全文获取类型
收费全文 | 230篇 |
免费 | 4篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 15篇 |
地球物理 | 16篇 |
地质学 | 119篇 |
海洋学 | 11篇 |
天文学 | 11篇 |
综合类 | 2篇 |
自然地理 | 61篇 |
出版年
2018年 | 1篇 |
2017年 | 1篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 7篇 |
2011年 | 5篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 20篇 |
1996年 | 13篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1968年 | 3篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1938年 | 1篇 |
排序方式: 共有239条查询结果,搜索用时 31 毫秒
231.
PAUL F. KARROW 《Boreas: An International Journal of Quaternary Research》1992,21(4):379-391
Till containing over 10% matrix carbonate extends in a belt 200–300 km wide south of the Hudson Bay Paleozoic basin source. The southern boundary is represented by the 'carbonate line', extending from Wawa to near Timmins and Cochrane in the study area. Higher silt content and lighter color are associated with the higher carbonate till. The carbonate tine corresponds approximately to the Chapleau moraine and correlative moraines to the northwest and may signify a discrete stratigraphic unit (possibly identifiable with the Matheson Till) formed by a glacial readvance. Glaciolacustrine sediments have higher carbonate content than nearby till and similarly form widespread sediment blankets even beyond that of the carbonate-rich till. Radiocarbon dating of amorphous organic sediments may be at risk because of old carbon error on such terrain and there may be some risk even in areas of much smaller carbonate content. A greater effort should be made to establish chronologies based on terrestrial plant matter, now more often possible with AMS radiocarbon dating. 相似文献
232.
233.
Images can contain chemical information and many chemical methods can generate image data. For anefficient extraction of chemical data from images, data analysis techniques are necessary, It is a greatadvantage to be able to work on multivariate images. Many imaging techniques allow the extraction ofchemical information. Inorganic analytical chemistry seems to have the longest tradition here, butorganic chemistry and biochemistry may soon be catching up. Also large data arrays from non-imagingtechniques can be combined with image analysis in a useful way, provided certain conditions are fulfilled. 相似文献
234.
235.
236.
PAUL BENJAMIN CRILLY 《地理学报(英文版)》1990,(4)
The use of a cross-correlation prefiltering technique to enhance the ability of Jansson's iterativedeconvolution procedure to deconvolve extremely noisy chromatographic data is investigated.Test casesinclude peaks whose resolutions are as low as 0.35 and whose signal-to-noise ratios are as low as 1:1.Evaluation criteria include RMS error,relative peak error and peak area repeatability.For comparisonpurposes,relative peak area errors and peak area variances are also evaluated for noisy but well resolvedpeaks that have only been prefiltered with the cross-correlation filter.Jansson's method in conjunctionwith cross-correlation prefiltering is shown not only to resolve overlapped peaks but in some cases toimprove their signal-to-noise ratios.The study also establishes some limits to the capabilities of Jansson'smethod will regard to adverse data conditions. 相似文献
237.
ANDREAS PAUL JOHN J. G. REIJMER JÖRN FÜRSTENAU HANNO KINKEL CHRISTIAN BETZLER 《Sedimentology》2012,59(5):1640-1658
A piston core from the Maldives carbonate platform was investigated for carbonate mineralogy, grain‐size distributions, calcium carbonate content and organic carbon. The sedimentary record was linked to Late Pleistocene sea‐level variations, using an age model based on oxygen isotopes obtained from planktonic foramanifera, nannofossil biostratigraphy and 14C age determinations. The correlation between the sedimentary record and Late Pleistocene sea‐level showed that variations in aragonite and mud during the past 150 000 years were clearly related to flooding and sea floor exposure of the main lagoons of the atolls of the Maldives carbonate platform. Platform flooding events were characterized by strongly increased deposition of aragonite and mud within the Inner Sea of the Maldives. Exposure events, in contrast, can be recognized by rapid decreases in the values of both proxy records. The results show that sediments on the Maldives carbonate platform contain a continuous record of Pleistocene sea‐level variations. These sediments may, therefore, contribute to a better understanding of regional and even global sea‐level changes, and yield new insights into the interplay between ocean currents and carbonate platform morphology. 相似文献
238.
REE and PGE Geochemical Constraints on the Formation of Dunites in the Luobusa Ophiolite, Southern Tibet 总被引:19,自引:0,他引:19
ZHOU MEI-FU; ROBINSON PAUL T.; MALPAS JOHN; EDWARDS STEPHEN J.; QI LIANG 《Journal of Petrology》2005,46(3):615-639
The Luobusa ophiolite, Southern Tibet, lies in the IndusYarlungZangbo suture zone that separates Eurasia to the north fromthe Indian continent to the south. The ophiolite contains awell-preserved mantle sequence consisting of harzburgite, clinopyroxene(cpx)-bearing harzburgite and dunite. The harzburgite containsabundant pods of chromitite, most of which have dunite envelopes,and the cpx-bearing harzburgites host numerous dunite dykes.Dunite also exists as a massive unit similar to those of themantlecrust transition zones in other ophiolites. Allof the dunites in the ophiolite have a similar mineralogy, comprisingmainly olivine with minor orthopyroxene and chromite and tracesof clinopyroxene. They also display similar chemical compositions,including U-shaped chondrite-normalized REE patterns. Mantle-normalizedPGE patterns show variable negative Pt anomalies. Detailed analysisof a chromite-bearing dunite dyke, which grades into the hostcpx-bearing harzburgite, indicates that LREE and Ir decrease,whereas HREE, Pd and Pt increase away from the dunite. Thesefeatures are consistent with formation of the dunite dykes byinteraction of MORB peridotites with boninitic melts from whichthe chromitites were formed. Because the transition-zone dunitesare mineralogically and chemically identical to those formedby such meltrock reaction, we infer that they are ofsimilar origin. The Luobusa ultramafic rocks originally formedas MORB-source upper mantle, which was subsequently trappedas part of a mantle wedge above a subduction zone. Hydrous meltsgenerated under the influence of the subducted slab at depthmigrated upward and reacted with the cpx-bearing harzburgitesto form the dunite dykes. The modified melts ponded in smallpockets higher in the section, where they produced podiformchromitites with dunite envelopes. At the top of the mantlesection, pervasive reaction between melts and harzburgite producedthe transition-zone dunites. KEY WORDS: meltrock interaction; REE; PGE; hydrous melt; mantle; ophiolite; Tibet 相似文献
239.
Noble Metal Enrichment Processes in the Merensky Reef, Bushveld Complex 总被引:14,自引:7,他引:14
We have analysed sulphides, silicates, and chromites of theMerensky Reef for platinum-group elements (PGEs), Re and Auusing laser ablation-inductively coupled plasma mass spectrometryand synthetic pyrrhotite standards annealed with known quantitiesof noble metals. Os, Ir and Ru reside in solid solution in pyrrhotiteand pentlandite, Rh and part of the Reefs Pd in pentlandite,whereas Pt, Au, Re and some Pd form discrete phases. Olivineand chromite, often suspected to carry Os, Ir and Ru, are PGEfree. All phases analysed contain noble metals as discrete micro-inclusionswith diameters typically <100 nm. Inclusions in sulphidescommonly have the element combinations OsIrPtand PtPdAu. Inclusions in olivine and chromiteare dominated by Pt ± AuPd. Few inclusion spectracan be related to discrete noble metal phases, and few inclusionshave formed by sub-solidus exsolution. Rather, some PGE inclusions,notably those in olivine and chromite, are early-magmatic nuggetstrapped when their host phases crystallized. We suggest thatthe silicate melt layer that preceded the Merensky Reef wasPGE oversaturated at early cumulus times. Experiments combinedwith available sulphidesilicate partition coefficientssuggest that a silicate melt in equilibrium with a sulphidemelt containing the PGE spectrum of the Merensky ore would indeedbe oversaturated with respect to the least soluble noble metals.Sulphide melt apparently played little role in enriching thenoble metals in the Merensky Reef; rather, its role was to immobilizea pre-existing in situ stratiform PGE anomaly in the liquid-stratifiedmagma chamber. KEY WORDS: Bushveld Complex; Merensky Reef; laser-ablation ICP-MS; platinum-group mineralization 相似文献