全文获取类型
收费全文 | 248篇 |
免费 | 13篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 13篇 |
地球物理 | 48篇 |
地质学 | 88篇 |
海洋学 | 21篇 |
天文学 | 65篇 |
自然地理 | 19篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 23篇 |
2010年 | 17篇 |
2009年 | 13篇 |
2008年 | 24篇 |
2007年 | 13篇 |
2006年 | 17篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有265条查询结果,搜索用时 281 毫秒
71.
Xander Olsthoorn Peter van der Werff Laurens M. Bouwer Dave Huitema 《Climatic change》2008,91(1-2):103-122
What could happen to the Netherlands if, in 2030, the sea level starts to rise and eventually, after 100 years, a sea level of 5 m above current level would be reached? This question is addressed by studying literature, by interviewing experts in widely differing fields, and by holding an expert workshop on this question. Although most experts believe that geomorphology and current engineering skills would enable the country to largely maintain its territorial integrity, there are reasons to assume that this is not likely to happen. Social processes that precede important political decisions – such as the growth of the belief in the reality of sea level rise and the framing of such decisions in a proper political context (policy window) – evolve slowly. A flood disaster would speed up the decision-making process. The shared opinion of the experts surveyed is that eventually part of the Netherlands would be abandoned. 相似文献
72.
Jason Cosford Hairuo Qing Yin Lin Bruce Eglington Dave Mattey Yue Gau Chen Meiliang Zhang Hai Cheng 《Quaternary Research》2010,73(3):541-549
Stalagmite J1 from Jintanwan Cave, Hunan, China, provides a precisely dated, decadally resolved δ18O proxy record of paleoclimatic changes associated with the East Asian monsoon from ∼29.5 to 14.7 ka and from ∼12.9 to 11.0 ka. At the time of the last glacial maximum (LGM), the East Asian summer monsoon weakened and then strengthened in response to changes in Northern Hemisphere insolation. As the ice sheets retreated the East Asian summer monsoon weakened, especially during Heinrich event H1, when atmospheric and oceanic teleconnections transferred the climatic changes around the North Atlantic to the monsoonal regions of Eastern Asia. A depositional hiatus between ∼14.7 and 12.9 ka leaves the deglacial record incomplete, but an abrupt shift in δ18O values at ∼11.5 ka marks the end of the Younger Dryas and the transition into the Holocene. Comparisons of the J1 record to other Chinese speleothem records indicate synchronous climatic changes throughout monsoonal China. Further comparisons to a speleothem record from western Asia (Socotra Island) and to Greenland ice cores support hemispherical-scale paleoclimatic change. Spectral and wavelet analyses reveal centennial- and decadal-scale periodicities that correspond to solar frequencies and to oscillations in atmospheric and oceanic circulation. 相似文献
73.
Dave Craw Phaedra Upton Bing-Sheng Yu Travis Horton Yue-Gau Chen 《Mineralium Deposita》2010,45(7):631-646
Gold-bearing vein systems in the high mountains of Taiwan are part of the youngest tectonic-hydrothermal system on Earth.
Tectonic collision initiated in the Pliocene has stacked Eocene–Miocene marine sedimentary rocks to form steep mountains nearly
4 km high. Thinner portions of the sedimentary pile (∼5 km) are currently producing hydrocarbons in a fold and thrust belt,
and orogenic gold occurs in quartz veins in thicker parts of the pile (∼10 km) in the Slate Belt that underlies the mountains.
Metamorphic fluids (2–5 wt.% NaCl equivalent) are rising from the active greenschist facies metamorphic zone and transporting
gold released during rock recrystallisation. Metamorphic fluid flow at the Pingfengshan historic gold mine was focussed in
well-defined (4 km3) fracture zones with networks of quartz veins, whereas large surrounding volumes of rock are largely unveined. Gold and arsenopyrite
occur in several superimposed vein generations, with ankeritic alteration of host rocks superimposed on chlorite–calcite alteration
zones as fluids cooled and became out of equilibrium with the host rocks. Mineralising fluids had δ18O near +10‰, δ13C was between −1‰ and −6‰ and these fluids were in isotopic equilibrium with host rocks at ∼350°C. Ankeritic veins were emplaced
in extensional sites in kink fold axial surfaces, formed as the rock mass was transported laterally from compressional to
extensional regimes in the orogen. Rapid exhumation (>2 mm/year) of the Slate Belt is causing a widespread shallow conductive
thermal anomaly without igneous intrusions. Meteoric water is penetrating into the conductive thermal anomaly to contribute
to crustal fluid flow and generate shallow boiling fluids (∼250°C) with fluid temperature greater than rock temperature. The
meteoric-hydrothermal system impinges on, but causes only minor dilution of, the gold mineralisation system at depth. 相似文献
74.
Dave Craw 《Ore Geology Reviews》2010,37(3-4):224-235
The giant gold placer system on the Otago Schist of southern New Zealand was derived from Mesozoic orogenic gold deposits in the underlying schist basement. The core of the schist basement was exhumed in the middle Cretaceous, coeval with the accumulation of the oldest preserved nonmarine sedimentary rocks in the area (ca 112 Ma). Those sedimentary rocks contain quartz clasts, with distinctive ductile deformation textures, that were derived from structural zones in, or adjacent to, major orogenic gold deposits. Quartz textures in these structural zones are readily distinguishable from the rest of the schist belt, and hence provide a fingerprint for erosion of gold. The earliest sedimentary rocks on the margins of the gold-bearing schist belt are immature, and were derived from unoxidised outcrops in areas of high relief. Gold was not liberated from unoxidised basement rocks during erosion, and was removed from the system without placer concentration. Placer concentration did not begin until about 20 million years later, when oxidative alteration of gold deposits had facilitated gold grain size enhancement from micron scale (primary) to millimetre scale (secondary). Subsequent erosion and recycling of gold in the early Cenozoic, and again in the late Cenozoic, caused additional concentration of gold in progressively younger deposits. The Klondike giant placer goldfield of Canada had a similar geological history to the Otago placer field, and Klondike placer accumulation occurred in the late Cenozoic, at least 70 million years after Mesozoic exhumation of orogenic gold. The giant placer deposit on the western slopes of the Sierra Nevada in California occurs in Eocene and younger sedimentary rocks, at least 40 million years younger than the timing of major exhumation of the source rocks. Circum-Pacific giant gold placers formed under entirely different tectonic regimes from the emplacement of their source orogenic deposits, and these giant placer deposits do not form in foreland basins associated with convergent orogens. Formation of giant placers requires less active erosion and more subdued topography than the collisional orogenic activity that accompanied emplacement of source gold deposits in basement rocks, as well as oxidative alteration of the primary deposits to liberate gold from sulfide minerals and enhance secondary gold grain size. 相似文献
75.
Yves Goddéris Jennifer Z. Williams Dave Pollard 《Geochimica et cosmochimica acta》2010,74(22):6357-6374
Anthropogenic and natural climate change affect processes in the atmosphere, biosphere, hydrosphere, and pedosphere. The impact of climate on soil evolution has not been well-explored, largely due to slow rates and the complexity of coupled processes that must be observed and simulated. The rates of mineral weathering in loess deposited 23 kyr ago and experiencing soil formation for 13 kyr are explored here using the WITCH model for weathering and the GENESIS model for climate simulation. The WITCH model, which uses rigorous kinetic parameters and laws with provision for the effect on rates of deviation from equilibrium, can successfully simulate the depletion profiles in the soil for dolomite and albite if soil CO2 is assumed to rise over the last 10 kyr up to about 30-40× the present atmospheric pressure, and if the solubility product of the Ca-smectite is assumed equal to that of an Fe(III)-rich Ca-montmorillonite. Such simulations document that dissolution behavior for silicates and carbonates are strongly coupled through pH, and for Ca-smectite and feldspars through dissolved silica. Such coupling is not incorporated in simple geometric and analytical models describing mineral dissolution, and therefore probably contributes to the long-standing observation of discrepancies among laboratory and field mineral dissolution rates. 相似文献
76.
Constanze Haug Tim Rayner Andrew Jordan Roger Hildingsson Johannes Stripple Suvi Monni Dave Huitema Eric Massey Harro van Asselt Frans Berkhout 《Climatic change》2010,101(3-4):427-445
Climate change is widely recognised as a ‘wicked’ policy problem. Agreeing and implementing governance responses is proving extremely difficult. Policy makers in many jurisdictions now emphasise their ambition to govern using the best available evidence. One obvious source of such evidence is the evaluations of the performance of existing policies. But to what extent do these evaluations provide insights into the difficult dilemmas that governors typically encounter? We address this question by reviewing the content of 262 evaluation studies of European climate policies in the light of six kinds of dilemma found in the governance literature. We are interested in what these studies say about the performance of European climate policies and in their capacity to inform evidence-based policy-making. We find that the evaluations do arrive at common findings: that climate change is framed as a problem of market and/or state failure; that voluntary measures tend to be ineffective; that market-based instruments tend to be regressive; that EU-level policies have driven climate policies in the latecomer EU Member States; and that lack of monitoring and weak enforcement are major obstacles to effective policy implementation. However, we also conclude that the evidence base these studies represent is surprisingly weak for such a high profile area. There is too little systematic climate policy evaluation work in the EU to support systematic evidence-based policy making. This reduces the scope for sound policy making in the short run and is a constraint to policy learning in the longer term. 相似文献
77.
A technique for replicating large rock outcrops has been developed so that casts of these surfaces can be archived in their present stage of preservation. Researchers can then study these casts in the laboratory under optimum lighting conditions, sometimes revealing new fossil evidence, while students and members of the public can be shown geological features that might otherwise be inaccessible to them. 相似文献
78.
79.
The use of the metaphors of general fitness and N-K spaces can assist in the understanding of the development of the physical landscape. Different modes of change can be viewed as different types of movement in, and distortions of, these phase spaces. Visualized in this manner landscape change can be viewed as both channelized, constrained and random. 相似文献
80.
David Clements and Amanda Baker report on the RAS Careers Session at the NAM 2001, which examined barriers to progress from fixed-term contract posts. 相似文献