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991.
Back analysis of an excavated slope failure in highly fractured rock mass: the case study of Kargar slope failure (Iran) 总被引:2,自引:1,他引:1
Mostafa Sharifzadeh Mohsen Sharifi S. Mohammad Delbari 《Environmental Earth Sciences》2010,60(1):183-192
This paper examines the failure of Kargar cut slope located at the south part of Esfahan subway using analytical and numerical
back analysis methods. The excavated trench has 27 m depth with near vertical walls due to the space limitation around it.
The geology of the area comprises weathered and heavily jointed shale and sandstone overlaid by alluvium deposits. Despite
the slope being supported by shotcrete and fully grouted rock bolts, a catastrophic failure occurred at the east wall. Due
to the uncertainty about the causes of failure initiation, back analyses have been performed via both the limit equilibrium
and numerical method for considering various probable mechanisms. In the back analysis with limit equilibrium method, the
rock mass is assumed as an equivalent continuum and Hoek–Brown failure criterion and geological strength index (GSI) are applied
to calculate the shear strength parameters. The results show that GSI value was 33 in the failed mass. In the numerical back
analysis, the distinct element method is applied to study the contribution of rock joints to the failure and progressive rock
mass strength degradation until failure. The results show that threshold values of joint cohesion and friction were 0.2 MPa
and 30°, respectively. Also the modeled slip surface being step-shaped agrees with the observed one. 相似文献
992.
Organochlorinated compounds in Caspian Sea sediments 总被引:2,自引:0,他引:2
de Mora S Villeneuve JP Sheikholeslami MR Cattini C Tolosa I 《Marine pollution bulletin》2004,48(1-2):30-43
Several organochlorinated contaminants, including numerous pesticides, were determined in coastal sediments from the Caspian Sea. The most important contaminants were p,p'-DDT (up to 7400 pg g(-1)) and its breakdown products, p,p'-DDD (up to 3400 pg g(-1)) and p,p'-DDE (up to 1300 pg g(-1)). Although the contamination was most severe in Azerbaijan, the sediment concentrations and percentage distribution of the three DDT-related compounds indicated that such contamination constitutes a contemporary and ubiquitous problem in the Caspian Sea. Lindane represented the second most significant contaminant, particularly in the Russian Federation, with concentrations up to 609 pg g(-1). The concentrations of HCB and other chlorinated pesticides (cis- and trans-chlordane, methoxychlor, heptachlor, heptachlor epoxide, aldrin, endrin, and endosulfans) were lower and not generally of concern, but the pesticides did demonstrate markedly different distributions reflecting differing agricultural usage in the region. The concentrations of Sigma PCBs were also quite low and ranged from 0.03 to 6.4 ng g(-1), with the highest amounts in the Russian Federation and Azerbaijan. 相似文献
993.
Contamination by organochlorine compounds in sturgeons from Caspian Sea during 2001 and 2002 总被引:2,自引:0,他引:2
Kajiwara N Ueno D Monirith I Tanabe S Pourkazemi M Aubrey DG 《Marine pollution bulletin》2003,46(6):741-747
Organochlorine compounds (OCs) were determined in the five species of sturgeons collected from coastal waters of Caspian Sea in Kazakhstan, Azerbaijan, Turkmenistan and Iran during 2001 and 2002 to understand their status of contamination and accumulation features. Among OCs examined, concentrations of DDTs (DDT and its metabolites) were predominant in all the sturgeon samples with concentrations ranging from 73 to 31,000 ng/g on lipid weight basis, followed by PCBs, CHLs, HCHs, HCB, dieldrin, TCPMOH, and heptachlor epoxide in order. The concentrations of OCs in beluga (Huso huso) were the highest among all the five species. When comparing residue levels among same species, OC residues were highest in sturgeons from Azerbaijan and Kazakhstan and lowest in Turkmenistan. However, the concentrations of HCHs, dieldrin, and heptachlor epoxide in sturgeons showed less geographical variability. 相似文献
994.
Hossein Jalalifar Naj Aziz Muhammad Hadi 《Geotechnical and Geological Engineering》2006,24(5):1203-1227
Fully encapsulated rock bolting has, in recent years, become a universally accepted system of ground reinforcement in mining
and tunnel construction. The application of bolting systems extends both to rebar as well as cable bolting. The effectiveness
of the bolt application has been studied in shear, both by laboratory tests as well as by numerical modeling. A specially
constructed double shearing apparatus (DSA) was used to examine the shearing behaviour of a bolt installed perpendicularly
across two joints. The experimental study was complemented with three-dimensional numerical analysis. Parameters examined
include, the effect of reinforced material on tension/compression zones along the sheared bolt, shear resistance, shear displacement
and induced strains and stresses during bolt bending process. The study was undertaken at both free load and pretension conditions.
The conclusions drawn from the study were the level of bolt resistance to shear was influenced by bolt profile configuration,
the strength of the rock or medium influenced the level of load generated on the bolt and the increased bolt pretension contributed
to increased shearing load of the bolted medium. The numerical simulation of the bolt/medium interaction and deformational
behaviour were found to be in close agreement with the experimental test results. 相似文献
995.
Rock joint modeling using a visco-plastic multilaminate model at constant normal load condition 总被引:2,自引:0,他引:2
Reza Mahin Roosta Mohammad Hossein Sadaghiani Ali Pak Yaser Saleh 《Geotechnical and Geological Engineering》2006,24(5):1449-1468
Rock joints play an important role in the behavior of rock masses under normal and shear loading conditions. Numerical simulation
of the behavior of jointed rock masses is not an easy task due to complexities involved in the problem such as joint roughness,
joint shear strength, hardening and softening phenomenon and mesh dependency. In this study for modeling purposes, a visco-plastic
multilaminate model considering hardening and softening effects has been employed. For providing the necessary data for numerical
simulation, a series of laboratory experiments have been carried out on regular tooth-shape asperities made by gypsum, under
constant normal load conditions. Shear stress–shear displacement and normal displacement–shear displacement of artificial
joint specimens are simulated using the proposed numerical model at constant normal load condition (CNL). The results indicate
the capability of the model for simulating rock joints behavior in both strength and deformation field. Although the numerical
model has been developed for simulating the behavior of artificial joints, the concept of the method can also be used for
natural rock joints. 相似文献
996.
997.
Mohammad Al-Harahsheh Sam Kingman Frank Rutten David Briggs 《International Journal of Mineral Processing》2006,80(2-4):205-214
Chalcopyrite is known to be slow reacting mineral in hydrometallurgical systems and is considered one of the most inert sulphide minerals with respect to leaching. Such character of chalcopyrite seems to be linked to a formation of a passive layer on its surface. This work reports that freshly fractured chalcopyrite surfaces exhibit highly selective reactivity depending on the exposed fracture planes. ToF-SIMS was used to qualitatively characterize various fracture planes in freshly fractured chalcopyrite particles, prior to and after hydrometallurgical treatment. It was found that, prior to treatment, certain areas exhibited pronounced contamination from atmospheric hydrocarbons; whereas, others were highly unreactive and remarkably free from adventitious hydrocarbon contamination. The positive ion spectra recorded from these areas were found to be dominated by peaks from Fe- and Cu-elements and related compounds. The negative ion spectra for the reactive areas on the other hand showed a high content of oxidized (sulphur) species.The differences between the areas of low and high reactivity, as detected after leaching, were more subtle than prior to leaching; whereas, SEM analysis showed clear evidence for selective attack of ferric sulphate to specific planes. Furthermore, it was shown that, when chalcopyrite is in intimate contact with pyrite, it experiences an enhanced oxidation compared to when there is no electric contact with pyrite.Attempts were made to explain the preferential oxidation observed based on the different chemistry of the fracture surfaces. 相似文献
998.
Ralph Bridle Nikolai Barsoukov Mohammad Al-Homaili Robert Ley Ameerah Al-Mustafa 《Geophysical Prospecting》2006,54(6):667-680
We present a seismic Test Line, provided by Saudi Aramco for various research teams, to highlight a few major challenges in land data processing due to near‐surface anomalies. We discuss state‐of‐the‐art methods used to compensate for shallow distortions, including single‐layer, multilayer, plus/minus, refraction and tomostatics methods. They are a starting point for the new technologies presented in other papers, all dealing with the same challenging data described here. The difficulties on the Test Line are mostly due to the assumption of vertical raypaths, inherent in classical applications of near‐surface correction statics. Even the most detailed velocity/depth model presents difficulties, due to the compleX‐raypath. There is a need for methods which are based on more complex models andtheories. 相似文献
999.
The archaeological site of Qasr Tilah, in the Wadi Araba, Jordan is located on the northern Wadi Araba fault segment of the Dead Sea Transform. The site contains a Roman-period fort, a late Byzantine–Early Umayyad birkeh (water reservoir) and aqueduct, and agricultural fields. The birkeh and aqueduct are left-laterally offset by coseismic slip across the northern Wadi Araba fault. Using paleoseismic and archaeological evidence collected from a trench excavated across the fault zone, we identified evidence for four ground-rupturing earthquakes. Radiocarbon dating from key stratigraphic horizons and relative dating using potsherds constrains the dates of the four earthquakes from the sixth to the nineteenth centuries. Individual earthquakes were dated to the seventh, ninth and eleventh centuries. The fault strand that slipped during the most recent event (MRE) extends to just below the modern ground surface and juxtaposes alluvial-fan sediments that lack in datable material with the modern ground surface, thus preventing us from dating the MRE except to constrain the event to post-eleventh century. These data suggest that the historical earthquakes of 634 or 659/660, 873, 1068, and 1546 probably ruptured this fault segment. 相似文献
1000.
Uncertainty analysis of statistical downscaling methods using Canadian Global Climate Model predictors 总被引:1,自引:0,他引:1
Three downscaling models, namely the Statistical Down‐Scaling Model (SDSM), the Long Ashton Research Station Weather Generator (LARS‐WG) model and an artificial neural network (ANN) model, have been compared in terms of various uncertainty attributes exhibited in their downscaled results of daily precipitation, daily maximum and minimum temperature. The uncertainty attributes are described by the model errors and the 95% confidence intervals in the estimates of means and variances of downscaled data. The significance of those errors has been examined by suitable statistical tests at the 95% confidence level. The 95% confidence intervals in the estimates of means and variances of downscaled data have been estimated using the bootstrapping method and compared with the observed data. The study has been carried out using 40 years of observed and downscaled daily precipitation data and daily maximum and minimum temperature data, starting from 1961 to 2000. In all the downscaling experiments, the simulated predictors of the Canadian Global Climate Model (CGCM1) have been used. The uncertainty assessment results indicate that, in daily precipitation downscaling, the LARS‐WG model errors are significant at the 95% confidence level only in a very few months, the SDSM errors are significant in some months, and the ANN model errors are significant in almost all months of the year. In downscaling daily maximum and minimum temperature, the performance of all three models is similar in terms of model errors evaluation at the 95% confidence level. But, according to the evaluation of variability and uncertainty in the estimates of means and variances of downscaled precipitation and temperature, the performances of the LARS‐WG model and the SDSM are almost similar, whereas the ANN model performance is found to be poor in that consideration. Further assessment of those models, in terms of skewness and average dry‐spell length comparison between observed and downscaled daily precipitation, indicates that the downscaled daily precipitation skewness and average dry‐spell lengths of the LARS‐WG model and the SDSM are closer to the observed data, whereas the ANN model downscaled precipitation underestimated those statistics in all months. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献