全文获取类型
收费全文 | 312篇 |
免费 | 10篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 10篇 |
地球物理 | 71篇 |
地质学 | 152篇 |
海洋学 | 35篇 |
天文学 | 26篇 |
自然地理 | 30篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 17篇 |
2012年 | 27篇 |
2011年 | 21篇 |
2010年 | 16篇 |
2009年 | 20篇 |
2008年 | 20篇 |
2007年 | 19篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 14篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1973年 | 1篇 |
1965年 | 1篇 |
1960年 | 1篇 |
1957年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有327条查询结果,搜索用时 15 毫秒
221.
222.
Giovanna T. Sapienza William L. Griffin Suzanne Y. O’Reilly Lauro Morten 《Contributions to Mineralogy and Petrology》2009,157(1):1-22
In situ trace-element and isotopic (87Sr/86Sr) data and whole-rock Sr–Nd–Hf data on 12 gabbro xenoliths from the Hyblean Plateau (south-eastern Sicily) illustrate the complex petrogenetic evolution of this lithospheric segment. The gabbros formed by precipitation of plagioclase + clinopyroxene from a HIMU-type alkaline melt, then were cryptically metasomatized by a low-Rb, high-87Sr/86Sr fluid, and finally infiltrated by an exotic, late Fe–Ti-rich melt with 87Sr/86Sr ~ 0.7055, carrying high concentrations of Sr, Rb and HFSE. The geochemical and isotopic features of both the metasomatizing fluid and the Fe–Ti-rich melt are compatible with their common derivation by the progressive melting of an amphibole–phlogopite–ilmenite metasomatic domain (MARID-type?) that probably resided within the subcontinental lithospheric mantle. Therefore, both the astenosphere and the lithosphere underneath the Hyblean Plateau contributed to the petrogenesis of the gabbros. Sm–Nd dating yields an age of 253 ± 60 Ma for the cumulitic pile, roughly coinciding with a hydrothermal event recorded by crustal zircons in the area. We suggest that the Hyblean Plateau suffered a thermal event—probably related to lithospheric thinning and upwelling and melting of the asthenosphere—in Permo-Triassic time (the opening of the Ionian Basin?). The induced perturbation in the lithosphere caused consequent melting of some previously metasomatised portions. 相似文献
223.
Jonathan Irwin Suzanne Aigrain Jerome Bouvier Leslie Hebb Simon Hodgkin Mike Irwin Estelle Moraux 《Monthly notices of the Royal Astronomical Society》2009,392(4):1456-1466
We report on the results of a time-series photometric survey of M50 (NGC 2323), a ∼130 Myr open cluster, carried out using the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco telescope and Mosaic-II detector as part of the Monitor project. Rotation periods were derived for 812 candidate cluster members over the mass range 0.2 ≲ M /M⊙ ≲ 1.1 . The rotation period distributions show a clear mass-dependent morphology, statistically indistinguishable from those in NGC 2516 and M35 taken from the literature. Due to the availability of data from three observing runs separated by ∼10 and 1 month time-scales, we are able to demonstrate clear evidence for evolution of the photometric amplitudes, and hence spot patterns, over the 10 month gap. We are not able to constrain the time-scales for these effects in detail due to limitations imposed by the large gaps in our sampling, which also prevent the use of the phase information. 相似文献
224.
The Dead Sea region holds the archives of a complex relationship between an ever-changing nature and ancient civilisations. Regional pollen diagrams show a Roman-Byzantine period standing out in the recent millennia by its wetter climate that allowed intensive arboriculture. During that period, the Dead Sea formed laminites that display mostly a seasonal character. A multidisciplinary study focused on two earthquakes, 31 BC and AD 363, recorded as seismites in the Ze’elim gully A unit III which has been well dated by radiocarbon in a previous study. The sampling of the sediment was done at an annual resolution starting from a few years before and finishing a decade after each earthquake. A clear drop in agricultural indicators (especially Olea and cereals) is shown. These pollen indicators mostly reflect human activities in the Judean Hills and coastal oases. Agriculture was disturbed in large part of the rift valley where earthquake damage affected irrigation and access to the fields. It took 4 to 5 yr to resume agriculture to previous conditions. Earthquakes must be seen as contributors to factors damaging societies. If combined with other factors such as climatic aridification, disease epidemics and political upheaval, they may lead to civilisation collapse. 相似文献
225.
226.
Suzanne O’Keefe 《Applied geography (Sevenoaks, England)》2012,32(1):66-72
This case study considers the economic implications of various growth policies in the Sacramento region over the last decade. Counties and cities throughout the Sacramento region have varying policies and attitudes toward residential and commercial growth. Over the last decade we have seen extremes in development in the region, from the Roseville area which experienced a residential and retail explosion, to Davis, which has restricted growth to relatively few projects. Growth has impacted property and sales tax revenue, and city and county expenditures. Changes in the housing market and the economy over the past few years have had a large impact on new construction activity. This paper examines how cities and counties in the Sacramento region have weathered the housing boom and bust, based on their growth policies during the past decade. The relationship between growth policies, measured by building permits, local government revenue, housing markets, and employment is assessed. Comparisons are presented through charts and panel data regression. Rapid development leads to higher levels of sales tax revenue, coupled with greater volatility in sales tax revenue. Employment rises more quickly in areas that have a high level of non-residential construction relative to residential construction. 相似文献
227.
A fluid inclusion investigation of the polymetallic mineralization at Yinshan from the Le–De metallogenic belt in Jiangxi Province of China has been carried out using petrographic and microthermometric techniques. The data obtained here indicate that three major types of fluids were involved during the formation of the deposit. They are type I vapor-rich, type II liquid-rich and type III halite-bearing inclusions within the H2O–NaCl system. The high salinity fluids represented by type III inclusions, being unusual to the distal part of an intrusion-centered ore-forming system such as Yinshan, have been interpreted as the product of direct exsolution of a crystallizing magma, rather than a result of fluid immiscibility from a low salinity fluid. Evidence used to support such an interpretation includes the mode of homogenization of type III inclusions exclusively via halite dissolution, spatial separation of type I and type III inclusions on microscopic scale, the consistent phase ratios within the inclusions concerned, and considerable deviation in homogenization temperature for both type I and type III inclusions. Trapping conditions for type I inclusions were estimated to be around 440 °C and 260 bars, while type III inclusions were constrained to be trapped at least above 900 bars and > 500 °C. The formation temperatures for type II inclusions range from 270 to 390 °C if a lithostatic pressure of 260 bars is assumed. Pressure fluctuation determined by this fluid inclusion study coupled with decreases in salinity and temperature as result of the potential fluid mixing are supposed to have played an important role in triggering the precipitation of ore minerals from the hydrothermal solution. 相似文献
228.
Andy Breckenridge Thomas C. Johnson Suzanne Beske-Diehl John S. Mothersill 《Quaternary Science Reviews》2004,23(23-24):2355-2367
We analyze both new and previously published paleomagnetic records of secular variation (PSV) from Lake Superior sediment cores and compare these records to correlated rhythmite (varve) thickness records to determine post-glacial sedimentation rates and to reassess the termination of glaciolacustrine varves in the basin. The results suggest that offshore sedimentation rates have exhibited considerable spatial variation over the past 8000 years, particularly during the mid-Holocene. We attribute offshore, mid-Holocene sedimentation changes to alterations in whole basin circulation, perhaps precipitated by a greater dominance of the Gulf of Mexico air mass during the summer season. Nearshore bays are characterized by high sedimentation rates for at least 1000 years after varve cessation and during a period between around 4500 and 2000 cal. BP. After 2000 cal. BP, sedimentation rates subsided to earlier rates. The increases between 4500 and 2000 cal. BP are probably due to lake level fall after the Nipissing II highstand.The older glaciolacustrine varve thickness records suggest that the influx of glacially derived sediment ended abruptly everywhere in the lake, except near the Lake Nipigon inlets. Multiple sediment cores reveal 36 anomalously thick varves, previously ascribed to the formation of the Nakina moraine, which were deposited just prior to varve cessation in the open lake. The PSV records support the observation that the cessation of these thick varves is a temporally correlative event, occurring at 9035±170 cal. BP (calibrated years before 1950, ca 7950–8250 14C BP). This date would correlate to the eastern diversion of Lake Agassiz and glacial meltwater into Lake Ojibway. 相似文献
229.
Alkaline magmatism in the Southern Highlands Province, New South Wales, Australia is associated with continental rifting. Near-primary liquids have a wide range in Nd and Sr isotope composition that indicates gross isotopic and chemical heterogeneities in a mantle source region depleted in light rare earth elements (LREE) for much of Earth's history. The large-ion lithophile element and LREE-enriched nature of the primary lavas ((Ce)N = 95–182 and (Yb)N = 8.5–13.3) is consistent with an enriched mantle source region. This elemental enrichment may be accomplished by veining of the subcontinental mantle with volatile-rich phases like amphibole, apatite and carbonate which provide the volatile flux necessary to trigger anatexis.Degassing of mantle CO2 has led to migration of LREE-enriched fluids and local transformation of the lherzolitic mantle to pyroxenite veined by apatite ± kaersutite ± mica ± diopside. The mantle veining event may be related to upwelling of silica-undersaturated incompatible element-enriched magmas similar to the host magma of the Kiama xenoliths. In a relatively short period of time (100 m.y.), the Sr and Nd isotopes in essentially LREE-depleted mantle have evolved in response to low Sm/Nd and low Rb/Sr ratios, and now define a near-vertical vector on a isotope-isotope plot. From this rather unique signature we can infer that CO2- and LREE-rich, Rb-poor mantle is a potentially suitable mantle source region for the genesis of alkali-potassic volcanic rocks characterized by a narrow range in87Sr/86Sr ratio and a wide range in143Nd/144Nd ratio (e.g. Leucite Hills). 相似文献
230.
A 6.500-meter reach of western Chesapeake Bay shoreline (lower Mayo Peninsula) lost about 1.1×106 cubic meters of sediment (equivalent to 170 cubic meters lost per meter of shoreline) between 1846 and 1932, when the first
aerial photographs show the shoreline already substantially protected by a system of groins and intermittent bulkheading.
These structures have eliminated the fastland as a source of erodable material, and have starved the supply of sand for littoral
drift, thus limiting the extent of the beaches to the remaining groin fields.
Volumes of sediment involved in these impacts are small in the overall sediment budget. Bulkheads produce no deficit in the
budget since scouring of the beaches on their seaward sides makes up for the decreased erosion of protected fastland. Groins
trap little of the potential littoral drift (computed to be about 104 cubic meters per meter of shoreline per year). The sand supply in the remaining beaches is nearly equivalent to the annual
loss of sediment from the entire shoreline system due to the long-term rate of erosion of the shoreline and nearshore between
1846 and 1932. 相似文献