全文获取类型
收费全文 | 2989篇 |
免费 | 606篇 |
国内免费 | 154篇 |
专业分类
化学 | 92篇 |
力学 | 1236篇 |
综合类 | 39篇 |
数学 | 1526篇 |
物理学 | 856篇 |
出版年
2024年 | 9篇 |
2023年 | 33篇 |
2022年 | 49篇 |
2021年 | 57篇 |
2020年 | 113篇 |
2019年 | 75篇 |
2018年 | 62篇 |
2017年 | 111篇 |
2016年 | 111篇 |
2015年 | 95篇 |
2014年 | 122篇 |
2013年 | 218篇 |
2012年 | 145篇 |
2011年 | 181篇 |
2010年 | 170篇 |
2009年 | 167篇 |
2008年 | 180篇 |
2007年 | 161篇 |
2006年 | 175篇 |
2005年 | 170篇 |
2004年 | 142篇 |
2003年 | 142篇 |
2002年 | 131篇 |
2001年 | 108篇 |
2000年 | 103篇 |
1999年 | 100篇 |
1998年 | 84篇 |
1997年 | 71篇 |
1996年 | 63篇 |
1995年 | 59篇 |
1994年 | 38篇 |
1993年 | 43篇 |
1992年 | 45篇 |
1991年 | 31篇 |
1990年 | 43篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1959年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有3749条查询结果,搜索用时 500 毫秒
41.
In this paper, a tumor immune model with time delay is studied. First, the stability of nonnegative equilibria is analyzed. Then the time delay τ is selected as a bifurcation parameter and the existence of Hopf bifurcation is proved. Finally, by using the canonical method and the central manifold theory, the criteria for judging the direction and stability of Hopf bifurcation are given. 相似文献
42.
A novel system is developed for measuring the thermal resistance across thin layers of sintered copper wicks of varying porosity. Wicks to be tested are integrated into a passive vertical thermosyphon system, and the resistance is measured for a series of input power levels. The wicks are sintered to a thermally conducting pedestal above a pool of deionized water and heated from below. The apparent thermal resistance across the wick (from the pedestal/wick interface to the vapor space) under the evaporative operating conditions encountered in heat pipes is measured using thermocouples. The apparent thermal resistance across the wick is measured to be as low as 0.01°C/W, corresponding to an evaporative heat transfer coefficient of greater than 128,000 W/m2K. 相似文献
43.
This paper deals with residual stress in polyethylene (PE) pipes as an important factor that influences their lifetime. Residual hoop stress distribution in a PE pipe was determined using a methodology previously carried out by the authors on polypropylene pipes. Axial residual stress magnitude was determined by comparison of experimental data and finite element modelling. Based on the obtained results, a new simplified methodology for determining the residual hoop stress is proposed. The method needs only one circular specimen made of pipe, but, unlike older methods, provides a more precise estimation of residual hoop stress distribution taking into account its exponential shape. Some older results from literature are recalculated using this method and residual hoop stress of various PE pipe grades and dimensions are then compared. To provide an idea of residual hoop stress influence on lifetime of a pipe, a lifetime estimation is carried out for the examined pipe. 相似文献
44.
The gas dynamics in an exhaust pipe is studied. In particular we focus on the warm up of the catalytic converter in very short times after the engine start. This is done by combustion a small unburnt part of the exhaust gas. This process is classically modelled by gas dynamic equations. Compared to the existing literature we improve the (one-dimensional) modelling approach using a small Mach number technique and a network ansatz for the full exhaust pipe. The final simplified model on one hand still describes the main features and on the other hand it is computationally a few orders of magnitude faster than the original model. Performing numerical simulations we compare the new model to the (classical) full model and to experimental results in the literature. 相似文献
45.
Molecular dynamics simulation was used to verify a speculation of the existence of a certain face-centred cubic (FCC) to body-centred cubic (BCC) phase transformation pathway. Four FCC metals, Ni, Cu, Au and Ag, were stretched along the [1?0?0] direction at various strain rates and temperatures. Under high strain rate and low temperature, and beyond the elastic limit, the bifurcation of the FCC phase occurred with sudden contraction along one lateral direction and expansion along the other lateral direction. When the lattice constant along the expansion direction converged with that of the stretched direction, the FCC phase transformed into an unstressed BCC phase. By reducing the strain rate or increasing the temperature, dislocation or ‘momentum-induced melting’ mechanisms began to control the plastic deformation of the FCC metals, respectively. 相似文献
46.
Hopf bifurcation control via a dynamic state-feedback control 总被引:1,自引:0,他引:1
To relocate two Hopf bifurcation points, simultaneously, to any desired locations in n-dimensional nonlinear systems, a novel dynamic state-feedback control law is proposed. Analytical schemes to determine the control gains according to the conditions for the emergence of Hopf bifurcation are derived. To verify the effectiveness of the proposed control law, numerical examples are provided. 相似文献
47.
In this paper, the nonlinear dynamical behavior of two coupled pipes conveying pulsating fluid is studied. The connection between the two pipes is considered as a distributed linear spring. Based on this consideration, the equations of motion of the coupled two-pipe system are obtained. The two coupled nonlinear partial differential equations, discretized using the fourth- order Galerkin method, are solved by a fourth-order Runge-Kutta integration algorithm. Results show that the connection stiffness has a significant effect on the dynamical behavior of the coupled system. It is found that for some parameter values the motion types of the two pipes might be synchronous. 相似文献
48.
49.
Applied Mathematics and Mechanics - The recently developed hard-magnetic soft (HMS) materials can play a significant role in the actuation and control of medical devices, soft robots, flexible... 相似文献
50.
Jianglin Zhao Yong Yan Lizhuang Huang Run Yang 《Mathematical Methods in the Applied Sciences》2019,42(11):3831-3847
This paper deals with a diffusive toxin producing phytoplankton‐zooplankton model with maturation delay. By analyzing eigenvalues of the characteristic equation associated with delay parameter, the stability of the positive equilibrium and the existence of Hopf bifurcation are studied. Explicit results are derived for the properties of bifurcating periodic solutions by means of the normal form theory and the center manifold reduction for partial functional differential equations. Numerical simulations not only agree with the theoretical analysis but also exhibit the complex behaviors such as the period‐3, 5, 6, 7, 8, 11, and 12 solutions, cascade of period‐doubling bifurcation in period‐2, 4, quasi‐periodic solutions, and chaos. The key observation is that time delay may control harmful algae blooms (HABs). Moreover, numerical simulations show that the chaotic states induced by the period‐doubling bifurcation are purely temporal, which is stationary in space and oscillatory in time. The investigations may provide some new insights on harmful phytoplankton blooms. 相似文献