全文获取类型
收费全文 | 8591篇 |
免费 | 275篇 |
国内免费 | 129篇 |
专业分类
测绘学 | 165篇 |
大气科学 | 709篇 |
地球物理 | 2004篇 |
地质学 | 3018篇 |
海洋学 | 797篇 |
天文学 | 1235篇 |
综合类 | 37篇 |
自然地理 | 1030篇 |
出版年
2022年 | 33篇 |
2021年 | 115篇 |
2020年 | 153篇 |
2019年 | 156篇 |
2018年 | 202篇 |
2017年 | 195篇 |
2016年 | 241篇 |
2015年 | 200篇 |
2014年 | 260篇 |
2013年 | 473篇 |
2012年 | 283篇 |
2011年 | 409篇 |
2010年 | 375篇 |
2009年 | 474篇 |
2008年 | 397篇 |
2007年 | 407篇 |
2006年 | 340篇 |
2005年 | 292篇 |
2004年 | 282篇 |
2003年 | 300篇 |
2002年 | 239篇 |
2001年 | 200篇 |
2000年 | 219篇 |
1999年 | 164篇 |
1998年 | 149篇 |
1997年 | 132篇 |
1996年 | 144篇 |
1995年 | 131篇 |
1994年 | 124篇 |
1993年 | 101篇 |
1992年 | 100篇 |
1991年 | 68篇 |
1990年 | 97篇 |
1989年 | 78篇 |
1988年 | 84篇 |
1987年 | 94篇 |
1986年 | 84篇 |
1985年 | 110篇 |
1984年 | 131篇 |
1983年 | 122篇 |
1982年 | 105篇 |
1981年 | 77篇 |
1980年 | 57篇 |
1979年 | 71篇 |
1978年 | 67篇 |
1977年 | 61篇 |
1976年 | 61篇 |
1975年 | 69篇 |
1974年 | 55篇 |
1973年 | 68篇 |
排序方式: 共有8995条查询结果,搜索用时 15 毫秒
141.
142.
143.
David J. Dunlop Hironobu Hyodo Todd Knight Alan G. Steele 《Geophysical Journal International》1985,83(3):699-720
Summary. After thermal and alternating field (AF) cleaning, the characteristic high blocking temperature A component of natural remanent magnetization (NRM) of the Tudor gabbro of southern Ontario has a mean direction D = 326°, I =–46° ( k = 132, α95 = 4.8°, N = 8 sites). The corresponding palaeopole, 133°E, 12°N ( dp = 4°, dm = 6°), confirms the palaeopole 137°E, 17°N (α95 = 8.4°) reported earlier by Palmer & Carmichael, based on AF cleaning only. The A NRM has unblocking temperatures > 515–525°C which exceed the estimated 500°C peak temperature reached locally during ∼ 1050 Ma Grenvillian regional metamorphism. The A NRM therefore predates metamorphism and is probably a primary thermoremanence (TRM). The age of the Tudor NRM has previously been taken to be about 675 Ma, but recent 40 Ar/39 Ar dating by Baksi has shown that this is the time of post-metamorphic cooling to 200–250°C. Hornblendes record initial cooling of the intrusion to 590±20°C at 1110 Ma and this is the best estimate of the age of the A remanence. Successful Thellier-type palaeointensity determinations on 11 Tudor samples confirm that the A NRM is a TRM and indicate a palaeofield at this time of 18–27 μT, about 50–70 per cent of the present field intensity at 27° magnetic latitude. The anomalous Tudor A palaeopole, which lies well to the west of both 1000–800 Ma Grenvillian palaeopoles and 1100–1050 Ma poles from Interior Laurentia, is interpreted as recording divergence between Grenvillia and Interior Laurentia just before the Grenvillian orogeny, rather than a post-metamorphic extension of the apparent polar wander path as previously assumed. 相似文献
144.
Cinema can be considered a useful tool for understanding different geographic concepts, showing physical and human factors and the interactions between them. Andres Wood's film Football Stories explores the Chilean territory allowing the observation of the differences between the north and south of the country. Geographic components such as landscapes, architectures, the impact of anthropogenic activities, social inequalities, ways of life, and city and countryside differences are analyzed, as well as the importance of location, the spatial environment, and cinematic narration. The study of geography through films could contribute to understanding of our world and to spatial knowledge. 相似文献
145.
In recent years, the urban political landscape has become infused with a potent and incendiary mixture of popular-democratic, anti-globalisation, and separatist rhetoric. One central process driving this has been the problematic relations between the nation-state and the city. This Debates and Interventions forum aims to prompt a debate about where the city should be situated intellectually in respect of the nation-state. Four questions are addressed: (1) How do contemporary processes of urban development reflect changing national geopolitical priorities? (2) To what extent are struggles around immigration, citizenship and recognition conducted within cities rather than around the nation-state? (3) To what degree does the city (as e.g. a physical form, social environment or discourse) help to mobilise, propel and/or contest this new urban politics? And (4) Is the concept of a “post-national” global order appropriate for understanding the city and urban politics today? 相似文献
146.
147.
David Delaney 《The Professional geographer》2002,54(1):6-14
This essay is a revision of a paper prepared for an NSF workshop on race and geography. Participants in the workshop were asked to offer their views on the topic and our suggestions for further research. This contribution explores some aspects of the relationship and relevance of geography to the question of race in North America. It touches on three “places” that constitute the discipline: the place of research, the place of teaching, and the workplace. With respect to research, it suggests some promising lines of inquiry. Among these are studies of the relationship of scale to the politics of identity and studies of “passing” in connection with studies of geographies of experience and geographies of power. 相似文献
148.
The stability functions for momentum and heat under a Richardson number formulation are derived from the nondimensional shear functions under a Monin-Obukhov formulation. The Prandtl number is also derived as a function of the Richardson number. Previously, this has been done only in a limited sense. Because the Richardson number formulation is expressed in closed form, iterative techniques are no longer needed in numerical models that use Monin-Obukhov similarity theory. This time-saving approach is made possible by deriving expressions for the friction velocity and temperature in terms of the Richardson-number-dependent stability functions. In addition, the Richardson number approximation in the lowest layer is made to depend explicitly upon the surface roughness. 相似文献
149.
150.
Seasonal and inter-annual relationships between vegetation and climate in central New Mexico, USA 总被引:8,自引:0,他引:8
Jeremy L. Weiss David S. Gutzler Julia E. Allred Coonrod Clifford N. Dahm 《Journal of Arid Environments》2004,57(4):507-534
Linear correlations between seasonal and inter-annual measures of meteorological variables and normalized difference vegetation index (NDVI) are calculated at six nearby yet distinct vegetation communities in semi-arid New Mexico, USA Monsoon season (June–September) precipitation shows considerable positive correlation with NDVI values from the contemporaneous summer, following spring, and following summer. Non-monsoon precipitation (October–May), temperature, and wind display both positive and negative correlations with NDVI values. These meteorological variables influence NDVI variability at different seasons and time lags. Thus vegetation responds to short-term climate variability in complex ways and serves as a source of memory for the climate system. 相似文献