全文获取类型
收费全文 | 474909篇 |
免费 | 2449篇 |
国内免费 | 743篇 |
专业分类
化学 | 213635篇 |
晶体学 | 7048篇 |
力学 | 28632篇 |
综合类 | 13篇 |
数学 | 75899篇 |
物理学 | 152874篇 |
出版年
2021年 | 4075篇 |
2020年 | 4411篇 |
2019年 | 5341篇 |
2018年 | 12585篇 |
2017年 | 12894篇 |
2016年 | 12638篇 |
2015年 | 5198篇 |
2014年 | 9154篇 |
2013年 | 17473篇 |
2012年 | 16788篇 |
2011年 | 24026篇 |
2010年 | 17540篇 |
2009年 | 18009篇 |
2008年 | 22190篇 |
2007年 | 24268篇 |
2006年 | 14082篇 |
2005年 | 15258篇 |
2004年 | 13262篇 |
2003年 | 12825篇 |
2002年 | 11876篇 |
2001年 | 11261篇 |
2000年 | 8919篇 |
1999年 | 6558篇 |
1998年 | 5967篇 |
1997年 | 5865篇 |
1996年 | 5524篇 |
1995年 | 4792篇 |
1994年 | 4933篇 |
1993年 | 4902篇 |
1992年 | 5100篇 |
1991年 | 5531篇 |
1990年 | 5401篇 |
1989年 | 5418篇 |
1988年 | 5192篇 |
1987年 | 5194篇 |
1986年 | 4866篇 |
1985年 | 5892篇 |
1984年 | 6181篇 |
1983年 | 5227篇 |
1982年 | 5424篇 |
1981年 | 5097篇 |
1980年 | 4714篇 |
1979年 | 5443篇 |
1978年 | 5475篇 |
1977年 | 5655篇 |
1976年 | 5734篇 |
1975年 | 5382篇 |
1974年 | 5212篇 |
1973年 | 5457篇 |
1972年 | 4416篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
D. N. Zaporozhets 《Journal of Mathematical Sciences》2006,137(1):4525-4530
In this note, we find the distibution of the number of real zeros of a random polynomial. We also derive a formula for the
expected number of complex zeros lying in a given domain of the complex plane. Bibliography: 7 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 320, 2004, pp. 69–79. 相似文献
45.
The main result of the paper is a theorem, using which a new proof of Roth’s theorem is obtained, a new solvability criterion
for the matrix equation AX-YB = C is proved, a formula for a particular solution of the latter is derived, and the least of
the orders of square nonsingular matrices containing a given rectangular matrix as a submatrix is determined. Bibliography:
5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 323, 2005, pp. 15–23. 相似文献
46.
47.
M. V. Kartikeyan G. Singh E. Borie B. Piosczyk M. Thumm 《International Journal of Infrared and Millimeter Waves》2006,27(5):657-670
The feasibility of an 84 GHz, 500 kW, CW gyrotron for ECRH on an experimental tokamak will be presented in this paper. Mode
competition and mode selection procedures are carefully investigated by considering various candidate modes and the TE10,4 mode is chosen as the operating mode. A conventional cylindrical cavity resonator with weak input and output tapers and parabolic
roundings is considered for interaction studies. Self-consistent, both single mode and time-dependent, calculations are carried
out and power and efficiencies are computed for a typical set of beam parameters. The results show that an output power of
well over 500 kW, CW and efficiency around 40% can be reached without a depressed collector. 相似文献
48.
I. N. Sergeev 《Journal of Mathematical Sciences》2006,135(1):2764-2793
The definition of the characteristic frequencies of zeroes and changes of sign for solutions is given. It is equal to the
upper medium (with respect to the time half-axis) of their number on the half-interval of length π. We also define the main frequencies for a linear homogeneous equation of order n. These main frequencies for an equation with constant coefficients coincide with the absolute values of the imaginary parts
of the roots of the corresponding characteristic polynomial. It is proved that for the second-order equation the main frequencies
are the same for all solutions and that they are stable with respect to uniformly small and infinitely small perturbations
of the coefficients. For the third-order equation they can be different, and for any of the main frequencies an example of
nonstability is given.
__________
Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 25, pp. 249–294, 2005. 相似文献
49.
J. C. Fabris S. V. B. Gonçalves P. E. de Souza 《General Relativity and Gravitation》2002,34(12):2111-2126
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate. 相似文献
50.
In this paper, a two-dimensional finite volume unstructured mesh method (FVUM) based on a triangular background interpolation mesh is developed for analysing the evolution of the saltwater intrusion into single and multiple coastal aquifer systems. The model formulation consists of a ground-water flow equation and a salt transport equation. These coupled and non-linear partial differential equations are transformed by FVUM into a system of differential/algebraic equations, which is solved using backward differentiation formulas of order one through five. Simulation results are compared with previously published solutions where good agreement is observed. 相似文献