全文获取类型
收费全文 | 47579篇 |
免费 | 852篇 |
国内免费 | 549篇 |
专业分类
测绘学 | 1285篇 |
大气科学 | 3471篇 |
地球物理 | 9720篇 |
地质学 | 16764篇 |
海洋学 | 4101篇 |
天文学 | 10710篇 |
综合类 | 87篇 |
自然地理 | 2842篇 |
出版年
2021年 | 299篇 |
2020年 | 364篇 |
2019年 | 410篇 |
2018年 | 863篇 |
2017年 | 827篇 |
2016年 | 1079篇 |
2015年 | 665篇 |
2014年 | 1068篇 |
2013年 | 2355篇 |
2012年 | 1226篇 |
2011年 | 1692篇 |
2010年 | 1484篇 |
2009年 | 2006篇 |
2008年 | 1834篇 |
2007年 | 1820篇 |
2006年 | 1813篇 |
2005年 | 1464篇 |
2004年 | 1488篇 |
2003年 | 1368篇 |
2002年 | 1341篇 |
2001年 | 1115篇 |
2000年 | 1156篇 |
1999年 | 1049篇 |
1998年 | 1020篇 |
1997年 | 1003篇 |
1996年 | 800篇 |
1995年 | 810篇 |
1994年 | 791篇 |
1993年 | 678篇 |
1992年 | 637篇 |
1991年 | 558篇 |
1990年 | 659篇 |
1989年 | 538篇 |
1988年 | 560篇 |
1987年 | 627篇 |
1986年 | 534篇 |
1985年 | 757篇 |
1984年 | 820篇 |
1983年 | 799篇 |
1982年 | 696篇 |
1981年 | 638篇 |
1980年 | 663篇 |
1979年 | 567篇 |
1978年 | 567篇 |
1977年 | 527篇 |
1976年 | 536篇 |
1975年 | 518篇 |
1974年 | 532篇 |
1973年 | 510篇 |
1972年 | 333篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
Jennifer M. Galloway Christine T. Doherty R. Timothy Patterson Helen M. Roe 《第四纪科学杂志》2009,24(4):322-335
A pollen‐based study from Tiny Lake in the Seymour‐Belize Inlet Complex of central coastal British Columbia, Canada, permits an evaluation of the dynamic response of coastal temperate rainforests to postglacial climate change. Open Pinus parklands grew at the site during the early Lateglacial when the climate was cool and dry, but more humid conditions in the later phases of the Lateglacial permitted mesophytic conifers to colonise the region. Early Holocene conditions were warmer than present and a successional mosaic of Tsuga heterophylla and Alnus occurred at Tiny Lake. Climate cooling and moistening at 8740 ± 70 14C a BP initiated the development of closed, late successional T. heterophylla–Cupressaceae forests, which achieved modern character after 6860 ± 50 14C a BP, when a temperate and very wet climate became established. The onset of early Holocene climate cooling and moistening at Tiny Lake may have preceded change at more southern locations, including within the Seymour‐Belize Inlet Complex, on a meso‐ to synoptic scale. This would suggest that an early Holocene intensification of the Aleutian Low pressure system was an important influence on forest dynamics in the Seymour‐Belize Inlet Complex and that the study region was located near the southern extent of immediate influence of this semi‐permanent air mass. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
202.
203.
204.
205.
Lightning discharge generated in the protoplanetary nebula is viewed as a temporally isolated surge in the flow of electrically charged particles, similar to that of terrestrial lightning. If the current is intense enough, a powerful circular impulse magnetic field is generated around the instantaneous virtual electric conductor. Such magnetic field is capable of magnetizing dust grains containing ferromagnetic components present in its vicinity to their saturation levels. As a result, dust grains attract one another, forming the aggregates. This magnetically driven attraction suggests an important process possibly operational at an early stage of the planetary accretion. Based on both a classical model for electric conductor, and the theory of Lienard–Wiechert electromagnetic potentials, our calculations show that the magnetic impulse due to a discharge channel of a few cm in diameter transferring a charge of about 104 electrons reaches as high as 10 T. At these magnetic fields, the ferromagnetic dust grains, and possibly the already-formed larger aggregates as well, are easily magnetized to the saturation levels, producing compact clusters exhibiting permanent magnetic moments. 相似文献
206.
207.
208.
This paper features the structural evolution of the eastern margin of Eurasia in Late Mesozoic and Cenozoic.It is characterized by three stages of development: the riftogenic stage (Jurassic-Early Cretaceous), the platform stage (Late Cretaceous) and the neotectonic one (Paleogene-Quarternary). The boundaries between these stages are distinctly fixed by the geological time limits of planetary range. It is demonstrated that the riftogenic and neotectonic stages were characterized by a high degree of geodynamic activity, and the platform one by a decrease in contrast of tectonic movements. The main river net was formed in the Early Cretaceous and in the Neogene. It experienced a serious reconstruction accompanied by the formation of the Amur River valley being similar to the modem one. 相似文献
209.
In this paper we show that a change in the signs of some of the metric components of the solution of the field equations for
the classical cosmic string results in a solution which we interpret as a time-dependent wall composed of tachyons. We show
that the walls have the property of focusing the paths of particles which pass through them. As an illustration of this focusing,
we demonstrate the results of a simple simulation of the interaction between one such tachyon wall and a rotating disk of
point masses. This interaction leads to the temporary formation of spiral structures. These spiral structures exist for a
time on the order of one galactic rotation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
210.
Guinevere Kauffmann Timothy M. Heckman Simon D. M. White Stéphane Charlot Christy Tremonti Jarle Brinchmann Gustavo Bruzual Eric W. Peng Mark Seibert Mariangela Bernardi Michael Blanton Jon Brinkmann Francisco Castander Istvan Csábai Masataka Fukugita Zeljko Ivezic Jeffrey A. Munn Robert C. Nichol Nikhil Padmanabhan Aniruddha R. Thakar David H. Weinberg Donald York 《Monthly notices of the Royal Astronomical Society》2003,341(1):33-53