit a faster decrease ofM than the uncoupled films. We propose that this thermal stabilization of the magnetization in very thin ferromagnetic films is due to quenching of the long wavelength spin modes. 相似文献
918.
The hyperfine structure of various absorption lines of molecular iodine with wavenumbers between 12980 and 13890 cm–1 has been resolved using Doppler-free polarization spectroscopy. The wavenumbers of theo-component of 17 rovibrational lines of I2 due to the transitionB
3
ou
+
–X1
g
+
with even rotational quantum numbers have been determined with an accuracy of 0.001 cm–1. A comparison of the centers of gravity of these 17 lines with the values of the iodine atlas of Gerstenkorn et al. yields a difference of
thus corroborating the data of the iodine atlas in the red region within limits of error. 相似文献
919.
The analogue of the Edwards-Anderson model for isotropic vector spin glasses, but taking three-component quadrupoles instead of spins at each lattice site, is studied on the square lattice with extensive Monte Carlo calculations, using a nearest-neighbor symmetric gaussian interaction.It is shown that at low temperaturesT the model develops a short range order both with respect to glass like correlations and with respect to ferromagnetic correlations among the quadrupoles. The associated correlation lengths and susceptibilities diverge asT0, and the critical exponents for this zero-temperature phase transition are estimated.Dynamic correlation functions are analyzed as well and it is shown that the dacay of spatially displaced correlations displays a Kohlrausch-Williams-Watts behavior similar to the self-correlation function of the quadrupole moments.Some quantities are compared to their corresponding counterparts on the threedimensional simple cubic lattice, which also has a zero-temperature transition but at corresponding temperatures has stronger short-range-order. 相似文献
920.
D. E. Popov 《Russian Physics Journal》1989,32(8):654-658
The influence of a magnetic field on the motion and radiation of an electron is considered for planar channeling in a monocrystal. It is shown that discrete levels analogous to Landau levels appear in the super-barrier domain of transverse energies instead of a continuous spectrum. The spectral composition and intensity of anomalous and normal waves are computed. The possibilities are discussed of the observation of electron radiation with Landau levels.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 88–93, August, 1989. 相似文献
|