全文获取类型
收费全文 | 6561篇 |
免费 | 155篇 |
国内免费 | 28篇 |
专业分类
化学 | 3814篇 |
晶体学 | 25篇 |
力学 | 179篇 |
数学 | 819篇 |
物理学 | 1907篇 |
出版年
2021年 | 68篇 |
2020年 | 72篇 |
2019年 | 70篇 |
2018年 | 54篇 |
2017年 | 45篇 |
2016年 | 138篇 |
2015年 | 111篇 |
2014年 | 142篇 |
2013年 | 302篇 |
2012年 | 291篇 |
2011年 | 340篇 |
2010年 | 198篇 |
2009年 | 156篇 |
2008年 | 288篇 |
2007年 | 352篇 |
2006年 | 311篇 |
2005年 | 328篇 |
2004年 | 311篇 |
2003年 | 234篇 |
2002年 | 177篇 |
2001年 | 131篇 |
2000年 | 122篇 |
1999年 | 76篇 |
1998年 | 57篇 |
1997年 | 76篇 |
1996年 | 90篇 |
1995年 | 68篇 |
1994年 | 81篇 |
1993年 | 91篇 |
1992年 | 114篇 |
1991年 | 78篇 |
1990年 | 91篇 |
1989年 | 76篇 |
1988年 | 53篇 |
1987年 | 67篇 |
1986年 | 66篇 |
1985年 | 110篇 |
1984年 | 101篇 |
1983年 | 81篇 |
1982年 | 76篇 |
1981年 | 86篇 |
1980年 | 64篇 |
1979年 | 68篇 |
1978年 | 74篇 |
1977年 | 66篇 |
1976年 | 56篇 |
1975年 | 71篇 |
1974年 | 71篇 |
1973年 | 83篇 |
1972年 | 57篇 |
排序方式: 共有6744条查询结果,搜索用时 78 毫秒
1.
Meccanica - The static limit analysis of axially symmetric masonry domes subject to pseudo-static seismic forces is addressed. The stress state in the dome is represented by the shell stress... 相似文献
2.
3.
4.
5.
We investigate the linear stability of the Bickley jet in the framework of the beta-plane approximation. Because singular inviscid neutral modes exist in the retrograde case , it is necessary to add viscosity to interpret them. One of these modes was found in closed form by Howard and Drazin [1] . However, its critical point is at the center of the jet and it was therefore not possible for these authors to ascertain the relationship of this mode to the stability problem or to discuss how to continue the eigenfunction across the singularity.
The viscous critical layer problem associated with this singularity is considerably more difficult than the usual one (which leads to integrals of the Airy function) because and, consequently, a second-order turning point is involved. Our analysis shows that the Howard–Drazin mode is degenerate in the domain where it is valid as a limit of the viscous problem (wavenumber α2 ≤ 9/2 ), that is, it corresponds to both an odd and an even mode. This conclusion is confirmed by direct numerical solution of the Orr–Sommerfeld equation which shows, in addition, that viscosity is destabilizing along portions of the stability boundary. For a retrograde jet, instability is found to occur beyond the inviscid critical value of β, that is, in the region where the flow would be stable according to the Rayleigh–Kuo condition. 相似文献
The viscous critical layer problem associated with this singularity is considerably more difficult than the usual one (which leads to integrals of the Airy function) because and, consequently, a second-order turning point is involved. Our analysis shows that the Howard–Drazin mode is degenerate in the domain where it is valid as a limit of the viscous problem (wavenumber α
6.
Let
d−1{(x1,…,xd)
d:x21+···+x2d=1} be the unit sphere of the d-dimensional Euclidean space
d. For r>0, we denote by Brp (1p∞) the class of functions f on
d−1 representable in the formwhere dσ(y) denotes the usual Lebesgue measure on
d−1,
and Pλk(t) is the ultraspherical polynomial.For 1p,q∞, the Kolmogorov N-width of Brp in Lq(
d−1) is given bythe left-most infimum being taken over all N-dimensional subspaces XN of Lq(
d−1).The main result in this paper is that for r2(d−1)2,where ANBN means that there exists a positive constant C, independent of N, such that C−1ANBNCAN.This extends the well-known Kashin theorem on the asymptotic order of the Kolmogorov widths of the Sobolev class of the periodic functions. 相似文献
7.
8.
Rebecca L Brown 《Journal of sound and vibration》2003,262(3):591-611
Most structural dynamic systems are of high order; however, they often exhibit phenomena that can be dealt with effectively using low order models. This paper presents a method for describing certain kinds of damage evolution in mechanical systems. The method relies on a simple principle that as damage evolves in a structural dynamic system, the damage indicator (i.e., diagnostic feature) behaves like a stable quasi-stationary equilibrium point in a subsidiary non-linear bifurcating system within the so-called damage center manifold. It is shown that just as linear normal modes govern the behavior of linear structures with idealized damping, so too do non-linear normal forms govern the evolution of damage within structures in many instances. The method is justified with citations from the literature on certain types of mechanical failure and then applied in an experimental case involving reversible damage in a bolted fastener. Off-line experiments on a rotorcraft fuselage show that the evolution of damage is sensitive to both temporal and spatial bifurcation parameters. A diagnostic sensing strategy whereby output-only transmissibility features are used to decrease the order of high order structural dynamic measurements is also described. 相似文献
9.
In this paper we define trace functionals on the algebra of pseudo-differential operators with cone-shaped exits to infinity. Furthermore, we improve the Weyl formula on the asymptotic distribution of eigenvalues and make use of it in order to establish inclusion relations between the interpolation normed ideals of compact operators in L
2(R
n
) and the above operator classes. 相似文献
10.
Richard Brown 《Geometriae Dedicata》2003,97(1):129-150
In this note, we show that given a closed, orientable genus-g surface S
g
, any hyperbolic toral automorphism has a positive power which induces a quadratic, orientable pseudo-Anosov homeomorphism on S
g
. To show this, we lift Anosov toral automorphisms through a ramified topological covering and present the lifted homeomorphism via a standard set of Lickorish twists. This construction provides a general method of producing pseudo-Anosov maps of closed surfaces with predetermined orientable foliations and quadratic dilatation. Since these lifted automorphisms have orientable foliations, this construction is a sort of converse to that of Franks and Rykken [Trans. Amer. Math. Soc. 1999], who established that one can associate to a quadratic pseudo-Anosov homeomorphism with oriented unstable foliation a hyperbolic toral automorphism. 相似文献