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11.
2020年7月12日,河北唐山发生MS5.1地震,河北省地震预警系统成功地处理并产出了这次地震预警各种结果数据,本文借助此次地震对河北地震预警网内震中距200km范围内台站产出质量以及地震预警前5次处理结果进行详细分析。此次地震发生在河北地震预警网内,平均台间距为10km,首台触发后3s、震后6s发布首次处理结果,与编目结果相比,震级偏差为-1.3,震中位置偏差为2.6km,盲区半径为18km。随着参与定位台站数量增多,震级与位置偏差越来越小,但震级仍整体偏小。河北地震预警网台站产出质量整体较高,其中烈度台作为地震预警最重要的组成部分,是决定预警效果的关键因素。本次地震震中距200km范围内,烈度台平均信噪比为48,震中距50km范围内平均信噪比为112,符合预警系统对信噪比的要求。本次地震预警结果表明,河北地震预警网内台站布局基本合理,波形质量较高,地震预警系统处理软件在本次地震中预警产出效果较好,已经具备了一定的地震预警能力。 相似文献
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《地学前缘(英文版)》2020,11(3):843-853
The combination of U-Pb and Lu-Hf compositions measured in zircon crystals is a remarkably powerful isotopic couplet that provides measures on both the timing of mineral growth and the radiogenic enrichment of the source from which the zircon grew.The U-Pb age documents the timing of zircon crystallization/recrystallization and Hf isotopes inform on the degree to which the host melt was derived from a radiogenic reservoir(e.g.depleted mantle) versus an unradiogenic reservoir(e.g.ancient continental crust),or some mixture of these sources.The ease of generating large quantities of zircon U-Pb and Lu-Hf data has been in large part facilitated by instrument advances.However,the dramatic increase in time constrained zircon Lu-Hf analyses in the Earth science community has brought to the fore the importance of careful data collection and reduction workflows,onto which robust geological interpretations may be based.In this work,we discuss the fundamentals of Lu-Hf isotopes in zircon,which then allows us to provide a robust,accessible,methodology for the assessment of data quality.Additionally,we discuss some novel techniques for:data visualization—that facilitates better transparency of data interpretation;integration of geographic information—that may reveal spatial trends where temporal trends were only apparent before;and some novel statistical evaluation tools—that may provide more rigorous interand intra-sample comparisons. 相似文献
13.
Radon transform is a powerful tool with many applications in different stages of seismic data processing, because of its capability to focus seismic events in the transform domain. Three-parameter Radon transform can optimally focus and separate different seismic events, if its basis functions accurately match the events. In anisotropic media, the conventional hyperbolic or shifted hyperbolic basis functions lose their accuracy and cannot preserve data fidelity, especially at large offsets. To address this issue, we propose an accurate traveltime approximation for transversely isotropic media with vertical symmetry axis, and derive two versions of Radon basis functions, time-variant and time-invariant. A time-variant basis function can be used in time domain Radon transform algorithms while a time-invariant version can be used in, generally more efficient, frequency domain algorithms. Comparing the time-variant and time-invariant Radon transform by the proposed basis functions, the time-invariant version can better focus different seismic events; it is also more accurate, especially in presence of vertical heterogeneity. However, the proposed time-invariant basis functions are suitable for a specific type of layered anisotropic media, known as factorized media. We test the proposed methods and illustrate successful applications of them for trace interpolation and coherent noise attenuation. 相似文献
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Mustafa Al-Marzooq Mamadou S. Diallo Vincent Etienne Thierry Tonellot SanLinn I. Kaka 《Geophysical Prospecting》2019,67(7):1825-1837
The Rub Al Khali region in Saudi Arabia is characterized by the presence of sand dunes separated by salt flats, also called Sabkhas. In general, the elevation of dunes in this region varies between 90 and 250 m above sea level. The presence of these sand dunes, along with the rapidly changing surface topography poses challenges for seismic data acquisition and processing. The high contrast in acoustic impedance between the dune base and the underlying formation often results in amplification of seismic waves that are recorded at stations located on the surface of sand dunes. Attempts to address the issue using conventional surface-consistent amplitude scaling methods without reducing these amplification effects generally fail, thus compromising the suitability of the processed data for amplitude versus offset analysis. In this study, we propose a new reference site technique to reduce the effects of sand dune amplification, enabling the production of data sets that are suitable for amplitude versus offset processing. The proposed technique uses a deterministic approach to derive surface-consistent, frequency-dependent de-amplification functions for shots and stations located on the dunes only. Two-dimensional synthetic and field data examples show that the technique significantly reduces the effects of sand dune amplification. 相似文献
15.
During the time taken for seismic data to be acquired, reservoir pressure may fluctuate as a consequence of field production and operational procedures and fluid fronts may move significantly. These variations prevent accurate quantitative measurement of the reservoir change using 4D seismic data. Modelling studies on the Norne field simulation model using acquisition data from ocean-bottom seismometer and towed streamer systems indicate that the pre-stack intra-survey reservoir fluctuations are important and cannot be neglected. Similarly, the time-lapse seismic image in the post-stack domain does not represent a difference between two states of the reservoir at a unique base and monitor time, but is a mixed version of reality that depends on the sequence and timing of seismic shooting. The outcome is a lack of accuracy in the measurement of reservoir changes using the resulting processed and stacked 4D seismic data. Even for perfect spatial repeatability between surveys, a spatially variant noise floor is still anticipated to remain. For our particular North Sea acquisition data, we find that towed streamer data are more affected than the ocean-bottom seismometer data. We think that this may be typical for towed streamers due to their restricted aperture compared to ocean-bottom seismometer acquisitions, even for a favourable time sequence of shooting and spatial repeatability. Importantly, the pressure signals on the near and far offset stacks commonly used in quantitative 4D seismic inversion are found to be inconsistent due to the acquisition timestamp. Saturation changes at the boundaries of fluid fronts appear to show a similar inconsistency across sub-stacks. We recommend that 4D data are shot in a consistent manner to optimize aerial time coverage, and that additionally, the timestamp of the acquisition should be used to optimize pre-stack quantitative reservoir analysis. 相似文献
16.
基于ROMS和4DVAR的沿轨与网格化SSH数据同化效果评价 总被引:1,自引:1,他引:0
Remote sensing products are significant in the data assimilation of an ocean model. Considering the resolution and space coverage of different remote sensing data, two types of sea surface height(SSH) product are employed in the assimilation, including the gridded products from AVISO and the original along-track observations used in the generation. To explore their impact on the assimilation results, an experiment focus on the South China Sea(SCS) is conducted based on the Regional Ocean Modeling System(ROMS) and the four-dimensional variational data assimilation(4 DVAR) technology. The comparison with EN4 data set and Argo profile indicates that, the along-track SSH assimilation result presents to be more accurate than the gridded SSH assimilation, because some noises may have been introduced in the merging process. Moreover, the mesoscale eddy detection capability of the assimilation results is analyzed by a vector geometry–based algorithm. It is verified that, the assimilation of the gridded SSH shows superiority in describing the eddy's characteristics, since the complete structure of the ocean surface has been reconstructed by the original data merging. 相似文献
17.
Estimating external magnetic field differences at high geomagnetic latitudes from a single station 下载免费PDF全文
Providing an accurate estimate of the magnetic field on the Earth's surface at a location distant from an observatory has useful scientific and commercial applications, such as in repeat station data reduction, space weather nowcasting or aeromagnetic surveying. While the correlation of measurements between nearby magnetic observatories at low and mid‐latitudes is good, at high geomagnetic latitudes () the external field differences between observatories increase rapidly with distance, even during relatively low magnetic activity. Thus, it is of interest to describe how the differences (or errors) in external magnetic field extrapolation from a single observatory grow with distance from its location. These differences are modulated by local time, seasonal and solar cycle variations, as well as geomagnetic activity, giving a complex temporal and spatial relationship. A straightforward way to describe the differences are via confidence intervals for the extrapolated values with respect to distance. To compute the confidence intervals associated with extrapolation of the external field at varying distances from an observatory, we used 695 station‐years of overlapping minute‐mean data from 37 observatories and variometers at high latitudes from which we removed the main and crustal fields to isolate unmodelled signals. From this data set, the pairwise differences were analysed to quantify the variation during a range of time epochs and separation distances. We estimate the 68.3%, 95.4% and 99.7% confidence levels (equivalent to the 1σ, 2σ and 3σ Gaussian error bounds) from these differences for all components. We find that there is always a small non‐zero bias that we ascribe to instrumentation and local crustal field induction effects. The computed confidence intervals are typically twice as large in the north–south direction compared to the east‐west direction and smaller during the solstice months compared to the equinoxes. 相似文献
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George A. Donoso Alireza Malehmir Nelson Pacheco Vitor Araujo Matthew Penney Joao Carvalho Bill Spicer Steve Beach 《Geophysical Prospecting》2020,68(1):44-61
Seismic methods are becoming an established choice for deep mineral exploration after being extensively tested and employed for the past two decades. To investigate whether the early European mineral-exploration datasets had potential for seismic imaging that was overlooked, we recovered a low-fold legacy seismic dataset from the Neves–Corvo mine site in the Iberian Pyrite Belt in southern Portugal. This dataset comprises six 4–6 km long profiles acquired in 1996 for deep targeting. Using today's industry-scale processing algorithms, the world-class, ca. 150 Mt, Lombador massive sulphide and other smaller deposits were better imaged. Additionally, we also reveal a number of shallow but steeply dipping reflections that were absent in the original processing results. This study highlights that legacy seismic data are valuable and should be revisited regularly to take advantage of new processing algorithms and the experiences gained from processing such data in hard-rock environments elsewhere. Remembering that an initial processing job in hard rock should always aim to first obtain an overall image of the subsurface and make reflections visible, and then subsequent goals of the workflow could be set to, for example understanding relative amplitude ratios. The imaging of the known mineralization implies that this survey could likely have been among one of the pioneer studies in the world that demonstrated the capability of directly imaging massive sulphide deposits using the seismic method. 相似文献