全文获取类型
收费全文 | 70601篇 |
免费 | 728篇 |
国内免费 | 550篇 |
专业分类
测绘学 | 1770篇 |
大气科学 | 4209篇 |
地球物理 | 12842篇 |
地质学 | 28346篇 |
海洋学 | 5942篇 |
天文学 | 15873篇 |
综合类 | 289篇 |
自然地理 | 2608篇 |
出版年
2022年 | 600篇 |
2021年 | 896篇 |
2020年 | 1013篇 |
2019年 | 1077篇 |
2018年 | 4169篇 |
2017年 | 3713篇 |
2016年 | 3313篇 |
2015年 | 1076篇 |
2014年 | 2048篇 |
2013年 | 3131篇 |
2012年 | 2891篇 |
2011年 | 4513篇 |
2010年 | 3923篇 |
2009年 | 4528篇 |
2008年 | 3838篇 |
2007年 | 4407篇 |
2006年 | 2580篇 |
2005年 | 1673篇 |
2004年 | 1601篇 |
2003年 | 1574篇 |
2002年 | 1471篇 |
2001年 | 1236篇 |
2000年 | 1106篇 |
1999年 | 804篇 |
1998年 | 846篇 |
1997年 | 836篇 |
1996年 | 667篇 |
1995年 | 654篇 |
1994年 | 656篇 |
1993年 | 527篇 |
1992年 | 525篇 |
1991年 | 530篇 |
1990年 | 602篇 |
1989年 | 455篇 |
1988年 | 443篇 |
1987年 | 497篇 |
1986年 | 374篇 |
1985年 | 569篇 |
1984年 | 547篇 |
1983年 | 506篇 |
1982年 | 519篇 |
1981年 | 437篇 |
1980年 | 481篇 |
1979年 | 375篇 |
1978年 | 425篇 |
1977年 | 341篇 |
1976年 | 327篇 |
1975年 | 336篇 |
1974年 | 314篇 |
1973年 | 341篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
A. B. Pushkarev D. C. Gabuzda Yu. N. Vetukhnovskaya V. E. Yakimov 《Monthly notices of the Royal Astronomical Society》2005,356(3):859-871
We present the results of multifrequency (15 + 8 + 5 GHz) polarization Very Long Baseline Array (VLBA) observations of the three BL Lacertae objects 0745+241, 1418+546 and 1652+398 together with 5-GHz VLBI Space Observatory Programme (VSOP) observations of 1418+546 and 1.6- and 5-GHz VSOP observations of the blazar 1055+018. The jets of all these sources have polarization structure transverse to the jet axis, with the polarization E vectors aligned with the jet along the jet spine and 'sheaths' of orthogonal E vectors at one or both edges of the jet. The presence of polarization aligned with the jet near the 'spine' may indicate that the jets are associated with helical B fields that propogate outward with the jet flow; the presence of orthogonal polarization near the edges of the jet may likewise be a consequence of a helical jet B field, or may be owing to an interaction with the ambient medium on parsec scales. We have tentatively detected interknot polarization in 1055+018 with E aligned with the local jet direction, consistent with the possibility that the jet of this source is associated with a helical B field. 相似文献
192.
193.
Andrew N. Wright 《Planetary and Space Science》1985,33(7):847-852
The problem of pitch angle scattering in field configurations similar to those found in the geomagnetic tail has been studied previously by Tsyganenko (1982). Tsyganenko used a scattering matrix to map pitch angle distributions through the current sheet. By using numerical solutions of the resulting integral equations he showed for weakly non-adiabatic particles the Stationary Distribution Function (SDF) was isotropic. Using his procedure the SDF was found to develop anisotropies with increasing non-adiabaticity. The work presented here shows analytically that for any degree of scattering the SDF must be isotropic for a general planar field reversal. Computations of particle trajectories have been used to verify some aspects of the analytic work. 相似文献
194.
R. K. Pant N. Basavaiah N. Juyal N. K. Saini M. G. Yadava E. Appel A. K. Singhvi 《第四纪科学杂志》2005,20(5):485-492
The southwest monsoon that dominated Central Himalaya has preserved loessic silt deposits preserved in patches that are proximal to periglacial areas. The occurrence of such silts suggests contemporary prevalence of cold and dry northwesterly winds. Field stratigraphy, geochemistry, mineral magnetism, infrared stimulated luminescence (IRSL) and radiocarbon dating has enabled reconstruction of an event chronology during the past 20 ka. Three events of loess accretion could be identified. The first two events of loess deposition occurred betweem 20 and 9 ka and were separated by a phase of moderate weathering. Pedogenesis at the end of this event gave rise to a well‐developed soil that was bracketed around 9 to > 4 ka. This was followed by the third phase of loess accretion that occurred around 4 to > 1 ka. Episodes of loess deposition and soil formation are interpreted in terms of changes in the strength of the Indian southwest monsoon. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
195.
V. V. Fidelis 《Astronomy Letters》2006,32(2):91-95
We consider the very-high-energy (VHE) gamma-ray observations of the blazar 3C 66A with the GT-48 Cherenkov telescope in the period 2002–2004 in comparison with the quasi-simultaneous ASM/RXTE observations in the energy range 2–10 keV. We show that there are positive correlations between the VHE gamma-ray and X-ray fluxes from this object recorded in the observing periods of 2002–2004. 相似文献
196.
197.
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
198.
199.
200.