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51.
Omar Saeed Baghabra Al-Amoudi 《Engineering Geology》1994,36(3-4):279-291
Vast expanses of arid, saline soils that occur along the Arabian Gulf seaboard and elsewhere possess a very low density and strength that necessitate improvement before any actual construction takesplace. For large-scale constructions, several field improvement techniques have recently been implemented with various degrees of success. In surficial, small-scale applications, chemical stabilization provides a potential technique to improve the inferior properties of these soils, known locally as sabkha. A literature search indicates that chemical stabilization of soils usingasphalt, lime and cement is usually conducted at lower moisture contents than the optimum. Such moisture contents are also much lower than the natural moisture content of sabkha, and if applied to sabkha in the field, this wouldrequire lowering the moisture content before any stabilization commenced; whichwould be neither feasible nor economical.
In this investigation, an eastern Saudi sabkha soil was chemically stabilized at its natural moisture level, which varies from 16% to 22%. In addition to the characterization of the soil and standard compaction tests, cement and lime sabkha mixtures were prepared at five additions and cured for up to 90 days in plastic wrap. Results indicate that cement-stabilized sabkha gained high strength with time and proved to have a potential use in construction. 相似文献
52.
The effects of foundation width on model tests for the bearing capacity of sand with geogrid reinforcement 总被引:1,自引:0,他引:1
Summary Laboratory model test results for the ultimate bearing capacity of surface strip foundations on geogrid-reinforced sand and
unreinforced sand are presented. A fine uniform sand and one type of geogrid (Tensar BX1000(SSO)) were used for the tests.
The width of the foundation and the relative density of sand were varied to determine their effects on the bearing capacity
ratio. It was found that the bearing capacity ratio of the sand-geogrid system decreased with an increase in foundation width.
However, above a certain foundation width (130–140 mm) a practically constant value of bearing capacity ratio was observed. 相似文献
53.
Summary The radon and thoron content in atmospheric air at Giza was determined through the period from January (1958 to July 1959) by using the emanometrical technique. The concentration of radon and its decay products was equal to (88±4) 10–18 Curie/c.c. and that of thoron and its decay products was equal to (51±11) 10–18 Curie/c.c. 相似文献
54.
Measurement of PM2.5 emission potential from soil using the UC Davis resuspension test chamber 总被引:2,自引:0,他引:2
Omar F. Carvacho Lowell L. Ashbaugh Michael S. Brown Robert G. Flocchini 《Geomorphology》2004,59(1-4):75
Human health effects have been linked to airborne concentrations of fine particulate matter. One source of fine particulate matter in the atmosphere is resuspended soil dust from a variety of activities, including agricultural operations. We have established a method to measure the potential of soil to emit fugitive dust in the PM10 or PM2.5 size range. The method is repeatable, and provides an index of PM10 or PM2.5 dust that is highly correlated to the soil texture. The ratio of the PM2.5 Index to the PM10 Index produced by this method is similar to field observations of ambient PM2.5 and PM10 concentrations downwind of agricultural operations in the San Joaquin Valley of California. The PM2.5 or PM10 Index will be a more useful parameter to estimate the potential of a soil to emit fugitive dust than the currently used dry silt content of soil. Research is currently underway to relate the PM10 and PM2.5 Index to measured emission factors, accounting for soil moisture and type of agricultural operation, so that a more reliable predictive equation can be developed for agricultural practices. 相似文献
55.
This paper presents results of analysis of full-scale pile load test data of 14 piles embedded in either loose or medium dense
sands. The analysis was performed using two methods, p–y curve approach and a more recently developed khmax approach. Comparison of the results obtained using both the methods is also presented. A step-by-step analysis procedure
is presented for predicting lateral load deflection response of single piles in sand using the khmax approach. The results presented show that the khmax approach has promise over the p–y curve approach because of its simplicity and the fact that it provides upper- and lower-bound curves, which are valuable
guides to making engineering decisions. For loose sands, a new range of khmax values is recommended to better predict the lateral load–deflection response of single piles. 相似文献
56.
57.
Reliability‐based control algorithms for nonlinear hysteretic systems based on enhanced stochastic averaging of energy envelope
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Current reliability‐based control techniques have been successfully applied to linear systems; however, incorporation of stochastic nonlinear behavior of systems in such control designs remains a challenge. This paper presents two reliability‐based control algorithms that minimize failure probabilities of nonlinear hysteretic systems subjected to stochastic excitations. The proposed methods include constrained reliability‐based control (CRC) and unconstrained reliability‐based control (URC) algorithms. Accurate probabilistic estimates of nonlinear system responses to stochastic excitations are derived analytically using enhanced stochastic averaging of energy envelope proposed previously by the authors. Convolving these demand estimates with capacity models yields the reliability of nonlinear systems in the control design process. The CRC design employs the first‐level and second‐level optimizations sequentially where the first‐level optimization solves the Hamilton–Jacobi–Bellman equation and the second‐level optimization searches for optimal objective function parameters to minimize the probability of failure. In the URC design, a single optimization minimizes the probability of failure by directly searching for the optimal control gain. Application of the proposed control algorithms to a building on nonlinear foundation has shown noticeable improvements in system performance under various stochastic excitations. The URC design appears to be the most optimal method as it reduced the probability of slight damage to 8.7%, compared with 11.6% and 19.2% for the case of CRC and a stochastic linear quadratic regulator, respectively. Under the Kobe ground motion, the normalized peak drift displacement with respect to stochastic linear quadratic regulator is reduced to 0.78 and 0.81 for the URC and CRC cases, respectively, at comparable control force levels. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
58.
Correa Oscar García Francisco Bernal Gabriel Cardona Omar Darío Rodriguez Carlos 《Natural Hazards》2020,100(1):345-361
Natural Hazards - A methodology to define rainfall-landslide thresholds, using a probabilistic model in which the accumulated rainfall at any time is treated as a random variable, is proposed. The... 相似文献
59.
Realistic models of solar prominence flux ropes are numerically constructed. The models are in 2.5 dimensions, including the effects of non-isothermal temperature, density and gravity, and pressure. Stability of the equilibria to pressure- and gravity-driven instabilities is numerically investigated, using the ballooning formalism of fusion plasma theory. The equilibrium models can become unstable to pressure- and gravity-driven modes at plasma parameters characteristic of prominences. 相似文献
60.
Mohamad Nor Omar Colin Peter Abbiss Mohd. Raihan Taha Khairul Anuar Mohd. Nayan 《Engineering Geology》2011,(4):259
This paper presents a method of calculating long-term settlement of a loaded pad on soft clay at Klang, Selangor, Malaysia where the soil model is treated as an anelastic material of viscoelastic property. Initially, an elastic shear modulus (G) value from shear wave velocity profiles of the seismic tests from spectral analysis of surface wave (SASW) and continuous surface wave (CSW) tests was obtained. A value of damping (D) at an equivalent elastic strain is then calculated from the hysteresis of the plate load tests corrected to equivalent strain using the Damping–Strain formula. The calculated elastic settlement and its equivalent damping are then used to calculate the long-term settlement by applying the generalised viscoelastic formula. Comparisons to traditional methods of settlement predictions were made and the viscoelastic formula has shown better agreement to the observed settlement. Further modification of the settlement formula is introduced to improve the settlement accuracy to 10%. 相似文献