全文获取类型
收费全文 | 466篇 |
免费 | 25篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 36篇 |
地球物理 | 153篇 |
地质学 | 146篇 |
海洋学 | 47篇 |
天文学 | 41篇 |
自然地理 | 76篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 17篇 |
2014年 | 10篇 |
2013年 | 27篇 |
2012年 | 21篇 |
2011年 | 17篇 |
2010年 | 25篇 |
2009年 | 20篇 |
2008年 | 37篇 |
2007年 | 20篇 |
2006年 | 17篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1968年 | 2篇 |
排序方式: 共有502条查询结果,搜索用时 234 毫秒
21.
Natural Hazards - Urbanization increases regional impervious surface area, which generally reduces hydrologic response time and therefore increases flood risk. The objective of this work is to... 相似文献
22.
Beach nourishment is increasingly being implemented to address problems of erosion. However, the ecological consequences of nourishment are poorly understood, especially in Australia. In Botany Bay, sand was piped from an intertidal borrow area at Elephant's Trunk to nourish the nearby eroding beach at Towra Point. The effects on an intertidal exoedicerotid amphipod, Exoediceros fossor (Stimpson, 1856), were examined using a beyond-BACI (Before–After, Control–Impact) sampling design. Sampling was conducted before and after engineering operations at sites within the borrow and nourishment locations and multiple control locations. Hypotheses concerning impact and recovery were tested using asymmetrical ANOVAs and two-tailed F-tests. These examined the effects on abundance and spatial variability, respectively. The impact of the engineering operations on abundance was very large at both borrow and nourishment locations. However, recovery started within several weeks and, using space × time interactions as a criterion, appeared to be complete within a year. This conclusion is made cautiously because of low statistical power and because other criteria for recovery suggest that it was not complete at some sites. As beach erosion is likely to increase in severity with rising sea levels and greater storm surges associated with climate change, management authorities will need a better understanding of the ecological effects of beach nourishment. 相似文献
23.
ABSTRACTProposals to change the names of entire urban centres are rare. We examine the case of Blenheim, New Zealand, where in 2016, representatives of local businesses campaigned for its renaming as Marlborough City, in recognition of the region’s wine industry. Although defeated the proposal threatened to over-write established settlement history. It presumed to rename Blenheim under the aegis of New Zealand Inc., a shorthand for the pervasive yet nebulous economic nationalism that seeks to yoke all local and national identity to enhancing export growth. Drawing on media reports, we interpret this example of toponymic commodification as a neoliberalized project of place-making. Ironically, Blenheim and Marlborough are colonial names that displaced a long-established Māori name. The proposal highlights both the perversities and the deeply contested claims-making that often underlie and animate toponymic politics. Ultimately, it illustrates some of the limits of rights claimed under neoliberalism. 相似文献
24.
25.
Christopher R. J. Charles Pierre-Yves F. Robin Donald W. Davis Phil J. A. McCausland 《Meteoritics & planetary science》2018,53(5):935-951
The approximately spherical shapes of chondrules has long been attributed to surface tension acting on ~1 mm melt droplets that formed and cooled in the microgravity field of the solar nebula. However, chondrule shapes commonly depart significantly from spherical. In this study, 109 chondrules in a sample of CR2 chondrite NWA 801 were imaged by X-ray computed tomography and best-fitted to ellipsoids. The analysis confirms that many chondrules are indeed not spherical, and also that the chondrules’ collective shape fabric records a definite 13% compaction in the host meteorite. Dehydration of phyllosilicates within chondrules may account for that strain. However, retro-deforming all chondrules shows that a large majority were already far from spherical prior to accretion. Possible models for these initial shapes include prior deformation of individual chondrules in earlier hosts, and, as suggested by previous authors, rotation of chondrules as they were solidifying, and/or “streaming” of molten chondrules by their differential velocities with their gaseous hosts after melting. More in situ 3-D work such as this study on a variety of unequilibrated chondrites, combined with detailed structural petrography, should help further constrain these models and refine our understanding of chondrite formation. 相似文献
26.
在合适的实验参数下(热力Rossby数R_(OT)=0.1,Taylor数T_a=2.2 ×10~7),在旋转斜压流中,大尺度地形强迫造成低频振荡以及大气环流中的“阻塞”流型。这是由于地形强迫造成的准静止波与行进波的相互作用及共振引起的。地形把波数单一的流动变成多波数的流动。地形强迫使波数减少。 相似文献
27.
28.
Robin Brett 《Geochimica et cosmochimica acta》1984,48(6):1183-1188
The oxygen fugacity (fO2) of the Earth's upper mantle appears to lie somewhat above that of the iron-wüstite buffer, its fO2 is assumed to have been similar to the present value at the time of core formation. In the upper mantle, the Fe-rich liquid protocore that would form under such conditions of fO2 at elevated temperatures would lie predominantly in the system Fe-S-O. Distribution coefficients for Co, Cu, Ni, Ir, Au, Ir, W, Re, Mo, Ag and Ga between such liquids and basalt are known and minimum values are known for Ge. From these coefficients, upper mantle abundances for the above elements can be calculated by assuming cosmic abundances for the whole Earth and equilibrium between the Fe-S-O protocore and upper mantle. These calculated abundances are surprisingly close to presently known upper mantle abundances; agreements are within a factor of 5, except for Cu, W, and Mo. Therefore, siderophile element abundances in the upper mantle based on known distribution coefficients do not demand a late-stage meteoritic bombardment, and a protocore formed from the upper mantle containing S and O seems likely.As upper mantle abundances fit a local equilibrium model, then either the upper mantle has not been mixed with the rest of the mantle since core formation, or else partition coefficients between protocore and mantle were similar for the whole mantle regardless of , , and fO2. The latter possibility seems unlikely over such a range. 相似文献
29.
Robin L. Dennis 《Climatic change》1987,11(1-2):81-96
This article demonstrates the importance of context on forecast errors. It de J.scribes the development of an unrealistic transportation planning forecast for Denver, Colorado, noting its influence on air quality planning for Denver. The importance of two contextual features, procedural rationality and conflict of interest, to the introduction of error is discussed. The case described implies that different decision-making contexts define different rules of rationality, and substantive rationality may not fit the rules. The type of context and not necessarily a code of ethics will determine this. 相似文献
30.
Claude Robin Philippe Mossand Guy Camus Jean-Marie Cantagrel Alain Gourgaud Pierre M. Vincent 《Journal of Volcanology and Geothermal Research》1987,31(1-2)
The evolution of the Colima volcanic complex can be divided into successive periods characterized by different dynamic and magmatic processes: emission of andesitic to dacitic lava flows, acid-ash and pumice-flow deposits, fallback nuées ardentes leading to pyroclastic flows with heterogeneous magma, plinian air-fall deposits, scoriae cones of alkaline and calc-alkaline nature. Four caldera-forming events, resulting either from major ignimbrite outbursts or Mount St. Helens-type eruptions, separate the main stages of development of the complex from the building of an ancient shield volcano (25 × 30 km wide) up to two summit cones, Nevado and Fuego.The oldest caldera, C1 (7–8 km wide), related to the pouring out of dacitic ash flows, marks the transition between two periods of activity in the primitive edifice called Nevado I: the first one, which is at least 0.6 m.y. old, was mainly andesitic and effusive, whereas the second one was characterized by extrusion of domes and related pyroclastic products. A small summit caldera, C2 (3–3.5 km wide), ended the evolution of Nevado I.Two modern volcanoes then began to grow. The building of the Nevado II started about 200,000 y. ago. It settled into the C2 caldera and partially overflowed it. The other volcano, here called Paleofuego, was progressively built on the southern side of the former Nevado I. Some of its flows are 50,000 y. old, but the age of its first outbursts is not known. However, it is younger than Nevado II. These two modern volcanoes had similar evolutions. Each of them was affected by a huge Mount St. Helens-type (or Bezymianny-type) event, 10,000 y. ago for the Paleofuego, and hardly older for the Nevado II. The landslides were responsible for two horseshoe-shaped avalanche calderas, C3 (Nevado) and C4 (Paleofuego), each 4–5 km wide, opening towards the east and the south. In both cases, the activity following these events was highly explosive and produced thick air-fall deposits around the summit craters.The Nevado III, formed by thick andesitic flows, is located close to the southwestern rim of the C3 caldera. It was a small and short-lived cone. Volcan de Fuego, located at the center of the C4 caldera, is nearly 1500 m high. Its activity is characterized by an alternation of long stages of growth by flows and short destructive episodes related to violent outbursts producing pyroclastic flows with heterogeneous magma and plinian air falls.The evolution of the primitive volcano followed a similar pattern leading to formation of C1 and then C2. The analogy between the evolutions of the two modern volcanoes (Nevado II–III; Paleofuego-Fuego) is described. Their vicinity and their contemporaneous growth pose the problem of the existence of a single reservoir, or two independent magmatic chambers, after the evolution of a common structure represented by the primitive volcano. 相似文献