全文获取类型
收费全文 | 557篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 20篇 |
地球物理 | 143篇 |
地质学 | 166篇 |
海洋学 | 68篇 |
天文学 | 82篇 |
综合类 | 1篇 |
自然地理 | 72篇 |
出版年
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 10篇 |
2013年 | 31篇 |
2012年 | 12篇 |
2011年 | 29篇 |
2010年 | 16篇 |
2009年 | 15篇 |
2008年 | 19篇 |
2007年 | 16篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 24篇 |
2002年 | 14篇 |
2001年 | 11篇 |
2000年 | 18篇 |
1999年 | 8篇 |
1998年 | 11篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1968年 | 5篇 |
1948年 | 3篇 |
排序方式: 共有572条查询结果,搜索用时 15 毫秒
121.
D.A. Wright 《Marine pollution bulletin》1985,16(8):299-300
122.
Abstract— A preliminary investigation into the carbon isotopic composition of deep-sea spherules has been undertaken. A variety of particles have been analysed including both melted and unmelted samples of type S (stony) and type I (iron) spherules, emphasis being placed on surveying the carbon in different sorts of particles rather than analysing large numbers of samples. Some general observations can be made: there appear to be four different sorts of carbonaceous materials in the spherules. Melted and unmelted spherules of either type I or S, apparently contain two forms of low temperature combustible carbon distinguished, not by combustion temperature, but by isotopic composition. The low temperature of combustion is commensurate with these forms of carbon being organic in nature. The most likely explanation for this carbon is terrestrial biogenic contamination although there exists the possibility that there are some indigenous organic materials. Unmelted type S spherules contain a high temperature carbon component, characterised by a very minor 13C-enrichment, which is considered to be indigenous to the sample. All melted samples contain only small amounts of high temperature carbon with an isotopic composition suggestive of handling blank. 相似文献
123.
W.A. Martin S.L. Larson D.R. Felt J. Wright C.S. Griggs M. Thompson J.L. Conca C.C. Nestler 《Applied Geochemistry》2008
Training activities at firing ranges, both civilian and military, deliver large quantities of Pb bullets into range soils where the physical and geochemical properties of the soil can influence Pb transport. Some best management practices (BMPs) developed for range managers include the addition of phosphate amendments, such as apatite, to immobilize Pb and other metals associated with firing ranges. In this study, the effect of the organic matter content of apatite II™ on its metal sorption properties was investigated. Batch and column experiments were conducted using mechanically, enzymatically, and thermally-treated forms of Apatite II™ to sorb soluble Pb. In batch experiments, mechanically and enzymatically-treated Apatite II™ reduced soluble Pb concentrations from 29% to 96%, depending on the age of the Apatite source. Thermally-treated Apatite II™ consistently reduced soluble Pb concentrations in solution by more than 90%, regardless of aging. The mechanically and enzymatically-treated Apatite II™ produced significantly higher dissolved organic carbon (DOC) and biochemical oxygen demand (BOD) concentrations while undergoing aging. This contrasts with the thermally-treated Apatite II™ that produced very low to non-detectable levels of DOC and BOD while aging. To determine the effects of thermal treatment on performance efficiencies, studies were performed using 500 mg L−1 Pb solutions in columns packed with Apatite II™ that had been preheated at various temperatures for 2 h. The column study showed Pb loading of the Apatite II™ at different thermal treatments that ranged from 10.5% to 16.8% Pb by weight of substrate. The Pb loading capacity (by weight of substrate) increased as the treatment temperature of the Apatite II™ increased. 相似文献
124.
Deniz Karagulle Charlie Frye Roger Sayre Sean Breyer Peter Aniello Randy Vaughan Dawn Wright 《Transactions in GIS》2017,21(5):1040-1060
In 1964, E.H. Hammond proposed criteria for classifying and mapping physiographic regions of the United States. Hammond produced a map entitled “Classes of Land Surface Form in the Forty‐Eight States, USA”, which is regarded as a pioneering and rigorous treatment of regional physiography. Several researchers automated Hammond?s model in GIS. However, these were local or regional in application, and resulted in inadequate characterization of tablelands. We used a global 250 m DEM to produce a new characterization of global Hammond landform regions. The improved algorithm we developed for the regional landform modeling: (1) incorporated a profile parameter for the delineation of tablelands; (2) accommodated negative elevation data values; (3) allowed neighborhood analysis window (NAW) size to vary between parameters; (4) more accurately bounded plains regions; and (5) mapped landform regions as opposed to discrete landform features. The new global Hammond landform regions product builds on an existing global Hammond landform features product developed by the U.S. Geological Survey, which, while globally comprehensive, did not include tablelands, used a fixed NAW size, and essentially classified pixels rather than regions. Our algorithm also permits the disaggregation of “mixed” Hammond types (e.g. plains with high mountains) into their component parts. 相似文献
125.
Williams L. Rootes Robert H. Chabreck Vernon L. Wright Bobby W. Brown Thomas J. Hess 《Estuaries and Coasts》1991,14(4):489-494
A comparative study of American alligator (Alligator mississippiensis) growth rates was made in estuarine and palustrine wetlands in southwestern Louisiana. In the estuarine wetlands, where characteristic salinity levels were ≤5%, alligators grew faster and therefore reached sexual maturity earlier than did those in palustrine wetlands, which are characterized by shallow, freshwater marsh vegetation. Slower growth rates in palustrine wetlands appeared to be related to prey density, indicated by previous studies to be lower than in estuarine wetlands. Males grew faster than females and therefore reached sexual maturity at an earlier age in both habitats. This study revealed a major limitation in using total lengths as an index upon which population age structure can be based even when alligators are in the same geographic region. 相似文献
126.
The lavas of the 1955 east rift eruption of Kilauea Volcano have been the object of considerable petrologic interest for two reasons. First, the early 1955 lavas are among the most differentiated ever erupted at Kilauea, and second, the petrographic character and chemical composition of the lava being erupted changed significantly during the eruption. This shift, from more differentiated (MgO=5.0–5.7%) to more magnesian (MgO=6.2–6.8%) lava, has been variously interpreted, as either due to systematic excavation of a zoned, differentiated magma body, or to invasion of the differentiated magma by more primitive magma, followed by rapid mixing and eruption of the resulting hybrid magmas. Petrologic examination of several nearvent spatter samples of the late 1955 lavas shows abundant evidence for magma mixing, including resorbed and/or reversely zoned crystals of olivine, augite and plagioclase. In addition, the compositional ranges of olivine, plagioclase and groundmass sulfide are very large, implying that the assemblages are hybrid. Core compositions of olivine phenocrysts range from Fo85 to Fo77. The most magnesian olivines in these samples must have originally crystallized from a melt containing 8.0–8.5% MgO, which is distinctly more magnesian than the bulk composition of the late 1955 lavas. The majorelement and trace-element data are either permissive or supportive of a hybrid origin for the late 1955 lavas. In particular, the compositional trends of the 1955 lavas on plots of CaO vs MgO, and the virtual invariance of Al2O3 and Sr in these plagioclase-phyric lavas are more easily explained by magma mixing than by fractionation. The pattern of internal disequilibrium/re-equilibration in the late 1955 spatter samples is consistent with reintrusion and mixing having occurred at least twice, during the latter part of the 1955 eruption. Plagioclase zonation preserves possible evidence for additional, earlier reintrusion events. Least-squares modelling the mixing of early 1955 bulk compositions with various summit lavas±olivine pick the 1952 summit lava as most like the primitive component. The results also indicate the primitive component had MgO=7.5–8.0%, corresponding to liquidus temperatures of 1165–1175°C. The absence of Fe-Ti oxide phenocrysts in the late 1955 lavas implies that the cooler component of the hybrid had T>1110°C. Thus the thermal contrast between the two components may have been as much as 55–65°C, sufficient to produce the conspicuous disequilibrium effects visible in the spatter samples. 相似文献
127.
128.
129.
130.