全文获取类型
收费全文 | 11831篇 |
免费 | 1956篇 |
国内免费 | 1313篇 |
专业分类
化学 | 5459篇 |
晶体学 | 76篇 |
力学 | 2194篇 |
综合类 | 62篇 |
数学 | 1437篇 |
物理学 | 5872篇 |
出版年
2024年 | 29篇 |
2023年 | 154篇 |
2022年 | 327篇 |
2021年 | 516篇 |
2020年 | 530篇 |
2019年 | 501篇 |
2018年 | 389篇 |
2017年 | 423篇 |
2016年 | 612篇 |
2015年 | 504篇 |
2014年 | 653篇 |
2013年 | 1152篇 |
2012年 | 686篇 |
2011年 | 731篇 |
2010年 | 640篇 |
2009年 | 772篇 |
2008年 | 796篇 |
2007年 | 811篇 |
2006年 | 707篇 |
2005年 | 547篇 |
2004年 | 424篇 |
2003年 | 400篇 |
2002年 | 376篇 |
2001年 | 318篇 |
2000年 | 313篇 |
1999年 | 272篇 |
1998年 | 270篇 |
1997年 | 181篇 |
1996年 | 158篇 |
1995年 | 134篇 |
1994年 | 142篇 |
1993年 | 103篇 |
1992年 | 78篇 |
1991年 | 66篇 |
1990年 | 54篇 |
1989年 | 48篇 |
1988年 | 40篇 |
1987年 | 43篇 |
1986年 | 26篇 |
1985年 | 30篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 25篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1976年 | 9篇 |
1971年 | 6篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
在对胶体晶体的研究中,带电粒子胶体晶体的形成机理比硬球胶体晶体更加复杂,对其形成条件目前还缺少有效的判断依据. 有效硬球模型判据提出以有效直径作为判断参数. 为了验证该判据的有效性,利用布朗动力学模拟研究了不同有效直径下带电粒子胶体晶体的特性. 为了更加定量地研究单因素对带电胶体晶体形成的影响,取有效直径为2.8至0.8,并对一定的有效直径,研究了粒子几何直径和排斥力不同情况下的结晶行为. 在布朗动力学模拟过程中,采用径向分布函数和键序参数方法检测体系的结构变化,并分析所形成的晶体结构. 结果表明,在判断带电粒子胶体体系能否形成有序结构方面,有效硬球模型判据有一定的合理性. 但是,并不能将有效直径作为唯一的判别参数,而是需要综合其他参数的影响,这显示出该判据的片面性.
关键词:
布朗动力学模拟
带电胶体晶体
有效硬球模型 相似文献
992.
993.
本文采用分子动力学方法模拟在常温常压下(1 atm,298 K)和在压水堆环境下(155 atm,626 K),水分子数为256,联氨(N2H4)分子数为0,25,50,75等不同数目时,水和联氨粒子系统的动力性质和微观结构.同时探讨了联氨分子的引入对水中溶解氧的影响.从模拟结果可知,在常温常压下,当联氨的分子数为0,25,50,75时,粒子系统的均方位移会随联氨分子数的增加而增加;联氨分子数为0与为25,50,75比较时会少一个数量级;压水堆环境下,联氨分子数
关键词:
分子动力学
压水堆
联氨 相似文献
994.
Using the density-functional linear response method, we study the dynamical properties of ground state zinc-blende and high pressure NaCl phases of platinum carbide (PtC). The calculated phonon dispersion curve does not show any soft modes for all wave vectors, indicating the dynamic stability of the ground state zinc-blende phase. The high pressure rock-salt phase exhibits imaginary frequencies, practically along all directions of the Brillouin zone, which means that PtC cannot exist in the NaCl phase at least up to a high pressure of 100 GPa. 相似文献
995.
In Hele-Shaw flows at vanishing surface tension, the boundary of a viscous fluid develops cusp-like singularities. In recent papers Lee et al. (2009, 2008) [8] and [9] we have showed that singularities trigger viscous shocks propagating through the viscous fluid. Here we show that the weak solution of the Hele-Shaw problem describing viscous shocks is equivalent to a semiclassical approximation of a special real solution of the Painlevé I equation. We argue that the Painlevé I equation provides an integrable deformation of the Hele-Shaw problem which describes flow passing through singularities. In this interpretation shocks appear as Stokes level-lines of the Painlevélinear problem. 相似文献
996.
We consider a quadratic Liénard equation with an unbounded homoclinic loop, which is a solution tending in forward and backward time to a non-hyperbolic equilibrium point located at infinity. Under small time-periodic perturbation, this equilibrium becomes a normally hyperbolic line of singularities at infinity. We show that the perturbed system may present homoclinic bifurcations, leading to the existence of transverse intersections between the stable and unstable manifolds of such a normally hyperbolic line of singularities. The global study concerning the infinity is performed using the Poincaré compactification in polar coordinates, from which we obtain a system defined on a set equivalent to a solid torus in R3, whose boundary plays the role of the infinity. The transversality of the manifolds is proved using the Melnikov method and implies, via the Birkhoff-Smale Theorem, a complex dynamical behaviour of the perturbed system solutions in the finite part of the phase space. Numerical simulations are performed in order to illustrate this behaviour, which could be called “the chaos arising from infinity”, since it depends on the global structure of the Liénard equation, including the points at infinity. Although applied to a particular case, the analysis presented provides a geometrical approach to study periodic perturbations of homoclinic (or heteroclinic) loops to infinity of any planar polynomial vector field. 相似文献
997.
A low power density single-pulse laser irradiation of the Si surface has been used for the study of formation and self-organization of silicon nanotips. A two dimensional regular array of hillock-like nanotips has been created in the central region, a disturbed array comprising crossed lines of hillocks in the near-central region, and the “V”-shaped array in the peripheral region. Therefore, the long-range organization of hillocks changes from the center toward the periphery, following the Gaussian-like laser power profile. The evolution of hillocks due to the flow instability of molten silicon is equivalent to the instability of a liquid layer falling down a vertical plate. The novel result is that the hillock-like soliton structures can be identified with the lump solitons resulting from the nonlinear hydrodynamic instability evolution. 相似文献
998.
Farouq Ahmed Ryo NagumoRyuji Miura Suzuki AiHideyuki Tsuboi Nozomu HatakeyamaAkira Endou Hiromitsu TakabaMomoji Kubo Akira Miyamoto 《Applied Surface Science》2011,257(24):10503-10513
The notion of “active sites” is fundamental to heterogeneous catalysis. However, the exact nature of the active sites, and hence the mechanism by which they act, are still largely a matter of speculation. In this study, we have presented a systematic quantum chemical molecular dynamics (QCMD) calculations for the interaction of hydrogen on different step and terrace sites of the Pd (3 3 2) surface. Finally the dissociative adsorption of hydrogen on step and terrace as well as the influence of surface hydrogen vacancy for the dissociative adsorption of hydrogen has been investigated through QCMD. This is a state-of-the-art method for calculating the interaction of atoms and molecules with metal surfaces. It is found that fully hydrogen covered (saturated) step sites can dissociate hydrogen moderately and that a monovacancy surface is suitable for significant dissociative adsorption of hydrogen. However in terrace site of the surface we have found that dissociation of hydrogen takes place only on Pd sites where the metal atom is not bound to any pre-adsorbed hydrogen atoms. Furthermore, from the molecular dynamics and electronic structure calculations, we identify a number of consequences for the interpretation and modeling of diffusion experiments demonstrating the coverage and directional dependence of atomic hydrogen diffusion on stepped palladium surface. 相似文献
999.
1000.