全文获取类型
收费全文 | 607篇 |
免费 | 34篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 23篇 |
地球物理 | 164篇 |
地质学 | 181篇 |
海洋学 | 54篇 |
天文学 | 139篇 |
综合类 | 1篇 |
自然地理 | 67篇 |
出版年
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 16篇 |
2017年 | 23篇 |
2016年 | 24篇 |
2015年 | 17篇 |
2014年 | 15篇 |
2013年 | 24篇 |
2012年 | 14篇 |
2011年 | 23篇 |
2010年 | 28篇 |
2009年 | 24篇 |
2008年 | 18篇 |
2007年 | 14篇 |
2006年 | 16篇 |
2005年 | 18篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1989年 | 4篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 8篇 |
1971年 | 6篇 |
1968年 | 6篇 |
排序方式: 共有644条查询结果,搜索用时 15 毫秒
81.
Martin R. Bates Carl Champness Andrew Haggart Richard I. Macphail Simon A. Parfitt Jean-Luc Schwenninger 《Proceedings of the Geologists' Association. Geologists' Association》2014
This paper discusses the results of the investigation of Pleistocene sediments at the Royal Oak Portal (ROP) site on the new Crossrail scheme near Paddington Station, London. The site was sampled and recorded in May 2011 by archaeologists from Oxford Archaeology commissioned by Crossrail Ltd. The investigation revealed a sedimentary sequence associated with cool climate waterlain deposition towards the edge of the River Westbourne floodplain. During excavation an assemblage of around 100 identifiable large mammal bones was recovered, dating to the Late Pleistocene. The major concentration of bones, from bison and reindeer, was located and excavated from a shallow sequence of sediments. Analysis of the bones indicates that they represent a natural death assemblage, scavenged and subsequently disarticulated, transported by water, exposed and further dispersed and broken by trampling. The site is of regional and national importance because the assemblage derives from a well-constrained geological context, with associated dating evidence suggesting accumulation during the later parts of Marine Isotope Stage (MIS) 5 and continuing within MIS 4. The site is also of significance because it is one of a growing number of recently discovered sites away from the main fluvial archive for the British Middle and Upper Pleistocene. These sites have the potential to add significantly to our understanding of parts of the Pleistocene record that remain difficult to document through the investigation of the more active systems associated with major rivers such as the Thames, Severn or Trent. 相似文献
82.
83.
Carl Heiles 《Astrophysics and Space Science》2004,292(1-4):77-88
We review observations of the physical properties of the diffuse ISM HI components, namely the Cold and Warm Neutral Media (CNM and WNM). There is somewhat more WNM than CNM, and at least half of the WNM is not thermally stable. The CNM has typical turbulent Mach number 3. Magnetic fields in the CNM are not as large as expected from the classical flux-freezing argument; neither are magnetic fields always strong enough for the Alfven velocity to equal the turbulent velocity. Nevertheless, they are usually strong enough to put CNM clouds in the magnetically subcritical regime. We identify a probable new source of turbulence for the diffuse ISM. We discuss one very cold cloud that has considerable internal turbulence and, because of its extreme thinness ~0.05 pc, a turbulent crossing time of only ~5 × 104 yr. 相似文献
84.
85.
86.
Near-simultaneous R- and J-band photometric measurements of the short-period Comets 2P/Encke and the Deep Impact mission target 9P/Tempel 1 were obtained. The resulting R-J colors are +0.82±0.08 mag and +1.46±0.13 mag for Encke and Tempel 1, respectively. Tempel 1's color is redder than the solar R-J color index of +0.76. The Tempel 1 observations directly detected the nucleus while the Encke observations likely suffered from coma contamination. 相似文献
87.
Voyager 1 imaging data have been used to investigate the color and morphology of several radial flow-like features at Ra Patera, a broad volcanic structure at approximately 8° latitude and 325° longitude on the Galilean satellite Io (J1). It was found that downstream progressions of flow color and morphology are consistent with lava of a predominately sulfur composition cooling radiatively and erupting in the range of 470 to 520°K at effusion rates at 1010 to 1011 cm3/sec. This implies global resurfacing rates by volcanic flows on Io of the order of 1 cm/year. Calculated energy content and effusion rates for flows at Ra Patera, using the physical parameters of sulfur, are of the order of the largest known terrestial basaltic eruptions and are consistent with calculations of globally available energy. 相似文献
88.
Carl J. Hansen 《Astrophysics and Space Science》1971,14(2):389-395
Results are presented which show the final abundances of the major nuclei produced in explosive, but partial, carbon-burning taking place in a rapidly expanding medium. the effects of energy deposition due to burning and expansive cooling are taken into account explicity. The results are compatible with those obtained by other authors but show the sensitivity of the final abundances to the assumed initial conditions. A conjecture is made as to the physical site of the burning.Of the National Bureau of Standards and University of Colorado. 相似文献
89.
90.
Three-dimensional grids representing a heterogeneous, ground water system are generated at 10 different resolutions in support of a site-scale flow and transport modeling effort. These grids represent hydrostratigraphy near Yucca Mountain, Nevada, consisting of 18 stratigraphic units with contrasting fluid flow and transport properties. The grid generation method allows the stratigraphy to be modeled by numerical grids of different resolution so that comparison studies can be performed to test for grid quality and determine the resolution required to resolve geologic structure and physical processes such as fluid flow and solute transport. The process of generating numerical grids with appropriate property distributions from geologic conceptual models is automated, thus making the entire process easy to implement with fewer user-induced errors. The series of grids of various resolutions are used to assess the level at which increasing resolution no longer influences the flow and solute transport results. Grid resolution is found to be a critical issue for ground water flow and solute transport. The resolution required in a particular instance is a function of the feature size of the model, the intrinsic properties of materials, the specific physics of the problem, and boundary conditions. The asymptotic nature of results related to flow and transport indicate that for a hydrologic model of the heterogeneous hydrostratigraphy under Yucca Mountain, a horizontal grid spacing of 600 m and vertical grid spacing of 40 m resolve the hydrostratigraphic model with sufficient precision to accurately model the hypothetical flow and solute transport to within 5% of the value that would be obtained with much higher resolution. 相似文献