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251.
William S. Burgett Michael M. Vick David S. Davis Matthew Colless Roberto De Propris Ivan Baldry Carlton Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Warrick Couch Nicholas Cross Gavin Dalton Simon Driver George Efstathiou Richard Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Will Percival Bruce Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,352(2):605-654
252.
253.
Ian Winterflood 《Geology Today》2001,17(4):143-148
In his famous address to the Geological Society of America in 1957, H. H. Read concluded that 'there are granites and granites'. This is equally true for ophiolites, slices of oceanic lithosphere produced by sea-floor spreading and preserved by obduction during plate collision. Although they form in similar ways, it is clear that there are different types of ophiolite which originate under different conditions. Compared to the 'classic' ophiolites of Oman, many, such as those in the Alps, lack a sheeted dyke complex and were for a long time considered abnormal. Analogues for this type have now been found forming today and they occur when the rate of spreading is slow. 相似文献
254.
Ian Shennan Sarah Bradley Glenn Milne Anthony Brooks Sophie Bassett Sarah Hamilton 《第四纪科学杂志》2006,21(6):585-599
While contributing <1 m equivalent eustatic sea‐level rise the British Isles ice sheet produced glacio‐isostatic rebound in northern Britain of similar magnitude to eustatic sea‐level change, or global meltwater influx, over the last 18 000 years. The resulting spatially variable relative sea‐level changes combine with observations from far‐field locations to produce a rigorous test for quantitative models of glacial isostatic adjustment, local ice‐sheet history and global meltwater influx. After a review of the attributes of relative sea‐level observations significant for constraining large‐scale models of the isostatic adjustment process we summarise long records of relative sea‐level change from the British Isles and far‐field locations. We give an overview of different global theoretical models of the isostatic adjustment process before presenting intercomparisons of observed and predicted relative sea levels at sites in the British Isles and far‐field for a range of Earth and ice model parameters in order to demonstrate model sensitivity and the resolving power available from using evidence from the British Isles. For the first time we show a good degree of fit between relative sea‐level observations and predictions that are based upon global Earth and ice model parameters, independently derived from analysis of far‐field data, with a terrain‐corrected model of the British Isles ice sheet that includes extensive glaciation of the North Sea and western continental shelf, that does not assume isostatic equilibrium at the Last Glacial Maximum and keeps to trimline constraints of ice surface elevation. We do not attempt to identify a unique solution for the model lithosphere thickness parameter or the local‐scale detail of the ice model in order to provide a fit for all sites, but argue that the next stage should be to incorporate an ice‐sheet model that is based on quantitative, glaciological model simulations. We hope that this paper will stimulate this debate and help to integrate research in glacial geomorphology, glaciology, sea‐level change, Earth rheology and quantitative modelling. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
255.
Emily A. McMillan Ian J. Fairchild Silvia Frisia Andrea Borsato Frank McDermott 《第四纪科学杂志》2005,20(5):423-433
Each of two calcitic stalagmites from Grotte de Clamouse, Herault, southern France, displays a discrete aragonite layer dated at around 1100 yr BP. The layer of fanning aragonite ray crystals is immediately preceded by calcite with Mg and Sr compositions that are uniquely high for the past 3 kyr. Trace element compositions close to the boundary between original aragonite and calcite are consistent with quasi‐equilibrium partitioning of trace elements between the phases. Study of modern dripwaters demonstrates that pronounced covariation of Mg/Ca and Sr/Ca ratios in dripwater occurs owing to large amounts of calcite precipitation upflow of the drips that fed the stalagmites. Trace element to Ca ratios are enhanced during seasonally dry periods. Ion microprobe data demonstrate a pronounced covariation of trace elements, including Mg and Sr in calcite, and Sr, U and Ba in aragonite. The mean peak spacing is close to the long‐term mean of annual growth rates determined by differences in U‐series ages and so the trace element peaks are interpreted as annual. The trace element chemistry of the stalagmites on annual to inter‐annual scales thus directly reflects the amounts of prior calcite precipitation, interpreted as an index of aridity. The longer‐term context is a multi‐decadal period of aridity (1200–1100 yr BP) possibly correlated with an analogous episode in Central America. The arid period culminated in the nucleation of aragonite, but within a decade was followed by a return to precursor conditions. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
256.
David B. Henley Ian R. Stevens Julian M. Pittard 《Monthly notices of the Royal Astronomical Society》2005,356(4):1308-1326
We present a new analysis of an archived Chandra HETGS X-ray spectrum of the WR+O colliding wind binary γ2 Velorum. The spectrum is dominated by emission lines from astrophysically abundant elements: Ne, Mg, Si, S and Fe. From a combination of broad-band spectral analysis and an analysis of line flux ratios we infer a wide range of temperatures in the X-ray-emitting plasma (∼4–40 MK). As in the previously published analysis, we find the X-ray emission lines are essentially unshifted, with a mean FWHM of 1240 ± 30 km s−1 . Calculations of line profiles based on hydrodynamical simulations of the wind–wind collision predict lines that are blueshifted by a few hundred km s−1 . The lack of any observed shift in the lines may be evidence of a large shock-cone opening half-angle (>85°), and we suggest this may be evidence of sudden radiative braking. From the R and G ratios measured from He-like forbidden-intercombination-resonance triplets we find evidence that the Mg xi emission originates from hotter gas closer to the O star than the Si xiii emission, which suggests that non-equilibrium ionization may be present. 相似文献
257.
A meteoritic event was observed from the vicinity of Prince George, British Columbia, at 5h 58m U.T., August 21, 1969, and an associated ground impact wave was recorded by several seismograph stations. An analysis of the visual and seismic data indicates that a mass of several tons must have reached the ground about 20 km southeast of Prince George. A helicopter search of the area and a study of aerial photographs have failed to locate the impact site 相似文献
258.
Ian M. Smith 《国际地质力学数值与分析法杂志》1979,3(2):205-211
Recently, instability of slender piles during installation has been analysed as a non-conservative buckling process. For these results to be of potential use in practice, simple procedures are necessary whereby piles of arbitrary cross-section installed in ground with arbitrarily varying properties can be treated. This paper lists discrete element matrices which enable the prediction of the onset of instability in piles assuming conservative or non-conservative ground resistance. The same matrices can then be used to incorporate effects of incipient instability in driveability analyses. 相似文献
259.
Conventional methods of analyzing sonic log data do not always yield accurate information on each velocity segment of a well. It is shown here that the velocity-depth parameters and the sections of approximately constant velocity may be more precisely defined by using an exponential spline to model the data. 相似文献
260.
From a determination of the transformation matrix for three pyrolysis product experimental data sets, an examination is given of both the applicability of the laboratory experimental data to the modeling of oil cracking in a sedimentary basin, and of the appropriateness of an inverse model. The results of the laboratory experimental data sets, which were done under different thermodynamic conditions and using different sources, show that the transformation matrix varies over each data set and also with time. Therefore, it is necessary to check the data sets before applying them to a basin for hydrocarbon modeling. The laboratory experimental data taken at lower temperature and over longer times appear more pertinent for the construction of an oil-cracking kinetic model suitable for geologic conditions. 相似文献