全文获取类型
收费全文 | 1827篇 |
免费 | 66篇 |
国内免费 | 33篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 136篇 |
地球物理 | 450篇 |
地质学 | 584篇 |
海洋学 | 194篇 |
天文学 | 365篇 |
综合类 | 4篇 |
自然地理 | 163篇 |
出版年
2021年 | 18篇 |
2020年 | 23篇 |
2019年 | 29篇 |
2018年 | 29篇 |
2017年 | 27篇 |
2016年 | 44篇 |
2015年 | 42篇 |
2014年 | 35篇 |
2013年 | 103篇 |
2012年 | 58篇 |
2011年 | 74篇 |
2010年 | 70篇 |
2009年 | 69篇 |
2008年 | 98篇 |
2007年 | 78篇 |
2006年 | 81篇 |
2005年 | 59篇 |
2004年 | 54篇 |
2003年 | 51篇 |
2002年 | 58篇 |
2001年 | 56篇 |
2000年 | 56篇 |
1999年 | 33篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 29篇 |
1995年 | 36篇 |
1994年 | 31篇 |
1993年 | 24篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 25篇 |
1989年 | 24篇 |
1988年 | 22篇 |
1987年 | 29篇 |
1986年 | 22篇 |
1985年 | 12篇 |
1984年 | 30篇 |
1983年 | 23篇 |
1982年 | 18篇 |
1981年 | 30篇 |
1980年 | 17篇 |
1979年 | 34篇 |
1978年 | 27篇 |
1977年 | 26篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1972年 | 10篇 |
排序方式: 共有1926条查询结果,搜索用时 31 毫秒
91.
92.
ABSTRACTProposals to change the names of entire urban centres are rare. We examine the case of Blenheim, New Zealand, where in 2016, representatives of local businesses campaigned for its renaming as Marlborough City, in recognition of the region’s wine industry. Although defeated the proposal threatened to over-write established settlement history. It presumed to rename Blenheim under the aegis of New Zealand Inc., a shorthand for the pervasive yet nebulous economic nationalism that seeks to yoke all local and national identity to enhancing export growth. Drawing on media reports, we interpret this example of toponymic commodification as a neoliberalized project of place-making. Ironically, Blenheim and Marlborough are colonial names that displaced a long-established Māori name. The proposal highlights both the perversities and the deeply contested claims-making that often underlie and animate toponymic politics. Ultimately, it illustrates some of the limits of rights claimed under neoliberalism. 相似文献
93.
94.
Christopher R. J. Charles Pierre-Yves F. Robin Donald W. Davis Phil J. A. McCausland 《Meteoritics & planetary science》2018,53(5):935-951
The approximately spherical shapes of chondrules has long been attributed to surface tension acting on ~1 mm melt droplets that formed and cooled in the microgravity field of the solar nebula. However, chondrule shapes commonly depart significantly from spherical. In this study, 109 chondrules in a sample of CR2 chondrite NWA 801 were imaged by X-ray computed tomography and best-fitted to ellipsoids. The analysis confirms that many chondrules are indeed not spherical, and also that the chondrules’ collective shape fabric records a definite 13% compaction in the host meteorite. Dehydration of phyllosilicates within chondrules may account for that strain. However, retro-deforming all chondrules shows that a large majority were already far from spherical prior to accretion. Possible models for these initial shapes include prior deformation of individual chondrules in earlier hosts, and, as suggested by previous authors, rotation of chondrules as they were solidifying, and/or “streaming” of molten chondrules by their differential velocities with their gaseous hosts after melting. More in situ 3-D work such as this study on a variety of unequilibrated chondrites, combined with detailed structural petrography, should help further constrain these models and refine our understanding of chondrite formation. 相似文献
95.
The lower part of the Old Red Sandstone in the Dingle Penisula has been previously assigned to one lithostratigraphic group (Dingle Group) despite marked variations in sedimentary facies. However the apparently oldest non-marine sequence in the northwest of the peninsula has sedimentary and lithological attributes that contrast strongly with those of the late Silurian-early Devonian Dingle Group to the south. This northern sequence, here renamed the Smerwick Group, evolved independently of the Dingle Group in a separate basin of deposition. Field relationships between the two groups in the north of the peninsula are interpreted as indicating that the Smerwick Group overlies, with angular unconformity, a normal Dingle Group succession. Similarly, it is argued that the Smerwick Group overlies, with angular unconformity, the Dingle Group in the northwest of the peninsula, but there the Dingle Group is attenuated, represented only by a conglomerate unit some 10 m thick. In the absence of biostratigraphic evidence the age of the Smerwick Group is poorly constrained. Nevertheless, we propose a tectonic model that suggests that the Smerwick Group evolved within a small extensional half-graben on the northern margin of the Munster Basin. This model accounts for the stratigraphic and structural relationships observed, and implies that the Smerwick Group is of Late Devonian age. 相似文献
96.
97.
I. S. Williams 《Australian Journal of Earth Sciences》2013,60(4):557-580
Progressive Early Silurian low‐pressure greenschist to granulite facies regional metamorphism of Ordovician flysch at Cooma, southeastern Australia, had different effects on detrital zircon and monazite and their U–Pb isotopic systems. Monazite began to dissolve at lower amphibolite facies, virtually disappearing by upper amphibolite facies, above which it began to regrow, becoming most coarsely grained in migmatite leucosome and the anatectic Cooma Granodiorite. Detrital monazite U–Pb ages survived through mid‐amphibolite facies, but not to higher grade. Monazite in the migmatite and granodiorite records only metamorphism and granite genesis at 432.8 ± 3.5 Ma. Detrital zircon was unaffected by metamorphism until the inception of partial melting, when platelets of new zircon precipitated in preferred orientations on the surface of the grains. These amalgamated to wholly enclose the grains in new growth, characterised by the development of {211} crystal faces, in the migmatite and granodiorite. New growth, although maximum in the leucosome, was best dated in the granodiorite at 435.2 ± 6.3 Ma. The combined best estimate for the age of metamorphism and granite genesis is 433.4 ± 3.1 Ma. Detrital zircon U–Pb ages were preserved unmodified throughout metamorphism and magma genesis and indicate derivation of the Cooma Granodiorite from Lower Palaeozoic source rocks with the same protolith as the Ordovician sediments, not Precambrian basement. Cooling of the metamorphic complex was relatively slow (average ~12°C/106y from ~730 to ~170°C), more consistent with the unroofing of a regional thermal high than cooling of an igneous intrusion. The ages of detrital zircon and monazite from the Ordovician flysch (dominantly composite populations 600–500 Ma and 1.2–0.9 Ga old) indicate its derivation from a source remote from the Australian craton. 相似文献
98.
Four sinkholes with varying surficial expressions were subjected to detailed stratigraphic and soil analysis by means of Standard
Penetration Tests (SPT) and Electric Friction Cone Penetration Tests (CPT) in order to evaluate applications of CPT to sinkhole
investigations. Although widely used, SPT data are of limited value and difficult to apply to sinkhole mapping. CPT is sensitive
to minor lithologic variability and is superior to SPT as a cost-effective technique for determining geotechnical properties
of sinkholes.
The effectiveness of CPT data results from the force measurements made along the sleeve of the cone. The friction ratio (ratio
of sleeve to tip resistance) is a good indicator of soil stratigraphy and properties. By smoothing the friction-ratio data,
general stratigraphy and changes in soil properties are easily identified.
Stratigraphy of the sinks has been complicated by intense weathering, karstification and marine, transgressions. The resulting
deposits include five stratigraphic units. I and II represent Plio-Pleistocene marine sediments with Unit II being the zone
of soil clay accumulation. III and IV are horizons residual from Miocene strata and indicate an episode of karstification
prior to deposition of Units I and II.
Conduit fill is a mixture of materials with low cohesion. The fill materials indicate centripetal and downward movement of
insoluble sediments derived from the surrounding strata. Loss of cohesion results in near-zero friction ratios. Very low friction
ratios, coupled with materials with little cohesion, indicate potentially-liquefiable soils in the immediate vicinity of zones
where piping failure may be imminent. SPT does not provide sufficient data to predict these zones of potential, failure.
CPT provides sufficient information for recognition of sinkhole stratigraphy and geotechnical properties. When coupled with
laboratory soil analysis, CPT provides unique information about sinkhole geometry and dynamics. In contrast, SPT data fail
to produce consistent indicators of sinkhole stratigraphy or properties. With laboratory soil data, SPT indicates general,
inconclusive trends. 相似文献
99.
Paul McMillan Masaki Akaogi Eiji Ohtani Quentin Williams Ronald Nieman Robert Sato 《Physics and Chemistry of Minerals》1989,16(5):428-435
We have obtained infrared and Raman spectra for garnets synthesized at high (static) pressures and temperatures along the join Mg3Al2Si3O12 (pyrope) — Mg4Si4O12 (magnesium majorite). The vibrational spectra of Mg-majorite show a large number of additional weak peaks compared with the spectra of cubic pyrope garnet, consistent with tetragonal symmetry for the MgSiO3 garnet phase. The Raman bands for this phase show no evidence for line broadening, suggesting that Mg and Si are ordered on octahedral sites in the garnet. The bands for the intermediate garnet compositions are significantly broadened compared with the end-members pyrope and Mg-majorite, indicating cation disorder in the intermediate phases. Solid state 27Al NMR spectroscopy for pyrope and two intermediate compositions show that Al is present only on octahedral sites, so the cation disorder is most likely confined to Mg-Al-Si mixing on the octahedral sites. We have also obtained a Raman spectrum for a natural, shock-produced (Fe,Mg) majorite garnet. The sharp Raman peaks suggest little or no cation disorder in this sample. 相似文献
100.
G. E. Williams 《Climatic change》1988,13(2):117-128
New observations from two late Precambrian (~800-650 Ma) sedimentary rhythmites in South Australia (Reynella Siltstone and Chambers Bluff Tillite) reveal cycles structurally similar to the ~12-laminae cycles of the ~650-Ma Elatina Formation but which comprise from 15 to 26 or more laminae. The new data are difficult to accomodate in depositional models for the Elatina Formation whereby its laminae are regarded as annual and the cyclicity ascribed to solar variability (Williams and Sonett, 1985) or to the combined influences of the sunspot cycle and the lunar nodal tide (Zahnle and Walker, 1987). If, however, the long-term Elatina Cycle and not the individual lamina is taken as a yearly climatic signal, the Elatina and other rhythmites studied may be interpreted as the deposits of marine ebb-tidal deltas that record variability in the velocity and range of paleo-ebb tides. The basic laminae-cycles would represent lunar fortnightly cycles of diurnal and/or semidiurnal laminae, commonly truncated through non-deposition at neap tides. Despite numerous empirical similarities between the Elatina and sunspot series, the ebb-tidal model for deposition is preferred because it accounts plausibly for observations from all three rhythmites studied. 相似文献