全文获取类型
收费全文 | 507779篇 |
免费 | 5181篇 |
国内免费 | 1604篇 |
专业分类
化学 | 255471篇 |
晶体学 | 7180篇 |
力学 | 25078篇 |
综合类 | 13篇 |
数学 | 79963篇 |
物理学 | 146859篇 |
出版年
2021年 | 3771篇 |
2020年 | 4197篇 |
2019年 | 4531篇 |
2018年 | 15601篇 |
2017年 | 15321篇 |
2016年 | 14506篇 |
2015年 | 6334篇 |
2014年 | 8797篇 |
2013年 | 20414篇 |
2012年 | 19036篇 |
2011年 | 28871篇 |
2010年 | 18675篇 |
2009年 | 18926篇 |
2008年 | 23713篇 |
2007年 | 25489篇 |
2006年 | 16433篇 |
2005年 | 15729篇 |
2004年 | 14930篇 |
2003年 | 13729篇 |
2002年 | 12649篇 |
2001年 | 13626篇 |
2000年 | 10330篇 |
1999年 | 8039篇 |
1998年 | 6726篇 |
1997年 | 6436篇 |
1996年 | 6268篇 |
1995年 | 5581篇 |
1994年 | 5464篇 |
1993年 | 5289篇 |
1992年 | 5882篇 |
1991年 | 5989篇 |
1990年 | 5715篇 |
1989年 | 5524篇 |
1988年 | 5546篇 |
1987年 | 5432篇 |
1986年 | 5144篇 |
1985年 | 6604篇 |
1984年 | 6737篇 |
1983年 | 5336篇 |
1982年 | 5425篇 |
1981年 | 5405篇 |
1980年 | 5002篇 |
1979年 | 5389篇 |
1978年 | 5528篇 |
1977年 | 5405篇 |
1976年 | 5344篇 |
1975年 | 4928篇 |
1974年 | 4896篇 |
1973年 | 4905篇 |
1972年 | 3473篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Joseph Majdalani Sjoerd W. Rienstra 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(2):289-308
The bidirectional vortex refers to the bipolar, coaxial swirling motion that can be triggered, for example, in cyclone separators
and some liquid rocket engines with tangential aft-end injectors. In this study, we present an exact solution to describe
the corresponding bulk motion in spherical coordinates. To do so, we examine both linear and nonlinear solutions of the momentum
and vorticity transport equations in spherical coordinates. The assumption will be that of steady, incompressible, inviscid,
rotational, and axisymmetric flow. We further relate the vorticity to some power of the stream function. At the outset, three
possible types of similarity solutions are shown to fulfill the momentum equation. While the first type is incapable of satisfying
the conditions for the bidirectional vortex, it can be used to accommodate other physical settings such as Hill’s vortex.
This case is illustrated in the context of inviscid flow over a sphere. The second leads to a closed-form analytical expression
that satisfies the boundary conditions for the bidirectional vortex in a straight cylinder. The third type is more general
and provides multiple solutions. The spherical bidirectional vortex is derived using separation of variables and the method
of variation of parameters. The three-pronged analysis presented here increases our repertoire of general mean flow solutions
that rarely appear in spherical geometry. It is hoped that these special forms will permit extending the current approach
to other complex fluid motions that are easier to capture using spherical coordinates. 相似文献
992.
N. M. Bogoliubov 《Journal of Mathematical Sciences》2007,143(1):2729-2737
We consider random walks of two essentially different classes of random walkers, namely, of vicious and friendly ones, on
one-dimensional lattices with periodic boundary conditions. The walkers are called vicious since, arriving at a lattice site,
they annihilate not only one another but all the remaining walkers as well. On the contrary, an arbitrary number of friendly
walkers can share the same lattice sites. It is shown that a natural model describing the behavior of friendly walkers is
an integrable model of the boson type. A representation of the generating function for the number of the lattice paths performed
by a fixed number of friendly walkers for a certain number of steps is obtained. Bibliography: 22 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 335, 2006, pp. 59–74. 相似文献
993.
In this paper, we study the homogenous quotient modules of the Hardy module on the bidisk. The essential normality of the
homogenous quotient modules is completely characterized. We also describe the essential spectrum for a general quotient module.
The paper also considers K-homology invariant defined in the case of the homogenous quotient modules on the bidisk.
This work is partially supported by the National Natural Science Foundation of China (Grant No. 10525106), the Young Teacher
Fund, the National Key Basic Research Project of China (Grant No. 2006CB805905) and the Specialized Research for the Doctoral
Program 相似文献
994.
995.
996.
Yu-hai WU~ 《中国科学A辑(英文版)》2007,50(7):925-940
This paper concerns the number and distributions of limit cycles in a Z_2-equivariant quintic planar vector field.25 limit cycles are found in this special planar polynomial system and four different configurations of these limit cycles are also given by using the methods of the bifurcation theory and the qualitative analysis of the differential equation.It can be concluded that H(5)≥25=5~2, where H(5)is the Hilbert number for quintic polynomial systems.The results obtained are useful to study the weakened 16th Hilbert problem. 相似文献
997.
Morten Nielsen 《Advances in Computational Mathematics》2007,27(2):195-209
Given a dilation matrix A :ℤd→ℤd, and G a complete set of coset representatives of 2π(A
−Tℤd/ℤd), we consider polynomial solutions M to the equation ∑
g∈G
M(ξ+g)=1 with the constraints that M≥0 and M(0)=1. We prove that the full class of such functions can be generated using polynomial convolution kernels. Trigonometric
polynomials of this type play an important role as symbols for interpolatory subdivision schemes. For isotropic dilation matrices,
we use the method introduced to construct symbols for interpolatory subdivision schemes satisfying Strang–Fix conditions of
arbitrary order.
Research partially supported by the Danish Technical Science Foundation, Grant No. 9701481, and by the Danish SNF-PDE network. 相似文献
998.
Yen-Shung TSAI 《中国科学A辑(英文版)》2007,50(7):1026-1034
By means of further investigation of solid codes,the problem“Is every fd-domain uni- formly dense”proposed by Yuqi Guo,C.M.Reis and G.Thierrin in 1988 is solved in this paper. 相似文献
999.
We present a study of the temporal compression of nanosecond laser pulses resulting from the coherent control peculiarities of the propagation dynamics in a regime of electromagnetically induced transparency. We describe the general theoretical framework and discuss the crucial conditions required in order to experimentally realize such a temporal compression scheme. A proof-of-concept experimental realization of a scheme of this type in a sample of hot sodium vapors is currently being implemented: we describe in detail the experimental setup designed for this purpose. 相似文献
1000.
T. M. Tovstik 《Vestnik St. Petersburg University: Mathematics》2007,40(3):250-252
An algorithm for calculating the discrepancy of finitely many points in the unit n-cube [0, 1]n is suggested. This algorithm is easy to program. For 2 ≤ n ≤ 4, the suggested algorithm is significantly faster than Bundschuh and Zhu’s algorithm. For larger n, whether this algorithm is faster depends on the number of points. 相似文献