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811.
812.
This study deals with the assimilation of TOPEX altimeter-derived sea level variability in a reduced-gravity model of the northwestern Indian Ocean. The assimilation has been done using variational assimilation method with adjoint technique. A cost function representing the misfit between the model and the data is minimized with the model equations acting as constraints. The initial conditions of the model are used as control parameters and the best-fit initial conditions are determined as a result of minimization carried out using a variable-storage quasi-Newton method. Experiment has been done with 10 days' cycle-averaged data of TOPEX. Assimilation for 10 days and 20 days has been performed and it has been seen that 20 days' assimilation of satellite data provides better results. 相似文献
813.
Seismic velocities ( V p and V s ) of compressional (P-) and shear (S-) waves are important parameters for the characterization of marine sediments with respect to their sedimentological and geotechnical properties. P- and S-wave velocity data of near-surface marine sediments (upper 9 m) of the continental slope of the Barents Sea are analysed and correlated to sedimentological and geotechnical properties. The results show that the S-wave velocity is much more sensitive to changes in lithology and mechanical properties than the P-wave velocity, which is characterized by a narrow range of values. The correlation coefficients between S-wave velocity and silt and clay content, wet bulk density, porosity, water content and shear strength are higher than 0.5 while the correlation coefficients of P-wave velocity and the same parameters are always lower than 0.4. Although the relationship between V s and clay content has been widely described, the data show that V s is better correlated with silt content than with clay content for the sediments of the area investigated. However, they show different trends. While V s increases with increasing clay content, it decreases with increasing silt content. 相似文献
814.
Sediment cores were collected from the remote subalpine Great Ghost Lake in southern Taiwan. Because the lake is anoxic the sediments are well preserved, distinctive past variations can be dated accurately. The vertical distributions of total and acid-leached metal concentrations for aluminum, arsenic, cadmium, cerium, chromium, cesium, copper, iron, magnesium, manganese, nickel, lead, rubidium, strontium, vanadium and zinc are measured and the fluxes determined. The dates of higher fluxes in the past 2600 years seem to correlate with dry spells. Further, trace metal fluxes show a large increase but Pb-206/Pb-207 ratios show a large decrease since 1950, suggesting a significant anthropogenic input. 相似文献
815.
台湾大鬼湖沉积物元素分布所反映的古环境意义 总被引:8,自引:2,他引:6
位于台湾省南部的大鬼湖,由于湖底常缺氧等特殊自然条件,使湖底沉积物免遭干扰,而能完整地记录过去气候的环境的变动.其岩芯中出现的白层,有明显较低的有机质含量和C/P、N/P、S/P及Si/Al比值.与较高的Si/P、Fe/C、Mn/C、Fe/Mn和Mg/Al比值,显示当时气候可能较干冷,集水区植生较差、湖水位较低,而且环境较氧化.相比之下,富含有机质的黑色沉积物,则反映气候较暖湿、湖水面至少升高2m,而且集水区土壤和水体较还原。 相似文献
816.
Heather?E.?GallEmail authorView authors OrcID profile Daniel?Schultz Tamie L.?Veith Sarah C.?Goslee Alfonso?Mejia Ciaran J.?Harman Cibin?Raj Paul?H.?Patterson 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(8):2369-2380
Vegetated filter strips (VFSs) are a best management practice (BMP) commonly implemented adjacent to row-cropped fields to trap overland transport of sediment and other constituents present in agricultural runoff. Although they have been widely adopted, insufficient data exist to understand their short and long-term effectiveness. High inter-event variability in performance has been observed, yet the majority of studies report average removal efficiencies over observed or simulated events, ignoring the disproportional effects of loads into and out of VFSs over longer periods of time. We argue that due to positively correlated sediment concentration-discharge relationships, disproportional contribution of runoff events transporting sediment over the course of a year (i.e., temporal inequality), decreased performance with increasing flow rates, and effects of antecedent moisture condition, VFS removal efficiencies over annual time scales may be significantly lower than reported per-event averages. By applying a stochastic approach, we investigated the extent of disparity between reporting average efficiencies from each runoff event over the course of 1 year versus the total annual load reduction. Additionally, we examined the effects of soil texture, concentration-discharge relationship, and VFS slope in contributing to this disparity, with the goal of revealing potential errors that may be incurred by ignoring the effects of temporal inequality in quantifying VFS performance. Simulation results suggest that ignoring temporal inequality can lead to overestimation of annual performance by as little as < 2% and to as much as > 20%, with the greatest disparities observed for soils with high clay content. 相似文献
817.
Nawa Raj Pradhan 《水文科学杂志》2019,64(7):771-788
A soil moisture retrieval method is proposed, in the absence of ground-based auxiliary measurements, by deriving the soil moisture content relationship from the satellite vegetation index-based evapotranspiration fraction and soil moisture physical properties of a soil type. A temperature–vegetation dryness index threshold value is also proposed to identify water bodies and underlying saturated areas. Verification of the retrieved growing season soil moisture was performed by comparative analysis of soil moisture obtained by observed conventional in situ point measurements at the 239-km2 Reynolds Creek Experimental Watershed, Idaho, USA (2006–2009), and at the US Climate Reference Network (USCRN) soil moisture measurement sites in Sundance, Wyoming (2012–2015), and Lewistown, Montana (2014–2015). The proposed method best represented the effective root zone soil moisture condition, at a depth between 50 and 100 cm, with an overall average R2 value of 0.72 and average root mean square error (RMSE) of 0.042. 相似文献
818.
Seismic analysis of a curved bridge considering deck‐abutment pounding interaction: an analytical investigation on the post‐impact response 下载免费PDF全文
Horizontal curved bridges are very common at intersections and at the changing angle of bridge alignment. Almost in every previous earthquake report, it can be seen that the columns of a curved segment experience torsional damage, and the curved decks are unseated from the abutment support. The main reason behind that phenomenon is the in‐plane deck rotation which results because of the complex dynamic coupling between two longitudinal directional vibrations. The curved decks are susceptible to deck rotation because in a curved segment, the centre of mass and the centre of stiffness generally lie outside the bridge deck and are not located at the same point. The pounding with the abutment often increases the rotational tendency of the deck. In this paper, a classical mechanics‐based approach is adopted to analytically estimate the deck rotation potential of curved bridge considering the deck‐abutment pounding interaction. The deck‐abutment pounding is modelled using non‐smooth techniques considering the Newton's impact law in the normal and Coulomb's friction in the tangential direction. Within the scope of this paper, a parametric study is performed to get the ideal combination of the column and bent arrangement and the gap distance. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
819.
This study proposes a Green’s function,an essential representation of water-saturated ground under moving excitation,to simulate ground borne vibration from trains.First,general solutions to the governing equations of poroelastic medium are derived by means of integral transform.Secondly,the transmission and reflection matrix approach is used to formulate the relationship between displacement and stress of the stratified ground,which results in the matrix of the Green’s function.Then the Green’s function is combined into a train-track-ground model,and is verified by typical examples and a field test.Additional simulations show that the computed ground vibration attenuates faster in the immediate vicinity of the track than in the surrounding area.The wavelength of wheel-rail unevenness has a notable effect on computed displacement and pore pressure.The variation of vibration intensity with the depth of ground is significantly influenced by the layering of the strata soil.When the train speed is equal to the velocity of the Rayleigh wave,the Mach cone appears in the simulated wave field.The proposed Green’s function is an appropriate representation for a layered ground with shallow ground water table,and will be helpful to understand the dynamic responses of the ground to complicated moving excitation. 相似文献
820.
A number of recent studies suggest that atmospheric changes that precede an earthquake might offer the hope of providing early warning. This study attempts to examine seismo-atmospheric anomalies around the time and the location of some of the major earthquakes in Greece in the period 2001–2015. Daily values of aerosol optical depth (AOD) and total ozone column (TOZ) obtained from satellite observations are used, in the time window between 25 days before and 14 days after each of these events, in a 1° × 1° area centred on the epicentre of each earthquake. For some of these earthquake events, abnormal increases in time series of AOD and TOZ data were detected before and after the occurrence of the earthquake. Nevertheless, in other cases, no clear anomalies were observed around the earthquake date. In addition, examining the statistics of AOD and TOZ daily values, there were many cases of prominent abnormal variations, without, however, being associated with an earthquake event. Therefore, no clear association was found between AOD and TOZ fluctuations and recent earthquakes in Greece. 相似文献