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411.
Gerald Grellet-Tinner Michael B.Thompson Lucas E.Fiorelli Eloísa Argaaraz Laura Codorniú E.Martín Hechenleitner 《地学前缘(英文版)》2014,5(6):759-765
The increasing number of fossil pterosaur eggs sheds light on nesting environments and breeding be- haviors of these extinct flying reptiles. Here we report the first partial three-dimensional egg of the pterosaur, Pteroduustro guinazui, from central Argentina. The specimen was discovered from the same Albian deposits as the exceptional R guinazui embryo described in 2004. Microscopic characterizations indicate a pristine preservation of the 50 Bm thick calcium carbonate, which differs significantly from the soft shell of Chinese pterosaur eggs. Estimate of the eggshell conductance implies that the nest had a minimum moisture content of 75%. This moisture estimate, combined with geological and taphonomical data, suggests that P. guinazui may have adopted a nesting strategy similar to those of grebes and flamingos rather than being buried on land, as previously hypothesized. Moreover, our results demon- strate that the nesting paleoenvironment of this pterosaur species was closely linked to a mesohaline lacustrine ecosystem in a basin governed by regional tectonic subsidence, a setting characteristic for the feeding and reproduction of modern flamingos. 相似文献
412.
Helmi Saidi Marzia Ciampittiello Claudia Dresti Laura Turconi 《Environmental Earth Sciences》2014,72(11):4607-4616
With regard to extreme events, it is well documented that an intensity of about 1 mm/min already represents an extreme intensity. Under alpine conditions, a precipitation event with an intensity of 3 mm/min has occurred. Therefore, the rain gauges in this region have to be able to measure in this and even in higher intensity ranges. This study deals with basic automated tipping-bucket rain (TBR) gauge and Bulk precipitation samplers, which are able to hold more than 95 % of the cumulative rainfall, that are verified within the space of the week without losses during the extreme events and with minimal evaporation loss. Bulk samplers collected more rainfall than TBR gauges in 110 of 221 extreme events analysed over the past 10 years. In 17 extreme events, an underestimation greater than 10 % was evaluated. The objective was to single out the counting errors associated with TBR gauge, during extreme events, so as to help the understanding of the measured differences between instruments in the field. We want to determine whether the automated precipitation gauge can provide a reliable and precise measurement of precipitation with particular interest regarding heavy and extreme events. 相似文献
413.
Full-scale Modelling of Falling Rock Protection Barriers 总被引:1,自引:0,他引:1
Full-scale impact tests, carried out to evaluate the behaviour of flexible falling rock protection barriers, are described
and relevant results presented and discussed. Falling rock protection barriers, which may be numbered among passive measures
against rockfall, are designed to intercept and stop falling rocks by dissipation of impact energies through the elasto-plastic
deformation of a system made up of metallic nets and supporting and connecting components. The testing programme involved
models of barriers subjected to the impact of free-falling blocks of kinetic energy ranging from 500 to 5,000 kJ. The experimental
test site, set-up in Fonzaso (Italy), and the experimental procedure were developed according to the new European testing
standards (ETAG 027) on falling rock protection kits. The paper is aimed at presenting an extensive and high quality database,
which can be extremely useful for a better understanding of the actual response of such structures and for any subsequent
analytical and numerical modelling. 相似文献
414.
Laura Gulia 《Natural Hazards》2010,53(2):229-249
The presence of quarry and mine blasts in seismic catalogues is detected using the Wiemer and Baer (Bull Seism Soc Am 90(2):525–530,
2000) algorithm. The procedure is based on the observation that quarry blasts generally take place during daytime hours: the areas
with a high ratio of daytime and night-time events are likely to be regions with quarry activity. In the first part of this
work we have tested the method, using both a synthetic and a regional catalogue; in the second part the procedure has been
applied to some of the European regional catalogues available on line. The comparison between the results obtained and the
location of known quarries and mines for the analysed catalogues confirms the reliability of the methodology in identifying
mining areas. 相似文献
415.
Laura Jones 《GeoJournal》2010,75(4):359-371
Conspiratorial thought has been highly visible in post-September 11th America, manifest through the continued growth of a
public ‘9/11 Truth Movement’ as well as at the state-level, through the Bush administration’s conspiracy rhetoric of Islamic
terrorists intent on infiltrating the US homeland. In this paper, I demonstrate how conspiracy can be understood as a ‘knowledge-producing
discourse’; dialectically engaged across multiple subject positions and through which geopolitical narratives are performatively
produced and contested at interconnected scales of bodies, homes, city streets and national ‘homelands’. Through drawing on,
and challenging, the conceptual and methodological approaches of a burgeoning feminist geopolitics, I ground my analysis in
the embodied performances of ‘patriotic dissent’ by members of the 9/11 Truth Movement in New York City, as well as through
my own situated and ethical engagement with positions of political difference. 相似文献
416.
417.
Gary R. O'Brien Darrell S. Kaufman Warren D. Sharp Viorel Atudorei Roderic A. Parnell Laura J. Crossey 《Quaternary Research》2006,65(3):366-379
Holocene and modern travertine formed in spring-fed Havasu Creek of the Grand Canyon, Arizona, was studied to determine the factors governing its oxygen-isotope composition. Analysis of substrate-grown travertine indicates that calculated calcite-formation temperatures compare favorably with measured water temperatures, and include silt-rich laminae deposited by monsoon-driven floods. Ancient spring-pool travertine is dated by U-series at 7380 ± 110 yr and consists of 14 travertine-silt couplets of probable annual deposition. One hundred eighty high-resolution δ18O analyses of this mid-Holocene sample average −11.0‰ PDB. The average value for modern travertine is 0.5‰ lower, perhaps because mid-Holocene temperature was higher or there was proportionally greater summer recharge. δ18O cyclicity in the mid-Holocene travertine has average amplitude of 1.9 ± 0.5‰ PDB, slightly less than the inferred modern-day annual temperature range of Havasu Creek. The annual temperature range might have been reduced during the 14-yr interval compared to present, although other non-temperature factors could account for the muted annual variation. Silt-rich laminae within isotopically lower calcite in the modern and mid-Holocene travertine verifies the seasonal resolution of both samples, and suggests that similar temperature-precipitation conditions, as well as monsoon-generated summer floods, prevailed in the mid-Holocene as they do throughout the Grand Canyon region today. 相似文献
418.
Localized zones of denitrification in a floodplain aquifer in southern Wisconsin, USA 总被引:1,自引:0,他引:1
A floodplain aquifer within an agricultural watershed near Madison, Wisconsin (USA), was studied to determine whether denitrification was occurring below the surface organic layer. Groundwater levels and concentrations of O2, Cl?, NO 3 ? , SO 4 2? , dissolved organic carbon (DOC), and major cations were monitored over a 1-year period along a 230-m transect between an agricultural field and a stream discharge point. Seventeen groundwater samples were analyzed for δ15NNO3 and δ18ONO3 composition. Samples in which NO 3 ? was too low for stable isotope analysis were analyzed for excess dissolved N2. Groundwater NO 3 ? concentrations declined between the agricultural field and the discharge point. Chloride and δ15NNO3/δ18ONO3 data indicated that the drop in NO 3 ? was caused primarily by dilution of shallow NO 3 ? -rich water with deeper, NO 3 ? -depleted groundwater. Two localized zones of denitrification were identified in the upland-wetland transition by their δ15NNO3 and δ18ONO3 signatures, and two in the stream hyporheic zone by the presence of excess dissolved N2. The combined stratigraphic, hydrologic, and geochemical data in these locations correspond to groundwater mixing zones where NO 3 ? is delivered to subsurface layers that support denitrification fueled by dissolved (e.g. DOC or dissolved Fe(II)) and/or solid-phase (e.g. particulate organic carbon, solid-associated Fe(II), or pyrite) electron donors. 相似文献
419.
James E. Amonette Jonathan L. Barr Laura M. Dobeck Kadie Gullickson Stephen J. Walsh 《Environmental Earth Sciences》2010,60(2):263-272
This study reports the first field test of a multi-channel, auto-dilution, steady-state, soil–CO2 flux monitoring system being developed to help understand the pathways by which fugitive CO2 from a geologic sequestration site migrates to the surface. The test was conducted from late August through mid-October 2008
at the Zero Emissions Research and Technology project site located in Bozeman, MT. Twenty steady-state and five non-steady-state
flux chambers were installed in a 10 × 15 m area, one boundary of which was directly above a shallow (2-m depth) horizontal
injection well located 0.5 m below the water table. A total flux of 52 kg CO2 day−1 was injected into the well for 13 days and the efflux from the soil was monitored by the chambers before, during, and for
33 days after the injection. The results showed a rapid increase in soil efflux once injection started, with maximal values
reached within 3–7 days in most chambers. Efflux returned to background levels within a similar time period after injection
ceased. A radial efflux pattern was observed to at least 2 m from the injection well, and evidence for movement of the CO2 plume during the injection, presumably due to groundwater flow, was seen. The steady-state chambers yielded very stable data,
but threefold to fivefold higher fluxes than the non-steady-state chambers. The higher fluxes were attributed to vacuum induced
in the steady-state chambers by narrow vent tubes. High winds resulted in significant decreases in measured soil CO2 efflux, presumably by enhancing efflux from soil outside the chambers. 相似文献
420.
Daniel Thomas Ralf Bender Ulrich Hopp Claudia Maraston Laura Greggio 《Astrophysics and Space Science》2003,284(2):599-602
We present kinematics and stellar population properties of 17 dwarf early-type galaxies in the luminosity range -14 ≥ M
B ≥ -19. Our sample fills the gap between the intensively studied giant elliptical and Local Group dwarf spheroidal galaxies.
The dwarf ellipticals of the present sample have constant velocity dispersion profiles within their effective radii and do
not show significant rotation, hence are clearly anisotropic. The dwarf lenticulars, instead, rotate faster and are, at least
partially, supported by rotation. From optical Lick absorption indices, we derive metallicities and element abundances. Combining
our sample with literature data of the Local Group dwarf spheroidals and giant ellipticals, we find a surprisingly tight linear
correlation between metallicity and luminosity over a wide range: -8 ≥ M
B ≥ -22. The α/Fe ratios of our dwarf ellipticals are significantly lower than the ones of giant elliptical galaxies, which
is in agreement with spectroscopy of individual stars in Local Group dwarf spheroidals. Our results suggest the existence
of a clear kinematic and stellar population dichotomy between dwarf and giant elliptical galaxies. This result is important
for theories of galaxy formation, because it implies that present-day dwarf ellipticals are not the fossiled building blocks
of giant ellipticals.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献