全文获取类型
收费全文 | 181762篇 |
免费 | 907篇 |
国内免费 | 284篇 |
专业分类
化学 | 90727篇 |
晶体学 | 2643篇 |
力学 | 9452篇 |
综合类 | 7篇 |
数学 | 21301篇 |
物理学 | 58823篇 |
出版年
2020年 | 1857篇 |
2019年 | 2303篇 |
2018年 | 3418篇 |
2017年 | 3541篇 |
2016年 | 4185篇 |
2015年 | 1871篇 |
2014年 | 3610篇 |
2013年 | 7119篇 |
2012年 | 5608篇 |
2011年 | 6696篇 |
2010年 | 5552篇 |
2009年 | 5669篇 |
2008年 | 6458篇 |
2007年 | 6436篇 |
2006年 | 5719篇 |
2005年 | 5078篇 |
2004年 | 4903篇 |
2003年 | 4438篇 |
2002年 | 4584篇 |
2001年 | 5038篇 |
2000年 | 3742篇 |
1999年 | 2849篇 |
1998年 | 2629篇 |
1997年 | 2483篇 |
1996年 | 2290篇 |
1995年 | 2081篇 |
1994年 | 2032篇 |
1993年 | 2095篇 |
1992年 | 2115篇 |
1991年 | 2416篇 |
1990年 | 2338篇 |
1989年 | 2417篇 |
1988年 | 2294篇 |
1987年 | 2338篇 |
1986年 | 2154篇 |
1985年 | 2697篇 |
1984年 | 2706篇 |
1983年 | 2342篇 |
1982年 | 2407篇 |
1981年 | 2311篇 |
1980年 | 2098篇 |
1979年 | 2423篇 |
1978年 | 2583篇 |
1977年 | 2664篇 |
1976年 | 2757篇 |
1975年 | 2570篇 |
1974年 | 2509篇 |
1973年 | 2667篇 |
1972年 | 2167篇 |
1971年 | 1982篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
J. Kudrna I. Pelant J. Štěpánek F. Trojánek P. Malý 《Applied Physics A: Materials Science & Processing》2002,74(2):253-256
We have studied ultra-fast carrier dynamics of photo-excited carriers in hydrogenated microcrystalline silicon prepared by
a very high frequency glow-discharge technique. We report on direct observation of two types of dynamics using selective photo-excitation
in picosecond pump and probe measurements. One type of the observed dynamics has been found to be independent of the sample
preparation, while the other reflects the relative weights of crystalline and amorphous fractions. We propose a simple rate-equation
model that describes the carrier dynamics in microcrystalline silicon in terms of the composition of those in Si microcrystallites
and in the a-Si:H tissue which surrounds the microcrystallites. The model without any fitting parameters reproduces the experimental
data very well when the dynamics are scaled with relative volume fractions as obtained from Raman spectra.
Received: 23 November 2000 / Accepted: 17 March 2001 / Published online: 23 May 2001 相似文献
182.
T. Temesvári C. De Dominicis I.R. Pimentel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):361-372
Symmetry considerations and a direct, Hubbard-Stratonovich type, derivation are used to construct a replica field-theory relevant
to the study of the spin glass transition of short range models in a magnetic field. A mean-field treatment reveals that two
different types of transitions exist, whenever the replica number n is kept larger than zero. The Sherrington-Kirkpatrick critical point in zero magnetic field between the paramagnet and replica
magnet (a replica symmetric phase with a nonzero spin glass order parameter) separates from the de Almeida-Thouless line,
along which replica symmetry breaking occurs. We argue that for studying the de Almeida-Thouless transition around the upper
critical dimension d = 6, it is necessary to use the generic cubic model with all the three bare masses and eight cubic couplings. The critical
role n may play is also emphasized. To make perturbative calculations feasible, a new representation of the cubic interaction is
introduced. To illustrate the method, we compute the masses in one-loop order. Some technical details and a list of vertex
rules are presented to help future renormalisation-group calculations.
Received 9 October 2001 相似文献
183.
R. A. Ganeev A. I. Ryasnyanskii M. K. Kodirov Sh. R. Kamalov V. A. Li R. I. Tugushev T. Usmanov 《Technical Physics》2002,47(8):991-995
Nonlinear optical parameters (nonlinear refractive indices and nonlinear absorption coefficients) of solutions of polyvinylpyrrolidone doped by cobalt to various concentrations are measured at the lasing and second-harmonic wavelengths of a picosecond Nd:YAG laser (λ=1064 and 532 nm, respectively, and τ=35 ps). Data on optical limitation in these solutions are presented. The absence of nonlinear absorption in the IR spectral range and its significant effect in the visible range are demonstrated. Optical limitation at a wavelength of 1064 nm is related to defocusing, whereas at 532 nm, this effect is caused by two-photon absorption and partially by inverse saturated absorption and defocusing. Nonlinear optical parameters of metal-polymer complexes are reported. 相似文献
184.
The present paper analyzes the properties of structural phase transitions under the extremal conditions of high pressures. In the context of the theory of density functional (TDF), the pressures of the B1–B2 transitions are calculated for small alkali-halide crystals as functions of the crystal size. The size effect of the B1–B2 transition – an increase in the transition pressure with the decreasing crystal grain radius – has been established for all investigated halides except lithium fluoride for which the dependence is reverse. 相似文献
185.
The influence of interatomic distances on magnetic ordering in RMnSi compounds (R=La, Y, Sm, and Gd)
S. A. Nikitin T. I. Ivanova Yu. A. Ovchenkova M. V. Maslennikova G. S. Burkhanov O. D. Chistyakov 《Physics of the Solid State》2002,44(2):308-311
Magnetic ordering in the RMnSi (R=La, Y, Sm, and Gd) compounds is investigated. It is found that the type of magnetic ordering depends on the d Mn-Mn distance between manganese atoms inside the magnetic layers located in the planes perpendicular to the c axis. This inference is based on the results of studies performed with SmMnSi and GdMnSi compounds in which the distances between manganese atoms are close to the critical value d Mn-Mn that corresponds to the crossover between ferromagnetic and antiferromagnetic ordering in RMnSi compounds. The introduction of lanthanum and yttrium atoms into the rare-earth sublattice leads to an increase and a decrease in the unit cell size, respectively, and brings about magnetic phase transitions in the compounds under investigation. 相似文献
186.
187.
N. L. Dmitruk O. Yu. Borkovskaya R. V. Konakova I. B. Mamontova S. V. Mamykin D. I. Voitsikhovskiy 《Technical Physics》2002,47(6):698-702
The effect of 60Co gamma irradiation at doses of 103-2×105 Gy on the photoconversion and dark I-V characteristics of Au/GaAs surface-barrier solar cells (SCs) is studied. The morphology of the interface microrelief is varied
to reach the highest photoconversion efficiency. Of the two types of microrelief morphology (dendritic and quasi-grating)
obtained by the chemical anisotropic etching of n-(100)GaAs, the latter is more promising, particularly for SCs designed for space application, since the associated SCs offer
higher efficiency and radiation resistance. 相似文献
188.
189.
N. Euler W. -H. Steeb L. G. S. Duarte I. C. Moreira 《International Journal of Theoretical Physics》1991,30(9):1267-1271
The techniques of invertible point transformations and the Painlevé analysis can be used to construct integrable ordinary differential equations. We compare both techniques for the second Painlevé transcendent. 相似文献
190.