全文获取类型
收费全文 | 69892篇 |
免费 | 6220篇 |
国内免费 | 4316篇 |
专业分类
化学 | 21291篇 |
晶体学 | 463篇 |
力学 | 4486篇 |
综合类 | 621篇 |
数学 | 13472篇 |
物理学 | 22717篇 |
无线电 | 17378篇 |
出版年
2024年 | 145篇 |
2023年 | 752篇 |
2022年 | 1305篇 |
2021年 | 1671篇 |
2020年 | 1746篇 |
2019年 | 1540篇 |
2018年 | 1409篇 |
2017年 | 1782篇 |
2016年 | 2231篇 |
2015年 | 1878篇 |
2014年 | 3058篇 |
2013年 | 4516篇 |
2012年 | 3421篇 |
2011年 | 3705篇 |
2010年 | 2825篇 |
2009年 | 3983篇 |
2008年 | 4303篇 |
2007年 | 4753篇 |
2006年 | 4054篇 |
2005年 | 3229篇 |
2004年 | 2784篇 |
2003年 | 3030篇 |
2002年 | 3259篇 |
2001年 | 2490篇 |
2000年 | 2336篇 |
1999年 | 1998篇 |
1998年 | 1884篇 |
1997年 | 1154篇 |
1996年 | 1107篇 |
1995年 | 975篇 |
1994年 | 1007篇 |
1993年 | 749篇 |
1992年 | 810篇 |
1991年 | 575篇 |
1990年 | 533篇 |
1989年 | 403篇 |
1988年 | 335篇 |
1987年 | 326篇 |
1986年 | 280篇 |
1985年 | 281篇 |
1984年 | 270篇 |
1983年 | 174篇 |
1982年 | 221篇 |
1981年 | 203篇 |
1980年 | 142篇 |
1979年 | 177篇 |
1978年 | 152篇 |
1977年 | 138篇 |
1976年 | 95篇 |
1973年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
101.
In this paper we study the Hankel convolution operators on the space of even and entire functions and on Schwartz distribution spaces. We characterize the Hankel convolution operators as those ones that commute with Hankel translations and with a Bessel operator. Also we prove that the Hankel convolution operators are hypercyclic and chaotic on the spaces under consideration. 相似文献
102.
103.
104.
105.
M. Gorkunov M. Lapine E. Shamonina K.H. Ringhofer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):263-269
Effective magnetic properties of a composite meta-material consisting of periodically arranged circular conductive elements
are studied theoretically. A general expression for the effective bulk permeability is obtained with mutual effects and lattice
ordering being taken into account. The resonance frequency of the permeability is found to be strongly dependent on the size
and shape of the unit cell. Frequency dispersion of the permeability is studied with special attention paid to the frequency
range, where negative values of the permeability are possible. Corresponding recommendations for optimisation of the meta-materials
with negative permeability are made. The results are confirmed by numerical simulations of the finite structure behaviour
in an external magnetic field.
Received 19 April 2002 Published online 31 July 2002 相似文献
106.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
107.
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
108.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
109.
110.
对红外热像仪参数双黑体测量装置的工作原理进行了介绍。装置采用双黑体及反射型靶标为温差辐射源,可实现黑体温度温差准直辐射的定期校准和红外热像仪参数测量量值的溯源,也可实现红外热像仪参数的可控性,以及对它进行稳定的、可复现的精确测量。推导出利用红外热像仪参数双黑体测量装置测量信号传递函数SiTF数学模型,分析了红外热像仪参数测量装置的客观因素——仪器常数,针对仪器常数对SiTF测量的影响进行了试验。试验结果表明,仪器常数对红外热像仪SiTF参数测量精度影响较大,并同时影响时域与空域NETD及3D噪声的准确测量。 相似文献