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41.
Croft William Lee Shi Wei Sack Jörg-Rüdiger Corriveau Jean-Pierre 《Journal of Geographical Systems》2017,19(3):221-248
Journal of Geographical Systems - Given the large volumes of detailed data now being collected, there is a high demand for the release of this data for research purposes. In particular,... 相似文献
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43.
Ansgar Greshake Richard Wirth Jörg Fritz Tomasz Jakubowski Ute Böttger 《Meteoritics & planetary science》2018,53(3):467-481
Libyan Desert Glass (LDG) is a SiO2-rich natural glass whose origin, formation mechanism, and target material are highly debated. We here report on the finding of a lens-shaped whitish inclusion within LDG. The object is dominantly composed of siliceous glass and separated from the surrounding LDG by numerous cristobalite grains. Within cristobalite, several regions rich in mullite often associated with ilmenite were detected. Mineral assemblage, chemical composition, and grain morphologies suggest that mullite was formed by thermal decomposition of kaolinitic clay at atmospheric pressure and T ≥ 1600 °C and also attested to high cooling rates under nonequilibrium conditions. Cristobalite contains concentric and irregular internal cracks and is intensely twinned, indicating that first crystallized β-cristobalite inverted to α-cristobalite during cooling of the SiO2-rich melt. The accompanied volume reduction of 4% induced the high density of defects. The whitish inclusion also contains several partly molten rutile grains evidencing that at least locally the LDG melt was at T ≥ 1800 °C. Based on these observations, it is concluded that LDG was formed by high-temperature melting of kaolinitic clay-, rutile-, and ilmenite-bearing Cenozoic sandstone or sand very likely during an asteroid or comet impact onto Earth. While melting and ejection occurred at high pressures, the melt solidified quickly at atmospheric pressure. 相似文献
44.
L. E. Sjöberg 《Journal of Geodesy》2001,75(5-6):283-290
The topographic and atmospheric effects of gravimetric geoid determination by the modified Stokes formula, which combines
terrestrial gravity and a global geopotential model, are presented. Special emphasis is given to the zero- and first-degree
effects. The normal potential is defined in the traditional way, such that the disturbing potential in the exterior of the
masses contains no zero- and first-degree harmonics. In contrast, it is shown that, as a result of the topographic masses,
the gravimetric geoid includes such harmonics of the order of several centimetres. In addition, the atmosphere contributes
with a zero-degree harmonic of magnitude within 1 cm.
Received: 5 November 1999 / Accepted: 22 January 2001 相似文献
45.
J. Höpfner 《Journal of Geodesy》2001,75(2-3):137-150
The annual and semiannual residuals derived in the axial angular momentum budget of the solid Earth–atmosphere system reflect
significant signals. They must be caused by further excitation sources. Since, in particular, the contribution for the wind
term from the atmospheric layer between the 10 and 0.3 hPa levels to the seasonal variations in length of day (LOD) is still
missing, it is necessary to extend the top level into the upper stratosphere up to 0.3 hPa. Under the conservation of the
total angular momentum of the entire Earth, variations in the oceanic angular momentum (OAM) and the hydrological angular
momentum (HAM) are further significant excitation sources at seasonal time scales. Focusing on other contributions to the
Earth's axial angular momentum budget, the following data are used in this study: axial atmospheric angular momentum (AAM)
data derived for the 10–0.3 hPa layer from 1991 to 1997 for computing the missing wind effects; axial OAM functions as generated
by oceanic general circulation models (GCMs), namely for the ECHAM3 and the MICOM models, available from 1975 to 1994 and
from 1992 to 1994, respectively, for computing the oceanic contributions to LOD changes, and, concerning the HAM variations,
the seasonal estimates of the hydrological contribution as derived by Chao and O'Connor [(1988) Geophys J 94: 263–270]. Using
vector representation, it is shown that the vectors achieve a close balance in the global axial angular momentum budget within
the estimated uncertainties of the momentum quantities on seasonal time scales.
Received: 6 April 2000 / Accepted: 13 December 2000 相似文献
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47.
Significance of Europium anomalies in silicate melts and crystal-melt equilibria: a re-evaluation 总被引:1,自引:0,他引:1
Although europium speciation in silicate melts partly reflects prevailing oxygen fugacities, melt composition and structure play the major role in determining Eu2+/ Eu3+ ratios and europium partitioning into mineral phases. Experimental evidence by different investigators on the magnitude of the compositional effect on Eu2+/Eu3+ provides consistent results only if account is taken of the oxygen buffer system employed in the experiments. The medium-dependent reduction of europium can be understood in terms of the preferential stabilization of Eu2+ by a strong aluminosilicate complex in the melt phase, and to a much lesser degree by metasilicate complexes. The stability of these complexes increases as the field strength of the associated cation species decreases. Hence Eu2+-aluminosilicate complexes are preferentially stabilized relative to trivalent lanthanides in melts of appropriate composition and their presence minimizes the enthalpy of the melt. The influence of these complexes is particularly pronounced in melts with a high feldspathic component and a strongly polymerized structure. Their petrogenetic influence is best documented through the behaviour of europium relative to the other lanthanides during anhydrous anatexis in high-grade metamorphic terrains and in the anomalous europium partition coefficients of phenocryst phases which formed during the crystallization of highly silicic magmas. 相似文献
48.
This paper presents one of the richest and most complete vertebrate faunas of the late Middle Miocene (~12 Ma) of Central Europe. Up to now, sixty-two vertebrate taxa, comprising all major groups (fishes, amphibians, reptiles, birds, mammals), have been recorded. Based on sedimentological and palaeobiological evidences, this Fossillagerstätte is assumed to originate from a floodplain paleosol formed on top of a braided river sequence. The fauna points to a highly structured, somewhat vegetated landscape with a wide array of habitats (e.g., fluvial channels, sporadically moist floodplains, short-lived ponds, savannah-like open areas and screes). It was preserved due to a rapid drowning and the switch to a freshwater lake environment. Palaeoclimatological data, derived from pedogenic features as well as from biota, indicate an overall semi-arid, subtropical climate with distinct seasonality (mean annual precipitation 486 ± 252 mm, mean annual temperature ~15°C). This underlines the late Middle/early Late Miocene dry-spell in Central Europe. From taphonomical point of view, the irregularly distributed but roughly associated larger vertebrate remains refer to an in situ accumulation of the bone bed. Splintered bones, gnawing marks as well as rhizoconcretions and root corrosion structures record some pre- and post-burial modification of the taphocoenose. However, the findings of pellet remains argue for a very fast burial and thus to a low degree of time-averaging. For this reason, the fossil fauna reflects the original vertebrate community rather well and is a cornerstone for the understanding of late Middle Miocene terrestrial ecosystems in this region. Certainly, Gratkorn will be one of the key faunas for a high-resolution continental biostratigraphy and the comprehension of Europe’s faunal interchanges near the Middle/Late Miocene transition. 相似文献
49.
N. V. Chukanov R. K. Rastsvetaeva S. M. Aksenov I. V. Pekov D. I. Belakovskiy G. Blass G. Möhn 《Geology of Ore Deposits》2013,55(8):663-668
A new mineral, lahnsteinite, has been found in the dump of the Friedrichssegen Mine, Bad Ems district, Rhineland-Palatinate (Rheinland-Pfalz), Germany. Lahnsteinite, occurring as colorless tabular crystals in the cavities of goethite, is associated with pyromorphite, hydrozincite, quartz, and native copper. The Mohs’ hardness is 1.5; the cleavage is perfect parallel to (001). D calc = 2.995 g/cm3, D meas = 2.98(2) g/cm3. The IR spectrum is given. The new mineral is optically biaxial, negative, α = 1.568(2), β = 1.612(2), γ = 1.613(2), 2V meas = 18(3)°, 2V calc = 17°. The chemical composition (wt %, electron microprobe data; H2O was determined by gas chromatography of ignition products) is as follows: 3.87 FeO, 1.68 CuO, 57.85 ZnO, 15.83 SO3, 22.3 H2O, total is 101.53. The empirical formula is (Zn3.3Fe0.27Cu0.11)Σ3.91(S0.98O4)(OH)5 · 3H2.10O. The crystal structure has been studied on a single crystal. Lahnsteinite is triclinic, space group P1, a = 8.3125(6), b = 14.545(1), c = 18.504(2) Å, α = 89.71(1), β = 90.05(1), γ = 90.13(1)°, V = 2237.2(3) Å3, Z = 8. The strong reflections in the X-ray powder diffraction pattern [d, Å (I, %)] are: 9.30 (100), 4.175 (18), 3.476 (19), 3.290 (19), 2.723 (57), 2.624 (36), 2.503 (35), 1.574 (23). The mineral has been named after its type locality near the town of Lahnstein. The type specimen of lahnsteinite is deposited in the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, registration number 4252/1. 相似文献
50.
A. M. Celal Şengör 《International Journal of Earth Sciences》1982,71(2):381-420
Two main schools of thought in global tectonics are recognized during the first half of the XXth century on the basis of their proponents' attitude towards the principle of uniformitarianism and their belief in an inherent order and regularity vs. disorder and irregularity in tectonics. One group, here called the Wegener-Argand school, had a unifomitarian approach to global tectonics and believed in an inherently irregular Nature, in which probability rather than determinism was believed to be a realistic approach. The other, here called the Kober-Stille school, was largely non-uniformitarian (neocatastrophist) and believed in an orderly, regular Nature. These two schools correspond to Argand's mobilists and fixists respectively. In this paper I show that Eduard Suess was a convinced uniformitarian as far as his views on global tectonics are concerned and denied any inherent regularity in tectonic phenomena, temporal or spatial. In his interpretations of the causes and nature of orogeny, nature of geosynclines, and causes and nature of stabilisation, Suess appears to be the predecessor of the Wegener-Argandians, i. e. of the mobilists and not of the Kober-Stilleans as hitherto assumed. Although he remained a fixist and contractionist to the end Suess seems to have paved the way for the mobilists much as he did for the nappists during the last quarter of the XIXth century.
Zusammenfassung Während der ersten Hälfte des XX. Jahrhunderts kann man zwei globaltektonische Denkungsweisen oder Großschulen unterscheiden, die gekennzeichnet sind durch ihre Stellungnahme zum aktualistischen Prinzip in der Tektonik und ob sie an eine ordentliche und regelmäßige Natur glaubten oder nicht. Die erste, hier die Wegener-Argand-Schule genannt, hatte die Gültigkeit des aktualistischen Prinzips in der Tektonik anerkannt und die Natur, im Grunde genommen, als unordentlich und unregelmäßig betrachtet. Die Anhänger dieser Denkweise glaubten, daß probablistische Lösungen tektonischer Probleme realistischer seien als deterministische. Die andere Großschule, hier die Kober-Stille-Schule genannt, war im Grunde genommen anti-aktualistisch (Neo-Katastrophistisch) und glaubte, daß die Natur ordentlich und regelmäßig sei. Diese zwei Schulen entsprechen Argands' Einteilung in Mobilisten und Fixisten. In diesem Artikel zeige ich, daß E. Suess ein überzeugter Aktualist in bezug auf seine tektonischen Ansichten war, und daß er jede Regelmäßigkeit, zeitlicher oder räumlicher Art, der tektonischen Ereignisse ablehnte. In seinen Interpretationen der Ursachen und der Art der Orogenese, der Art der Geosynklinalen und der Ursache und der Art der Erstarrung, erscheint Suess als ein Vorgänger der Wegener-Argand-Schule, d. h. der Mobilisten, deren Gedankengänge er viel näher stand als dem der Kober-Stille-Schule. Obwohl Suess selbst bis zuletzt ein Fixist und Kontraktionist blieb, bereitete er eigentlich den Weg für die Mobilisten, wie er es früher auch für die Nappisten getan hatte.
Résumé Durant la première moitié du XXe siêcle, on peut distinguer deux principales écoles de pensée en tectonique globale, selon l'attitude de ses adhérents envers le principe de l'actualisme et selon leur croyance ou non à un ordre et une régularité intrinsèques en tectonique. Le premier groupe, ici appelé l'école de Wegener-Argand, suivit une voie actualiste et crût la Nature essentiellement irrégulière, de telle sorte qu'un traitement probabiliste fût considéré plus réaliste qu'un traitement déterministe. L'autre, appelé ici l'école de Kober-Stille, était essentiellement non-actualiste (néo-catastrophiste) et crût à une Nature ordonnée, régulière. Ces deux écoles correspondent aux mobilistes et aux fixistes d'Argand. Dans cet article, je montre que E. Suess, fût un actualiste convaincu, du moins en ce qui concerne ses opinions sur la tectonique globale, et qu'il rejetta toute notion de régularité dans les phénomènes tectoniques, autant spatiaux que temporaux. Dans ses interprétations des causes et de la nature de l'orogenèse, de la nature des géosynclinaux, et des causes et de la nature de la «stabilisation», Suess est un des précurseurs des «Wegener-Argandiens», c'est à dire des mobilistes. Bien qui'il fût demeuré, jusqu'à la fin de sa vie, fixiste et un avocat de la contraction, il semble que Suess ait préparé la voie aux mobilistes, de la mème façon qu'il l'avait fait pour les nappistes pendant le derier quart du XIXe siècle.
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