全文获取类型
收费全文 | 728篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 33篇 |
地球物理 | 147篇 |
地质学 | 181篇 |
海洋学 | 86篇 |
天文学 | 217篇 |
综合类 | 3篇 |
自然地理 | 65篇 |
出版年
2021年 | 4篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 18篇 |
2017年 | 9篇 |
2016年 | 17篇 |
2015年 | 13篇 |
2014年 | 14篇 |
2013年 | 45篇 |
2012年 | 21篇 |
2011年 | 28篇 |
2010年 | 28篇 |
2009年 | 34篇 |
2008年 | 36篇 |
2007年 | 36篇 |
2006年 | 29篇 |
2005年 | 21篇 |
2004年 | 27篇 |
2003年 | 21篇 |
2002年 | 20篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 26篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 11篇 |
1974年 | 3篇 |
1973年 | 7篇 |
1971年 | 4篇 |
1912年 | 3篇 |
1910年 | 4篇 |
排序方式: 共有748条查询结果,搜索用时 218 毫秒
741.
The absence of memory in the climatic forcing of glaciers 总被引:1,自引:1,他引:0
Glaciers respond to both long-term, persistent climate changes as well as the year-to-year variability that is inherent to a constant climate. Distinguishing between these two causes of length change is important for identifying the true climatic cause of past glacier fluctuations. A key step in addressing this is to determine the relative importance of year-to-year variability in climate relative to more persistent climate fluctuations. We address this question for European climate using several long-term observational records: a century-long, Europe-wide atmospheric gridded dataset; longer-term instrumental measurements of summertime temperature where available (up to 250 years); and seasonal and annual records of glacier mass balance (between 30 and 50 years). After linear detrending of the datasets, we find that throughout Europe persistence in both melt-season temperature and annual accumulation is generally indistinguishable from zero. The main exception is in Southern Europe where a degree of interannual persistence can be identified in summertime temperatures. On the basis of this analysis, we conclude that year-to-year variability dominates the natural climate forcing of glacier fluctuations on timescales up to a few centuries. 相似文献
742.
Evaluating Light Availability,Seagrass Biomass,and Productivity Using Hyperspectral Airborne Remote Sensing in Saint Joseph’s Bay,Florida 总被引:1,自引:0,他引:1
Victoria J. Hill Richard C. Zimmerman W. Paul Bissett Heidi Dierssen David D. R. Kohler 《Estuaries and Coasts》2014,37(6):1467-1489
Seagrasses provide a number of critical ecosystem services, including habitat for numerous species, sediment stabilization, and shoreline protection. Ariel photography is a useful tool to estimate the areal extent of seagrasses, but recent innovations in radiometrically calibrated sensors and algorithm development have allowed identification of benthic types and retrieval of absolute density. This study demonstrates the quantitative ability of a high spatial resolution (1 m) airborne hyperspectral sensor (3.2 nm bandwidth) in the complex coastal waters of Saint Joseph’s Bay (SJB). Several benthic types were distinguished, including submerged and floating aquatic vegetation, benthic red algae, bare sand, and optically deep water. A total of 23.6 km2 of benthic vegetation was detected, indicating no dramatic change in vegetation area over the past 30 years. SJB supported high seagrass density at depths shallower than 2 m with an average leaf area index of 2.0?±?0.6 m2 m?2. Annual seagrass production in the bay was 13,570 t C year?1 and represented 41 % of total marine primary production. The effects of coarser spatial resolution were investigated and found to reduce biomass retrievals, underestimate productivity, and alter patch size statistics. Although data requirements for this approach are considerable, water column optical modeling may reduce the in situ requirements and facilitate the transition of this technique to routine monitoring efforts. The ability to quantify not just areal extent but also productivity of a seagrass meadow in optically complex coastal waters can provide information on the capacity of these environments to support marine food webs. 相似文献
743.
744.
Hill MC 《Ground water》2006,44(6):775-781
The advantages of starting with simple models and building complexity slowly can be significant in the development of ground water models. In many circumstances, simpler models are characterized by fewer defined parameters and shorter execution times. In this work, the number of parameters is used as the primary measure of simplicity and complexity; the advantages of shorter execution times also are considered. The ideas are presented in the context of constructing ground water models but are applicable to many fields. Simplicity first is put in perspective as part of the entire modeling process using 14 guidelines for effective model calibration. It is noted that neither very simple nor very complex models generally produce the most accurate predictions and that determining the appropriate level of complexity is an ill-defined process. It is suggested that a thorough evaluation of observation errors is essential to model development. Finally, specific ways are discussed to design useful ground water models that have fewer parameters and shorter execution times. 相似文献
745.
746.
P. G. Brown P. J. A. McCausland A. R. Hildebrand L. T. J. Hanton L. M. Eckart H. Busemann D. Krietsch C. Maden K. Welten M. W. Caffee M. Laubenstein D. Vida F. Ciceri E. Silber C. D. K. Herd P. Hill H. Devillepoix Eleanor K. Sansom Martin Cupák Seamus Anderson R. L. Flemming A. J. Nelson M. Mazur D. E. Moser W. J. Cooke D. Hladiuk Barbara Malečić Maja Telišman Prtenjak R. Nowell The Golden Meteorite Consortium 《Meteoritics & planetary science》2023,58(12):1773-1807
747.
Geoarchaeology and late glacial landscapes in the western lake superior region,Central North America
Christopher L. Hill 《Geoarchaeology》2007,22(1):15-47
The transition from full glacial to interglacial conditions along the southern margin of the Laurentide ice sheet resulted in dramatic changes in landscapes and biotic habitats. Strata and landforms resulting from the Wisconsin Episode of glaciation in the area directly west of Lake Superior indicate a context for late Pleistocene biota (including human populations) connected to ice margins, proglacial lakes, and postglacial drainage systems. Late Glacial landscape features that have the potential for revealing the presence of Paleoindian artifacts include abandoned shorelines of proglacial lakes in the Superior and Agassiz basins and interior drainages on deglaciated terrains. The linkage between Late Pleistocene human populations and Rancholabrean fauna has yet to be demonstrated in the western Lake Superior region, although isolated remains of mammoth ( Mammuthus) have been documented, as well as fluted points assigned to Clovis, Folsom, and Holcombe‐like artifact forms. Agate Basin and Hell Gap (Plano‐type) artifacts also imply the presence of human groups in Late Glacial landscapes associated with the Agassiz and Superior basins. © 2007 Wiley Periodicals, Inc. 相似文献
748.