全文获取类型

收费全文 |
3386篇 |

免费 |
958篇 |

国内免费 |
36篇 |

专业分类

化学 |
1087篇 |

晶体学 |
32篇 |

力学 |
1146篇 |

综合类 |
51篇 |

数学 |
720篇 |

物理学 |
1344篇 |

出版年

2024年 |
2篇 |

2023年 |
41篇 |

2022年 |
83篇 |

2021年 |
122篇 |

2020年 |
172篇 |

2019年 |
111篇 |

2018年 |
117篇 |

2017年 |
129篇 |

2016年 |
171篇 |

2015年 |
113篇 |

2014年 |
202篇 |

2013年 |
288篇 |

2012年 |
209篇 |

2011年 |
252篇 |

2010年 |
195篇 |

2009年 |
234篇 |

2008年 |
177篇 |

2007年 |
190篇 |

2006年 |
195篇 |

2005年 |
166篇 |

2004年 |
138篇 |

2003年 |
147篇 |

2002年 |
100篇 |

2001年 |
73篇 |

2000年 |
94篇 |

1999年 |
79篇 |

1998年 |
72篇 |

1997年 |
79篇 |

1996年 |
53篇 |

1995年 |
60篇 |

1994年 |
53篇 |

1993年 |
55篇 |

1992年 |
43篇 |

1991年 |
27篇 |

1990年 |
32篇 |

1989年 |
20篇 |

1988年 |
14篇 |

1987年 |
10篇 |

1986年 |
6篇 |

1985年 |
8篇 |

1984年 |
5篇 |

1983年 |
6篇 |

1982年 |
6篇 |

1981年 |
3篇 |

1980年 |
3篇 |

1979年 |
6篇 |

1978年 |
3篇 |

1971年 |
4篇 |

1969年 |
1篇 |

1957年 |
6篇 |

**排序方式：**共有4380条查询结果，搜索用时 89 毫秒

1.

2.

Global stability of humoral immunity virus dynamics models with nonlinear infection rate and removal

In this paper, we investigate the dynamical behavior of two nonlinear models for viral infection with humoral immune response. The first model contains four compartments; uninfected target cells, actively infected cells, free virus particles and B cells. The intrinsic growth rate of uninfected cells, incidence rate of infection, removal rate of infected cells, production rate of viruses, neutralization rate of viruses, activation rate of B cells and removal rate of B cells are given by more general nonlinear functions. The second model is a modification of the first one by including an eclipse stage of infected cells. We assume that the latent-to-active conversion rate is also given by a more general nonlinear function. For each model we derive two threshold parameters and establish a set of conditions on the general functions which are sufficient to determine the global dynamics of the models. By using suitable Lyapunov functions and LaSalle’s invariance principle, we prove the global asymptotic stability of the all equilibria of the models. We perform some numerical simulations for the models with specific forms of the general functions and show that the numerical results are consistent with the theoretical results. 相似文献

3.

Enrichment of adenosine using thermally responsive chromatographic materials under friendly pH conditions

*下载免费PDF全文* Yanli Liang Fangfang Geng Rongji Dai Yulin Deng 《Journal of separation science》2015,38(23):4036-4042

A thermally responsive boronate affinity chromatographic material, which showed thermal sensitivity, had been successfully applied for the enrichment and separation of

*cis‐*diol‐containing compounds, and the capture and release process could be facilitated by adjusting the temperature. However, in this system, the pH of the mobile phase must be higher than 9.8, and alkaline media can lead to the degradation of labile compounds; the use of silica beads also limits its use. In this study, thermally responsive boronate affinity chromatographic material, namely poly(*N‐*isopropylacrylamide‐co‐*N*‐acryloyl‐3‐aminophenylboronic acid) grafted silica, was successfully prepared by atom transfer radical polymerization. Its structure was confirmed by IR spectroscopy and the graft ratio was 20.8%, determined by thermogravimetric analysis. Furthermore, the capture/release of adenosine, a*cis*‐diol, was performed from pH 5.0–9.0 and 10–50°C. The elution of adenosine was remarkably retarded at decreased temperatures and adenosine could be captured completely at 10°C at pH values of 5.0–9.0. The enrichment of adenosine could be achieved by simply changing the temperature from 10 to 50°C. Therefore, this material not only improved the stability of the silica, but was also suitable for the capture of oxidation‐sensitive biological analytes. Moreover, it could be used for the enrichment of*cis*‐diol‐containing compounds in LC with MS. 相似文献4.

In this note we consider the definition of anisotropy with regard to the response of bodies described by implicit constitutive relations. The class of response relations under considerations in this work is implicit relations between the history of the stress, the history of the density, and the history of the deformation gradient. It is shown that the work of Noll [4] defining the anisotropy of bodies in terms of symmetry groups for Simple Materials can be very easily extended to define the anisotropy in terms of symmetry groups for materials whose response is described by relations between the histories of the stresses and the deformation gradient. While symmetry groups are defined, the more arduous task of developing representation theorems for bodies defined through implicit response relations is an important open task. 相似文献

5.

Eduardo González‐Olivares Lina M. Gallego‐Berrío Betsabé González‐Yañez Alejandro Rojas‐Palma 《Mathematical Methods in the Applied Sciences》2015,38(18):5183-5196

In this work, a modified Holling–Tanner predator–prey model is analyzed, considering important aspects describing the interaction such as the predator growth function is of a logistic type; a weak Allee effect acting in the prey growth function, and the functional response is of hyperbolic type. Making a change of variables and time rescaling, we obtain a polynomial differential equations system topologically equivalent to the original one in which the non‐hyperbolic equilibrium point (0,0) is an attractor for all parameter values. An important consequence of this property is the existence of a separatrix curve dividing the behavior of trajectories in the phase plane, and the system exhibits the bistability phenomenon, because the trajectories can have different

*ω*?*l**i**m**i**t*sets; as example, the origin (0,0) or a stable limit cycle surrounding an unstable positive equilibrium point. We show that, under certain parameter conditions, a positive equilibrium may undergo saddle‐node, Hopf, and Bogdanov–Takens bifurcations; the existence of a homoclinic curve on the phase plane is also proved, which breaks in an unstable limit cycle. Some simulations to reinforce our results are also shown. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献6.

Conventional numerical techniques, used to study the acoustics of a car passenger cabin, treat the cabin as an isolated cavity excited by the cavity boundaries. Realistically, other cavity volumes such as the trunk communicate with the cabin through the holes in the parcel shelf of the car. An extended acoustic model of a car is formed by the cavity volumes of the passenger compartment and the trunk as well as air leakages through the holes provided for electrical devices and ventilation on the parcel shelf. In this study, the dynamic influence of air leakages between the passenger and trunk compartments on the first and second coupled system modes was investigated experimentally using acoustic frequency response function. The response to the acoustic excitation was measured for four different configurations of trim and holes of the parcel shelf. The natural frequencies of the first and second coupled system modes increased with increasing holes size with and without the trim of the parcel shelf. The experimental results were in good agreement with the reported results of coupling effects of double cavities connected by a neck. In the low frequency region since the wavelength is longer compared to the holes dimension, these holes act as point sources. 相似文献

7.

Room response equalization systems are used for improving the listening experience in cinema theatres, home theatres, car hi-fi systems. In this paper, an adaptive multichannel and multiple position room response equalization system and its real-time implementation are described. An adaptive and accurate estimation of the room responses is provided introducing a normalized least mean square optimization approach with a variable step-size, and taking advantage of an interchannel coherence reduction technique based on the missing fundamental phenomenon. Then, the equalizer is designed in warp frequency domain for improving equalization in the low frequency region, reducing the computational cost of the design procedure, and deriving an algorithm capable of working in real time. Indeed, a real-time implementation of the proposed adaptive equalizer has been obtained on NU-Tech framework and has been used in order to provide a deep objective and subjective evaluation of the equalization system. The results of these evaluations illustrate the effectiveness of the proposed approach, also in comparison with other techniques of the state of the art. 相似文献

8.

9.

The probability density function for transient response of non-linear stochastic system is investigated through the stochastic averaging and Mellin transform. The stochastic averaging based on the generalized harmonic functions is adopted to reduce the system dimension and derive the one-dimensional Itô stochastic differential equation with respect to amplitude response. To solve the Fokker–Plank–Kolmogorov equation governing the amplitude response probability density, the Mellin transform is first implemented to obtain the differential relation of complex fractional moments. Combining the expansion form of transient probability density with respect to complex fractional moments and the differential relations at different transform parameters yields a set of closed-form first-order ordinary differential equations. The complex fractional moments which are determined by the solution of the above equations can be used to directly construct the probability density function of system response. Numerical results for a van der Pol oscillator subject to stochastically external and parametric excitations are given to illustrate the application, the convergence and the precision of the proposed procedure. 相似文献

10.

The turbulent flow behind a circular cylinder subjected to forced oscillation is numerically studied at a Reynolds number of 5500 by using three-dimensional Large Eddy Simulations (3-D LES) technique with the Smagorinsky model. The filtered equations are discretised using the finite volume method with an O-type structured grid and a second-order accurate method in both time and space. Firstly, the main wake parameters of a stationary cylinder are examined and compared in the different grid resolutions. Secondly, a transversely oscillating cylinder with a constant amplitude in a uniform flow is investigated. The cylinder oscillation frequency ranges between 0.75 and 0.95 of the natural Kármán frequency, and the excitation amplitude is moderate, 50% of the cylinder diameter. The flow characteristics of an oscillating cylinder are numerically examined and the corresponding wake modes are captured firstly in 3-D LES at Re=5500. A transition between different wake modes is firstly investigated in a set of numerical simulations. 相似文献