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841.
842.
A testing program was initiated to determine the stress-strain and strength behavior of two very different marine sands (a calcareous sediment from South Australia and a siliceous sediment from the United Kingdom) at elevated confining pressures. The testing matrix consisted of a series of isotropically consolidated, undrained (CIU) and drained (CID), triaxial compression tests on samples of naturally deposited calcareous and siliceous sediment and remolded calcareous sediment. It was found that the calcareous samples displayed little cemented behavior during shear. For tests conducted at pressures up to 1.5 MPa, a significant amount of particle crushing occurred in the calcareous samples but not in the siliceous samples. Particle degradation and reorientation facilitates transitions from dilative to contractive behavior with increases in confining stress. The calcareous sediment exhibited contractive behavior at confining pressures above approximately 500 kPa and the siliceous sediment remained dilative at stresses up to 1 MPa during undrained loading. Comparison with data collected by the University of Sydney (CID tests with confining pressures up to 60 MPa) showed that most of the variations in strength behavior occurred within the low stress range (up to 2 MPa) tests conducted at URI. This was evident in the friction angle data and in the reloading Young's modulus data. 相似文献
843.
844.
Erich F. Abel 《Marine Ecology》1993,14(4):291-312
Abstract. The blennies of the Mediterranean Sea were observed in nature by snorkeling and SCUBA diving. Particular attention was paid to their changeable basic patterns and colouring alternations as effected by ecological and ethological factors. Additionally, the tendency for colour change was tested in differently coloured tanks. These experiments failed to demonstrate the striking adaptations seen in the natural environment, except for a remarkable reaction to black and white. The summary of all known reports is supported by colour illustrations; the problems of the colouring alternations are discussed. 相似文献
845.
846.
This paper deals with the efficacy of creating artificial carbonate sand from crushed chalk to model the natural carbonate
sand. Direct drained shear using 100 mm shear box and compressibility tests using 150 mm Rowe cell have been performed on
artificial carbonate sand in order to determine the shear stress-strain and compressibility characteristics of the artificial
material. These are compared with data from natural carbonate sands given in the literature. The results obtained demonstrate
that shear stress-strain and compressibility characteristics of the artificial material closely mirror that of natural carbonate
soils. The artificial carbonate sand shows generally similar characteristics, which are in the range of the natural carbonate
material. 相似文献
847.
For 5 months before the 2001 Mt. Etna eruption, a progressive gravity decrease was measured along a profile of stations on
the southern slope of the volcano. Between January and July 2001, the amplitude of the change reached 80 μGal, while the wavelength
of the anomaly was of the order of 15 km. Elevation changes observed through GPS measurements during a period encompassing
the 5-month gravity decrease, remained within 4–6 cm over the entire volcano and within 2–4 cm in the zone covered by the
microgravity profile. We review both gravity and elevation changes by a model assuming the formation of new cracks, uniformly
distributed in a rectangular prism. The inversion problem was formulated following a global optimization approach based on
the use of Genetic Algorithms. Although it is possible to explain the observed gravity changes by means of the proposed analytical
formulation, the results show that calculated elevation changes are significantly higher than those observed. Two alternative
hypotheses are proposed to account for this apparent discrepancy: (1) that the assumptions behind the analytical formulation,
used to invert the data, are fallacious at Etna, and thus, numerical models should be utilized; (2) that a second process,
enabling a considerable mass decrease to occur without deformation, acted together with the formation of new cracks in the
source volume. 相似文献
848.
Comparison of historical and of post-seismic triangulation data is used to model vertical crustal movements in the vicinity of the Kapareli Fault (or the Alkynonides earthquakes North Fault), one of the two antithetic normal faults which reactivated during the 1981, Gulf of Corinth (Ms = 6.7) earthquakes. This fault is characterized by a much smaller geomorphological signature than the South (or Perachora) fault of the same seismic sequence. Analysis of geodetic data on the basis of polynomial filtering and elastic dislocation modelling, as well as analysis of structural and coastal change data permits us to conclude that the upper bound in the uncertainty level of most of the available elevation changes is 20–30 cm, usually lower than the corresponding dislocation signal. In addition, the available geodetic data have a systematic pattern and are consistent with structural data. For this reason they permit more precise constraints on the geometry and the role of the Kapareli Fault (or the Alkyonides earthquakes North Fault): its total length is estimated about 17 km, about 50% longer than its surface trace; about 30–40 cm subsidence of its hanging wall, as well as at least 15 cm maximum uplift of its footwall is also inferred. This new evidence suggests that although in the long-term the Kapareli fault may represent a rather secondary, antithetic fault to the Alkyonides earthquakes South (Perachora) fault, during the 1981 earthquakes it probably had a more important structural role. 相似文献
849.
850.
It is well known that axial force – bending moment interaction (N–M interaction) affects to a large extent the cyclic inelastic behaviour of structural elements, especially columns in framed structures, with reduction in bending capacity and loss of available ductility. A few studies have also shown that significant inelastic axial shortening affects the response of column elements subjected to medium–high levels of axial loads and cyclic bending. This paper is primarily aimed at evaluating the effects of column N–M interaction on the inelastic seismic response of steel frames. By considering the contemporaneous action of vertical loads, due to gravity, and of horizontal seismic excitation, it is shown that the progressive axial shortening of adjacent columns may differ substantially, thus inducing significant relative settlements at the ends of the connecting beams and, then, remarkable amplifications in beam plastic rotations. An evaluation of additional beam plastic rotations induced by column N–M interaction is carried out for real structures by investigating the inelastic response of steel frames designed according to European standards under horizontal and vertical earthquake excitations. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献