全文获取类型
收费全文 | 141025篇 |
免费 | 2362篇 |
国内免费 | 1128篇 |
专业分类
测绘学 | 3478篇 |
大气科学 | 9668篇 |
地球物理 | 27448篇 |
地质学 | 51852篇 |
海洋学 | 12394篇 |
天文学 | 31061篇 |
综合类 | 535篇 |
自然地理 | 8079篇 |
出版年
2022年 | 818篇 |
2021年 | 1420篇 |
2020年 | 1571篇 |
2019年 | 1701篇 |
2018年 | 4817篇 |
2017年 | 4450篇 |
2016年 | 4735篇 |
2015年 | 2320篇 |
2014年 | 3998篇 |
2013年 | 7022篇 |
2012年 | 4730篇 |
2011年 | 6864篇 |
2010年 | 6007篇 |
2009年 | 7519篇 |
2008年 | 6604篇 |
2007年 | 6851篇 |
2006年 | 5263篇 |
2005年 | 4172篇 |
2004年 | 4031篇 |
2003年 | 3838篇 |
2002年 | 3596篇 |
2001年 | 3143篇 |
2000年 | 3049篇 |
1999年 | 2435篇 |
1998年 | 2552篇 |
1997年 | 2364篇 |
1996年 | 2026篇 |
1995年 | 2022篇 |
1994年 | 1724篇 |
1993年 | 1611篇 |
1992年 | 1530篇 |
1991年 | 1485篇 |
1990年 | 1559篇 |
1989年 | 1349篇 |
1988年 | 1229篇 |
1987年 | 1479篇 |
1986年 | 1275篇 |
1985年 | 1570篇 |
1984年 | 1758篇 |
1983年 | 1682篇 |
1982年 | 1577篇 |
1981年 | 1428篇 |
1980年 | 1319篇 |
1979年 | 1239篇 |
1978年 | 1201篇 |
1977年 | 1050篇 |
1976年 | 1038篇 |
1975年 | 985篇 |
1974年 | 989篇 |
1973年 | 1030篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
721.
N. Kameswara Rao V. R. Venugopal A. Patnaik 《Journal of Astrophysics and Astronomy》1985,6(3):153-157
VLA observations at 2 and 6 cm have been obtained for six hydrogen-deficient stars R CrB, HD 160641, BD — 9°4395, V348 Sgr,
MV Sgr and Sgrv Upper limits to the massloss rates have been estimated for some of these using the upper limits to the radio flux density.
National Radio Astronomy Observatory’s Very Large Array is operated by Associated Universities Inc. under contract with National
Science Foundation, USA 相似文献
722.
723.
724.
725.
X. Bai T.K. Gaisser A. Karle K. Rawlins G.M. Spiczak Todor Stanev 《Astroparticle Physics》2006,25(6):361-367
The muon flux at the South Pole was measured for five zenith angles, 0°, 15°, 35°, 82.13° and 85.15° with a scintillator muon telescope incorporating ice Cherenkov tank detectors as the absorber. We compare the measurements with other data and with calculations. 相似文献
726.
D. Möhlmann 《Earth, Moon, and Planets》1985,33(2):201-214
It is shown by linear stability analysis that a preplanetary (presatellite) disk of dust and gas with Keplerian velocity field can become unstable due to the collective self-gravity of the disk. The radial distribution of rings, which may result from this instability, is derived. These rings later on can be the formation sites for planets around the Sun and for satellites around the planets. The derived orbits are shown to be in good agreement with that of the planets and the satellites (of Jupiter, Saturn, and Uranus). Predictions and conclusions seem to be possible for the existence of three yet unknown Uranian satellites, the origin of the early Moon and the possible radial extension of the planetary system. 相似文献
727.
Stephen M. White 《Astrophysics and Space Science》1985,116(1):173-187
The dispersion relation for longitudinal waves in a one-dimensional ultrarelativistic plasma is calculated. Analytical and numerical results for the growth rate and frequency of the two-stream instability are presented as a function of the energy spread in the denser stream when the dilute stream is cold. The case of energy spreads in both beams is investigated numerically: it is found that relatively small energy spreads in both streams can lead to suppression of the instability. 相似文献
728.
729.
730.
CO maps of the Bok globule B335 are presented and used to derive its density profile, mass distribution, and rotational velocity structure. It is found that the cloud is in nearly hydrostatic equilibrium with a density profile that varies roughly as r?1 in the core and r?3 in the envelope. The observed rotation is unimportant in the force balance at the present stage of evolution. 相似文献