全文获取类型
收费全文 | 20683篇 |
免费 | 2185篇 |
国内免费 | 1090篇 |
专业分类
化学 | 2274篇 |
晶体学 | 93篇 |
力学 | 2689篇 |
综合类 | 144篇 |
数学 | 13144篇 |
物理学 | 5614篇 |
出版年
2024年 | 41篇 |
2023年 | 207篇 |
2022年 | 260篇 |
2021年 | 394篇 |
2020年 | 637篇 |
2019年 | 580篇 |
2018年 | 578篇 |
2017年 | 568篇 |
2016年 | 639篇 |
2015年 | 548篇 |
2014年 | 886篇 |
2013年 | 2133篇 |
2012年 | 887篇 |
2011年 | 1247篇 |
2010年 | 986篇 |
2009年 | 1336篇 |
2008年 | 1312篇 |
2007年 | 1259篇 |
2006年 | 1162篇 |
2005年 | 899篇 |
2004年 | 808篇 |
2003年 | 801篇 |
2002年 | 754篇 |
2001年 | 598篇 |
2000年 | 616篇 |
1999年 | 539篇 |
1998年 | 468篇 |
1997年 | 423篇 |
1996年 | 349篇 |
1995年 | 238篇 |
1994年 | 233篇 |
1993年 | 197篇 |
1992年 | 148篇 |
1991年 | 123篇 |
1990年 | 117篇 |
1989年 | 89篇 |
1988年 | 73篇 |
1987年 | 72篇 |
1986年 | 54篇 |
1985年 | 79篇 |
1984年 | 109篇 |
1983年 | 52篇 |
1982年 | 71篇 |
1981年 | 68篇 |
1980年 | 64篇 |
1979年 | 69篇 |
1978年 | 61篇 |
1977年 | 33篇 |
1976年 | 29篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
91.
Kiyoshi Mochizuki 《Journal of Mathematical Analysis and Applications》2007,326(1):582-588
We show that the energy of solutions to the initial boundary value problem for the wave equation in exterior domains with a dissipation which is localized only near infinity tends to zero as the time goes to infinity. We do not make any geometrical condition like star-shapedness on the boundary. 相似文献
92.
Ben-Yuan Gu Yao Lu Tzong-Jer Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):493-502
We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached
to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model
scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal
or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the
case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump
in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic
flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance
dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially
modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve
symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure
can be well understood.
Received 6 November 2001 相似文献
93.
Based on the theory of calculus of variation, some suffcient conditions are given for some Euler-Lagrangcequations to be equivalently represented by finite or even infinite many Hamiltonian canonical equations. Meanwhile,some further applications for equations such as the KdV equation, MKdV equation, the general linear Euler Lagrangeequation and the cylindric shell equations are given. 相似文献
94.
S. P. Popov 《Computational Mathematics and Mathematical Physics》2006,46(6):983-994
Numerical solutions to three systems of integrable evolutionary equations from the Toda lattice hierarchy are analyzed. These are the classical Toda lattice, the second local dispersive flow, and the second extended dispersive flow. Special attention is given to the properties of soliton solutions. For the equations of the second local flow, two types of solitons interacting in a special manner are found. Solutions corresponding to various initial data are qualitatively outlined. 相似文献
95.
Microwave Activation of Processes in Mesopores: The Thiourea Electrooxidation at Mesoporous Platinum
《Electroanalysis》2006,18(8):793-800
In situ microwave activation is applied to the electrochemical oxidation of thiourea at low surface area (polished polycrystalline) and at high surface area (electrodeposited mesoporous platinum coated) platinum microelectrodes. The one electron oxidation of thiourea to formamidine disulfide is monitored as a function of the different activation parameters. In the absence of microwaves (ambient temperature, low mass transport) increasing the surface area (roughness) increases the thiourea oxidation response predominantly due to adsorption effects. In the presence of high microwave intensities, high mass transport and thermal effects further increase the oxidation current at mesoporous platinum. The most effective thickness of the mesoporous platinum film for the thiourea oxidation process is estimated as 3 μm independent of electrode diameter, temperature, or mass transport effects. 相似文献
96.
This study analyzes the economics of transshipping biomass from truck to train in a North American setting. Transshipment
will only be economic when the cost per unit distance of a second transportation mode is less than the original mode. There
is an optimum number of transshipment terminals which is related to biomass yield. Transshipment incurs incremental fixed
costs, and hence there is a minimum shipping distance for rail transport above which lower costs/km offset the incremental
fixed costs. For transport by dedicated unit train with an optimum number of terminals, the minimum economic rail shipping
distance for straw is 170 km, and for boreal forest harvest residue wood chips is 145 km. The minimum economic shipping distance
for straw exceeds the biomass draw distance for economically sized centrally located power plants, and hence the prospects
for rail transport are limited to cases in which traffic congestion from truck transport would otherwise preclude project
development. Ideally, wood chip transport costs would be lowered by rail transshipment for an economically sized centrally
located power plant, but in a specific case in Alberta, Canada, the layout of existing rail lines precludes a centrally located
plant supplied by rail, whereas a more versatile road system enables it by truck. Hence for wood chips as well as straw the
economic incentive for rail transport to centrally located processing plants is limited. Rail transshipment may still be preferred
in cases in which road congestion precludes truck delivery, for example as result of community objections. 相似文献
97.
98.
We present the explicit form of the symplectic structure of anti-self-dual Yang-Mills (ASDYM) equations in Yang’s J- and K-gauges in order to establish the bi-Hamiltonian structure of this completely integrable system. Dirac’s theory of constraints is applied to the degenerate Lagrangians that yield the ASDYM equations. The constraints are second class as in the case of all completely integrable systems which stands in sharp contrast to the situation in full Yang-Mills theory. We construct the Dirac brackets and the symplectic 2-forms for both J- and K-gauges. The covariant symplectic structure of ASDYM equations is obtained using the Witten-Zuckerman formalism. We show that the appropriate component of the Witten-Zuckerman closed and conserved 2-form vector density reduces to the symplectic 2-form obtained from Dirac’s theory. Finally, we present the Bäcklund transformation between the J- and K-gauges in order to apply Magri’s theorem to the respective two Hamiltonian structures. 相似文献
99.
脉冲中立型时滞抛物方程的振动性 总被引:6,自引:0,他引:6
本文研究了一类脉冲中立型时滞抛物方程解的振动性及强振动性,获得了此类脉冲中立型时滞抛物方程解振动和强振动的代数判据. 相似文献
100.
Boniface Nkemzi 《Mathematical Methods in the Applied Sciences》2006,29(9):1053-1080
This paper is concerned with the structure of the singular and regular parts of the solution of time‐harmonic Maxwell's equations in polygonal plane domains and their effective numerical treatment. The asymptotic behaviour of the solution near corner points of the domain is studied by means of discrete Fourier transformation and it is proved that the solution of the boundary value problem does not belong locally to H2 when the boundary of the domain has non‐acute angles. A splitting of the solution into a regular part belonging to the space H2, and an explicitly described singular part is presented. For the numerical treatment of the boundary value problem, we propose a finite element discretization which combines local mesh grading and the singular field methods and derive a priori error estimates that show optimal convergence as known for the classical finite element method for problems with regular solutions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献