全文获取类型
收费全文 | 3430篇 |
免费 | 331篇 |
国内免费 | 235篇 |
专业分类
化学 | 303篇 |
晶体学 | 29篇 |
力学 | 2081篇 |
综合类 | 25篇 |
数学 | 388篇 |
物理学 | 1170篇 |
出版年
2024年 | 10篇 |
2023年 | 36篇 |
2022年 | 82篇 |
2021年 | 61篇 |
2020年 | 113篇 |
2019年 | 89篇 |
2018年 | 80篇 |
2017年 | 130篇 |
2016年 | 142篇 |
2015年 | 110篇 |
2014年 | 157篇 |
2013年 | 175篇 |
2012年 | 152篇 |
2011年 | 195篇 |
2010年 | 130篇 |
2009年 | 144篇 |
2008年 | 147篇 |
2007年 | 192篇 |
2006年 | 188篇 |
2005年 | 178篇 |
2004年 | 191篇 |
2003年 | 172篇 |
2002年 | 123篇 |
2001年 | 115篇 |
2000年 | 110篇 |
1999年 | 102篇 |
1998年 | 117篇 |
1997年 | 68篇 |
1996年 | 72篇 |
1995年 | 48篇 |
1994年 | 57篇 |
1993年 | 45篇 |
1992年 | 41篇 |
1991年 | 48篇 |
1990年 | 41篇 |
1989年 | 33篇 |
1988年 | 25篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1971年 | 3篇 |
1957年 | 8篇 |
排序方式: 共有3996条查询结果,搜索用时 15 毫秒
81.
This paper uses the four-variable refined plate theory (RPT) for the free vibration analysis of functionally graded material (FGM) sandwich rectangular plates.Unlike other theories, there are only four unknown functions involved, as compared to five in other shear deformation theories. The theory presented is variationally consistent and strongly similar to the classical plate theory in many aspects. It does not require the shear correction factor, and gives rise to the transverse shear stress variation so that the transverse shear stresses vary parabolically across the thickness to satisfy free surface conditions for the shear stress. Two common types of FGM sandwich plates are considered, namely, the sandwich with the FGM facesheet and the homogeneous core and the sandwich with the homogeneous facesheet and the FGM core. The equation of motion for the FGM sandwich plates is obtained based on Hamilton's principle. The closed form solutions are obtained by using the Navier technique. The fundamental frequencies are found by solving the eigenvalue problems. The validity of the theory is shown by comparing the present results with those of the classical, the first-order, and the other higher-ordex theories. The proposed theory is accurate and simple in solving the free vibration behavior of the FGM sandwich plates. 相似文献
82.
Nikolay Banichuk Alexander Barsuk S. Y. Ivanova Juha Jeronen Evgeni Makeev 《基于设计的结构力学与机械力学》2018,46(1):1-17
We consider an infinite, homogenous linearly elastic beam resting on a system of linearly elastic supports, as an idealized model for a paper web in the middle of a cylinder-based dryer section. We obtain closed-form analytical expressions for the eigenfrequencies and the eigenmodes. The frequencies increase as the support rigidity is increased. Each frequency is bounded from above by the solution with absolutely rigid supports, and from below by the solution in the limit of vanishing support rigidity. Thus in a real system, the natural frequencies will be lower than predicted by commonly used models with rigid supports. 相似文献
83.
84.
The three-dimensional (3D) problem of the ground vibration isolation by an in-filled trench as a passive barrier is studied
theoretically. Integral equations governing Rayleigh wave scattering are derived based on the Green’s solution of Lamb problem.
The integral equations are solved accurately and efficiently with an iteration technique. They are used to evaluate the complicated
Rayleigh wave field generated by irregular scatterers embedded in an elastic half-space solid. The passive isolation effectiveness
of ground vibration by the in-filled trench for screening Rayleigh wave is further studied in detail. Effects of relevant
parameters on the effectiveness of vibration isolation are investigated and presented. The results show that a trench filled
with stiff backfill material gets a better isolation effect than a soft one, and increasing the depth or width of the in-filled
trench also improves its screening effectiveness. The effectiveness and the area of the screened zone are surging with the
increase in the length of the in-filled trench.
Supported by the National Natural Science Foundation of China (Grant Nos. 50678128 and 50538010) and the Research Fund for
PhD Student of Chinese College (Grant No. 20050247030) 相似文献
85.
孙元功 《纯粹数学与应用数学》2002,18(2):170-173
对于一类特殊的具有时滞的二阶次线性强迫微分方程x"(t) +a (t)|x(τ(t))|γsgnx(τ(t)) =g(t)(0<τ<1),给出了它的所有解振动的一个充要条件. 相似文献
86.
We considered the factors due to which the dependences between the uranium–oxygen distances R
0 and the frequencies of valence vibrations as for complex compounds of uranyl are described by two independent expressions generally represented by equations of the type R
0 = a + bas
–2/3 (b > 0) with the coefficients a and b differing in the regions R
0 < 0.178 nm and R
0 > 0.178 nm. It is shown that the reason is that there is a mutual effect of the ligands in the uranyl complex responsible for different partial contributions of the uranium orbitals and of the atoms of the first coordination sphere to the chemical bonding. 相似文献
87.
88.
In this paper we study the oscillations for a class of functional differential inequalities. By using these properties some forced oscillations to the boundary value problems of functional partial differential equations are established. 相似文献
89.
The dynamics of bistable oscillators driven by periodic dichotomous noise is described. The stochastic differential equation governing the flow implies smooth trajectories between noise switching events. The dynamics of the two-branched map induced by this flow is a Markov process. Harmonic and quartic models of the bistable potential are studied in the overdamped limit. In the linear (harmonic) case the dynamics can be reduced to a stochastic one-dimensional map with two branches. The moments decay exponentially in this case, although the invariant measure may be multifractal. For strong damping, relaxation induces a cascade leading to a Cantor set and anomalous decay of the density in this case is modeled by a Markov chain. For the physically more realistic case of a quartic potential many additional features arise since the contraction factor is distance dependent. By tuning the barrier-height parameter in the quartic potential, noise-induced transition rates with the characteristics of intermittency are found. 相似文献
90.
It is proposed in this paper to use the generalized cell mapping to locate strange attractors of dynamical systems and to determine their statistical properties. The cell-to-cell mapping method is based upon the idea of replacing the state space continuum by a large collection of state space cells and of expressing the evolution of the dynamical system in terms of a cell-to-cell mapping. This leads to a Markov chain which in turn allows us to compute all the statistical properties as well as the invariant distribution. After a general discussion, the method is applied in this paper to strange attractors of a variety of systems governed either by point mappings or by differential equations. The results indicate that it is a viable, effective and attractive method. Some comments on this method in comparison with the method of direct iteration will also be made. 相似文献