全文获取类型
收费全文 | 29015篇 |
免费 | 3573篇 |
国内免费 | 1694篇 |
专业分类
化学 | 18480篇 |
晶体学 | 368篇 |
力学 | 1277篇 |
综合类 | 67篇 |
数学 | 3932篇 |
物理学 | 10158篇 |
出版年
2023年 | 437篇 |
2022年 | 475篇 |
2021年 | 820篇 |
2020年 | 901篇 |
2019年 | 948篇 |
2018年 | 979篇 |
2017年 | 866篇 |
2016年 | 1487篇 |
2015年 | 1188篇 |
2014年 | 1522篇 |
2013年 | 2306篇 |
2012年 | 2290篇 |
2011年 | 2397篇 |
2010年 | 1631篇 |
2009年 | 1513篇 |
2008年 | 1853篇 |
2007年 | 1597篇 |
2006年 | 1490篇 |
2005年 | 1164篇 |
2004年 | 922篇 |
2003年 | 661篇 |
2002年 | 640篇 |
2001年 | 506篇 |
2000年 | 450篇 |
1999年 | 486篇 |
1998年 | 406篇 |
1997年 | 385篇 |
1996年 | 351篇 |
1995年 | 322篇 |
1994年 | 266篇 |
1993年 | 259篇 |
1992年 | 196篇 |
1991年 | 226篇 |
1990年 | 187篇 |
1989年 | 170篇 |
1988年 | 150篇 |
1987年 | 141篇 |
1986年 | 126篇 |
1985年 | 171篇 |
1984年 | 186篇 |
1983年 | 116篇 |
1982年 | 104篇 |
1981年 | 119篇 |
1980年 | 110篇 |
1979年 | 80篇 |
1978年 | 66篇 |
1977年 | 58篇 |
1976年 | 73篇 |
1975年 | 62篇 |
1973年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
31.
32.
In this paper, a bivariate generating function CF(x, y) =f(x)-yf(xy)1-yis investigated, where f(x)= n 0fnxnis a generating function satisfying the functional equation f(x) = 1 + r j=1 m i=j-1aij xif(x)j.In particular, we study lattice paths in which their end points are on the line y = 1. Rooted lattice paths are defined. It is proved that the function CF(x, y) is a generating function defined on some rooted lattice paths with end point on y = 1. So, by a simple and unified method, from the view of lattice paths, we obtain two combinatorial interpretations of this bivariate function and derive two uniform partitions on these rooted lattice paths. 相似文献
33.
A. I. Belogorokhov I. I. Ivanchik S. V. Ponomarev D. R. Khokhlov E. I. Slyn’ko 《JETP Letters》1996,63(5):353-357
Selective photoconductivity at frequency ω=155 cm− was discovered in PbTe(Ga) narrow-gap semiconductors at liquid-nitrogen temperatures. The corresponding energy is much lower
than all characteristic energies of the electronic spectrum of the semiconductor. The effect is attributed to optical excitation
of a local vibrational mode of an impurity center leading to delocalization of the electrons.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 342–346 (10 March 1996) 相似文献
34.
Ma Jiangle Yang Hong-shen Zhang Zhongxi Lu Zhong-zuo 《International Journal of Infrared and Millimeter Waves》1993,14(5):1069-1076
A simple method is introduced to improve the analysing accuracy of circular groove guide. With this method, the characteristic equation of circular groove guide is derived and its solution is given and discussed.The Project Supported by National Natural Science Foundation of P.R.China 相似文献
35.
36.
The dynamics of multiphoton transitions in a two-level spin system excited by transverse microwave and longitudinal RF fields with the frequencies ωmw and ωrf, respectively, is analyzed. The effective time-independent Hamiltonian describing the “dressed” spin states of the “spin + bichromatic field” system is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The direct detection of the time behavior of the spin system by the method of nonstationary nutations makes it possible to identify the multiphoton transitions for resonances ω0 = ωmw + rωrf (ω0 is the central frequency of the EPR line, r = 1, 2), to measure the amplitudes of the effective fields of these transitions, and to determine the features generated by the inhomogeneous broadening of the EPR line. It is shown that the Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening of spectral lines reduce only the nutation amplitude but do not change their frequencies. 相似文献
37.
38.
39.
A two-dimensional, nonlinear, compressible, diabatic, nonhydrostatic photochemical-dynamical gravity wave model has been advanced. The model includes diabetic process produced by photochemistry and the effect of gravity wave on atmospheric chemical species. In the horizontal direction, the pseudospectral method is used. The finite difference approximations are used in vertical direction z and time t. The FICE method is used to solve the model. The model results on small amplitude fluctuation are very close to those of linear theory, which demonstrates the correctness of the model.
相似文献40.