全文获取类型
收费全文 | 236617篇 |
免费 | 2299篇 |
国内免费 | 605篇 |
专业分类
化学 | 123126篇 |
晶体学 | 4074篇 |
力学 | 10118篇 |
综合类 | 4篇 |
数学 | 26840篇 |
物理学 | 75359篇 |
出版年
2021年 | 1957篇 |
2020年 | 2215篇 |
2019年 | 2511篇 |
2018年 | 3351篇 |
2017年 | 3511篇 |
2016年 | 5021篇 |
2015年 | 2750篇 |
2014年 | 4572篇 |
2013年 | 10444篇 |
2012年 | 8166篇 |
2011年 | 9578篇 |
2010年 | 7210篇 |
2009年 | 7240篇 |
2008年 | 9044篇 |
2007年 | 8814篇 |
2006年 | 8418篇 |
2005年 | 7481篇 |
2004年 | 6964篇 |
2003年 | 6315篇 |
2002年 | 6228篇 |
2001年 | 7074篇 |
2000年 | 5259篇 |
1999年 | 4033篇 |
1998年 | 3468篇 |
1997年 | 3285篇 |
1996年 | 3005篇 |
1995年 | 2822篇 |
1994年 | 2786篇 |
1993年 | 2700篇 |
1992年 | 3048篇 |
1991年 | 3036篇 |
1990年 | 2933篇 |
1989年 | 2872篇 |
1988年 | 2801篇 |
1987年 | 2763篇 |
1986年 | 2614篇 |
1985年 | 3370篇 |
1984年 | 3502篇 |
1983年 | 3076篇 |
1982年 | 3194篇 |
1981年 | 2922篇 |
1980年 | 2885篇 |
1979年 | 3055篇 |
1978年 | 3204篇 |
1977年 | 3165篇 |
1976年 | 3130篇 |
1975年 | 3028篇 |
1974年 | 2993篇 |
1973年 | 3139篇 |
1972年 | 2126篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
891.
892.
L. V. Giurgiu M. N. Grecu X. Filip O. Raita Al. Darabont D. Gavre J. Blasco 《Applied magnetic resonance》2003,24(3-4):351-360
We report an electron paramagnetic resonance (EPR) investigation of the spin dynamics in the paramagnetic regime of the colossal magnetoresistive manganites La2/3Ca1/3Mn1?x Me x O3 (Me=Al, In;x≤0.05). The temperature dependences of the EPR linewidth and integral intensity have been analyzed in terms of the bottleneck spin relaxation and small-polaron hopping models. The exchange coupling integral between Mn3+ and Mn4+ ions and the polaron activation energy decrease with increasing doping level. A discussion is given concerning the factors which could explain the observed changes. 相似文献
893.
Translated from Matematicheskie Zametki, Vol. 49, No. 5, pp. 37–44, May, 1991. 相似文献
894.
895.
896.
E. S. Moskalenko M. Larsson K. F. Karlsson P. O. Holtz B. Monemar W. V. Schoenfeld P. M. Petroff 《Physics of the Solid State》2007,49(10):1995-1998
We report on low-temperature microphotoluminescence (μ-PL) measurements of InAs/GaAs quantum dots (QDs) exposed to a lateral
external electric field. It is demonstrated that the QDs’ PL signal could be increased severalfold by altering the external
and/or the internal electric field, which could be changed by an additional infrared laser. A model which accounts for a substantially
faster lateral transport of the photoexcited carriers achieved in an external electric field is employed to explain the observed
effects. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity
measured in our experiment—a finding which could be used to tailor the properties of QD-based optoelectronic applications.
The text was submitted by the authors in English. 相似文献
897.
N. B. Voznesensky E. V. Gavrilov A. P. Zhevlakov V. K. Kirillovskiĭ P. V. Orlov 《Technical Physics》2007,52(2):271-275
Methods and schemes to inspect the EUV mirror shape are developed on the basis of a point diffraction interferometer with computer processing of interferograms. A measurement accuracy to within 0.001 of a wavelength in the visual range is achieved. 相似文献
898.
A. R. M. Castro M. M. Serna R. N. Faria N. B. Lima 《Journal of magnetism and magnetic materials》2004,280(2-3):273-280
In this study, magnetic domains in Pr16Fe76B8 sintered magnets have been observed by Kerr effect and a histogram of the angular distribution of domain orientations has been used to determine the magnetic texture (cos Φ). The degree of easy-axis alignment of Pr2Fe14B matrix grains in these magnets has been also determined by X-ray pole figure analysis using the (0 0 4) reflection. The (0 0 4) pole figure measurements were carried out by the Schultz's reflection method. The (0 0 4) normalized intensity data has been fitted for a Gaussian distribution and the degree of crystal alignment, cos Θ, has been calculated using the Stoner–Wohlfarth model. Comparison of these methods has been carried out. It has been shown that in magnets with medium and high degrees of crystallographic alignment, the pole figure values are higher than that obtained by the Kerr effect method. Conversely, in magnets with low degrees of alignment, cos Θ is lower than cos Φ. 相似文献
899.
Passive methods of remote analysis of waste gases of industrial enterprises and aircrafts engines and gases ejected in eruptions of volcanos, in fires, and in other processes disturbing the atmosphere are now of limited utility because of the lack of well-developed mathematical techniques for solving the inverse problems of gas analysis. However, the advantage of these methods is obvious, since the equipment is limited to a receiving device and the gas medium serves as a radiator. At the same time, in modern techniques, the interpretation of measurements of emissivities of gases is performed using a phenomenological approach such that experimental data on radiation characteristics of various objects are approximated by simple polynomial relations whose coefficients are determined by minimization methods. This approach does not allow one to investigate the mechanism of the processes occurring in a radiating medium and gives no way of solving the inverse problem of monitoring the composition and thermodynamic parameters of a medium which disturbs the atmosphere by thermal effects. In elaborating theoretical methods of gas analysis, the elaboration of the direct problem of calculation of radiating characteristics of gases is of importance, since it is not clear how the emissivity of a gas medium depends on its thermodynamic parameters. This paper is devoted to the above problem. Here, the error is estimated that arises in modeling a nonuniform gas medium with an actual temperature distribution, which linearly depends on coordinate, by a uniform gas layer. It is shown that the difference between the radiation intensities calculated for uniform and nonuniform media can be significant in the practically important case where the recording device is in a zone of normal temperatures. This implies that the error of reconstruction of the spectroscopic and molecular parameters of gaseous compounds from high-temperature measurements of the radiating and absorbing characteristics should take into account the thermodynamic nonuniformity of the medium. 相似文献
900.
Alexander G. Ramm Alexandra B. Smirnova Angelo Favini 《Annali di Matematica Pura ed Applicata》2003,182(1):37-52
A nonlinear operator equation F(x)=0, F:H→H, in a Hilbert space is considered. Continuous Newton’s-type procedures based on a construction of a dynamical system with
the trajectory starting at some initial point x
0 and becoming asymptotically close to a solution of F(x)=0 as t→+∞ are discussed. Well-posed and ill-posed problems are investigated.
Received: June 29, 2001; in final form: February 26, 2002?Published online: February 20, 2003
This paper was finished when AGR was visiting Institute for Theoretical Physics, University of Giessen. The author thanks
DAAD for support 相似文献