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221.
Hydrodynamics and sediment resuspension events, induced at the shoreline by a deep-draft vessel passing nearby, are described.
Measurements (pressure, currents and turbidity) were obtained at 4 Hz, on a lower beach ~50 m from a channel where large car
ferries operate in Wootton Creek, Isle of Wight. The study focuses on a representative 8-min 32-s-long record, during which
two large vessels passed the channel section. At the shore, the passage of each vessel induced a long-period water-level drawdown,
followed by a water-level oscillation (seiche) of similar period, and the short-period waves of the wake. Both drawdowns were
the main constituents of the prevailing wave pattern. The second drawdown was the largest in amplitude, in response to a higher
speed of the ferry, and the influence of the seiche which had been activated during the preceding event. Two successive peaks
of turbidity were observed shortly after this drawdown. Analyses of current velocity and direction indicate that the sediments
resuspended originated from the shallower upper beach. Anthropogenically induced erosion of the foreshore is predicted at
Wootton Creek. 相似文献
222.
A.?Maestro-GonzálezEmail author P.?Bárcenas J.?T.?Vázquez V.?Díaz-del-Río 《Geo-Marine Letters》2008,28(1):53-64
Fractures associated with volcanic rock outcrops on the inner shelf of Alboran Island, Western Mediterranean, were mapped
on the basis of a side-scan sonar mosaic. Absolute maximum fracture orientation frequency is NW–SE to NNW–SSE, with several
sub-maxima oriented NNE–SSW, NE–SW and ENE–WSW. The origin of the main fracture systems in Neogene and Quaternary rocks of
the Alboran Basin (south Spain) appears to be controlled by older structures, namely NE–SW and WNW–ESE to NW–SE faults which
cross-cut the basement. These faults, pre-Tortonian in origin, have been reactivated since the early Neogene in the form of
strike-slip and extensional movements linked to the recent stress field in this area. Fracture analysis of volcanic outcrops
on the inner continental shelf of Alboran Island suggests that the shelf has been deformed into a narrow shear zone limited
by two NE–SW-trending, sub-parallel high-angle faults, the main orientation and density of which have been influenced by previous
WNW–ESE to NW–SE basement fractures. 相似文献
223.
Hua?YuEmail author Yingqian?Xiong Zhenxia?Liu Serge?Berné Chi-Yue?Huang Guodong?Jia 《Geo-Marine Letters》2008,28(3):131-136
Based on new and existing data on oxygen isotopes, alkenone-surface seawater temperature trends, planktonic foraminifers,
lithology, and clay mineral composition of piston cores, a distinct cooling event has been identified around 8,200 cal a b.p. in the middle Okinawa Trough, northwest Pacific. This corresponds to the 8,200 a b.p. cooling event recorded in many places of the Northern Hemisphere. During this event, the local temperature decreased by
1°C, and the δ18O value increased by 0.6‰. A strengthened Asian winter monsoon is the most probable cause for this event, which thus adds
further credibility to the contention that we are dealing here with a global phenomenon. 相似文献
224.
A large artisanal fleet made up of small-sized vessels fishes along the Galician coastline using passive gear and traps. The aim of this study is to analyse the economic profitability of this fleet in the last 5 years by looking at the average rate of return on the vessel and the investment payback period. The results show a slight drop in the return per vessel half-way through the period studied caused by the effects of the Prestige oil spill, to quickly recover over the following 2 years. Considerably high profitability rates from fishing activity were observed, especially in the second half of the period, and slightly lower payback periods, in general, than the average life of a standard fleet vessel. 相似文献
225.
The sea level of Northeast Atlantic Ocean is calculated for the period between 1958 and 2001 using a state-of-the-art barotropic model with a grid size of 10′ × 15′ (long × lat). The model includes astronomic effects, considering seven components of the tide, and the meteorological effects of wind and atmospheric pressure, allowing obtaining the astronomic tide, the atmospheric residuals and the non-linear addition of both components of sea level. 相似文献
226.
R. Len L. Somoza C.J. Gimnez-Moreno C.J. Dabrio G. Ercilla D. Praeg V. Díaz-del-Río M. Gmez-Delgado 《Marine and Petroleum Geology》2009,26(8):1564-1579
This paper presents a computational model for mapping the regional 3D distribution in which seafloor gas hydrates would be stable, that is carried out in a Geographical Information System (GIS) environment. The construction of the model is comprised of three primary steps, namely: (1) the construction of surfaces for the various variables based on available 3D data (seafloor temperature, geothermal gradient and depth-pressure); (2) the calculation of the gas function equilibrium functions for the various hydrocarbon compositions reported from hydrate and sediment samples; and (3) the calculation of the thickness of the hydrate stability zone. The solution is based on a transcendental function, which is solved iteratively in a GIS environment.The model has been applied in the northernmost continental slope of the Gulf of Cadiz, an area where an abundant supply for hydrate formation, such as extensive hydrocarbon seeps, diapirs and fault structures, is combined with deep undercurrents and a complex seafloor morphology. In the Gulf of Cadiz, the model depicts the distribution of the base of the gas hydrate stability zone for both biogenic and thermogenic gas compositions, and explains the geometry and distribution of geological structures derived from gas venting in the Tasyo Field (Gulf of Cadiz) and the generation of BSR levels on the upper continental slope. 相似文献
227.
228.
Daphne Cuvelier Joze Sarrazin Ana Colao Jon Copley Daniel Desbruyres Adrian G. Glover Paul Tyler Ricardo Serro Santos 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):2026-2040
Whilst the fauna inhabiting hydrothermal vent structures in the Atlantic Ocean is reasonably well known, less is understood about the spatial distributions of the fauna in relation to abiotic and biotic factors. In this study, a major active hydrothermal edifice (Eiffel Tower, at 1690 m depth) on the Lucky Strike vent field (Mid-Atlantic Ridge (MAR)) was investigated. Video transects were carried out by ROV Victor 6000 and complete image coverage was acquired. Four distinct assemblages, ranging from dense larger-sized Bathymodiolus mussel beds to smaller-sized mussel clumps and alvinocaridid shrimps, and two types of substrata were defined based on high definition photographs and video imagery. To evaluate spatial variation, faunal distribution was mapped in three dimensions. A high degree of patchiness characterizes this 11 m high sulfide structure. The differences observed in assemblage and substratum distribution were related to habitat characteristics (fluid exits, depth and structure orientation). Gradients in community structure were observed, which coincided with an increasing distance from the fluid exits. A biological zonation model for the Eiffel Tower edifice was created in which faunal composition and distribution can be visually explained by the presence/absence of fluid exits. 相似文献
229.
The physical and orbital elements of the binary star ADS 1156 = B 1164 (α1900 = 01h 22m.0, δ1900 = + 04°50′) are determined. The absolute visual magnitudes of the two components are 3m.72 resp. 3m.97, the masses 1.43 M⊙ resp. 1.33 M⊙. 相似文献
230.
Altimeter data and output from the HYbrid Coordinate Ocean Model global assimilation run are used to study the seasonal variation
of eddy shedding from the Kuroshio intrusion in the Luzon Strait. The results suggest that most eddy shedding events occur
from December through March, and no eddy shedding event occurs in June, September, or October. About a month before eddy shedding,
the Kuroshio intrusion extends into the South China Sea and a closed anticyclonic eddy appears inside the Kuroshio loop which
then detaches from the Kuroshio intrusion. Anticyclonic eddies detached from December through February move westward at a
speed of about 0.1 m s−1 after shedding, whereas eddies detached in other months either stay at the place of origin or move westward at a very slow
speed (less than 0.06 m s−1). The HYCOM outputs and QuikSCAT wind data clearly show that the seasonal variation of eddy shedding is influenced by the
monsoon winds. A comparison between eddy volume and integrated Ekman transport indicates that, once the integrated Ekman transport
exceeds 2 × 1012 m3 (which roughly corresponds to the volume of an eddy), the Kuroshio intrusion expands and an eddy shedding event occurs within
1 month. We infer that the Ekman drift of the northeasterly monsoon pushes the Kuroshio intrusion into the SCS, creates a
net westward transport into the Strait, and leads to an eddy detachment from the Kuroshio. 相似文献