全文获取类型
收费全文 | 434篇 |
免费 | 14篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 17篇 |
地球物理 | 91篇 |
地质学 | 188篇 |
海洋学 | 12篇 |
天文学 | 63篇 |
综合类 | 1篇 |
自然地理 | 65篇 |
出版年
2023年 | 3篇 |
2020年 | 4篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 19篇 |
2012年 | 16篇 |
2011年 | 15篇 |
2010年 | 12篇 |
2009年 | 30篇 |
2008年 | 15篇 |
2007年 | 14篇 |
2006年 | 19篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 21篇 |
2001年 | 6篇 |
2000年 | 13篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1955年 | 3篇 |
1949年 | 2篇 |
排序方式: 共有452条查询结果,搜索用时 43 毫秒
101.
Hermann L. F. Meyer 《International Journal of Earth Sciences》1916,7(5-6):193-248
Ohne Zusammenfassung 相似文献
102.
This paper describes an effort to develop a predictive tool for the design of a new promising marine transport — the WIG craft. The presented mathematical model of the WIG craft is capable of modeling the aerodynamics of a WIG system including the ground effect, the hydrodynamics of a stepped planing hull with a hydrofoil and also the simulation of motion for the craft. Based on extensive experience using the model, it is shown that the most important and necessary features of WIG aero- and hydrodynamics are taken into account. The results of simulations have been validated through comparison with other theoretical approaches and also with model experiments. The mathematical model is applied to investigate the dynamics of the small manually piloted WIG craft: “Hydrowing VT01”. The numerical study resulted in recommendations allowing the pilot to overcome the pitch-up tendency and also to perform the take-off manoeuvre smoothly. The stability of the WIG with a hydrofoil and also the dynamic properties of anti-collision manoeuvres have been studied and are presented. 相似文献
103.
The Austurhorn intrusive complex in southeastern Iceland represents an exhumed Tertiary central volcano. The geometry of the intrusion and geochemistry of the mafic and felsic rocks indicate Austurhorn was a volcanic center analogous to Eyjafjallajökull and Torfajökull in Iceland's eastern neovolcanic zone (EVZ). Early transitional tholeiitic basalt magmatism at Austurhorn formed a shallow crustal chamber 5 km in diameter. Apparent rhythmic modal layering of, and intrusive contacts within, the gabbro indicate the mafic chamber was replenished frequently as it cooled and crystallized. Felsic activity postdated near-solidification of the gabbro; numerous granitic magmas intruded along gabbro margins and within the adjacent crust. Field relations indicate that infrequent felsic replenishment prevented convective mixing of the Austurhorn chamber during this time, although commingled mafic and felsic magmas are observed in an extensive net veined complex. Late stage mafic dikes intrude the entire complex, suggesting that magmatic heat was abundantly available throughout the evolution of the Austurhorn system. Plagioclase and clinopyroxene compositions in mafic through felsic rocks, including gabbros, support a model of progressive differentiation. Field relations constrain the felsic magmas to originate at P1 kbar, presumably by fractional crystallization. The structure and geochemistry of the Austurhorn intrusive complex suggest formation in an immature rift environment similar to the modern EVZ. The proposed rift segment was parallel to the western and eastern neovolcanic zones, and probably resulted from a reorganization of plate boundaries 7 Ma (Saemundsson 1979; Helgason 1985; Jancin et al. 1985) triggered by activity of the Iceland mantle plume. 相似文献
104.
Historical Landscape Change in Yellowstone National Park: Demonstrating the Value of Intensive Field Observation and Repeat Photography 下载免费PDF全文
Although transportation and outdoor recreation are well‐recognized aspects of national parks, few studies have explored these aspects from the perspective of human geography as a means of analyzing historical landscape change. This paper offers an innovative synthesis of methods for studying cultural landscape change over time through a case study of the historical geography of transportation, tourism, and outdoor recreation along the Howard Eaton Trail (HET) in Yellowstone National Park. We conducted research through a field course that combined repeat photography, archival research, Geographic Information Systems (GIS), and traditional field methods. Results indicate that a combination of repeat photography and other methods can create an effective means of evaluating cultural landscape change; even short field courses provide opportunities for students and faculty to conduct collaborative research that provides powerful, multidimensional, situated‐learning experiences; and repeat photography creates datasets that may benefit future research and teaching. 相似文献
105.
Neogene exhumation and relief evolution in the eastern Betics (SE Spain): Insights from the Sierra de Gador 下载免费PDF全文
Marianne Janowski Nicolas Loget Cécile Gautheron Jocelyn Barbarand Nicolas Bellahsen Jean Van Den Driessche Julien Babault Bertrand Meyer 《地学学报》2017,29(2):91-97
The Betics are a key area to study an orogenic landscape disrupted by late‐orogenic extension. New low‐temperature thermochronology (LTT) data (AHe and AFT) coupled with geomorphic constraints in the Sierra de Gador (Alpujarride complex) are used to reconstruct the cooling history and evolution of relief during the Neogene. We document three stages: (1) a fast cooling event between 23 and 16 Ma associated with the well‐known extensive tectonic exhumation of the Alpujarride unit, (2) a period of slow cooling between 16 and 7.2 Ma related to a planation event and (3) a post‐7.2 Ma surface uplift associated with the inversion of the Alboran domain undetected by LTT. The planation event followed by this late uplift can explain the occurrence of inherited low‐relief surfaces overlain by Tortonian–Messinian platform deposits at the top of the range. Finally, we propose that the Sierra de Gador is a more transient landscape than the nearby Sierra Nevada. 相似文献
106.
GOCE: assessment of GPS-only gravity field determination 总被引:2,自引:1,他引:1
107.
Summary The Palim granite, hosted by the metasedimentary country rocks in the Bastar tin province, is a heterogeneous pluton that
comprises hornblende granite, biotite granite and two-mica granite. Spherical inhomogeneous surmicaceous enclaves occur within
the granites with coarse grained cores of muscovite mantled by finer muscovite-quartz-biotite (± sillimanite) rims. Geochemical
features imply that the granites are highly evolved and geochemically distinct. Petrographic and geochemical considerations
point towards a transition from metaluminous I-type hornblende-bearing granite in the south to peraluminous volatile-enriched
S-type like lithologies (biotite and two-mica granites) towards north. Modeling of highly incompatible elements such as Nb
and Cs, implies 31 to 33% assimilated fractional crystallization of a melt with an initial composition close to that of the
hornblende granite to form the two-mica granite. Hornblende geobarometry, plagioclase-hornblende thermometry (in hornblende
granite) and phengite barometry (in two-mica granite), yield P-T estimates of 5–7 kb/725°–760 °C, and 6 kb/700 °C, respectively.
The study further implies that a genetic link exists between granite magmatism and the formation of tin pegmatites in the
region. The preponderance of peripheral pegmatites to the north-east of the Palim granite is regarded a result of outward
crystal-melt fractionation and tectonic tilting of the pluton.
Received October 21, 1999; revised version accepted December 12, 2000 相似文献
108.
Recent large-magnitude floods and their impact on valley-floor environments of northeastern Yellowstone 总被引:1,自引:0,他引:1
The Lamar River watershed of northeastern Yellowstone contains some of the most diverse and important habitat in the national park. Broad glacial valley floors feature grassland winter range for ungulates, riparian vegetation that provides food and cover for a variety of species, and alluvial channels that are requisite habitat for native fish. Rapid Neogene uplift and Quaternary climatic change have created a dynamic modern environment in which catastrophic processes exert a major influence on riverine–riparian ecosystems. Uplift and glacial erosion have generated high local relief and extensive cliffs of friable volcaniclastic bedrock. As a result, steep tributary basins produce voluminous runoff and sediment during intense precipitation and rapid snowmelt. Recent major floods on trunk streams deposited extensive overbank gravels that replaced loamy soils on flood plains and allowed conifers to colonize valley-floor meadows. Tree-ring dating identifies major floods in 1918, ca. 1873, and possibly ca. 1790. In 1996 and 1997, discharge during snowmelt runoff on Soda Butte Creek approached the 100-year flood estimated by regional techniques, with substantial local bank erosion and channel widening. Indirect estimates show that peak discharges in 1918 were approximately three times greater than in 1996, with similar duration and much greater flood plain impact. Nonetheless, 1918 peak discharge reconstructions fall well within the range of maximum recorded discharges in relation to basin area in the upper Yellowstone region. The 1873 and 1918 floods produced lasting impacts on the channel form and flood plain of Soda Butte Creek. Channels may still be locally enlarged from flood erosion, and net downcutting has occurred in some reaches, leaving the pre-1790 flood plain abandoned as a terrace. Gravelly overbank deposits raise flood-plain surfaces above levels of frequent inundation and are well drained, therefore flood-plain soils are drier. Noncohesive gravels also reduce bank stability and may have persistent effects on channel form. Overall, floods are part of a suite of catastrophic geomorphic processes that exert a very strong influence on landscape patterns and valley-floor ecosystems in northeastern Yellowstone. 相似文献
109.
Dr. Hans-Peter Geis 《International Journal of Earth Sciences》1962,51(2):375-384
Zusammenfassung Spilite sind Gesteine, die bei ihrer primären Platznahme starke Veränderungen erfahren haben. Eine wesentliche Rolle spielt dabei wahrscheinlich das Meerwasser. Die Metamorphose ist ein späterer Vorgang. Sie kann aus Spiliten wie normalen basischen Gesteinen die gleichen Produkte erzeugen.Je ein Beispiel grüner Gesteine aus den Kaledoniden und den Kareliden werden in ihrem petrographischen Aufbau kurz beschrieben. Auf Grund der allgemeinen geologischen Verhältnisse ist es wahrscheinlich, daß es sich um metamorphisierte Spilite handelt. Petrographisch kann dies jedoch nicht mit Sicherheit nachgewiesen werden. 相似文献
110.
B. Zhao N. Clauer L. J. Robb H. Zwingmann T. Toulkeridis F. M. Meyer 《Mineralogy and Petrology》1999,66(1-3):149-170
Summary White micas from metamorphosed and hydrothermally-altered basaltic lavas, conglomerates, quartzites and shales in and around the Ventersdorp Contact Reef of the Witwatersrand Basin, South Africa, were dated by the K-Ar method to constrain post-depositional thermal and mineralization processes. The minerals were separated into various grain sizes between < 0.4 and 10m, and characterized in terms of composition, paragenetic sequence and texture, by XRD, SEM and TEM techniques. The K-Ar isochron of all white micas in the basaltic lavas suggests an age of 1994 ± 60 Ma, and that of the smaller mica particles (< 2m) in the quartzites defines a younger age of 1917 ± 66 Ma. This range is considered to reflect the timing of long-lived hydrothermal alteration in the Ventersdorp Contact Reef. The older age is slightly younger than the intrusion of the Bushveld Complex (2060–2054 Ma) and the Vredefort catastrophism (2020 Ma), which are well-documented events that were superimposed onto the Witwatersrand Basin. The younger age may be associated with the Eburnian orogenesis along the western edge of the Kaapvaal Craton resulting in continental-scale fluid migration and hydrothermal activity that extended throughout the Griqualand Basin and even into the Witwatersrand Basin. The K-Ar ages obtained here for the white mica fractions of the Ventersdorp Contact Reef in the Witwatersrand Basin confirm that the period between 2.0 and 1.9 Ga was significant, as far as alteration, and possibly also gold mobilization, was concerned.
K-Ar Datierung von Hellglimmern aus dem hentersdorp Contact Reef des Witwatersrand Beckens, Südafrika: die zeitliche Eingrenzung der nach der Sedimentablagerung erfolgten Alteration
Zusammenfassung Hellglimmer von metamorph und hydrothermal überprägtem Basalt, Konglomerat, Quarzit und Pelit aus dem Ventersdorp Contact Reef im Witwatersrand Becken, Südafrika, wurden mittels der K-Ar Methode datiert, um das Alter der postsedimentären thermischen Überprägung einzugrenzen. Mineralkörner wurden in einzelne Fraktionen zwischen < 0.4 und 10m separiert und auf deren Zusammensetzung, Paragenese und Textur mittels Röntgendiffraktometrie und Elektronenmikroskopie untersucht. Das Isochronenalter für alle Hellglimmerproben aus dem Metabasalt liegt bei 1994 ± 60 Ma, jenes für die Glimmer mit einer Korngröße < 2m im Quarzit bei 1917 ± 66 Ma. Diese Altersspanne wird als Ausdruck einer lang anhaltenden hydrothermalen Veränderung des Ventersdorp Contact Reef interpretiert. Das ältere Alter ist etwas jünger als die Intrusion des Bushveld Komplex (2060–2054 Ma) und die Vredefort Katastrophe (2020 Ma) - zwei gut dokumentierte Ereignisse, die das Witwatersrand Becken erfaßten. Das jüngere Alter könnte mit der eburnischen Orogenese entlang des Westrandes des Kaapvaal Kratons in Zusammenhang stehen, während der es zu Fluid Migration und hydrothermaler Aktivität quer über den Kontinent vom Griqualand Becken bis in das Witwatersrand Becken kam. Die neuen K-Ar Alter bestätigen somit, daß die Zeitspanne von 2.0–1.9 Ga wesentlich für die Alteration und möglicherweise auch für die Mobilisierung von Gold im Witwatersrand Becken war.相似文献