全文获取类型
收费全文 | 689048篇 |
免费 | 5917篇 |
国内免费 | 2022篇 |
专业分类
化学 | 355329篇 |
晶体学 | 10055篇 |
力学 | 33160篇 |
综合类 | 19篇 |
数学 | 89854篇 |
物理学 | 208570篇 |
出版年
2021年 | 5933篇 |
2020年 | 6478篇 |
2019年 | 7422篇 |
2018年 | 9751篇 |
2017年 | 9805篇 |
2016年 | 13817篇 |
2015年 | 7868篇 |
2014年 | 12833篇 |
2013年 | 30928篇 |
2012年 | 23406篇 |
2011年 | 28259篇 |
2010年 | 20526篇 |
2009年 | 20369篇 |
2008年 | 26281篇 |
2007年 | 26218篇 |
2006年 | 23934篇 |
2005年 | 21590篇 |
2004年 | 19953篇 |
2003年 | 17910篇 |
2002年 | 17779篇 |
2001年 | 19003篇 |
2000年 | 14687篇 |
1999年 | 11466篇 |
1998年 | 9882篇 |
1997年 | 9780篇 |
1996年 | 9126篇 |
1995年 | 8344篇 |
1994年 | 8214篇 |
1993年 | 8067篇 |
1992年 | 8569篇 |
1991年 | 9093篇 |
1990年 | 8704篇 |
1989年 | 8611篇 |
1988年 | 8453篇 |
1987年 | 8191篇 |
1986年 | 7876篇 |
1985年 | 10220篇 |
1984年 | 10686篇 |
1983年 | 8972篇 |
1982年 | 9479篇 |
1981年 | 8931篇 |
1980年 | 8535篇 |
1979年 | 9041篇 |
1978年 | 9488篇 |
1977年 | 9210篇 |
1976年 | 9367篇 |
1975年 | 8758篇 |
1974年 | 8717篇 |
1973年 | 9171篇 |
1972年 | 6460篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
C. Fallnich B. Ruffing Th. Herrmann A. Nebel R. Beigang R. Wallenstein 《Applied physics. B, Lasers and optics》1995,60(5):427-436
We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency. 相似文献
22.
Brian R. Hunt 《Proceedings of the American Mathematical Society》1998,126(3):791-800
The Weierstrass nowhere differentiable function, and functions constructed from similar infinite series, have been studied often as examples of functions whose graph is a fractal. Though there is a simple formula for the Hausdorff dimension of the graph which is widely accepted, it has not been rigorously proved to hold. We prove that if arbitrary phases are included in each term of the summation for the Weierstrass function, the Hausdorff dimension of the graph of the function has the conjectured value for almost every sequence of phases. The argument extends to a much wider class of Weierstrass-like functions.
23.
A. M. Nikitin 《Journal of Mathematical Sciences》1997,87(6):4138-4146
An explicit way for producing invariants for 6-valent graphs with rigid vertices within the framework of Kauffman's approach
to graph invariants is presented. These invariants can be used to detect the chirality of a 6-valent graph with rigid vertices.
A relevant example is considered. Bibliography: 19 titles.
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 223, 1995, pp. 251–262.
Translated by A. M. Nikitin 相似文献
24.
A. K. Lopatin 《Ukrainian Mathematical Journal》1997,49(1):51-74
We consider the method of normal forms, the Bogolyubov averaging method, and the method of asymptotic decomposition proposed by Yu. A. Mitropol’skii and the author of this paper. Under certain assumptions about group-theoretic properties of a system of zero approximation, the results obtained by the method of asymptotic decomposition coincide with the results obtained by the method of normal forms or the Bogolyubov averaging method. We develop a new algorithm of asymptotic decomposition by a part of the variables and its partial case — the algorithm of averaging on a compact Lie group. For the first time, it became possible to consider asymptotic expansions of solutions of differential equations on noncommutative compact groups. 相似文献
25.
26.
We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity,
which causes the conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease gradually with density, to vanish
at a critical density n
c
, 2∼2×1012 cm−2, and then to have the opposite sign at n>n
c
,2. The second critical density sets the upper limit on the existence region of the 2D metal, whereas the conductivity at the
critical point, G
c
,2∼120e
2/h, sets an upper (low-temperature) limit on its conductivity.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 497–501 (25 September 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
27.
S. A. Gurevich T. A. Zaraiskaya S. G. Konnikov V. M. Mikushkin S. Yu. Nikonov A. A. Sitnikova S. E. Sysoev V. V. Khorenko V. V. Shnitov Yu. S. Gordeev 《Physics of the Solid State》1997,39(10):1691-1695
The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material. 相似文献
28.
A converging perturbation series that can be summed analytically has been obtained for intersubband transitions of electrons
coherently tunneling through the middle of a dimensionally quantized level in an asymmetric double-barrier structure in a
high-frequency terahertz electric field. The possibility of a substantial increase in tunneling current accompanied by either
absorption or emission of a photon has been demonstrated. The quantum efficiency of radiative transitions between dimensionally
quantized levels can be up to 66%.
Zh. éksp. Teor. Fiz. 112, 237–245 (July 1997) 相似文献
29.
L. K. Aminov I. N. Kurkin D. A. Lukoyanov K. P. Chernov 《Physics of the Solid State》1997,39(8):1184-1186
Results are reported for measurements of the spin-lattice relaxation times of E′1 centers in quartz glass, produced by neutron irradiation, with the measurements made at two frequencies 9.25 and 24.0 GHz
over a wide temperature interval 1.5–300 K. The experimental data are interpreted on the basis of interaction mechanisms of
the spins with two-level systems with excitation energies ∼6, ∼26, and ∼420 cm−1. A small modification of the existing theory allows us to explain a number of features of the observed temperature and frequency
dependence of the relaxation rate. The results are compared with the data available in the literature on spin-lattice relaxation
of irradiation centers in crystalline quartz and quartz glass.
Fiz. Tverd. Tela (St. Petersburg) 39, 1335–1337 (August 1997) 相似文献
30.
V. A. Krakovskii 《Russian Physics Journal》1997,40(1):6-12
The problem of exciting bulk elastic waves at the surface of a piezoelectric with symmetries 422,622 has been solved by a
successive approximation method. In the approximation of a fixed electric field, created at the surface of the piezoelectric
crystal by a two-electrode transducer, the distributions are found for the shear wave stress and the energy flux density in
the far zone. The equivalent circuit parameters for a two-electrode radiator are determined taking account of the dynamic
piezoelectric correction obtained in the second approximation. The equivalent circuit parameters and the transducer loss are
treated for TeO2 crystals. A realistic possibility of using surface transducers in the development of acousto-optic modulators in the s.h.f.
region is shown.
Tomsk State Academy of Control Systems and Radio Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika,
No. 1, pp. 8–15, January, 1997. 相似文献