全文获取类型
收费全文 | 478698篇 |
免费 | 4626篇 |
国内免费 | 1343篇 |
专业分类
化学 | 248302篇 |
晶体学 | 7841篇 |
力学 | 21628篇 |
综合类 | 16篇 |
数学 | 54589篇 |
物理学 | 152291篇 |
出版年
2021年 | 4122篇 |
2020年 | 4548篇 |
2019年 | 5108篇 |
2018年 | 6688篇 |
2017年 | 6928篇 |
2016年 | 9796篇 |
2015年 | 5720篇 |
2014年 | 9455篇 |
2013年 | 22477篇 |
2012年 | 17018篇 |
2011年 | 20453篇 |
2010年 | 14907篇 |
2009年 | 14828篇 |
2008年 | 18289篇 |
2007年 | 18135篇 |
2006年 | 16885篇 |
2005年 | 14873篇 |
2004年 | 13777篇 |
2003年 | 12322篇 |
2002年 | 12134篇 |
2001年 | 14437篇 |
2000年 | 10867篇 |
1999年 | 8399篇 |
1998年 | 6944篇 |
1997年 | 6773篇 |
1996年 | 6397篇 |
1995年 | 5719篇 |
1994年 | 5569篇 |
1993年 | 5293篇 |
1992年 | 6197篇 |
1991年 | 6320篇 |
1990年 | 6058篇 |
1989年 | 6048篇 |
1988年 | 5804篇 |
1987年 | 5917篇 |
1986年 | 5573篇 |
1985年 | 7134篇 |
1984年 | 7190篇 |
1983年 | 5857篇 |
1982年 | 6054篇 |
1981年 | 5866篇 |
1980年 | 5579篇 |
1979年 | 6115篇 |
1978年 | 6154篇 |
1977年 | 6250篇 |
1976年 | 6092篇 |
1975年 | 5667篇 |
1974年 | 5541篇 |
1973年 | 5587篇 |
1972年 | 3935篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
821.
In this paper, we consider a queueing system in which there are two exponential servers, each having his own queue, and arriving
customers will join the shorter queue. Based on the results given in Flatto and McKean, we rewrite the formula for the probability
that there are exactlyk customers in each queue, wherek = 0, 1,…. This enables us to present an algorithm for computing these probabilities and then to find the joint distribution
of the queue lengths in the system. A program and numerical examples are given. 相似文献
822.
It is shown how, with the help of approximate integral manifolds, to solve the reduction problem in stability theory in the nonsingular critical case. A generalization of the first fundamental Lyapunov-Malkin theorem in critical cases is obtained.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 10, pp. 1324–1329, October, 1991. 相似文献
823.
H. Tsertos E. Berdermann F. Bosch M. Clemente S. Huchler P. Kienle W. Koenig C. Kozhuharov 《Zeitschrift für Physik A Hadrons and Nuclei》1992,342(1):79-94
We present the results obtained from systematic studies of positron creation for a series of heavy-collision systems, with united chargeZ u =Z 1 +Z 2 ranging fromZ u =164 (Pb + Pb) toZ u =184 (U+U) at bombarding energies close to the Coulomb barrier, using the Orangeβ-spectrometer at GSI. For each collision system studied, the dominating continuous distributions due to quasiatomic and nuclear positron emission are determined accurately. This is essential in obtaining the characteristics of the still unexplained monoenergetic positron lines which appear in the energy range between 200 keV and 400 keV. Our results are compared with coupled-channels calculations for quasi-atomic positron creation. The latter describe quite well the global features of the measured spectra, but overestimate systematically their absolute values. From the comparison, a common normalization factor of about 0.75 can be established for the calculated spectra. In particular, the dependence onZ u of the measured emission probabilities was found to follow a power law (∝Z u 195±1), in fair agreement with the theoretical prediction. 相似文献
824.
J. Kircher M. Cardona M. Alouani S. Gopalan O. Jepsen O. K. Andersen
E. Kaldis
J. Karpinski S. Rusieki 《Physica C: Superconductivity and its Applications》1992,200(3-4):413-417We report results of ellipsometric measurements of the dielectric tensor of YBa2Cu4O8 as well as calculations employing density functional theory in the local density approximation (LDA). For the computation of the one-electron eigenvalues and states the linear-muffin-tin-orbital method (LMTO) was used. Measured and calculated results show good agreement. In particular, the calculation predicts different band structures for YBa2Cu3O7 and YBa2Cu4O8 in the vicinity of the Fermi energy which lead to significant differences in the optical spectra. One such difference is a region of small ε2 in the near infrared which is a fingerprint of the high (relative to the top of the highest fully occupied band) Fermi energy as compared to the situation in YBa2Cu3O7. Our experimental results confirm the theoretical findings. 相似文献
825.
826.
K. W. Kopp W. Kasparek E. Holzhauer 《International Journal of Infrared and Millimeter Waves》1992,13(10):1619-1631
Maxwell's equations are solved using finite difference equations to obtain the near and the far field distribution of electromagnetic waves in front of corrugated mirrors. We treat the case of perpendicular incidence to obtain both the phaseshift between TE- and TM-modes in polarisation twisters and mode converters as well as the amplitude of the electromagnetic field. 相似文献
827.
828.
A. T. Barabanov G. A. Agranovich A. S. Golikov 《Journal of Mathematical Sciences》1992,60(2):1399-1402
A problem of constructing algorithms of optimal estimation of states of a discrete system accounting for deterministic and stochastic measurements is considered. A low order estimation algorithm is proposed in the form of a two-stage procedure for each instant of time obtained by direct application of the Kaiman optimal filtering algorithm.Translated from Dinamicheskie Sistemy, No. 4, pp. 85–89, 1985. 相似文献
829.
V. D. Levchenko A. I. Morozov A. S. Sigov 《Journal of Experimental and Theoretical Physics》2002,94(5):985-991
Multilayer ferromagnet-layered antiferromagnet (Fe/Cr) structures frustrated because of roughness of interlayer boundaries were studied by mathematical modeling methods. The phase diagram of a three-layer system (plotted as film thickness versus the degree of roughness of the interfaces) was obtained, and the order parameter distributions in each phase were determined. The character of phase transitions in this system was studied. The applicability range of the Slonczewski magnetic proximity model was determined. 相似文献
830.