全文获取类型
收费全文 | 745篇 |
免费 | 29篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 42篇 |
地球物理 | 135篇 |
地质学 | 313篇 |
海洋学 | 74篇 |
天文学 | 108篇 |
综合类 | 2篇 |
自然地理 | 95篇 |
出版年
2022年 | 4篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 19篇 |
2017年 | 12篇 |
2016年 | 29篇 |
2015年 | 13篇 |
2014年 | 22篇 |
2013年 | 35篇 |
2012年 | 15篇 |
2011年 | 32篇 |
2010年 | 29篇 |
2009年 | 29篇 |
2008年 | 39篇 |
2007年 | 32篇 |
2006年 | 26篇 |
2005年 | 25篇 |
2004年 | 18篇 |
2003年 | 35篇 |
2002年 | 23篇 |
2001年 | 26篇 |
2000年 | 17篇 |
1999年 | 12篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 9篇 |
1970年 | 3篇 |
排序方式: 共有784条查询结果,搜索用时 15 毫秒
111.
Elspeth Graham 《The Professional geographer》1982,34(3):251-260
The idea of a cognitive or mental map has been a source of confusion in the geographical literature for some time. Downs suggests that the confusion can be removed if we give consideration to the role of maps in metaphors and analogies. This raises important questions, but treating the map as a double metaphor does nothing to clarify these issues. Cartographic skills are not the result of introspection and hypothesizing such maps-in-the-head can only impede our understanding of spatial behavior. 相似文献
112.
113.
114.
115.
The Menderes Massif, in western Anatolia, has been described as a lithological succession comprising a basal ‘Precambrian gneissic core of sedimentary origin’ overlain in sequence by ‘Palaeozoic schist’ and ‘Mesozoic-Cenozoic marble’ forming the envelope. The boundary between core and schist envelope was interpreted as a major unconformity, the ‘Supra-Pan-African unconformity’. By contrast, our field observations and geochemical data show that around the southern side of Besparmak Mountain, north of Selimiye (Milas), the protoliths of highly deformed, mylonitized augen gneisses are granitoid rocks intrusive into the adjacent Palaeozoic metasedimentary schists. The field relationships indicate the age of intrusion to be younger than late Permian and there is no evidence for the existence of either an exposed Precambrian basement or the ‘Supra-Pan-African unconformity’ in this sector of the Menderes Massif. 相似文献
116.
Graham Ryder 《Meteoritics & planetary science》1984,19(2):79-83
Precise microprobe determinations of minor elements in olivine from Marjalahti show averages of 0.067% CaO; 0.0211% Cr2O3; less than 0.0045% TiO2; 0.288% MnO; and 30 ppm Ni. The calcium is as high as in some terrestrial plutonic olivines (e.g. Stillwater) but lower than in terrestrial nodule (high-temperature mantle?) olivines, consistent with very slow cooling to low temperatures. The chromium is discrepant with some earlier determinations, and possibly chromium is zoned in most pallasitic olivines. The Ti, Mn, and Ni data are consistent with previous determinations. 相似文献
117.
In the wake of the report of the World Health Organisation's Commission on the Social Determinants of Health, Closing the gap in a generation (Marmot 2008), this invited commentary considers the scope for geographical research on global health. We reflect on current work and note future possibilities, particularly those that take a critical perspective on the interplay of globalisation, security and health. 相似文献
118.
Lara C. Whitely Binder Jennifer Krencicki Barcelos Derek B. Booth Meriel Darzen Marketa McGuire Elsner Richard Fenske Thomas F. Graham Alan F. Hamlet John Hodges-Howell J. Elizabeth Jackson Catherine Karr Patrick W. Keys Jeremy S. Littell Nathan Mantua Jennifer Marlow Don McKenzie Michael Robinson-Dorn Eric A. Rosenberg Claudio O. Stöckle Julie A. Vano 《Climatic change》2010,102(1-2):351-376
Climate change is expected to bring potentially significant changes to Washington State’s natural, institutional, cultural, and economic landscape. Addressing climate change impacts will require a sustained commitment to integrating climate information into the day-to-day governance and management of infrastructure, programs, and services that may be affected by climate change. This paper discusses fundamental concepts for planning for climate change and identifies options for adapting to the climate impacts evaluated in the Washington Climate Change Impacts Assessment. Additionally, the paper highlights potential avenues for increasing flexibility in the policies and regulations used to govern human and natural systems in Washington. 相似文献
119.
To better understand the implications of anthropogenic climate change for three major Mid-Atlantic estuaries (the Chesapeake Bay, the Delaware Bay, and the Hudson River Estuary), we analyzed the regional output of seven global climate models. The simulation given by the average of the models was generally superior to individual models, which differed dramatically in their ability to simulate twentieth-century climate. The model average had little bias in its mean temperature and precipitation and, except in the Lower Chesapeake Watershed, was able to capture the twentieth-century temperature trend. Weaknesses in the model average were too much seasonality in temperature and precipitation, a shift in precipitation’s summer maximum to spring and winter minimum to fall, interannual variability that was too high in temperature and too low in precipitation, and inability to capture the twentieth-century precipitation increase. There is some evidence that model deficiencies are related to land surface parameterizations. All models warmed over the twenty-first century under the six greenhouse gas scenarios considered, with an increase of 4.7 ± 2.0°C (model mean ± 1 standard deviation) for the A2 scenario (a medium-high emission scenario) over the Chesapeake Bay Watershed by 2070–2099. Precipitation projections had much weaker consensus, with a corresponding increase of 3 ± 12% for the A2 scenario, but in winter there was a more consistent increase of 8 ± 7%. The projected climate averaged over the four best-performing models was significantly cooler and wetter than the projected seven-model-average climate. Precipitation projections were within the range of interannual variability but temperature projections were not. The implied research needs are for improvements in precipitation projections and a better understanding of the impacts of warming on streamflow and estuarine ecology and biogeochemistry. 相似文献
120.
Subcalcic, high-Cr (G10) garnets are found as inclusions within diamonds and in peridotitic xenoliths. The strong spatial associations between G10 garnets and diamond make them an important tool in the investigation of diamond genesis. We present an integrated study of the major and trace element composition and oxygen-Sr-Nd-Hf isotopic ratios of eight G10 garnets from the Ekati mine (NWT-Canada) and four from the Murowa mine (Zimbabwe) in an attempt to determine their petrogenetic evolution and to further examine a possible relationship between the metasomatic agents responsible for G10 garnet signatures and diamond forming fluids.All garnets display sinusoidal to mildly sinusoidal REE patterns and have negative Ti, Sr and positive U anomalies. They have variably radiogenic 87Sr/86Sr (0.703261-0.731191) and non-radiogenic εNd values (−8.1 to −27.1), except for one sample from Murowa that has a positive εNd of 2.5. One Ekati sample has an extremely low εHf value of −61.6. The Ekati garnets we have studied all appear to come from a single depth in the Slave lithospheric mantle. On the base of Cr-Ca relations they have crystallized at 4.9 GPa and display dunitic Ca intercept values. Their δ18O values range between +5.23‰ and +5.42‰.The Ekati G10 garnets record a complex, multi-stage metasomatic history involving the interaction of several components during their genesis. One metasomatic agent was enriched in HFSE, LREE, Sr, and depleted in Nb. This agent had the least radiogenic Sr. Another metasomatic agent had highly radiogenic Sr, and was enriched in LREE, Sr, Nb, Th and U.The G10 garnets have very low εNd and εHf values combined with radiogenic Sr, thus, they require an early lithospheric mantle enrichment event at some stage during their genesis or during the evolution of any precursor material that they formed from. The only Hf isotope composition measurable from the Ekati suite is so unradiogenic (εHf = −61) that it yields a Lu/Hf model age of 3521 Ma. This indicates that the lithospheric enrichment event seen by the Ekati garnets or their precursors may have occurred in the early stages of the craton stabilization, during the diamond forming event [Westerlund K., Shirey S., Richardson S., Carlson R., Gurney J. and Harris J. (2006) A subduction wedge origin for Paleoarchean peridotitic diamonds and harzburgites from the Panda kimberlite, Slave craton: evidence from Re-Os isotope systematics. Contrib. Mineral. Petrol.152(3), 275-294]. Although our data cannot unequivocally discriminate between a variety of models for the genesis of subcalcic garnets it is clear that the host peridotite originated via melting at shallow depths followed by subduction and that the observed geochemical fingerprint of the garnets is strongly influenced by diamond forming fluids. Diamond forming fluids sampled from fibrous diamonds, have steep REE patterns, negative Ti and Sr anomalies and very low Sm/Nd ratios that are very similar to G10 garnet characteristics. These diamond forming fluids have been recently shown to have extreme Sr and Nd isotopic compositions [Klein-BenDavid O., Pearson D. G., Nowell G. M. and Cantigny P. (2008) Origins of diamond forming fluids—constraints from a coupled Sr-Nd isotope and trace element approach. Extended abstracts to the 9th International Kimberlite Conference, Frankfurt, Germany, 9IKC-A-00118.] that are closely concordant with G10 garnets. The fluids are also rich in LREE, P, K and water, sharing these features with mica-rich metasomes. These similarities suggest that ancient lithospheric metasomes could either provide a source region for, or be a product of diamond forming fluids. Diamond forming fluids appear to be intimately involved in the evolution of G10 garnets in the lithospheric mantle, either acting as a metasomatic agent, or being integral to triggering or enhancing garnet growth in a Cr-rich protolith. Such a link explains the strong association between G10 garnets and diamonds. 相似文献