全文获取类型
收费全文 | 2471篇 |
免费 | 128篇 |
国内免费 | 22篇 |
专业分类
测绘学 | 102篇 |
大气科学 | 165篇 |
地球物理 | 856篇 |
地质学 | 868篇 |
海洋学 | 165篇 |
天文学 | 292篇 |
综合类 | 14篇 |
自然地理 | 159篇 |
出版年
2022年 | 20篇 |
2021年 | 29篇 |
2020年 | 56篇 |
2019年 | 44篇 |
2018年 | 81篇 |
2017年 | 78篇 |
2016年 | 117篇 |
2015年 | 102篇 |
2014年 | 102篇 |
2013年 | 139篇 |
2012年 | 118篇 |
2011年 | 138篇 |
2010年 | 123篇 |
2009年 | 151篇 |
2008年 | 126篇 |
2007年 | 98篇 |
2006年 | 87篇 |
2005年 | 66篇 |
2004年 | 54篇 |
2003年 | 64篇 |
2002年 | 50篇 |
2001年 | 55篇 |
2000年 | 44篇 |
1999年 | 44篇 |
1998年 | 37篇 |
1997年 | 31篇 |
1996年 | 30篇 |
1995年 | 21篇 |
1994年 | 21篇 |
1993年 | 14篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 14篇 |
1986年 | 26篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 29篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 19篇 |
1978年 | 17篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 18篇 |
1973年 | 16篇 |
1972年 | 10篇 |
排序方式: 共有2621条查询结果,搜索用时 15 毫秒
991.
Early geophysical maps dealing with seismology, geomagnetism, geothermics, and volcanology published by A. Petermann in his journal Geographische Mittheilungen between 1855 and 1878 are shown. Six maps of the highest cartographic standard are reproduced and commented. In Appendix an overview of geological maps edited by A. Petermann is added. 相似文献
992.
Arctic Ocean manganese contents and sediment colour cycles 总被引:5,自引:0,他引:5
Cyclical variations in colour and manganese content in sediments from the central Arctic Ocean have been interpreted to represent climatically controlled changes in the input of Mn from the Siberian hinterland, and/or variations in the intermediate and deep water ventilation of the Arctic basins, although a diagenetic origin has not been excluded. A reinvestigation of core 96/12-1pc using an Itrax X-ray fluoresence (XRF) core scanner confirms that these colour cycles are indeed controlled by variations in Mn content, although changes in the source region of the sediment may override the Mn colour signal in certain intervals. The prominent Mn cycles show no correspondence to any of the other measured elements. This decoupling of Mn and the bulk chemistry of the sediment is taken to indicate that the cycles observed are caused by variations in water column ventilation and riverine input, rather than variations in sediment source or diagenesis. We therefore conclude that the Mn maxima do represent warm phases with increased ventilation and/or riverine input, and that they therefore could be used for chronostratigraphic correlation between cores from the central Arctic Ocean, where traditional isotope stratigraphy is difficult or impossible to establish because of the lack of calcareous microfossils. 相似文献
993.
Novaya Zemlya was covered by the eastern part of the Barents–Kara ice sheet during the glacial maximum of marine isotope stage 2 (MIS 2). We obtained 14 C ages on 37 samples of mollusc shells from various sites on the islands. Most samples yielded ages in the range of 48–26 14 C Ky. Such old samples are sensitive to contamination by young 14 C, and therefore their reliability was assessed using replicate analyses and amino acid geochronology. The extent of aspartic acid racemization (Asp D/L) indicates that many of the 14 C ages are correct, whereas some are minimum ages only. The results indicate that a substantial part of Novaya Zemlya was ice-free about 35–27 14 C Kya, and probably even earlier. Corresponding shorelines up to >140 m a.s.l. indicate a large Barents–Kara ice sheet during early MIS 3. These results are consistent with findings from Svalbard and northern Russia: in both places a large MIS 4/3 Barents–Kara ice sheet is postulated to have retreated about 50 Kya, followed by an ice-free interstadial that lasted until up to ca. 25 Kya. The duration of the MIS 2 glaciation in Novaya Zemlya was calculated by applying the D/L values to a kinetic equation for Asp racemization. This indicates that the islands were ice covered for less than 3000 years if the basal temperature was 0o C, and for less than 10 000 years if it was −5o C. 相似文献
994.
We develop an approach that allows us to invert for the mantle velocity structure within a finely parametrized region as a perturbation with respect to a low-resolution, global tomographic model. We implement this technique to investigate the upper-mantle structure beneath Eurasia and present a new model of shear wave velocity, parametrized laterally using spherical splines with ∼2.9° spacing in Eurasia and ∼11.5° spacing elsewhere. The model is obtained from a combined data set of surface wave phase velocities, long-period waveforms and body-wave traveltimes. We identify many features as narrow as few hundred kilometres in diameter, such as subducting slabs in eastern Eurasia and slow-velocity anomalies beneath tectonically active regions. In contrast to regional studies in which these features have been identified, our model encompasses the structure of the entire Eurasian continent. Furthermore, including mantle- and body-wave waveforms helped us constrain structures at depths larger than 250 km, which are poorly resolved in earlier models. We find that up to +9 per cent faster-than-average anomalies within the uppermost ∼200 km of the mantle beneath cratons and some orogenic regions are separated by a sharp gradient zone from deeper, +1 to +2 per cent anomalies. We speculate that this gradient zone may represent a boundary separating the lithosphere from the continental root, which might be compositionally distinct from the overlying lithosphere and remain stable either due to its compositional buoyancy or due to higher viscosity compared with the suboceanic mantle. Our regional model of anisotropy is not significantly different from the global one. 相似文献
995.
Jan Anderssohn Hans-Ulrich Wetzel Thomas R. Walter Mahdi Motagh Yahya Djamour Hermann Kaufmann 《Geophysical Journal International》2008,174(1):287-294
Fluid storage systems, such as oil, gas, magma or water reservoirs, are often controlled by the host rock structure and faulted terrain. In sedimentary basins, where no direct information about underlying structure is available, the pattern of ground deformation may allow us to assess the buried fault arrangement. We provide an example in the semi-arid area of Iran, in the Kashmar Valley, a region subject to land subsidence due to water overexploitation. Geodetically determined subsidence rates in the Kashmar Valley exceed 15–30 cm yr−1 . The pattern of surface deformation is strongly non-uniform and displays NE–SW elongated bowls of subsidence. The trend resembles old Cretaceous-to-Tertiary faults that evolved during early alpine tectonic deformation. Although these early alpine structures are considered tectonically inactive in the present day, the observed land subsidence pattern indicates significant structural control on the geometry of the aquifer basin and its deformation during reservoir drainage. 相似文献
996.
Commonly, the most costly part of geomorphological distribution modelling studies is gathering the data. Thus, guidance for researchers concerning the quantity of field data needed would be extremely practical. This paper scrutinises the relationship between the sample size (the number of observations varied from 20 to 600) and the predictive ability of the generalized linear model (GLM), generalized additive model (GAM), generalized boosting method (GBM) and artificial neural network (ANN) in two data settings, i.e., independent and split-sample approaches. The study was performed using empirical data of periglacial processes from an area of 600 km2 in northernmost Finland at grid resolutions of 1 ha (100 × 100 m) and 25 ha (500 × 500 m). A rather sharp increase in the predictive ability of the models was observed when the number of observations increased from 20 to 100, and the level of robust predictions was reached with 200 observations. The result indicates that no more than a few hundred observations are needed in geomorphological distribution modelling at a medium scale resolution (ca. 0.01–1 km2). 相似文献
997.
A. Pepliski P. Artymowicz G. Mellema 《Monthly notices of the Royal Astronomical Society》2008,387(3):1063-1079
We present a numerical study of rapid, so-called type III migration for Jupiter-sized planets embedded in a protoplanetary disc. We limit ourselves to the case of outward migration, and study in detail its evolution and physics, concentrating on the structure of the corotation and circumplanetary regions, and processes for stopping migration. We also consider the dependence of the migration behaviour on several key parameters. We perform this study using global, two-dimensional hydrodynamical simulations with adaptive mesh refinement. We find that the outward-directed type III migration can be started if the initial conditions support the initial average non-dimensional migration rate bigger than one. Unlike the inward-directed migration, in the outward migration the migration rate increases due to the growing of the volume of the co-orbital region. We find the migration to be strongly dependent on the rate of the mass accumulation in the circumplanetary disc, leading to two possible regimes of migration, fast and slow. The structure of the co-orbital region and the stopping mechanism differs between these two regimes. 相似文献
998.
Jan Svoren Pavel Spurny Vladimir Porubcan Zuzana Kanuchova 《Earth, Moon, and Planets》2008,102(1-4):253-256
The European Fireball Network (EN) is operating since 1963 and one of its stable stations, from the very beginning, is the
station at the Skalnate Pleso Observatory in the High Tatras. The station is sited at a height of 1788 m. More than 2900 expositions
has been made at the Skalnate Pleso station since 1964 and among them one significant and spectacular event was recorded––bolide
Turji-Remety in 2001 followed by a fall of about 450 kg meteorite (Spurny and Porubcan [in: Warmbein (ed.) Asteroids Comets
Meteors, 2002]). A systematic search for the meteorite was unsuccessful. The new station having an ideal horizon will be operating
since July 2007 on the top of Lomnicky Stit (2636 m above the sea level). This station will be equipped with an Autonomous
Fireball Observatory of the Astronomical Institute of the Czech Academy of Sciences, which are already utilized in the Czech
part of the EN for several years. 相似文献
999.
Sedimentary regimes in Arctic's Amerasian and Eurasian Basins: Clues to differences in sedimentation rates 总被引:2,自引:0,他引:2
A standard lithostratigraphic model based on cores retrieved 1963–1973 from the ice island T-3 was developed by Clark et al. [Stratigraphy and glacial-marine sediments of the Amerasian Basin, central Arctic Ocean. Geological Society of America Special Paper, 181, 1–57, 1980] for the Amerasian Basin of the Arctic Ocean. We have investigated whether or not it is possible to apply this lithostratigraphy to cores from the Lomonosov Ridge, which can be correlated to Eurasian Basin cores, for the purpose of correlating the Amerasian and Eurasian stratigraphies. Published averaged sedimentary proxies from a selected set of T-3 cores are used to correlate with the identical published proxies for the included Lomonosov Ridge cores. The standard lithostratigraphic classification could not be applied to the Lomonosov Ridge cores, which is interpreted to result from differences in sedimentary regimes in the Amerasian and Eurasian Basins. These differences also apply to the barrier between the two basins, the Lomonosov Ridge. The general sedimentation rates are three to four times lower in the Amerasian Basin than in the Eurasian Basin if the first down-core paleomagnetic inclination change is used to correlate between the two basins whereas correlation based on sediment coarse fraction suggests only two times lower rates in the Amerasian Basin. 相似文献
1000.