全文获取类型
收费全文 | 1952篇 |
免费 | 60篇 |
国内免费 | 24篇 |
专业分类
测绘学 | 59篇 |
大气科学 | 161篇 |
地球物理 | 476篇 |
地质学 | 715篇 |
海洋学 | 167篇 |
天文学 | 310篇 |
综合类 | 12篇 |
自然地理 | 136篇 |
出版年
2021年 | 26篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 54篇 |
2017年 | 35篇 |
2016年 | 56篇 |
2015年 | 31篇 |
2014年 | 50篇 |
2013年 | 99篇 |
2012年 | 57篇 |
2011年 | 107篇 |
2010年 | 76篇 |
2009年 | 86篇 |
2008年 | 87篇 |
2007年 | 70篇 |
2006年 | 58篇 |
2005年 | 63篇 |
2004年 | 45篇 |
2003年 | 40篇 |
2002年 | 57篇 |
2001年 | 37篇 |
2000年 | 52篇 |
1999年 | 54篇 |
1998年 | 33篇 |
1997年 | 48篇 |
1996年 | 43篇 |
1995年 | 34篇 |
1994年 | 30篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 34篇 |
1986年 | 18篇 |
1985年 | 24篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 35篇 |
1981年 | 21篇 |
1980年 | 29篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1976年 | 21篇 |
1975年 | 25篇 |
1974年 | 18篇 |
1973年 | 18篇 |
1971年 | 12篇 |
排序方式: 共有2036条查询结果,搜索用时 10 毫秒
151.
152.
The Mesoarchean emergence of modern-style subduction 总被引:6,自引:4,他引:6
Well-preserved volcanic sequences span the Paleoarchean to Neoarchean evolution of the Pilbara Craton, in northwestern Australia. This region provides the best physical evidence bearing on the stage of Earth's history when modern-style tectonic processes began. Paleoarchean assemblages in the eastern nucleus of the craton (the 3.51–3.24 Ga Pilbara Supergroup) show few features that can reasonably be interpreted as evidence for modern-style subduction processes. Incompatible trace element-enriched felsic volcanic horizons show geochemical evidence for the interaction between mafic magmas and crust, but this evidence, on its own, can equally well be interpreted in terms of either a subduction-enriched mantle source or local and limited assimilation of felsic crust into the voluminous tholeiitic magmas that dominate the Pilbara Supergroup. Viewed in context within the thick autochthonous and consistently upward-younging Pilbara Supergroup, these felsic units are most likely related to the same plume-dominated processes that formed the basalts that dominate the supergroup. It is very unlikely that modern-style plate tectonic processes played any role in the Paleoarchean evolution of the Pilbara Craton, although some form of non-uniformitarian (e.g. flat) subduction process may have operated.In stark contrast, the Mesoarchean units of the West Pilbara Terrane and the late-tectonic basins that cover that boundary between the West and East Pilbara Terranes, show clear evidence for modern-style convergent margin processes. Igneous rocks in this belt, which flanks the old eastern cratonic nuclei, have enriched geochemical signatures that cannot be accounted for by crustal contamination. This region is also characterised by a linear magmatic and structural fabric, by the presence of lithologically and geochronologically exotic belts, and by the presence of a broad belt of isotopically more juvenile crust. The collective strength of these arguments provides compelling evidence that a modern-style oceanic arc fringed the East Pilbara Terrane at 3.12 Ga and accreted to that terrane by 2.97 Ga. These assemblages mark the minimum age for the birth of modern-style plate subduction process. 相似文献
153.
Liner design for waste disposal sites 总被引:5,自引:0,他引:5
Since the beginning of the 1980s waste disposal has become a particularly sensitive issue. This has led to the development
of new legislations in the European Community and internationally which resulted in an array of regulations concerning landfill
liner design. This paper comments on different "engineered" containment methods with particular reference to landfill liner
design. Suggestions based on the review of the different methodologies are given and a case study is presented.
Received: 25 February 1997 · Accepted: 16 December 1997 相似文献
154.
J. D. Van Wees A. Arche C. G. Beijdorff J. Lpez-Gmez S. A. P. L. Cloetingh 《Tectonophysics》1998,300(1-4):285-310
By subsidence analysis on eighteen surface sections and 6 wells, which cover large part of the Iberian Basin (E Spain) and which are marked by high-resolution stratigraphy of the Permian, Triassic, Jurassic and Cretaceous, we quantify the complex Permian and Mesozoic tectonic subsidence history of the basin. Backstripping analysis of the available high resolution and high surface density of the database allows to quantify spatial and temporal patterns of tectonically driven subsidence to a much higher degree than previous studies. The sections and wells have also been forward modelled with a new ‘automated' modelling technique, with unlimited number of stretching phases, in order to quantify variations in timing and magnitude of rifting. It is demonstrated that the tectonic subsidence history in the Iberian Basin is characterized by pulsating periods of stretching intermitted by periods of relative tectonic quiescence and thermal subsidence. The number of stretching phases appears to be much larger than found by earlier studies, showing a close match with stretching phases found in other parts of the Iberian Peninsula and allowing a clear correlation with discrete phases in the opening of the Tethys and Atlantic. 相似文献
155.
The Woodlands Formation (uppermost Pretoria Group) of eastern Botswana overlies thick quartzites of the Sengoma Formation (Magaliesberg Formation) and comprises a lower unit of interbedded mudrocks and fine-grained recrystallised quartzitic sandstones, succeeded by chaotic and very coarse-grained inferred slump deposits. Within the adjacent western region of South Africa, interbedded mudrocks and quartzitic sandstones stratigraphically overlying the Magaliesberg Formation are now assigned to the lower Woodlands Formation. Within the entire region, interference folding produced by northeast-southwest (F1 and F3) and northwest-southeast (F2) compression, and concomitant faulting characterised inversion of the Pretoria Group basin. This deformation is of pre-Bushveld age and affected all units in the Pretoria Group, including the uppermost Silverton, Magaliesberg and Woodlands Formations, and intrusive Marico Hypabyssal Suite (pre-Bushveld) mafic sills. The Nietverdiend lobe of the Bushveld Complex, intrusive into this succession, was not similarly deformed. Movement along the major Mannyelanong Fault in the northwest of the study area post-dated Transvaal Basin inversion, after which the “upper Woodlands” chaotic slump deposits were formed. The latter must thus belong to a younger stratigraphical unit and is possibly analogous to apparently syntectonic sedimentary rocks (Otse Group) in the Otse Basin of eastern Botswana. 相似文献
156.
A series of Hokkaido events, recorded by the FBV Broadband Seismograph System at the KHC Seismic Station, is used to study the structure of the earthquake magnitude scale on the basis of maximum velocity amplitudesA
vmax of teleseismicPwaves in different period bands. Amplitude-periodband (APB) diagrams are constructed for each event. According to the shape of the APB diagrams the events investigated can be divided into three types: (a) events with largestA
vmax values in the intermediate period range (periods ofA
vmax from 2.2 to 23 sec), (b) events with largestA
vmax values in the short-period range (periods ofA
vmax from 1 to 2 sec), (c) events exhibiting anomalous APB diagrams. Type (a) events seem to represent the process of wave generation that prevails for shallow earthquakes. Type (b) events approach to explosive-like generation of seismic waves. The nature of the exceptionally occurring type (c) events must be clarified in further investigations. The influence of the type of earthquake on the magnitude values estimated on the basis of standard class A and B (short-period and intermediate-band) seismograms is demonstrated. It appears that for estimating correct values of earthquake magnitudes complementary information on the process of seismic wave generation in the focus is necessary. At teleseismic distances this information can be obtained from either APB diagrams or amplitude spectra ofP waves recorded, e.g., by broadband velocity sensing instruments. 相似文献
157.
Summary The morphology of the Wadati-Benioff zone in the Kermadec region, based on the distribution of 1100 earthquake foci, verified the existence of an intermediate aseismic gap and its relation to active andesitic volcanism, and the non-uniformity of subduction due to the hampering effect of the main structural features of the subducting Pacific plate. Two cycles of the recently active subduction in the Tonga-Kermadec island arc were found. 相似文献
158.
Petr Vaníček 《Physics of the Earth and Planetary Interiors》1978,17(3):265-280
The aim of this investigation is to develop a simple technique that would allow us to use the sea-level records for detecting contemporary vertical crustal movements of duration from several months to several years. The choice of auxiliary data needed for any such analysis is restricted to the regularly available meteorological data to make this approach possible in routine search for precursory movements in earthquake-prone areas. A linear mathematical model is designed to evaluate the effect of atmospheric temperature and pressure variations, river discharge, long periodic tides and Chandlerian motion. Spectra of the residual sea-level variations are also shown. It is concluded that local episodic crustal movements of a magnitude larger than some 10 cm may be detectable by this approach. If finer resolution is needed then it it necessary to also account for steric level, wind, and sea-current variations, for which data are largely non-existent. 相似文献
159.
160.
Tjeerd H. Van Andel 《Earth and Planetary Science Letters》1975,26(2):187-194
From late Jurassic to early Cenozoic time the calcite compensation depth (CCD) in the world oceans was shallow (above 4000 m). About 40 m.y. ago it dropped to about 4500 m, sharply in the Indian and Pacific oceans and gradually in the Atlantic. In the early Miocene it began to rise again, reaching a very shallow peak 10–15 m.y. ago, then descended to its present deep position. In the Pacific, fluctuations during the last 40 m.y. appear to result mainly from changes in bottom-water structure related to the progressive glaciation of the Antarctic and Arctic regions. Analogous explanations hold for CCD fluctuations during this period in the Indian and Atlantic oceans. The very shallow CCD prior to about 50 m.y., on the other hand, cannot be explained in this manner but must be attributed either to a low input of calcium in the oceans from deeply weathered continents or, more probably, to large changes in the distribution of carbonate deposition between shallow and deep seas. 相似文献