全文获取类型
收费全文 | 12181篇 |
免费 | 2369篇 |
国内免费 | 1174篇 |
专业分类
化学 | 3270篇 |
晶体学 | 224篇 |
力学 | 3165篇 |
综合类 | 155篇 |
数学 | 1385篇 |
物理学 | 7525篇 |
出版年
2024年 | 34篇 |
2023年 | 124篇 |
2022年 | 389篇 |
2021年 | 395篇 |
2020年 | 375篇 |
2019年 | 336篇 |
2018年 | 339篇 |
2017年 | 452篇 |
2016年 | 570篇 |
2015年 | 503篇 |
2014年 | 707篇 |
2013年 | 1098篇 |
2012年 | 783篇 |
2011年 | 897篇 |
2010年 | 752篇 |
2009年 | 800篇 |
2008年 | 830篇 |
2007年 | 879篇 |
2006年 | 768篇 |
2005年 | 674篇 |
2004年 | 546篇 |
2003年 | 535篇 |
2002年 | 442篇 |
2001年 | 384篇 |
2000年 | 360篇 |
1999年 | 294篇 |
1998年 | 324篇 |
1997年 | 203篇 |
1996年 | 157篇 |
1995年 | 120篇 |
1994年 | 125篇 |
1993年 | 104篇 |
1992年 | 72篇 |
1991年 | 67篇 |
1990年 | 54篇 |
1989年 | 38篇 |
1988年 | 34篇 |
1987年 | 32篇 |
1986年 | 28篇 |
1985年 | 35篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1959年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Conducting drop tests to investigate impact behavior and identify failure mechanisms of small-size electronic products is
generally expensive and time-consuming. Nevertheless, strict drop/impact performance criteria for hand-held electronic products
such as cellular phones play a decisive role in the design because they must withstand unexpected shocks. The design of product
durability on impact has heavily relied on the designer's intuition and experience. In this study, a reliable drop/impact
simulation for a cellular phone is carried out using the explicit code LS-DYNA. Subsequently globallocal experimental verification
is accomplished by means of high-speed photography and impact response measurement. Using this methodology, we predict potential
damage locations in a cellular phone and compare them with real statistical data. It is envisaged that development of a reliable
methodology of drop/impact simulation will provide us with a powerful and efficient vehicle for improvement of the design
quality and reduction of the product development cycle. 相似文献
63.
64.
65.
A striking size dependence of the mean-square displacement of diffusing particles in the two-dimensional lattice gas of hard squares has been observed by Monte Carlo simulation. It is shown that the size effect is due to the formation of a stable cage structure in small lattices when the particle concentration is high. The formation of cages is governed by a new type of percolation problem related to bootstrap percolation. 相似文献
66.
Spatio temporal dynamics of the positive column of a dc neon glow discharge is studied and investigated experimentally and theoretically. Spatio temporal analysis by means of biorthogonal decomposition method (BOD) gives insights into the mechanism of irregularity and can be employed for characterization of spatio‐ temporal complexity. In the weak nonlinear region, the wave dynamics is approximated by an amplitude equation of the Ginzburg‐Landau equation (CGLE) with complex coefficients and an additional integral term based on a fluid model. In the present work we deal with irregular spatio‐temporal data. A comparison between the numerical analysis of the experimental data and simulation results are studied. A good agreement between the dynamical behaviour for experimental space‐time data and theoretical simulation space‐time results was obtained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
67.
An efficient technique for drag reduction uses dilute solutions of a few p.p.m. of polymers. A possible reduction in drag of up to 80% is achieved. Several experimental observations have been made which tend to indicate that the polymers modify the turbulence structures within the buffer layer. Flow visualisations have shown that the changes consist of a weakening of the strength of the streamwise vortices. Existing literature reveals no attempts of numerical simulation of this phenomenon. In this paper an approach is pursued by using a constitutive equation which relates the elongation viscosity to the local properties of the flow. According to this model this viscosity is large in zones where the amount of strain rate is greater than the amount of vorticity, and is zero when the vorticity exceeds the strain rate. Simulations have been performed in a “minimal channel” to give good resolution with a limited number of grid points. The accuracy of the method is tested by comparison with the results of other techniques. For simulations with polymers, quantitative comparisons cannot be made, but the results reproduce the qualitative outputs of the experiments. The mean streamwise velocity is modified in the buffer layer; the peak of the streamwise turbulent intensity, in wall units, increases and its maximum moves far from the wall; and the vertical turbulent intensity is largely reduced in the wall region. An interesting outcome from both the simulation and the experiments is that the strength of the longitudinal vortices is reduced when the polymers are present. 相似文献
68.
69.
多级轴流压气机全工况特性计算 总被引:1,自引:0,他引:1
本文使用三维粘性流动计算软件Fine/Numeca,对某十五级轴流压气机进行了内流流场和全工况特性的数值计算尝试。分析了该压气机在设计工况和非设计工况的性能,同时把整机计算结果和前七级叶片的计算结果进行了比较。计算结果表明,当计算的级数较少时,目前的软件和硬件平台可以比较合理地预测压气机的全工况特性;而当计算的级数较多时,准确的数值模拟仍需要更为准确的多级模型和数值方法。 相似文献
70.
Hydrogels have been widely used in microelectromechanical systems (MEMS) and Bio‐MEMS devices. In this article, the equilibrium swelling/deswelling of the pH‐stimulus cylindrical hydrogel in the microchannel is studied and simulated by the meshless method. The multi‐field coupling model, called multi‐effect‐coupling pH‐stimulus (MECpH) model, is presented and used to describe the chemical field, electric field, and the mechanical field involved in the problem. The partial differential equations (PDEs) describing these three fields are either nonlinear or coupled together. This multi‐field coupling and high nonlinear characteristics produce difficulties for the conventional numerical methods (e.g., the finite element method or the finite difference method), so an alternative—meshless method is developed to discretize the PDEs, and the efficient iteration technique is adopted to solve the nonlinear problem. The computational results for the swelling/deswelling diameter of the hydrogel under the different pH values are firstly compared with experimental results, and they have a good agreement. The influences of other parameters on the mechanical properties of the hydrogel are also investigated in detail. It is shown that the multi‐field coupling model and the developed meshless method are efficient, stable, and accurate for simulation of the properties of the stimuli‐sensitive hydrogel. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 326–337, 2006 相似文献