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71.
The change in strength and deformation behavior of a typical marine clay deposit formed under shallow water is presented and discussed for the conditions of changing water table. This is a costal marine clay deposit with moderate carbonates along the east coast of India. The soil samples were taken from tidal flats where the sea had receded some time back, and the behavior of this deposit had been studied for the conditions of 1976, with high water table, and for the conditions of 2001, with depleted water table. Undisturbed soil samples were taken from sheeted open test pits. Standard consolidation and triaxial shear tests were conducted. Consolidation tests conducted on the samples taken for 1976 conditions with high water contents indicate that cementation effect are erased out under moderate stresses. Beyond this stress range, it behaves like soft, normally consolidated clay. In contrast, the results obtained from samples taken during 2001, with depleted water table, clearly indicate that the soil behaves like an over-consolidated one, and the improvement in the system is due to the chemical bonding and desiccation. 相似文献
72.
Thomas K. Greathouse Matthew Richter Julianne Moses Therese Encrenaz Dan Jaffe 《Icarus》2011,214(2):606-621
Using TEXES, the Texas Echelon cross Echelle Spectrograph, mounted on the Gemini North 8-m telescope we have mapped the spatial variation of H2, CH4, C2H2 and C2H6 thermal-infrared emission of Neptune. These high-spectral-resolution, spatially resolved, thermal-infrared observations of Neptune offer a unique glimpse into the state of Neptune’s stratosphere in October 2007, LS = 275.4° just past Neptune’s southern summer solstice (LS = 270°). We use observations of the S(1) pure rotational line of molecular hydrogen and a portion of the ν4 band of methane to retrieve detailed information on Neptune’s stratospheric vertical and meridional thermal structure. We find global-average temperatures of 163.8 ± 0.8, 155.0 ± 0.9, and 123.8 ± 0.8 K at the 7.0 × 10−3-, 0.12-, and 2.1-mbar levels with no meridional variations within the errors. We then use the inferred temperatures to model the emission of C2H2 and C2H6 in order to derive stratospheric volume mixing ratios (hence forth, VMR) as a function of pressure and latitude. There is a subtle meridional variation of the C2H2 VMR at the 0.5-mbar level with the peak abundance found at −28° latitude, falling off to the north and south. However, the observations are consistent within error to a meridionally constant C2H2 VMR of at 0.5 mbar. We find that the VMR of C2H6 at 1-mbar peaks at the equator and falls by a factor of 1.6 at −70° latitude. However, a meridionally constant VMR of at the 1-mbar level for C2H6 is also statistically consistent with the retrievals. Temperature predictions from a radiative-seasonal climate model of Neptune that assumes the hydrocarbon abundances inferred in this paper are lower than the measured temperatures by 40 K at 7 × 10−3 mbar, 30 K at 0.12 mbar and 25 K at 2.1 mbar. The radiative-seasonal model also predicts meridional temperature variations on the order of 10 K from equator to pole, which are not observed. Assuming higher stratospheric CH4 abundance at the equator relative to the south pole would bring the meridional trends of the inferred temperatures and radiative-seasonal model into closer agreement.We have also retrieved observations of C2H4 emission from Neptune’s stratosphere using TEXES on the NASA Infrared Telescope Facility (IRTF) in June 2003, LS = 266°. Using the observations from the middle of the planet and an average of the middle three latitude temperature profiles from the 2007 observations (9.5° of LS later, the seasonal equivalent of 9.5 Earth days within Earth’s seasonal cycle), we infer a C2H4 VMR of at 1.5 × 10−3 mbar, a value that is 3.25 times that predicted by global-average photochemical models. 相似文献
73.
Undrained strength behaviour of a cemented marine clay under monotonic and cyclic loading 总被引:1,自引:0,他引:1
The paper presents the results of a series of monotonic and cyclic triaxial shear tests carried out to study the influence of the strain effect and load cycles on the undrained shear strength of a cemented marine clay from the East coast of India. The undrained shear strength of Indian coastal marine clay has been established from a detailed shear testing carried out in three phases. Undisturbed soil samples taken out from the seabed were used in the test. In the first part, a comprehensive monotonic shear testing has been carried out under both stress-controlled and strain rate-controlled conditions. In the second phase on identical soil specimen, undrained cyclic shear tests were carried out at various cyclic stress ratios (CSR) and these stress levels are chosen in such a way so that no failure occurred during testing. In the final phase post cyclic monotonic shear testing was conducted to qualitatively evaluate the damage caused by cyclic loading. The monotonic shear test results bring out the influence of cementation that can be detected by the stress-controlled test. The cyclic stress results are analysed in terms of CSR. Further, the results are correlated in terms of stress path. 相似文献
74.
Bahuguna I. M. Nayak Shailesh Tamilarsan V. Moses J. 《Journal of the Indian Society of Remote Sensing》2003,31(2):101-105
Journal of the Indian Society of Remote Sensing - The study aims at investigating the relative role of landforms and lineaments as an integrated unit for the assessment of groundwater availability... 相似文献
75.
Neupert W.M. Newmark J. Delaboudinière J.-P. Thompson B.J. Catura R.C. Moses J.D. Gurman J.B. Portier-Fozzani F. Maucherat A.J. Defise J.M. Jamar C. Rochus P. Dere K.P. Howard R.A. Michels D.J. Freeland S. Lemen J.R. Stern R.A. 《Solar physics》1998,183(2):305-321
Solar EUV images recorded by the EUV Imaging Telescope (EIT) on SOHO have been used to evaluate temperature and density as a function of position in two largescale features in the corona observed in the temperature range of 1.0–2.0 MK. Such observations permit estimates of longitudinal temperature gradients (if present) in the corona and, consequently, estimates of thermal conduction and radiative losses as a function of position in the features. We examine two relatively cool features as recorded in EIT's Feix/x (171 Å) and Fexii (195 Å) bands in a decaying active region. The first is a long-lived loop-like feature with one leg, ending in the active region, much more prominent than one or more distant footpoints assumed to be rooted in regions of weakly enhanced field. The other is a near-radial feature, observed at the West limb, which may be either the base of a very high loop or the base of a helmet streamer. We evaluate energy requirements to support a steady-state energy balance in these features and find in both instances that downward thermal conductive losses (at heights above the transition region) are inadequate to support local radiative losses, which are the predominant loss mechanism. The requirement that a coronal energy deposition rate proportional to the square of the ambient electron density (or pressure) is present in these cool coronal features provides an additional constraint on coronal heating mechanisms. 相似文献
76.
77.
A reversal of the conventional carbon isotope relationship, “terrestrial-lighter-than-marine” organic matter, has been documented for two Pennsylvanian (Desmoinesian) cyclothemic sequence cores from the Midcontinent craton of the central United States. “Deep” water organic-rich phosphatic black shales contain a significant proportion of algal-derived marine organic matter (as indicated by organic petrography, Rock-Eval hydrogen index and
ratios) and display the lightest δ13C-values (max −27.80‰ for kerogen) while shallower water, more oxic facies (e.g. fossiliferous shales and limestones) contain dominantly terrestrial organic matter and have heavier δ13Ckerogen-values (to −22.87‰ for a stratigraphically adjacent coal). δ13C-values for extract fractions were relatively homogeneous for the organic-rich black shales with the lightest fraction (often the aromatics) being only 1‰, or less, more negative than the kerogen. Differences between extract fractions and kerogens were much greater for oxic facies and coals (e.g. saturates nearly 5‰ lighter than the kerogen).A proposed depositional model for the black shales calls upon a large influx of nutrients and humic detritus to the marine environment from the laterally adjacent, extremely widespread Pennsylvanian (peat) swamps which were rapidly submerged by transgression of the epicontinental seas. In this setting marine organisms drew upon a CO2-reservoir which was in a state of disequilibrium with the atmosphere, being affected by isotopically light “recycled-CO2” derived from the decomposition of peaty material in the water column and possibly from the anoxic diagenesis of organic matter in the sediments. 相似文献
78.
Foundations of offshore structures are designed to withstand a combination of static and cyclic loads due to ocean waves. Wave action on offshore structures can cause a significant amount of cyclic horizontal and vertical forces to be transmitted to the soil through the foundation. In all these cases, these cyclic loads are considered to be superimposed over the initial sustained static stress due to the self-weight of structures. This study considers various factors that influence the development of deformation and pore water pressure in a typical cemented marine clay. These results show that the sustained static shear stress significantly influences the strength and deformation behavior of marine clay under cyclic loading. Up to a certain range of sustained static stress, there is an improvement in strength during cyclic loading and the cyclic strains are greatly reduced. 相似文献
79.
The Preflight Photometric Calibration of the Extreme-Ultraviolet Imaging Telescope EIT 总被引:1,自引:0,他引:1
Dere K.P. Moses J.D. Delaboudinière J.-P. Brunaud J. Carabetian C. Hochedez J.-F. Song X.Y. Catura R.C. Clette F. Defise J.-M. 《Solar physics》2000,195(1):13-44
This paper presents the preflight photometric calibration of the Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO). The EIT consists of a Ritchey–Chrétien telescope with multilayer coatings applied to four quadrants of the primary and secondary mirrors, several filters and a backside-thinned CCD detector. The quadrants of the EIT optics were used to observe the Sun in 4 wavelength bands that peak near 171, 195, 284, and 304 Å. Before the launch of SOHO, the EIT mirror reflectivities, the filter transmissivities and the CCD quantum efficiency were measured and these values are described here. The instrumental throughput in terms of an effective area is presented for each of the various mirror quadrant and filter wheel combinations. The response to a coronal plasma as a function of temperature is also determined and the expected count rates are compared to the count rates observed in a coronal hole, the quiet Sun and an active region. 相似文献
80.
S. T. Wu W. P. Guo M. D. Andrews G. E. Brueckner R. A. Howard M. J. Koomen C. M. Korendyke D. J. Michels J. D. Moses D. G. Socker K. P. Dere P. L. Lamy A. Llebaria M. V. Bout R. Schwenn G. M. Simnett D. K. Bedford C. J. Eyles 《Solar physics》1997,175(2):719-735
We present a qualitative and quantitative comparison of a single coronal mass ejection (CME) as observed by LASCO (July 28–29,
1996) with the results of a three-dimensional axisymmetric time-dependent magnetohydrodynamic model of a flux rope interacting
with a helmet streamer. The particular CME considered was selected based on the appearance of a distinct ‘tear-drop’ shape
visible in animations generated from both the data and the model.
The CME event begins with the brightening of a pre-existing coronal streamer which evolves into a ‘tear-drop’ shaped loop
followed by a Y-shaped structure. The brightening moves slowly outward with significant acceleration reaching velocities of
∼450 km s-1 at 30 R⊙.
The observed CME characteristics are compared with the model results. On the basis of this comparison, we suggested that the
observed features were caused by the evacuation of a flux rope in the closed field region of the helmet streamer (i.e., helmet
dome). The flux rope manifests itself as the cavity of the quasi-static helmet streamer and the whole system becomes unstable
when the flux rope reaches a threshold strength. The observed ‘tear-drop’ structure is due to the deformed flux rope. The
leading edge of the flux rope interacts with the helmet dome to form the typical loop-like CME. The trailing edge of this
flux rope interacts with the local bi-polar field to form the observed Y-shaped structure. The model results for the evolution
of the magnetic-field configurations, velocity, and polarization brightness are directly compared with observations.
Animations have been generated from both the actual data and the model to illustrate the good agreement between the observation
and the model. These animations can be found on the CD-ROM which accompanies this volume.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004923016322 相似文献