全文获取类型
收费全文 | 345篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 43篇 |
地球物理 | 75篇 |
地质学 | 149篇 |
海洋学 | 4篇 |
天文学 | 64篇 |
综合类 | 2篇 |
自然地理 | 8篇 |
出版年
2021年 | 3篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 7篇 |
2011年 | 7篇 |
2010年 | 10篇 |
2009年 | 17篇 |
2008年 | 12篇 |
2007年 | 13篇 |
2006年 | 20篇 |
2005年 | 12篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 11篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1964年 | 3篇 |
1957年 | 3篇 |
1956年 | 3篇 |
1954年 | 3篇 |
1950年 | 4篇 |
排序方式: 共有349条查询结果,搜索用时 15 毫秒
341.
Carbon,sulfur, oxygen and strontium isotope records,organic geochemistry and biostratigraphy across the Permian/Triassic boundary in Abadeh,Iran 总被引:6,自引:0,他引:6
Christoph?KorteEmail author Heinz?W.?Kozur Michael?M.?Joachimski Harald?Strauss Ján?Veizer Lorenz?Schwark 《International Journal of Earth Sciences》2004,93(4):565-581
Pelagic deposits at Abadeh represent a complete biostratigraphic record across the Permian/Triassic boundary (PTB). The presumed water depth during deposition of these sediments was between 60 and 90 m. Similar to other Permian/Triassic boundary sections, the succession at Abadeh is characterised by a negative carbon isotope shift of approximately 4. The values start to decrease in the lower C. changxingensis - C. deflecta s.l. Zone, reach –0.12 (V-PDB) in the uppermost Permian just below the PTB, remain low to the early I. isarcica Zone (–0.32) and increase subsequently in the upper I. isarcica Zone. For the time interval of the PTB negative carbon isotope excursion, between the C. iranica and the I. isarcica Zones, no correlation exists between the 13Ccarb and the 18Ocarb. The above observations argue against the conclusion of Heydari et al. (2001) that the carbon isotope event at the P/T transition is an alteration artefact and not a global signal. The decrease in 13Ccarb is accompanied by a ~5 (and potentially up to 10) increase in 34SSSS. Together, these features are thought to reflect a complex global event, notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves. For the carbon isotope drop, other factors, such as the collapse of ocean primary productivity may also have played a role. The 87Sr/86Sr ratios of Dzhulfian seawater show only a minor increase from 0.70705 to 0.70710, reaching 0.70720 in the Dorashamian. The increase becomes steeper in the Early Triassic reaching 0.70754 in the N. dieneri Zone. The rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost Permian (C. meishanensis - H. praeparvus Zone) and the lack of a dense land vegetation in the Early Triassic, prior to the Spathian (Upper Olenekian). 相似文献
342.
Heinz G. Scharbert 《Mineralogy and Petrology》1963,8(4):591-598
Ohne Zusammenfassung 相似文献
343.
CK chondrites constitute the most oxidized anhydrous carbonaceous chondrite group; most of the Fe occurs in magnetite and in FeO-rich mafic silicates. The two observed CK falls (Karoonda and Kobe), along with thirteen relatively unweathered CK finds, have unfractionated siderophile-element abundance patterns. In contrast, a sizable fraction of CK finds (9 of 24 investigated) shows fractionated siderophile abundance patterns including low abundances of Ni, Co, Se and Au; the most extreme depletions are in Ni (0.24 of normal CK) and Au (0.14 of normal CK). This depletion pattern has not been found in other chondrite groups. Out of the 74 CK chondrites listed in the Meteoritical Bulletin Database (2006; excluded considerably paired specimens; see http://tin.er.usgs.gov/meteor/metbull.php) we analyzed 24 and subclassified the CK chondrites in terms of their chemical composition and sulfide mineralogy: sL (siderophiles low; six samples) for large depletions in Ni, Co, Se and Au (>50% of sulfides lost); sM (siderophiles medium; two CKs) for moderately low Ni and Co abundances (sulfides are highly altered or partly lost); sH (siderophiles high; one specimen) for enrichments in Ni, Co, Se and Au; ‘normal’ for unfractionated samples (13 samples). The sole sH sample may have obtained additional sulfide from impact redistribution in the parent asteroid. We infer that these elements became incorporated into sulfides after asteroidal aqueous processes oxidized nebular metal; thermal metamorphism probably also played a role in their mineral siting. The siderophile losses in the sL and sM samples are mainly the result of oxidation of pentlandite, pyrite and violarite by terrestrial alteration followed by leaching of the resulting phases. Some Antarctic CK chondrites have lost most of their sulfides but retained Ni, Co, Se and Au, presumably as insoluble weathering products. 相似文献
344.
The normalised Hénon–Heiles family exhibits a degenerate bifurcation when passing through the separable case =0. We clarify the relation between this degeneracy and the integrability at =0. Furthermore we show that the degenerate bifurcation carries over to the Hénon–Heiles family itself. 相似文献
345.
GeoJournal - The geography of education issues has long been an under-researched area in geography literature. This article reviews studies on school segregation and white flight and emphasizes the... 相似文献
346.
Groundwater temperatures, especially in shallow (quaternary) aquifers respond to ground surface temperatures which in turn depend on climate and land use. Groundwater temperatures, therefore, are modified by climate change and urban development. In northern temperate climate regions seasonal temperature cycles penetrate the ground to depths on the order of 10–15 m. In this paper, we develop and apply analytic heat transfer relationships for 1-D unsteady effective diffusion of heat through an unsaturated zone into a flowing aquifer a short distance below the ground surface. We estimate how changes in land use (urban development) and climate change may affect shallow groundwater temperatures. We consider both long-term trends and seasonal cycles in surface temperature changes. Our analysis indicates that a fully urbanized downtown area at the latitude of Minneapolis/St. Paul is likely to have a groundwater temperature that is nearly 3 °C warmer than an undeveloped agricultural area at the same geographic location. Pavements are the main cause of this change. Data collected by the Minnesota Pollution Control Agency (MPCA) in the St. Cloud, MN area confirm that land use influences groundwater temperatures. Ground surface temperatures are also projected to rise in response to global warming. In the extreme case of a doubling of atmospheric carbon dioxide (2 × CO2 climate scenario), groundwater temperatures in the Minneapolis/St. Paul metropolitan area could therefore rise by up to 4 °C. Compounding a land use change from “undeveloped” to “fully urbanized” and a 2 × CO2 climate scenario, groundwater temperatures are projected to rise by about 5 °C at the latitude of Minneapolis/St. Paul. 相似文献
347.
B. Heinz S. Birk R. Liedl T. Geyer K. L. Straub J. Andresen K. Bester A. Kappler 《Environmental Geology》2009,57(4):797-808
The concurrent use of karst aquifers as drinking water resources and receptors of combined sewer overflow lacking appropriate pre-treatment may cause conflicts between drinking water supply and storm water management. A storm water tank (SWT) for combined wastewater is identified as the source of sporadic contamination of a karst spring (Gallusquelle, “Schwäbische Alb”, SW Germany) used for public water supply. Spring water quality was examined by routine and event sampling and by evaluating physicochemical and microbiological parameters. The total number of microbial colonies growing at 20°C and the number of Escherichia coli colonies rose to values up to four orders of magnitude higher than background, 2–5 days after overflow of the SWT. High concentrations of chloride, sodium, and total organic carbon (TOC) and high values of turbidity coincide with this increase. However, high bacterial contamination is also observed while turbidity and TOC are low. Several wastewater-related organic micro-pollutants such as chlorinated and non-chlorinated organophosphates were detected in the SWT and, depending on their Kow values and their biodegradability, in lower concentrations at the spring. 相似文献
348.
Heinz Tiersch 《Astronomische Nachrichten》1989,310(3):251-251
349.