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891.
金矿赋存于三叠系中统忙怀组上段第二层(T2m2-2)的蚀变安山岩的地层中,矿体受断层及火山岩双重控制,近矿围岩蚀变主要有硅化、黄(褐)铁矿化、毒砂化、方解石化等.认为该矿区金矿床成因类型为与火山作用、构造作用有关的蚀变岩型金矿床,并总结了矿区的找矿标志,对在该区域寻找该类型的金矿床具有一定的指导意义. 相似文献
892.
Using field data from Agnico-Eagle’s Meliadine gold project located in Nunavut Territory in northern Canada, a coupled DFN–DEM approach was used to evaluate the rock mass mechanical properties at REV. Variability in the structural data gathered on site and the variability associated with the stochastic modeling process have an impact on discrete fracture model (DFN) properties. Through a sensitivity analysis, this paper assesses the influence of a variation in the DFN model input parameters’ values on the rock mass peak properties – uniaxial compressive strength, Young modulus and Poisson ratio. The results not only highlight the possibilities associated with DFN–DEM modeling in characterizing rock mass properties at the engineering scale, they also provide a systematic way to assess the critical structural parameters controlling the rock mass properties. 相似文献
893.
Two analytical solutions are derived to model the heated flow-through experiments for granite fractures in the literature. The first model, which assumes an identical/continuous temperature between the bulk fluid and fracture surfaces, represents an upper bound solution of water temperature in rock fractures. The second model including the empirical parameter of heat transfer coefficient is used to calculate the average heat transfer coefficient based on the available experimental data. The obtained heat transfer coefficients are smaller than that from the thermal boundary layer theory for flat plates, but larger than the previous estimates. A power function is fitted to describe the relation between heat transfer coefficient and flow velocity. Both models show that water temperature increases non-linearly along fracture plane. 相似文献
894.
A numerical model is proposed for the simulation of rock blasting. A bonded particle system is utilized to mimic the behavior of rock. The particles interact at the contact points through normal and shear springs to simulate rock elasticity. To withstand the deviatoric stresses, the particles are glued to each other. If the applied force exceeds the contact strength, local failure occurs and microcracks are developed in the synthetic rock. For simulation of gas flow, the smooth particle hydrodynamic method is implemented. The interaction of gas particles with the rock grains is assumed to follow a perfect plastic collision model in which the initial momentum of the colliding particles is preserved. A detailed examination of the interaction of gas with blast hole is investigated. It is shown that the proposed hybrid model is capable of simulating the induced shock waves in the gas together with wave propagation in the rock material. The model successfully mimics crack propagation in rock. In particular, the crushed zone around the borehole, radial cracks, and surface spalling are all captured successfully. The results of numerical analysis suggest that gas–rock interaction can, in fact, generate a few successive compressive waves in the rock specimen, causing further extension of radial cracks with time as the weaker secondary and tertiary waves interact with the crack tips. 相似文献
895.
The paper provides a comprehensive review on rock joint roughness measurement and quantification procedures. Superiority of fractal based methods over JRC, statistical parameters and statistical functions in quantifying roughness is discussed in the paper. Two of the best fractal based methodologies available in the literature, the modified 2-D divider and variogram methods, are used to quantify natural rock joint roughness in 3-D and 2-D, respectively. The capability of these two methods in accurate quantification of natural rock joint roughness is shown in the paper by applying the procedures to four natural rock joints. A good comparison has been obtained from the values obtained through the two methods. Both these methodologies have two parameters to capture the stationary roughness. The fractal dimension captures the spatial auto correlation of roughness; the other parameter captures the amplitude of roughness. Anisotropic roughness has been studied by applying two other methodologies: (a) a triangular plate methodology and (b) a light source methodology to the same four natural rock joints. A reasonably good comparison has been obtained through the results of these two methodologies. All four roughness quantification methodologies can be applied to any size of sample covering from laboratory to field scales. The results of the triangular plate and light source methodologies provided possible sliding direction values (under the gravitational loading) close to that reported in the literature for the rough discontinuity planes used in the study. 相似文献
896.
Shear failure is a common failure mechanism in underground coal mine roadways. This paper presents an innovative numerical approach to simulate shear failure of a coal mine roadway roof. The distinct element code, UDEC, incorporating a proposed Trigon logic is employed for the study. Using this approach, shear failure in the mine roof characterized by fractured initiation and propagation is successfully captured. The results suggest that shear failure of the roadway roof initiates at the roadway corners and then progressively propagates deeper into the roof, finally forming a large scale roof failure. The numerical results confirmed the time sequence of marked microseismic activity, significant stress changes and accelerated displacement during the process of a roof fall. The effect of rock bolting in the control of roof shear failure in a roadway is evaluated using the UDEC Trigon approach. It is found that the installation of rock bolts constrains rock dilation, reduces failure of rock bridges and maintains rock strength thereby leading to a significant decrease in roof sag. 相似文献
897.
Underground mining and oil and gas drilling have increasingly encroached on public water reservoirs and dams because of the overwhelming demand for energy combined with the growing population. Cases of surface water reservoirs and mine waste impoundments being drained, as well as dam infrastructure being damaged, due to accidents have been documented. The methods used by regulators and industry for determining mining or drilling offset distances are based primarily on three approaches and studies performed in the early 1970s. The former US Bureau of Mines Information Curricular 8741 was the culmination of these studies and continues in use for determining offset distances for underground mining with respect to dams and reservoirs. This study used analytical and empirical methods based on subsidence effects to recommend offset distance extents specifically for miners' safety. A major limitation of the previous studies is that they did not detail the affect mining operations have on changes in groundwater flow due to soil and overburden permeability changes triggered by vertical ground surface subsidence that could lead to increased risk hazards for a reservoir or dam infrastructure. This paper presents a review of international literature related to mining under surface bodies of water (reservoirs) and presents a risk-based event tree analysis quantifying the probability of changes in subsurface permeability due to overburden strain changes. A sensitivity analysis quantifying probabilities of increased subsurface permeability in terms of offset distances from a reservoir is presented and discussed. Empirical results indicate the probability of permeability changes at a 350 ft (107 m) deep mine located at offsets of: 200, 400, and 600 ft (61, 122, and 183 m) were at 41, 0.66, and 0.0067%, respectively. 相似文献
898.
The failure mechanism of a Late Glacial Sturzstrom in the Subalpine Molasse (Leckner Valley, Vorarlberg, Austria) 总被引:2,自引:0,他引:2
A number of prehistoric landslides and rock avalanches occurred in the folded and faulted section of the Molasse Zone in Vorarlberg, Austria. Some developed into a Sturzstrom, defined as a ‘rapidly moving fluidised mass movement of large volumes of rock, derived from the disintegration of a falling rock mass, that spread under the influence of gravity’. Their impact on the landscape usually is related to obstruction of rivers and valleys.In this paper, we analyse the geomorphology and the failure mechanism of a relative small ‘Sturzstrom’. The failure mechanism can be described as a ‘buckling failure’. The morphological situation indicates that failure took place after local deglaciation by the end of the Upper Würm. The period of failure coincides with glacial and ice-marginal remnants, which developed between 15.000 and 14.600 BP. The lithological sequence and rock structure, as well as the impact of the processes related to the former glacial environment, were major causal conditions. The rock sequence consists of conglomerates, sandstone layers, and marls. Next to glacial scouring, which increased the inclination of the valley slopes, the effect of late-glacial unloading and postglacial processes, such as weathering and fluvial erosion, subsequently weakened the mass rock fabric until failure occurred.Discontinuity orientation measurements, geostructural and geomechanical conditions, and the former hydrological and geomorphological conditions support bucklings failure. In fact, three-hinge buckling may have occurred. The frontal section of the Sturzstrom consists mainly of large conglomerate blocks, averaging 1.5 m3 in volume, although megablocks, reaching of up to 4000 m3, are present as well. The volume of the entire Sturzstrom equals approximately 10×107 m3. Present activity is only restricted to minor rock falls derived from the conglomerates and mudflows originating from the marl layers. 相似文献
899.
900.