全文获取类型
收费全文 | 4143篇 |
免费 | 696篇 |
国内免费 | 380篇 |
专业分类
化学 | 507篇 |
晶体学 | 88篇 |
力学 | 335篇 |
综合类 | 40篇 |
数学 | 1402篇 |
物理学 | 2364篇 |
无线电 | 483篇 |
出版年
2024年 | 12篇 |
2023年 | 53篇 |
2022年 | 112篇 |
2021年 | 89篇 |
2020年 | 106篇 |
2019年 | 99篇 |
2018年 | 96篇 |
2017年 | 93篇 |
2016年 | 110篇 |
2015年 | 115篇 |
2014年 | 201篇 |
2013年 | 311篇 |
2012年 | 195篇 |
2011年 | 184篇 |
2010年 | 203篇 |
2009年 | 261篇 |
2008年 | 266篇 |
2007年 | 263篇 |
2006年 | 235篇 |
2005年 | 237篇 |
2004年 | 194篇 |
2003年 | 184篇 |
2002年 | 231篇 |
2001年 | 171篇 |
2000年 | 162篇 |
1999年 | 156篇 |
1998年 | 145篇 |
1997年 | 108篇 |
1996年 | 81篇 |
1995年 | 70篇 |
1994年 | 63篇 |
1993年 | 46篇 |
1992年 | 37篇 |
1991年 | 35篇 |
1990年 | 26篇 |
1989年 | 27篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 30篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 12篇 |
1972年 | 4篇 |
排序方式: 共有5219条查询结果,搜索用时 15 毫秒
831.
In this paper, we study a coupled modified Volterra lattice equation which is an integrable semidiscrete version of the coupled KdV and the coupled mKdV equation. By using the Darboux transformation, we obtain its new explicit solutions including multi-soliton and multi-positon. Furthermore, an integrable discretization of the coupled modified Volterra lattice equation is constructed. 相似文献
832.
833.
ABSTRACTThe majority of proteins perform their cellular function after folding into a specific and stable native structure. Additionally, for many proteins less compact ‘molten globule’ states have been observed. Current experimental observations show that the molten globule state can show varying degrees of compactness and solvent accessibility; the underlying molecular cause for this variation is not well understood. While the specificity of protein folding can be studied using protein lattice models, current design procedures for these models tend to generate sequences without molten globule-like behaviour. Here we alter the design process so the distance between the molten globule ensemble and the native structure can be steered; this allows us to design protein sequences with a wide range of folding pathways, and sequences with well-defined heat-induced molten globules. Simulating these sequences we find that (1) molten globule states are compact, but have less specific configurations compared to the folded state, (2) the nature of the molten globule state is highly sequence dependent, (3) both two-state and multi-state folding proteins may show heat-induced molten globule states, as observed in heat capacity curves. The varying nature of the molten globules and typical heat capacity curves associated with the transitions closely resemble experimental observations. 相似文献
834.
A feedback control model of lattice hydrodynamic model is proposed by taking the information of the historic optimal velocity into account for the traffic system. The modern control theory is applied for the linear stability condition with feedback control signal. The result shows that the stability of traffic flow is closely related to the information of the historic optimal velocity. Furthermore, numerical simulations conform that the new feedback control did increase the stability of traffic flow efficiently, which is in accord with theoretical analysis. 相似文献
835.
836.
We study the thermodynamics of the classical anisotropic antiferromagnetic Heisenberg model in a checkerboard lattice. The checkerboard lattice is distinguished from the antiferromagnetic square lattice (with coupling constant J) by the presence of a diagonal crossing (coupling constant ) in half of the sites. This lattice model is the direct analog of the three-dimensional pyrochlore lattice on a two-dimensional surface. Besides, we considered a single-ion anisotropy D that breaks the symmetry and contributes to planar spin fields. Since the model is two-dimensional endowed with an symmetry, a Berezinskii–Kosterlitz–Thouless (BKT) transition is expected to take place. We also investigated the BKT temperature as a function of the coupling constants and D. The problem is developed through a continuous representation given by the Nonlinear Sigma Model (NLSM). Computer simulations were also carried out, and the results were in accordance with the analytical model. 相似文献
837.
A novel nonlinear stochastic interacting price dynamics is proposed and investigated by the bond percolation on Sierpinski gasket fractal-like lattice, aim to make a new approach to reproduce and study the complexity dynamics of real security markets. Fractal-like lattices correspond to finite graphs with vertices and edges, which are similar to fractals, and Sierpinski gasket is a well-known example of fractals. Fractional ordinal array entropy and fractional ordinal array complexity are introduced to analyze the complexity behaviors of financial signals. To deeper comprehend the fluctuation characteristics of the stochastic price evolution, the complexity analysis of random logarithmic returns and volatility are preformed, including power-law distribution, fractional sample entropy and fractional ordinal array complexity. For further verifying the rationality and validity of the developed stochastic price evolution, the actual security market dataset are also studied with the same statistical methods for comparison. The empirical results show that this stochastic price dynamics can reconstruct complexity behaviors of the actual security markets to some extent. 相似文献
838.
We study a stacked triangular lattice Ising model with both intra- and inter-plane antiferromagnetic interactions in a field, by Monte Carlo simulation. We find only one phase transition from a paramagnetic to a partially disordered phase, which is of second order and 3D XY universality class. At low temperatures we identify two highly degenerate phases: at smaller (larger) fields the system shows long-range ordering in the stacking direction (within planes) but not in the planes (stacking direction). Nevertheless, crossovers to these phases do not have a character of conventional phase transitions but rather linear-chain-like excitations. 相似文献
839.
J. Kplé S. Massou F. Hontinfinde E. Albayrak 《Chinese Journal of Physics (Taipei)》2018,56(3):1252-1261
A bilayer spin-1/2 Ising model consisting of two superposed Bethe lattices with antiferromagnetic/ferromagnetic interactions is studied by the use of exact recursion relations in a pairwise approach in the presence of an external staggered magnetic field. Besides the ground state phase diagrams calculated in different possible planes of the model parameters space, the thermal variations of the order-parameters and the free energy are investigated to obtain the temperature-dependent phase diagrams of the model for different values of the coordination numbers q. Our calculations reveal that depending on the strength of the model parameters, the model exhibits a variety of interesting phase transitions and therefore phase diagrams. 相似文献
840.
采用格子Boltzmann方法,考虑Soret和Dufour效应,对内置高浓度发热圆的方腔内部双扩散自然对流现象进行数值模拟.高浓度发热圆位于方腔中心,四周壁面均为低温低浓度.在该模型中,用三个独立的LBGK方程分别模拟速度场、温度场和浓度场,并通过Boussinesq近似将它们耦合起来.分析Soret数和Dufour数对方腔内部双扩散自然对流的影响,得到流线图、等温线图、等浓度线图、发热圆表面平均Nusselt数和平均Sherwood数.结果表明:Soret和Dufour效应对方腔内双扩散自然对流影响明显,不能忽略. 相似文献