全文获取类型
收费全文 | 1514篇 |
免费 | 73篇 |
国内免费 | 9篇 |
专业分类
化学 | 1012篇 |
晶体学 | 8篇 |
力学 | 35篇 |
数学 | 238篇 |
物理学 | 303篇 |
出版年
2024年 | 1篇 |
2023年 | 23篇 |
2022年 | 35篇 |
2021年 | 67篇 |
2020年 | 45篇 |
2019年 | 57篇 |
2018年 | 48篇 |
2017年 | 38篇 |
2016年 | 91篇 |
2015年 | 43篇 |
2014年 | 82篇 |
2013年 | 102篇 |
2012年 | 136篇 |
2011年 | 126篇 |
2010年 | 70篇 |
2009年 | 62篇 |
2008年 | 81篇 |
2007年 | 95篇 |
2006年 | 79篇 |
2005年 | 71篇 |
2004年 | 57篇 |
2003年 | 31篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 4篇 |
1974年 | 1篇 |
排序方式: 共有1596条查询结果,搜索用时 109 毫秒
131.
Giorgio Metafune Diego Pallara 《Journal of Mathematical Analysis and Applications》2011,377(1):170-179
Given a second-order elliptic operator on Rd, with bounded diffusion coefficients and unbounded drift, which is the generator of a strongly continuous semigroup on L2(Rd) represented by an integral, we study the time behavior of the integral kernel and prove estimates on its decay at infinity. If the diffusion coefficients are symmetric, a local lower estimate is also proved. 相似文献
132.
J. Rodrigo Vélez-Cordero Diego Sámano Pengtao Yue James J. Feng Roberto Zenit 《ournal of non Newtonian Fluid Mechanics》2011,166(1-2):118-132
The interaction of two bubbles rising in shear-thinning inelastic fluids was studied. The experimental results were complemented by numerical simulations conducted with the arbitrary Lagrangian–Eulerian technique. Different initial alignments of the bubble pair were considered. Similarities and differences with the Newtonian fluids were found. The most noticeable difference is the so-called drafting–kissing–tumbling (DKT) process: for the case of bubbles rising in thinning fluids, the tumbling phase does not occur and the pair tends to form a stable doublet. The DKT process is also influenced by the amount of inertia and deformability of the individual bubbles and the initial angle between them. The experimental and numerical results suggest that the thinning wake formed behind the bubbles plays an important role in the speed of the pair and the formation of clusters in thinning fluids. 相似文献
133.
Saturated nanotubes consisting of 2–10 and 20 layers of cyclic units of six-membered rings, each one having a pyrimidine-like
framework (i.e., –C–C–C–N–C–N–), were studied by quantum chemistry methods using Density Functional Theory (DFT) at the B3LYP/6-31G*
level of theory. Four different nanotube (NT) configurations were theoretically studied in this work. They were formed by
covalently arranging each layer over the other, with uniform relative rotations of 0°, 60°, 120°, and 180° with respect to
each of the layers. Different structures can be created by modulating the relative rotation as layers are added to the main
nanostructure. NTs with a relative rotation of 60° showed both greater stabilities and highest potential for catalytic activity.
All of them showed band gaps of around 0.2 eV. Charges and other properties can be controlled by appropriate layer arrangement.
The studied families of NTs have a very small diameter and could find potential applications in chemistry, physics, and medicine. 相似文献
134.
Diego Adolfo Santamaría Razo Luca Pallavidino Edoardo Garrone Francesco Geobaldo Emiliano Descrovi Angelica Chiodoni Fabrizio Giorgis 《Journal of nanoparticle research》2008,10(7):1225-1229
A sol-gel synthesis procedure based on the method proposed by Stöber et al. (J Colloid Interface Sci 26:302–315, 1968) has been adopted for the one-step preparation of mono-dispersed silica nanospheres. An excellent control of the particle diameter over a wide range is obtained by varying the amount of silicon alkoxide only, while the concentration of all other components is kept fixed: this allows the fabrication of artificial opals with a finely tuned and precisely predictable lattice parameter. 相似文献
135.
Towards the end of 1999, the building of one of the main communication routes in Spain was finished, the A-3 motorway, which connects Madrid and Valencia. So far, this road was running through the town Motilla de Palancar, province of Cuenca. The opening of the last section of the motorway on 3 December 1999, re-routes all the traffic passing through the town. This study makes a comparative of the noise levels before and after the opening of the motorway that goes through Motilla de Palancar. 相似文献
136.
Diego Dominici 《The Ramanujan Journal》2008,15(3):303-338
We analyze the Krawtchouk polynomials K
n
(x,N,p,q) asymptotically. We use singular perturbation methods to analyze them for N→∞, with appropriate scalings of the two variables x and n. In particular, the WKB method and asymptotic matching are used. We obtain asymptotic approximations valid in the whole domain
[0,N]×[0,N], involving some special functions. We give numerical examples showing the accuracy of our formulas.
相似文献
137.
Apparently, no rigorous results exist for the dynamics of a classical point particle interacting with the electromagnetic field, as described by the standard Maxwell-Lorentz equations. Some results are given here for the corresponding linearized system (dipole approximation) in the presence of a mechanical linear restoring force. We consider a regularization of the system (Pauli-Fierz model), and explicitly solve the Cauchy problem in terms of normal modes. Then we study the limit of the particle's motion as the regularization is removed. We prove that the particle's motion corresponding to smooth initial data for the field has a well-defined limit if mass is renormalized, while the motion is trivial (i.e. the particle does not move at all) if mass is not renormalized. Moreover, the limit particle's motion corresponding to an interesting class of initial data satifies exactly the Abraham-Lorentz-Dirac equation. Finally, for generic initial data the limit motion is runaway. 相似文献
138.
Fausto Pedro García Márquez Diego Jose Pedregal Tercero Felix Schmid 《European Journal of Operational Research》2007
Railways are experiencing a fundamental transformation. The introduction of high speed networks and the increased traffic levels on suburban routes and freight lines require new technologies for both railway infrastructure and trains, all of which must be subjected to rigorous quality control before and during operation and must be supported with effective maintenance processes during their operating lives. Safety in railway infrastructure provision must be ensured by all the main components operating reliably all the time. From an economic, quality and safety point of view, points are probably one of the most critical infrastructure elements in railway transportation. 相似文献
139.
Linear programming duality is well understood and the reduced cost of a column is frequently used in various algorithms. On the other hand, for integer programs it is not clear how to define a dual function even though the subadditive dual theory has been developed a long time ago. In this work we propose a family of computationally tractable subadditive dual functions for integer programs. We develop a solution methodology that computes an optimal primal solution and an optimal subadditive dual function. We present computational experiments, which show that the new algorithm is tractable. 相似文献
140.
We prove surface and volume mean value formulas for classical solutions to uniformly parabolic equations in the divergence form with low regularity of the coefficients. We then use them to prove the parabolic strong maximum principle and the parabolic Harnack inequality. We emphasize that our results only rely on the classical theory, and our arguments follow the lines used in the original theory of harmonic functions. We provide two proofs relying on two different formulations of the divergence theorem, one stated for sets with almost C1-boundary, the other stated for sets with finite perimeter. 相似文献