全文获取类型
收费全文 | 29555篇 |
免费 | 493篇 |
国内免费 | 225篇 |
专业分类
测绘学 | 735篇 |
大气科学 | 2264篇 |
地球物理 | 5751篇 |
地质学 | 10861篇 |
海洋学 | 2555篇 |
天文学 | 6287篇 |
综合类 | 65篇 |
自然地理 | 1755篇 |
出版年
2021年 | 271篇 |
2020年 | 298篇 |
2019年 | 302篇 |
2018年 | 727篇 |
2017年 | 726篇 |
2016年 | 841篇 |
2015年 | 467篇 |
2014年 | 802篇 |
2013年 | 1561篇 |
2012年 | 925篇 |
2011年 | 1222篇 |
2010年 | 1053篇 |
2009年 | 1363篇 |
2008年 | 1185篇 |
2007年 | 1172篇 |
2006年 | 1160篇 |
2005年 | 841篇 |
2004年 | 840篇 |
2003年 | 766篇 |
2002年 | 768篇 |
2001年 | 712篇 |
2000年 | 702篇 |
1999年 | 551篇 |
1998年 | 518篇 |
1997年 | 598篇 |
1996年 | 468篇 |
1995年 | 473篇 |
1994年 | 471篇 |
1993年 | 380篇 |
1992年 | 387篇 |
1991年 | 358篇 |
1990年 | 373篇 |
1989年 | 342篇 |
1988年 | 344篇 |
1987年 | 368篇 |
1986年 | 325篇 |
1985年 | 423篇 |
1984年 | 414篇 |
1983年 | 445篇 |
1982年 | 415篇 |
1981年 | 365篇 |
1980年 | 403篇 |
1979年 | 324篇 |
1978年 | 302篇 |
1977年 | 294篇 |
1976年 | 266篇 |
1975年 | 264篇 |
1974年 | 269篇 |
1973年 | 254篇 |
1971年 | 173篇 |
排序方式: 共有10000条查询结果,搜索用时 47 毫秒
271.
Implementation of reconstructed geomorphologic units in landslide susceptibility mapping: the Melen Gorge (NW Turkey) 总被引:6,自引:2,他引:4
In the international literature, although considerable amount of publications on the landslide susceptibility mapping exist,
geomorphology as a conditioning factor is still used in limited number of studies. Considering this factor, the purpose of
this article paper is to implement the geomorphologic parameters derived by reconstructed topography in landslide susceptibility
mapping. According to the method employed in this study, terrain is generalized by the contours passed through the convex
slopes of the valleys that were formed by fluvial erosion. Therefore, slope conditions before landsliding can be obtained.
The reconstructed morphometric and geomorphologic units are taken into account as a conditioning parameter when assessing
landslide susceptibility. Two different data, one of which is obtained from the reconstructed DEM, have been employed to produce
two landslide susceptibility maps. The binary logistic regression is used to develop landslide susceptibility maps for the
Melen Gorge in the Northwestern part of Turkey. Due to the high correct classification percentages and spatial effectiveness
of the maps, the landslide susceptibility map comprised the reconstructed morphometric parameters exhibits a better performance
than the other. Five different datasets are selected randomly to apply proper sampling strategy for training. As a consequence
of the analyses, the most proper outcomes are obtained from the dataset of the reconstructed topographical parameters and
geomorphologic units, and lithological variables that are implemented together. Correct classification percentage and root
mean square error (RMSE) values of the validation dataset are calculated as 86.28% and 0.35, respectively. Prediction capacity
of the different datasets reveal that the landslide susceptibility map obtained from the reconstructed parameters has a higher
prediction capacity than the other. Moreover, the landslide susceptibility map obtained from the reconstructed parameters
produces logical results. 相似文献
272.
B. Bühn 《Mineralogy and Petrology》2008,92(3-4):453-470
Summary Two bimodal carbonatite complexes in Namibia of Cretaceous age are explored as to the presence and composition of a coexisting
carbonatitic fluid. The Kalkfeld and Ondurakorume complexes contain both Ca- and Mg/Fe-carbonatites, composed of calcite alone
or calcite with ferroan dolomite, fluorapatite and strontianite. The major element evolution in the bulk rocks from s?vites
to beforsites is due to crystallization of calcite and fluorapatite. All carbonatites show a negative Y anomaly in normalised
REE plots. Fractionation is accompanied by successively lower HREE contents between Tb and Yb, expressed by the ratios Nd/Ho
and Ho/Lu. The evolution of this downward-facing hump goes along with decreasing Y contents in bulk rocks and minerals. All
this requires an additional phase coexisting with the carbonate liquid during fractionation. Comparison between the bulk rocks
and the expelled fluid shows that the latter had preferentially accumulated the HREE and Y. Further evidence for this process
are hydrothermal, HREE, Y-rich fluorites in other carbonatite complexes which reflect the composition of the expelled fluid.
The high strength of fluoride complexes suggests that fluoride complexing in the carbonatitic fluid is the process responsible
for extracting HREE and Y from the carbonatite magma, leaving fractionated carbonatite rocks depleted in these elements. The
geochemical evolution of carbonatite magmas along fractionation has therefore to be considered in a melt-mineral-fluid system.
Correspondence: B. Bühn, Instituto de Geociências, Universidade de Brasilia, Campus Universitário Darcy Ribeiro, Brasilia
70910-900, Brazil 相似文献
273.
The Messinian Sicilian stratigraphy revisited: new insights for the Messinian salinity crisis 总被引:1,自引:0,他引:1
Controversies around the Messinian salinity crisis (MSC) are because of the difficulties in establishing genetic and stratigraphic relationships between its deep and shallow‐water record. Actually, the Sicilian foreland basin shows both shallow and deep‐water Messinian records, thus offering the chance to reconstruct comprehensive MSC scenarios. The Lower Gypsum of Sicily comprises primary and resedimented evaporites separated in space and time by the intra‐Messinian unconformity. A composite unit including halite, resedimented gypsum and Calcare di Base accumulated between 5.6 and 5.55 Ma in the main depocentres; it records the acme of the Messinian Salinity Crisis during a tectonic phase coupled with sea‐level falls at glacials TG14‐TG12. These deposits fully post‐date primary gypsum, which precipitated in shallow‐water wedge‐top and foreland ramp basins between 5.96 and 5.6 Ma. This new stratigraphic framework results in a three‐stage MSC scenario characterized by different primary evaporite associations: selenite in the first and third stages, carbonate, halite and potash salt in the second one associated with hybrid resedimented evaporites. 相似文献
274.
G. R. Cooper G. Petrie A. D. N. Smith M. Sowton K. B. Atkinson 《The Photogrammetric Record》1969,6(33):239-258
The International Society for Photogrammetry held the Xlth International Congress at Lausanne during July 1968. The authors review the activities of five of the seven I.S.P. Commissions. 相似文献
275.
B. Haurwitz 《Meteorology and Atmospheric Physics》1962,12(4):426-434
Zusammenfassung Auf Grund von Beobachtungsdaten und theoretischen Erwägungen wird eine Darstellung der Hauptglieder der täglichen Temperaturschwankung und ihrer Verteilung über die Erde in Form von Reihen von trigonometrischen undLegendre-Funktionen gegeben. Ein Vergleich mit einer rein theoretisch erhaltenen Darstellung vonKertz zeigt in großen Zügen eine befriedigende Übereinstimmung beider Ergebnisse.
Die vorliegende Untersuchung wurde während eines Aufenthaltes am Meteorologischen Institut der Universität München ausgeführt. 相似文献
Summary A representation is given of the main terms of the daily temperature variation and their global distribution as a series of trigonometric andLegendre functions, based partly on observational data, partly on theoretical considerations. A comparison with a representation obtained byKertz on a purely theoretical basis shows in general a satisfactory agreement.
Résumé Partant de données d'observations et de considérations théoriques, l'auteur a établi, au moyen de séries de fonctions trigonométriques et deLegendre, une représentation des éléments principaux de la variation diurne de la température ainsi que de sa répartition sur le globe. La comparaison du résultat à une représentation semblable faite parKertz sur une base purement théorique indique une similitude satisfaisante.
Die vorliegende Untersuchung wurde während eines Aufenthaltes am Meteorologischen Institut der Universität München ausgeführt. 相似文献
276.
277.
A. B. Roy M. Sc. 《Pure and Applied Geophysics》1963,56(1):53-57
Summary The paper deals with the disturbances in an infinite slab of finite thickness, the medium being homogeneous, isotropic and perfectly elastic. 相似文献
278.
Dr. C. B. Raleigh 《Contributions to Mineralogy and Petrology》1965,11(7):719-741
A study of the structural petrology of a peridotite exposed on Cypress Island in Skagit Co., Washington, U.S.A. has been carried out. The Cypress peridotite is, by virtue of its composition, structure and associations, typical of ultramafics of the alpine type. It contains relict layering and accumulative textures which show it to have originated by crystal settling from a magma of unknown initial composition. Parallelism of lineations and b-axes of folds in the layering with well-developed [100]-maxima in the fabrics of olivine crystals is considered to have arisen through a penetrative deformation of the mass accompanied by plastic flow or recrystallization of the olivine. An indication of the minimum temperature of the deformation is provided by cross-cutting veins of pyroxenite which have not participated in the folding. The most satisfactory interpretation of the overall fabric of the peridotite is that it was deformed, possibly during intrusion, as a crystal mush, and that filter pressing due to compaction of the solid particles by plastic flow or recrystallization removed all but a small percentage of the magmatic fraction which then crystallized following cessation of the movements. 相似文献
279.
Summary The present note, as its title implies, is concerned with the investigation of disturbances in an infinite elastic medium containing an initial magnetic field in the axial direction. The equations ofMaxwell, those of elasticity have been effectively made use of to solve the problem. 相似文献
280.
Gully erosion has for many years been a problem in Rhodesia1s Tribal Trust Lands. This paper describes how Soil Conservation Service staff, with no previous ground knowledge of these areas, used good quality 1/25,000 scale aerial photographs to measure the extent of the gully erosion and to pinpoint erosion “black spots.” This enabled quick and reliable estimates of the cost of reclamation work to be made without the need for time-consuming field survey. The survey method discussed is capable of wide application wherever gully erosion occurs and needs to be brought under control. 相似文献