全文获取类型
收费全文 | 7495篇 |
免费 | 94篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 99篇 |
大气科学 | 1161篇 |
地球物理 | 1809篇 |
地质学 | 3829篇 |
海洋学 | 210篇 |
天文学 | 276篇 |
综合类 | 20篇 |
自然地理 | 198篇 |
出版年
2018年 | 274篇 |
2017年 | 170篇 |
2016年 | 113篇 |
2015年 | 64篇 |
2014年 | 93篇 |
2013年 | 166篇 |
2012年 | 68篇 |
2011年 | 131篇 |
2010年 | 121篇 |
2009年 | 152篇 |
2008年 | 102篇 |
2007年 | 88篇 |
2006年 | 110篇 |
2005年 | 93篇 |
2004年 | 83篇 |
2003年 | 81篇 |
1996年 | 97篇 |
1993年 | 68篇 |
1992年 | 155篇 |
1991年 | 157篇 |
1990年 | 149篇 |
1989年 | 140篇 |
1988年 | 144篇 |
1987年 | 178篇 |
1986年 | 137篇 |
1985年 | 123篇 |
1984年 | 156篇 |
1983年 | 172篇 |
1982年 | 187篇 |
1981年 | 189篇 |
1980年 | 155篇 |
1979年 | 188篇 |
1978年 | 160篇 |
1977年 | 149篇 |
1976年 | 118篇 |
1975年 | 140篇 |
1974年 | 126篇 |
1973年 | 141篇 |
1972年 | 131篇 |
1971年 | 137篇 |
1970年 | 144篇 |
1969年 | 101篇 |
1968年 | 130篇 |
1967年 | 124篇 |
1966年 | 86篇 |
1965年 | 97篇 |
1964年 | 100篇 |
1962年 | 92篇 |
1960年 | 104篇 |
1954年 | 67篇 |
排序方式: 共有7602条查询结果,搜索用时 0 毫秒
51.
The age and thermal history of Cerro Rico de Potosi, Bolivia 总被引:1,自引:0,他引:1
C. G. Cunningham R. E. Zartman E. H. McKee R. O. Rye C. W. Naeser O. Sanjinés V G. E. Ericksen F. Tavera V 《Mineralium Deposita》1996,31(5):374-385
Cerro Rico de Potosi, Bolivia, is the world’s largest silver deposit and has been mined since the sixteenth century for silver,
and for tin and zinc during the twentieth century, together with by-product copper and lead. The deposit consists primarily
of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and
explosion breccia. The deposit is compositionally and thermally zoned, having a core of cassiterite, wolframite, bismuthinite,
and arsenopyrite surrounded by a peripheral, lower-temperature mineral assemblage consisting principally of sphalerite, galena,
lead sulfosalt, and silver minerals. The low-temperature assemblage also was superimposed on the high-temperature assemblage
in response to cooling of the main hydrothermal system. Both the dacite dome and the ore fluids were derived from a larger
magmatic/hydrothermal source at depth. The dome was repeatedly fractured by recurrent movement on the fault system that guided
its initial emplacement. The dome was extruded at 13.8±0.2 Ma (2σ), based on U-Th-Pb dating of zircon. Mineralization and
alteration occurred within about 0.3 my of dome emplacement, as indicated by a 40Ar/39Ar date of 13.76±0.10 Ma (1σ) for sericite from the pervasive quartz-sericite-pyrite alteration associated with the main-stage,
high-temperature, mineralization. The last thermal event able to reset zircon fission tracks occurred no later than 12.5±1.1 Ma
(1σ), as indicated by fission-tract dating. Minor sericite, and magmatic-steam alunite veins, were episodically formed around
11 Ma and between 8.3 and 5.7 Ma; the younger episodes occurring at the time of extensional fracturing at Cerro Rico and widespread
volcanism in the adjacent Los Frailes volcanic field. None of these younger events appear to be significant thermal/mineralizing
events; the exceptionally flat thermal release pattern of 39Ar from sericite and the results of the fission-tract dating of zircon show that none of the younger events was hot enough,
and lasted long enough, to cause significant loss of Ar or annealing of zircon fission tracks. U-Th-Pb dating of zircon cores
indicates a Precambrian progenitor for some zircons, and REE analyses of dated samples of hydrothermally altered dacite show
the presence of a prominent positive Eu anomaly, which constrains interpretations of the origin and evolution of the magmatic/hydrothermal
system.
Received: 14 October 1995/Accepted: 29 January 1996 相似文献
52.
Batrice Ledsert Janie Joffre Andr Ambls Paul Sardini Albert Genter Alain Meunier 《Journal of Volcanology and Geothermal Research》1996,70(3-4)
Organic matter has been observed in cores of the Soultz-sous-Forêts granite (Alsace, France) at depths between 2158 and 2160 m, in a highly fractured and altered zone. The granite is overlain by a 1400-m-thick sedimentary cover containing petroleum (Pechelbronn oil field). The Soultz area is devoted to Hot Dry Rock geothermics thanks to a high geothermal gradient (up to 100 °C/km). During drilling operations, an artesian source produced oil in a fractured zone of the sedimentary cover (Buntsandstein). Its gas-chromatography and mass-spectrometry (GC-MS) analysis revealed the presence of normal alkanes (n-alkanes, i.e. linear hydrocarbons) centered on C17, branched alkanes with a major C19 peak, and few unsaturated hydrocarbons. The aromatic fraction is present in small amounts. In the Soultz granite, where it is altered, organic matter is exclusively associated with tosudite (interstratified clay mineral) which crystallized in plagioclase sites during a hydrothermal alteration episode. Organic matter has been later displaced and concentrated along veinlets in which illite and carbonates have crystallized during another hydrothermal alteration stage. The soluble organic matter analyzed by GC-MS is composed of aliphatic acids, n-alkanes with a bimodal C18 and C24-C25 centered distribution, alkylbenzenes and aromatic acids. Organic compounds in the granite would either originate from a single source (immature sediments) or from two sources (immature sediments and migration of the Pechelbronn oil). No real evidence was found to prove which hypothesis is the best one. The presence of organic matter in the granite shows the importance of fluid flows between the sedimentary cover and the granitic basement through major fractures. In addition, the impregnation of plagioclase pseudomorphs with organic matter is made possible due to their high interconnection degree and to the intergranular microfracturation of the granite. The succession of several hydrothermal events with different physico-chemical characteris- tics may also be inferred from the occurrence of organic matter found in association with neoformed clay minerals in the granite. 相似文献
53.
Prof. Dr. Luigi Castoldi 《Pure and Applied Geophysics》1950,18(1):160-161
Riassunto Si fa uso di una formula di derivazione di un integrale di superficie per dimostrare un teorema meteorologico diV. Bjerknes.
Summary Use is made of a differentiation's formula for surface integrals in showing aV. Bjerknes' meteorological theorem.相似文献
54.
Prof. Dr. Dr. h. c. H. Rosenthal 《Ocean Dynamics》1991,44(5-6):281-282
55.
56.
Input-output models 总被引:2,自引:0,他引:2
Summary Elementary mass balance and export models are explored in relation to eutrophication as caused by phosphorus and nitrogen.
New criteria for phosphorus loading are given in relation to the ratio ‘mean depth-water fill-in-time’
. The results suggest that lakes having long water renewal times are much more sensitive to phosphorus loading than would
appear from mean depth only.
Further, from comparison of the relative residence time of nitrogen and phosphorus, it is deduced that—with increasing eutrophication—the
nitrogen metabolism is speeded up beyond the point of simple proportionality which would explain the transition from phosphorus
to nitrogen limitation in highly eutrophied lakes.
It is further suggested that the principles derived from eutrophication in regard to the metabolism of phosphorus and nitrogen
in lakes are applicable also to other environmental compartments and stress factors.
Paper given at the Conference on Chemical-Ecological Considerations for Defining the Goals of Water Pollution Control, Kastanienbaum, Switzerland, April 19–21, 1972. 相似文献
Zusammenfassung Elementare Massenbilanzen und Exportmodelle werden bezüglich ihrer Bedeutung für die Eutrophierung von Seen mit Phosphor und Stickstoff untersucht. Als neues Kriterium für die Phosphorbelastung wird das Verh?ltnis ?mittlere Wassertiefe-Zeit der Wassererneuerung? eingeführt. Die Beobachtungen lassen vermuten, dass Seen mit langen Wassererneuerungsperioden viel empfindlicher auf die Phosphorbelastung ansprechen, als aus ihrer mittleren Tiefe geschlossen werden k?nnte. Aus dem Vergleich der mittleren Aufenthaltszeiten von Stickstoff und Phosphor ergibt sich, dass mit zunehmender Eutrophie der Stickstoffumsatz weit st?rker beschleunigt wird, als der einfachen Proportionalit?t zu seiner Konzentrationszunahme entsprechen würde. Dies erkl?rt die Verschiebung von Phosphor zu Stickstoff als limitierendem Faktor in hocheutrophierten Seen. Es wird vermutet, dass die Prinzipien, welche bezüglich der Eutrophierung aus dem Umsatz von Phosphor und Stickstoff in Seen abgeleitet werden, auch für andere Lebensr?ume und andere Belastungsfaktoren angewendet werden k?nnen.
Résumé Un équilibre massive élémentaire et des modèles de sortie ont été explorés en relation avec l’eutrophisation provoquée par le phosphore et l’azote. De nouveaux critères ont été décrits en relation avec le taux ?profondeur moyenne?—durée de remplissage d’eau? . Les résultats suggèrent que les lacs dont la durée de renouvellement de l’eau est longue, sont beaucoup plus sensibles aux charges de phosphore, que ne laisserait appara?tre le critère seul de la profondeur moyenne. De plus, en comparant les durées relatives de séjour de l’azote et du phosphore, on déduit que—avec la progression de l’eutrophisation—le métabolisme de l’azote est accéléré au delà du point de simple proportionalité qui expliquerait la transition du phosphore à l’azote en tant que nutriment limitant dans des lacs fortement eutrophes. En outre, il est suggéré que les principes, dérivant de l’eutrophisation des lacs en relation avec le métabolisme du phosphore et de l’azote, sont également applicables à d’autres compartiments et facteurs de containte de l’environnement.
Paper given at the Conference on Chemical-Ecological Considerations for Defining the Goals of Water Pollution Control, Kastanienbaum, Switzerland, April 19–21, 1972. 相似文献
57.
Jim Wild recounts the rationale and success of AuroraWatch, a service that alerts you when you might be able to see aurorae. 相似文献
58.
Reinterpretation of the RRISP-77 Iceland shear-wave profiles 总被引:1,自引:0,他引:1
59.
60.