全文获取类型
收费全文 | 476篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
化学 | 136篇 |
晶体学 | 2篇 |
力学 | 9篇 |
数学 | 184篇 |
物理学 | 102篇 |
无线电 | 53篇 |
出版年
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 25篇 |
2012年 | 32篇 |
2011年 | 26篇 |
2010年 | 19篇 |
2009年 | 17篇 |
2008年 | 29篇 |
2007年 | 21篇 |
2006年 | 27篇 |
2005年 | 15篇 |
2004年 | 17篇 |
2003年 | 14篇 |
2002年 | 18篇 |
2001年 | 9篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 13篇 |
1997年 | 3篇 |
1996年 | 10篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有486条查询结果,搜索用时 15 毫秒
41.
We consider the Beltrami equation for hydrodynamics and we show that its solutions can be viewed as instanton solutions of a more general system of equations. The latter are the equations of motion for an sigma model on 4‐dimensional worldvolume (which is taken locally HyperKähler) with a 4‐dimensional HyperKähler target space. By means of the 4D twisting procedure originally introduced by Witten for gauge theories and later generalized to 4D sigma‐models by Anselmi and Fré, we show that the equations of motion describe triholomophic maps between the worldvolume and the target space. Therefore, the classification of the solutions to the 3‐dimensional Beltrami equation can be performed by counting the triholomorphic maps. The counting is easily obtained by using several discrete symmetries. Finally, the similarity with holomorphic maps for sigma on Calabi‐Yau space prompts us to reformulate the problem of the enumeration of triholomorphic maps in terms of a topological sigma model. 相似文献
42.
Yosef E. Maruvka Nadav M. Shnerb Sorin Solomon Gur Yaari David A. Kessler 《Journal of statistical physics》2011,142(6):1302-1316
The inference of past demographic parameters from current genetic polymorphism is a fundamental problem in population genetics.
The standard techniques utilize a reconstruction of the gene-genealogy, a cumbersome process that may be applied only to small
numbers of sequences. We present a method that compares the total number of haplotypes (distinct sequences) with the model
prediction. By chopping the DNA sequence into pieces we condense the immense information hidden in sequence space into a function
for the number of haplotypes versus subsequence size. The details of this curve are robust to statistical fluctuations and
are seen to reflect the process parameters. This procedure allows for a clear visualization of the quality of the fit and,
crucially, the numerical complexity grows only linearly with the number of sequences. Our procedure is tested against both
simulated data as well as empirical mtDNA data from China and provides excellent fits in both cases. 相似文献
43.
In the present paper, we deal with the complex Szasz-Durrmeyer operators and study Voronovskaja type results with quantitative estimates for these operators attached to analytic functions of exponential growth on compact disks. Also, the exact order of approximation is found. 相似文献
44.
Ion Grosu Lo?c Toupet Gerard Plé Sorin Mager Eugen Mesaros Andreea Varga Elena Bogdan 《Monatshefte für Chemie / Chemical Monthly》2000,54(5):277-286
The synthesis and stereochemistry of new dibrominated spiro-1,3-dioxane derivatives are reported. Investigations by means
of NMR methods and single crystal X-ray diffraction for two compounds revealed the high regio- and diastereoselectivity of
the bromination reaction of some new spiro-1,3-dioxanes and the asymmetric induction of the chiral carbon atom located in
the spiro skeleton. 相似文献
45.
The globalization of telecommunicative ties between nations is studied from a heterogenization perspective. A theoretical model inspired by Appadurai’s “disjuncture hypothesis,” which stipulates that global flows of communication are multidimensional and reinforce regional/local identities, is tested empirically on an international voice traffic dataset. Spatial-statistical measures (global and local versions of Moran’s I) indicate that countries that share the same linguistic (English, Spanish, or French) or civilizational (Catholic, Protestant, and Buddhist–Hindu) background are more likely to be each other’s “telecommunicative neighbors” and that this tendency has increased over time (1989–1999). 相似文献
46.
47.
We find asymptotic expansions in the “string mass” μ for μ-deformed Γ-functions and Neumann coefficients characterizing the
three-string vertex in the light-cone gauge of the field theory of open superstrings on a maximally supersymmetric pp-wave
background.
Dedicated to the 80th birthday of Academician Anatolii Alekseevich Logunov
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 149, No. 3, pp. 381–385, December, 2006. 相似文献
48.
M. Yu. Novikov A. S. Sorin V. Yu. Tseitlin V. P. Shelest 《Theoretical and Mathematical Physics》1986,69(1):977-987
Conclusions Thus, we have shown that in QED3 systematic allowance for screening makes it possible to eliminate infrared divergences and in this respect advance further than in QCD4, in which the question of the mechanism of their elimination remains open. The comparative simplicity of the model also makes it possible to study systematically the more important question of the general structure of the series of skeleton perturbation theory and the excitation spectrum. We are currently working on this question.All-Union Scientific-Research Center for the Study of Surface and Vacuum Properties. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 69, No. 1, pp. 25–39, October, 1986. 相似文献
49.
Elisabetta Barletta Sorin Dragomir Howard Jacobowitz 《Complex Analysis and Operator Theory》2017,11(8):1685-1713
The total space \({\mathfrak M} \approx {\mathbb H}_1 \times S^1\) of the canonical circle bundle over the 3-dimensional Heisenberg group \({\mathbb H}_1\) is a space–time with the Lorentzian metric \(F_{\theta _0}\) (Fefferman’s metric) associated to the canonical Tanaka–Webster flat contact form \(\theta _0\) on \({\mathbb H}_1\). The matter and energy content of \(\mathfrak M\) is described by the energy-momentum tensor \({T}_{\mu \nu }\) (the trace-less Ricci tensor of \(F_{\theta _0}\)) as an effect of the non flat nature of Feferman’s metric \(F_{\theta _0}\). We study the gravitational field equations \(R_{\mu \nu } - (1/2) \, R \, g_{\mu \nu } = {T}_{\mu \nu }\) on \({\mathfrak M}\). We consider the first order perturbation \(g = F_{\theta _0} + \epsilon \, h\), \(\epsilon<< 1\), and linearize the field equations about \(F_{\theta _0}\). We determine a Lorentzian metric g on \({\mathfrak M}\) which solves the linearized field equations corresponding to a diagonal perturbation h. 相似文献
50.
The authors discuss the existence and uniqueness up to isometries of Enof immersions φ : Ω R~n→ E~n with prescribed metric tensor field(g ij) : Ω→ S~n, and discuss the continuity of the mapping(gij) →φ defined in this fashion with respect to various topologies. In particular, the case where the function spaces have little regularity is considered. How, in some cases, the continuity of the mapping(gij) →φ can be obtained by means of nonlinear Korn inequalities is shown. 相似文献