全文获取类型
收费全文 | 487714篇 |
免费 | 4823篇 |
国内免费 | 1425篇 |
专业分类
化学 | 254557篇 |
晶体学 | 7931篇 |
力学 | 21836篇 |
综合类 | 16篇 |
数学 | 55967篇 |
物理学 | 153655篇 |
出版年
2021年 | 4201篇 |
2020年 | 4662篇 |
2019年 | 5224篇 |
2018年 | 6776篇 |
2017年 | 7024篇 |
2016年 | 9965篇 |
2015年 | 5891篇 |
2014年 | 9683篇 |
2013年 | 22888篇 |
2012年 | 17532篇 |
2011年 | 21106篇 |
2010年 | 15228篇 |
2009年 | 15116篇 |
2008年 | 18860篇 |
2007年 | 18735篇 |
2006年 | 17515篇 |
2005年 | 15537篇 |
2004年 | 14337篇 |
2003年 | 12783篇 |
2002年 | 12574篇 |
2001年 | 14558篇 |
2000年 | 10974篇 |
1999年 | 8505篇 |
1998年 | 7070篇 |
1997年 | 6911篇 |
1996年 | 6533篇 |
1995年 | 5807篇 |
1994年 | 5664篇 |
1993年 | 5379篇 |
1992年 | 6269篇 |
1991年 | 6380篇 |
1990年 | 6105篇 |
1989年 | 6093篇 |
1988年 | 5852篇 |
1987年 | 5962篇 |
1986年 | 5608篇 |
1985年 | 7212篇 |
1984年 | 7264篇 |
1983年 | 5907篇 |
1982年 | 6107篇 |
1981年 | 5932篇 |
1980年 | 5643篇 |
1979年 | 6161篇 |
1978年 | 6191篇 |
1977年 | 6281篇 |
1976年 | 6109篇 |
1975年 | 5693篇 |
1974年 | 5565篇 |
1973年 | 5606篇 |
1972年 | 3949篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
151.
In this note we consider asymptotic results for self-intersections of closed geodesics on surfaces for which the angle of the intersection occurs in a given arc. We do this by extending Bonahon's definition of intersection forms for surfaces.
152.
E. K. Bashkirov 《Laser Physics》2006,16(8):1218-1226
An exact solution is found for the collective model of two identical two-level atoms that resonantly interact with a two-mode quantum electromagnetic field in an ideal cavity via two-photon nondegenerate transitions. In the case under study, at the initial moment, both field modes are in the coherent state and atoms are in the excited state. The time dependences of the atomic probabilities, the mean number of photons in the modes, and the statistics and squeezing of the photon modes are studied based on the exact solution. 相似文献
153.
In the Bogoliubov theory, a condensate initially prepared in its ground state described by a stationary Bogoliubov vacuum and later perturbed by a time-dependent potential or interaction strength evolves into a time-dependent excited state which is a dynamical Bogoliubov vacuum. The dynamical vacuum has a simple diagonal form in a time-dependent orthonormal basis of single-particle modes. This diagonal representation leads to a Gaussian probability distribution for possible density-measurement outcomes in position and momentum space. 相似文献
154.
The drawbacks of our earlier report of preparing fuel cell catalyst arrays by borohydride reduction of inkjet prepared arrays of metal salts are discussed along with the need for inclusion of state-of-the-art metrics in all array screening. An alternative method for screening of hydrogen/air cathode catalysts, direct methanol fuel cell (DMFC) anode catalysts, and catalyst loading studies is provided. State-of-the-art Johnson Matthey catalysts were used in control experiments to demonstrate the utility of the array fuel cell for high throughput screening of fuel cell catalysts in the 3-4 mg/cm2 range. This report lays out hard learned rules for high throughput screening and demonstrates that the array fuel cell can be used for very precise screening of libraries of membrane electrode assembly (MEA) components without the pitfalls discussed in the introduction. 相似文献
155.
In this paper, we show that in some cases, no proper covering of a locally compact group topologically generated by left translations
of a topological loop can occur as the group topologically generated by left translations of a topological loop.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 22, Algebra
and Geometry, 2004. 相似文献
156.
S. A. Nazarov 《Journal of Mathematical Sciences》2006,132(1):91-102
For the second order derivatives of eigenvectors in a thin anisotropic heterogeneous plate Ωh, we derive estimates of their weighted L2-norms with majorants whose dependence on the plate thickness h and on the eigenvalue number is expressed explicitly. These
estimates maintain the asymptotic sharpness throughout the entire spectrum, whereas inside its low-frequency band the majorants
remain bounded as h → +0. The latter is a rather unexpected fact, because for the first eigenfunction u1 of a similar boundary-value problem for a scalar second order differential operator with variable coefficients, the norm
‖∇
x
2
u0; L2(Ωh)‖ is of order h−1 and grows as h tends to zero. Bibliography: 35 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 308, 2004, pp. 161–180. 相似文献
157.
S. K. Godunov V. T. Zhukov O. B. Feodoritova 《Computational Mathematics and Mathematical Physics》2006,46(6):971-982
An algorithm is constructed for calculating invariant subspaces of symmetric hyperbolic systems arising in electromagnetic, acoustic, and elasticity problems. Discrete approximations are calculated for subspaces that correspond to minimal eigenvalues and smooth eigenfunctions. Difficulties related to the presence of an infinite-dimensional kernel in the differential operator are successfully handled. The efficiency of the algorithm is demonstrated using acoustics equations. 相似文献
158.
Multi-quantum well heterostructures (MQWHs) of the novel Ga(NAsP)/GaP material system have been grown, pseudomorphically strained to GaP-substrate. The crystalline perfection is verified by transmission electron microscopy (TEM). For As-concentrations in excess of about 70%, a direct band structure and adequate luminescence efficiency for laser device application is observed. Temperature-dependent photoluminescence (PL) investigations show the influence of carrier localisation and non-radiative recombination processes typical for dilute nitride materials. With rising N content in the active material, the emission wavelength shifts towards longer wavelength, leading to Ga(NAs)/GaP MQW structures with photon energies below the indirect band gap of silicon (Si). At the same time the luminescence intensity drops due to an increase in non-radiative carrier traps and/or structural degradation. 相似文献
159.
Bairamov R. K. Ermakov A. I. Vedernikova N. R. 《Russian Journal of Applied Chemistry》2002,75(3):408-410
The influence exerted by the nature and concentration of a number of organic and mineral acids on the composition of products formed in electric-spark dispersion of aluminum was studied. 相似文献
160.
Using Brown's construction (J. Algebra 15 (1970) 103) of an exact 6-term sequence for a fibration of groupoids we show how an exact 9-term sequence can be associated to a fibration of bigroupoids. Applications to topology and algebra are given. 相似文献