全文获取类型
收费全文 | 70727篇 |
免费 | 1370篇 |
国内免费 | 1257篇 |
专业分类
测绘学 | 1679篇 |
大气科学 | 4605篇 |
地球物理 | 14175篇 |
地质学 | 27020篇 |
海洋学 | 6405篇 |
天文学 | 15719篇 |
综合类 | 354篇 |
自然地理 | 3397篇 |
出版年
2022年 | 708篇 |
2021年 | 1068篇 |
2020年 | 1099篇 |
2019年 | 1179篇 |
2018年 | 2520篇 |
2017年 | 2369篇 |
2016年 | 2522篇 |
2015年 | 1302篇 |
2014年 | 2315篇 |
2013年 | 3578篇 |
2012年 | 2807篇 |
2011年 | 3428篇 |
2010年 | 3041篇 |
2009年 | 3646篇 |
2008年 | 3201篇 |
2007年 | 3388篇 |
2006年 | 3140篇 |
2005年 | 2408篇 |
2004年 | 2415篇 |
2003年 | 2096篇 |
2002年 | 1663篇 |
2001年 | 1509篇 |
2000年 | 1357篇 |
1999年 | 1028篇 |
1998年 | 1084篇 |
1997年 | 1095篇 |
1996年 | 869篇 |
1995年 | 863篇 |
1994年 | 775篇 |
1993年 | 674篇 |
1992年 | 660篇 |
1991年 | 630篇 |
1990年 | 730篇 |
1989年 | 622篇 |
1988年 | 581篇 |
1987年 | 666篇 |
1986年 | 519篇 |
1985年 | 686篇 |
1984年 | 789篇 |
1983年 | 706篇 |
1982年 | 689篇 |
1981年 | 618篇 |
1980年 | 630篇 |
1979年 | 527篇 |
1978年 | 567篇 |
1977年 | 517篇 |
1976年 | 464篇 |
1975年 | 457篇 |
1974年 | 457篇 |
1973年 | 526篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
74.
75.
76.
R. L. Macklin 《Astrophysics and Space Science》1985,115(1):71-83
Neutron capture measurements made on a sample of fission-product zirconium containing 20%93Zr(t
1/2=1.5×106a) at the Oak Ridge Electron Linear Accelerator time-of-flight facility resulted in the identification of 138 resonance peaks for the93Zr isotope at neutron energies up to 21.5 keV. Average capture cross sections from 20 to 300 keV were derived by subtracting neutron capture yields of the stable zirconium isotopes90, 91, 92, 94, 96Zr and additional backgrounds. The average cross sections found were significantly less than those of JENDL-1. While generally 30% higher than those of ENDF/B —V below 60 keV, the binned data overlapped the smooth ENDF/B —V curve. The average for a Maxwellian neutron spectrum withkT=30 keV is (95±10) mb and the resonance contribution to the capture resonance integral is (15.0±0.5)b.Research sponsored by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract DE-AC05-840R21400 with the Martin Marietta Energy Systems, Inc. 相似文献
77.
L. Zaninetti 《Astrophysics and Space Science》1985,108(2):401-407
A complete sample of symmetric double radio-galaxies has been investigated by inferring the propagation of a jet along the radio-axis and computing velocities with the aid of different models. A best linear fit between radio-luminosity and velocity is proposed in the range 1040 ergs s–145 ergs s–1. 相似文献
78.
Using the basic Boussinesq's equation, the expression for the vertical stress distribution (σz) underneath any point on the ground surface due to a general triangular loaded region in a preferred orientation with a linearly varied loading has been successfully derived. When the triangle is not in a preferred orientation, a simple axis transformation is required and the expression will be equally applicable. Based on this expression, σz due to an arbitrarily shaped loaded foundation can simply be determined by first triangulating the loaded area and summing up the contributions from each generated triangular region. The procedures for triangulating and calculating the stress distribution can be simply automated through computer programs. 相似文献
79.
A. Greco G. Zimbardo P. Veltri A.L. Taktakishvili L.M. Zelenyi 《Astrophysics and Space Science》2001,277(1-2):35-38
We study the ion dynamics in a magnetic field reversal with a constant electric field and with a model of three dimensional
magnetic turbulence. By computing the mean square displacements in the plane of the current sheet we find superdiffusive and
superballistic transport regimes. Since velocity increases with the length of the free path, we have accelerated Lévyflights.
The possibility to generate power law velocity distribution functions is pointed out, as well as the long memory effects and
non local properties of ion transport.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.
We report on SWS and LWS observations of the circumstellar disks of young stars of a few solar masses. The ISO spectra of
these objects present a diversity of emission features of carbon-rich and oxygen-rich grains. The similarity of the forsterite
spectra observed for Comet Hale-Bopp and the Haebe star HD100546 is particularly striking and provides a new argument that
huge comet swarms are formed in the disks surrounding young stars. While the data suggest that the formation of crystalline
silicates in the dust disks essentially occurs when a Haebe star has already reached the main sequence, no clear correlation
with stellar age only is apparent.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献