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961.
For first time, during 1991, seismic activity was recorded during an eruption at Colima volcano. We analyze these data to
obtain a stress pattern using a composite focal mechanism technique. From the analysis of regional seismicity, the Tamazula
Fault and the Armeria River appear as active features and the dip of the slab east of the Jalisco Block is approximately 12°.
Southwest of Colima volcano a vertical alignment of seismic events was observed. We estimate five different composite focal
mechanism solutions from our data set, which indicate a change of the stress field at the volcano after the 1991 eruption.
These solutions suggest that the stress field in the volcanic edifice was controlled by stresses related to the emplacement
of magma superimposed on the regional stress field. No evidence of active local faults in the volcanic edifice was found.
We propose a model for the eruptive process that involves tilting of the volcanic edifice.
Received: 15 October 1995 / Accepted: 26 October 1998 相似文献
962.
F. Díaz García J. R. Martínez Catalán R. Arenas P. González Cuadra 《International Journal of Earth Sciences》1999,88(2):337-351
An important detachment is described in the allochthonous Ordenes Complex, in the NW Iberian Massif, and its meaning is related
to the kinematics of contemporaneous convergent structures. The Corredoiras Detachment (CD) separates a hangingwall unit,
characterised by a medium-pressure metamorphic gradient, from a footwall high-pressure and high-temperature unit and an underlying
ophiolitic unit. An associated ductile shear zone, nearly 2000 m thick, developed in the lower part of the hangingwall unit,
where the Corredoiras Orthogneiss, a Lower Ordovician metagranite, was progressively transformed into augengneisses, mylonitic
and ultramylonitic gneisses. The attitude of the stretching and mineral lineation in the mylonites varies due to late refolding
at map scale, but the sense of movement can be estimated, being roughly top to the SE. According to crosscutting relationships,
the CD developed subsequent to the thrusting of the high-pressure/high-temperature unit onto the ophiolitic unit, and prior
to younger extensional detachments, upright folding and strike-slip tectonics. The geometric relationships of the CD with
the previous structures in the footwall unit, the subtractive character of the metamorphic gap between its hangingwall and
footwall, and the available isotopic data suggest that the CD is an early Variscan, ductile extensional detachment, the movement
of which was roughly simultaneous with the onset of thrusting of the allochthonous complexes over their relative autochthon.
Received: 17 November 1998 / Accepted: 4 April 1999 相似文献
963.
P. Szafián G. Tari F. Horváth S. Cloetingh 《International Journal of Earth Sciences》1999,88(1):98-110
The crustal structure of the transition zone between the Eastern Alps and the western part of the Pannonian depression (Danube
basin) is traditionally interpreted in terms of subvertical Tertiary strike-slip and normal faults separating different Alpine
tectonic units. Reevaluation of approximately 4000-km-long hydrocarbon exploration reflection seismic sections and a few deep
seismic profiles, together with data from approximately 300 wells, suggests a different structural model. It implies that
extensional collapse of the Alpine orogene in the Middle Miocene was controlled by listric normal faults, which usually crosscut
Alpine nappes at shallow levels, but at depth merge with overthrust planes separating the different Alpine units. The alternative
structural model was tested along a transect across the Danube basin by gravity model calculations, and the results show that
the model of low-angle extensional faulting is indeed viable. Regarding the whole lithosphere of the western Pannonian basin,
gravity modelling indicates a remarkable asymmetry in the thickness minima of the attenuated crust and upper mantle. The approximately
160 km lateral offset between the two minima suggests that during the Miocene extension of the Pannonian basin detachment
of the upper crust from the mantle lithosphere took place along a rheologically weak lower crust.
Received: 13 July 1998 / Accepted: 18 March 1999 相似文献
964.
Labour shortage was an integral feature of the communist system of economic management and one that seemed most unlikely to
persist in the face of systemic transformation. A casual examination of the unemployment rates that have emerged throughout
most of Central and Eastern Europe (CEE) during the course of the past decade might suggest that this early assumption was
correct. However, within the region the aggregate rate of joblessness, as well as the behaviour of national output, mask the
fact that certain, major urban centres appear to have weathered well the storms caused by exposure to western markets and
stringent fiscal and monetary policies. In these centres transformation has meant, to a greater or lesser degree, industrial
modernisation and this begs the question of whether the human capital portfolios of the inherited labour force match up to
the requirements of the new environment. This paper examines the meaning of the concept of labour shortage and presents the
findings from a survey of employers in four leading cities of three major CEE economies designed to elicit if, and how, manpower
requirements are being met in the present climate. The results indicate that, somewhat paradoxically, labour shortage persists
in the more flexible markets of the post-communist era and that firms do not expect the situation to change radically in the
near future.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
965.
966.
A. Hernández M. Jébrak P. Higueras R. Oyarzun D. Morata J. Munhá 《Mineralium Deposita》1999,34(5-6):539-548
The Almadén district is the largest mercury concentration in the world, with a total content of about 250 000 t of mercury,
nearly one third of the known total mercury resources of the Earth. Mercury has been exploited since the Celtic and Roman
times, with peak production during the Renaissance and between 1939–1945. The district is hosted by a Paleozoic synclinorium
overlying Precambrian rocks. The Paleozoic sequence comprises epicontinental quartz arenite rocks, including black shales
and quartzites. Diatremes, alkaline lavas of different composition, and late tholeiitic diabases account for the Ordovician
to Devonian magmatism. The tectonic setting of this complex suite corresponds to the intraplate type. The mercury deposits
of Almadén can be classified into two main types: type 1, early stratiform type ores characterized by cinnabar deposition
on the lower Silurian quartzites (Criadero quartzite; e.g. the Almadén and El Entredicho deposits), and type 2, late discordant
orebodies (e.g. Las Cuevas), largely hosted or related to diatremes (the `frailesca rocks') of alkaline basaltic composition.
In type 1 cinnabar was deposited during diagenesis, in relation to hydrothermal circulation driven by magmatic activity. Type
2 include a variety of deposits having in common the discordant character of the orebodies (e.g. veins, stockworks, massive
replacements), and their wide dispersion along the stratigraphic column, i.e. from Lower Silurian (e.g. Nueva Concepción)
to Upper Devonian (e.g. Corchuelo).
Received: 23 October 1998 / Accepted: 4 January 1999 相似文献
967.
J. C. Balanyá J. Galindo-Zaldívar A. Jabaloy G. Leitchenkov A. Maldonado J. Rodríguez-Fernández O. Vinnikovskaya 《Geo-Marine Letters》1999,18(3):215-224
The structure of the South Powell Ridge (SPR), separating the Late Cenozoic ocean-floored Powell Basin and the Mesozoic Weddell
Sea domain, is revealed by multichannel seismic data. The SPR appears as a basement high, bounded northward by transtensional
faults and by normal and major reverse faults to the south. These margin features seem to be linked to the Powell Basin southern
strike-slip margin and to the Jane Arc paleotrench, respectively. We suggest the ridge evolved from the Antarctic Peninsula
passive margin to become the deformational front of the Scotia/Antarctica Plate boundary, later being welded to the Antarctic
Plate.
Received: 18 August 1997 / Revision received: 4 May 1998 相似文献
968.
Santiago Hernández-León Lutz Postel Javier Arístegui May Gómez María Fernanda Montero Santiago Torres Carlos Almeida Eugen Kühner Ullrich Brenning Eberhard Hagen 《Journal of Oceanography》1999,55(4):471-482
Plankton biomass and indices of metabolism and growth [electron transport system (ETS), glutamate dehydrogenase (GDH) and aspartate transcarbamylase (ATC) activities] were studied over a 2,800 km east-west section of the tropical North Atlantic Ocean (21°N) in <200, 200–500 and >;500 µm size classes. On the large-scale, zooplankton (>;200 µm) enzymatic activities increased westward in the study section, where large cyanobacteria chains (Trichodesmium spp.) were observed. Parallel to it, an increase in medium calanoids (1–2 mm length) was observed towards the western part of the transect, whereas small calanoids (<1 mm) were dominant throughout the boundary area of the subtropical gyre. Microplankton ETS and mesoplankton ETS and ATC activities seemed to match the wave length of low frequency waves. Our results suggest that such waves are related to the observed enhancement of metabolic activity of micro- and mesoplankton. The large-scale and mesoscale variability observed give evidence of the inadequacy of assuming a steady-state picture of the euphotic zone of tropical and subtropical waters. 相似文献
969.
Real-time envelope cross-correlation detector: application to induced seismicity in the Insheim and Landau deep geothermal reservoirs 总被引:1,自引:0,他引:1
Margarete Vasterling Ulrich Wegler Jan Becker Andrea Brüstle Monika Bischoff 《Journal of Seismology》2017,21(1):193-208
We develop and test a real-time envelope cross-correlation detector for use in seismic response plans to mitigate hazard of induced seismicity. The incoming seismological data are cross-correlated in real-time with a set of previously recorded master events. For robustness against small changes in the earthquake source locations or in the focal mechanisms we cross-correlate the envelopes of the seismograms rather than the seismograms themselves. Two sequenced detection conditions are implemented: After passing a single trace cross-correlation condition, a network cross-correlation is calculated taking amplitude ratios between stations into account. Besides detecting the earthquake and assigning it to the respective reservoir, real-time magnitudes are important for seismic response plans. We estimate the magnitudes of induced microseismicity using the relative amplitudes between master event and detected event. The real-time detector is implemented as a SeisComP3 module. We carry out offline and online performance tests using seismic monitoring data of the Insheim and Landau geothermal power plants (Upper Rhine Graben, Germany), also including blasts from a nearby quarry. The comparison of the automatic real-time catalogue with a manually processed catalogue shows, that with the implemented parameters events are always correctly assigned to the respective reservoir (4 km distance between reservoirs) or the quarry (8 km and 10 km distance, respectively, from the reservoirs). The real-time catalogue achieves a magnitude of completeness around 0.0. Four per cent of the events assigned to the Insheim reservoir and zero per cent of the Landau events are misdetections. All wrong detections are local tectonic events, whereas none are caused by seismic noise. 相似文献
970.
Frontal dynamics boost primary production in the summer stratified Mediterranean sea 总被引:1,自引:1,他引:0
Antonio Olita Arthur Capet Mariona Claret Amala Mahadevan Pierre Marie Poulain Alberto Ribotti Simón Ruiz Joaquín Tintoré Antonio Tovar-Sánchez Ananda Pascual 《Ocean Dynamics》2017,67(6):767-782
Bio-physical glider measurements from a unique process-oriented experiment in the Eastern Alboran Sea (AlborEx) allowed us to observe the distribution of the deep chlorophyll maximum (DCM) across an intense density front, with a resolution (~ 400 m) suitable for investigating sub-mesoscale dynamics. This front, at the interface between Atlantic and Mediterranean waters, had a sharp density gradient (Δρ ~ 1 kg/m3 in ~ 10 km) and showed imprints of (sub-)mesoscale phenomena on tracer distributions. Specifically, the chlorophyll-a concentration within the DCM showed a disrupted pattern along isopycnal surfaces, with patches bearing a relationship to the stratification (buoyancy frequency) at depths between 30 and 60 m. In order to estimate the primary production (PP) rate within the chlorophyll patches observed at the sub-surface, we applied the Morel and Andrè (J Geophys Res 96:685–698 1991) bio-optical model using the photosynthetic active radiation (PAR) from Argo profiles collected simultaneously with glider data. The highest production was located concurrently with domed isopycnals on the fresh side of the front, suggestive that (sub-)mesoscale upwelling is carrying phytoplankton patches from less to more illuminated levels, with a contemporaneous delivering of nutrients. Integrated estimations of PP (1.3 g C m?2d?1) along the glider path are two to four times larger than the estimations obtained from satellite-based algorithms, i.e., derived from the 8-day composite fields extracted over the glider trip path. Despite the differences in spatial and temporal sampling between instruments, the differences in PP estimations are mainly due to the inability of the satellite to measure DCM patches responsible for the high production. The deepest (depth > 60 m) chlorophyll patches are almost unproductive and probably transported passively (subducted) from upper productive layers. Finally, the relationship between primary production and oxygen is also investigated. The logarithm of the primary production in the DCM interior (chlorophyll (Chl) > 0.5 mg/m3) shows a linear negative relationship with the apparent oxygen utilization, confirming that high chlorophyll patches are productive. The slope of this relationship is different for Atlantic, mixed interface waters and Mediterranean waters, suggesting the presence of differences in planktonic communities (whether physiological, population, or community level should be object of further investigation) on the different sides of the front. In addition, the ratio of optical backscatter to Chl is high within the intermediate (mixed) waters, which is suggestive of large phytoplankton cells, and lower within the core of the Atlantic and Mediterranean waters. These observations highlight the relevance of fronts in triggering primary production at DCM level and shaping the characteristic patchiness of the pelagic domain. This gains further relevance considering the inadequacy of optical satellite sensors to observe DCM concentrations at such fine scales. 相似文献