全文获取类型
收费全文 | 1221篇 |
免费 | 163篇 |
国内免费 | 71篇 |
专业分类
化学 | 146篇 |
晶体学 | 2篇 |
力学 | 361篇 |
综合类 | 7篇 |
数学 | 188篇 |
物理学 | 751篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 38篇 |
2020年 | 37篇 |
2019年 | 29篇 |
2018年 | 28篇 |
2017年 | 53篇 |
2016年 | 52篇 |
2015年 | 52篇 |
2014年 | 93篇 |
2013年 | 71篇 |
2012年 | 60篇 |
2011年 | 80篇 |
2010年 | 73篇 |
2009年 | 83篇 |
2008年 | 76篇 |
2007年 | 70篇 |
2006年 | 72篇 |
2005年 | 53篇 |
2004年 | 58篇 |
2003年 | 58篇 |
2002年 | 41篇 |
2001年 | 42篇 |
2000年 | 34篇 |
1999年 | 30篇 |
1998年 | 23篇 |
1997年 | 12篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1455条查询结果,搜索用时 140 毫秒
61.
本文利用有限单元法对干涉光谱仪精密动镜驱动装置进行了分析,得到了该装置的固有频率和主振型。 相似文献
62.
Acceleration waves propagating in isotropic solids at finite temperatures are studied by applying the method of singular surfaces to a new continuum model derived statistical-mechanically from a three-dimensional lattice model. The continuum model explicitly takes into account the microscopic thermal vibrations of the constituent atoms as one of the field variables. The propagation speeds and the ratios of mechanical and thermal amplitudes for both longitudinal and transverse waves are consistently determined. The differential equations that govern the time variation of the amplitudes of the waves are also derived. The analytical results, which are valid over a wide temperature range that includes the melting point, are evaluated numerically for several materials, and their physical implications are discussed. One of the findings to be emphasized is that of the singularities of the characteristic quantities at the melting point.Received: 13 March 2003, Accepted: 20 June 2003PACS:
62.30. + d, 65.40.-bM. Sugiyama: Correspondence to
Dedicated to Prof. Ingo Müller on the occasion of his 65th birthday. 相似文献
63.
64.
65.
Mustapha Ishak 《Foundations of Physics》2007,37(10):1470-1498
Associated with the cosmic acceleration are the old and new cosmological constant problems, recently put into the more general context of the dark energy problem. In broad terms, the old problem is related to an unexpected order of magnitude of this component while the new problem is related to this magnitude being of the same order of the matter energy density during the present epoch of cosmic evolution. Current plans to measure the equation of state or density parameters certainly constitute an important approach; however, as we discuss, this approach is faced with serious feasibility challenges and is limited in the type of conclusive answers it could provide. Therefore, is it really too early to seek actively for new tests and approaches to these problems? In view of the difficulty of this endeavor, we argue in this work that a good place to start is by questioning some of the assumptions underlying the formulation of these problems and finding new ways to put this questioning to the test. First, we calculate how much fine tuning the cosmic coincidence problem represents. Next, we discuss the potential of some cosmological probes such as weak gravitational lensing to identify novel tests to probe dark energy questions and assumptions and provide an example of consistency tests. Then, motivated by some theorems in General Relativity, we discuss if the full identification of the cosmological constant with vacuum energy is unquestionable. We discuss some implications of the simplest solution for the principles of General Relativity. Also, we point out the relevance of experiments at the interface of astrophysics and quantum field theory, such as the Casimir effect in gravitational and cosmological contexts. We conclude that challenging some of the assumptions underlying the cosmological constant problems and putting them to the test may prove useful and necessary to make progress on these questions. 相似文献
66.
This paper describes measurements of a vibrating object with rough surface by the time-averaged method of holography using a newly designed optically addressed liquid crystal spatial light modulator with a resolution of 102 lp/mm and a diffraction efficiency of 16%. An object vibrating faster than several tens of Hz could be visualized. The pattern obtained by the method provides the locus of vibrating nodes. The advantage of this method is that a high contrast pattern of a vibrating object can be imaged in near-real-time, although the sensitivity of vibration is decreased. 相似文献
67.
Accelerating flames in tubes—an analysis 总被引:1,自引:0,他引:1
C. Regis L. Bauwens Luc Bauwens Ida Wierzba 《Proceedings of the Combustion Institute》2007,31(2):2381-2388
Flame acceleration in tubes is studied. A tube filled with flammable mixture is closed at one end and open to the atmosphere at its second end. When ignition takes place near the closed end, it is well-known from experiments that the flame may accelerate, oscillate and eventually reach considerable speeds. A one-dimensional analysis is presented, based upon the assumption that the flame front propagates at a speed that is small compared to the speed of sound. The analysis leads to a construction of the complete unsteady solution. Results from the analysis and from a numerical simulation are compared. They are similar enough to validate the analysis. The tube acoustics are set in motion by the expansion of the fluid due to ignition at the closed end. Subsequently, both spectrum and amplitude evolve because of the motion of the temperature interface, and because of forcing by the flame front, which the analysis precisely quantifies. Oscillations in the front position are strong enough to result in flow reversal. In addition, the induced periodic acoustic acceleration of the temperature and density interface will periodically make the flame front Rayleigh–Taylor unstable, which should result in the dramatic increase in the propagation speed seen in experiments. 相似文献
68.
基于最小加速度原理的刚塑性动力问题 总被引:2,自引:0,他引:2
应用有限变形的最小加速度原理,推导出了小变形或有限变形构件受到刚性飞射物撞击时的刚塑性运动方程,指出该方法具有直接、简捷和可靠的特点。 相似文献
69.
A kind of function-valued Padé-type approximant via the formal orthogonal polynomials (FPTAVOP) is introduced on the polynomial space and an algorithm is sketched by means of the formal orthogonal polynomials. This method can be applied to approximate characteristic values and the corresponding characteristic function of Fredholm integral equation of the second kind. Moreover, theoretical analyses show that FPTAVOP method is the most effective one for accelerating the convergence of a sequence of functions. In addition, a typical numerical example is presented to illustrate when the estimates of characteristic value and characteristic function by using this new method are more accurate than other methods. 相似文献
70.
Image restoration is a fundamental problem in image processing. Blind image restoration has a great value in its practical application. However, it is not an easy problem to solve due to its complexity and difficulty. In this paper, we combine our robust algorithm for known blur operator with an alternating minimization implicit iterative scheme to deal with blind deconvolution problem, recover the image and identify the point spread function(PSF). The only assumption needed is satisfy the practical physical sense. Numerical experiments demonstrate that this minimization algorithm is efficient and robust over a wide range of PSF and have almost the same results compared with known PSF algorithm. 相似文献