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821.
Occurrence of native gold in ultramafic rocks is rather rare. Such occurrences serve as snapshots of the underlying processes leading to their formation and modifications thereafter. Presence of native gold as flakes were earlier reported from the chromites of rock massifs of Kraka, southern Urals, Russia (Kovalev et al. 2007). Gold spherules also occur as tiny inclusions (5–30 μm) in olivine, pyrrohotite and magnetite grains from the ultrabasic rocks of Loveld deposit, South Africa (Rozhkov, 1967). Here we report, probably for the first time, occurrence of native gold from the chromitites of the Mesoarchaean Tagadur Mines of the Nuggihalli Schist Belt (NSB), Dharwar Craton, south India. Geological Survey of India (2006) has already reported significant gold content from the bulk ultramafic rocks of Kempinakote area far south of the current study area. A short discussion on the preliminary petrographic features of the gold grains and its significance is presented. 相似文献
822.
N. V. Chalapathi Rao Bernd Lehmann B. K. Panwar Alok Kumar Datta Mainkar 《Journal of the Geological Society of India》2013,82(6):595-600
We report the occurrence of garnierite (a general term referring to Ni-Mg bearing hydrous silicates in laterites) from the crater-facies Tokapal kimberlite of the Bastar craton, Central India. Garnierite occurs as discrete ovoid or amoeboid segregations (up to 200 mm) or as veinlets with up to 18.1 wt% NiO and high iron contents (up to 36.2 wt% FeOT). Chemical composition of the garnierite implies its derivation from a magnesium-rich protolith. Extensive lateritisation of the large crater-facies (~2.5 km diameter) saucer-shaped kimberlite under tropical weathering conditions, aided by suitable topography, drainage and favourable structural set-up, are the factors inferred to be responsible for the formation of garnierite in the Tokapal system. As lateritic nickel ores constitute significant resources for nickel exploration, the perspective of the Tokapal kimberlite as a nickel prospect needs to be investigated. 相似文献
823.
S. Viswanathan K. Surya Prakash Rao B. Mahabaleswar 《Journal of the Geological Society of India》2013,82(6):621-627
Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours. 相似文献
824.
B. K. Rastogi Santosh Kumar Sandeep K. Aggrawal Kapil Mohan Nagabhushan Rao N. Purnachandra Rao Girish Ch. Kothyari 《Natural Hazards》2013,65(2):1197-1216
The Talala (Sasangir) area in the Saurashtra region of Gujarat, western India, is experiencing tremors since 2001. The swarm type of earthquake activity in 2001, 2004, and every year from 2007 onward has occurred after the monsoon and lasted 2?C3?months each time. In 2007 some 200 shocks (largest Mw 5.0) and in 2011 about 400 shocks down to M1 are well recorded with 1?C2?km location error. The focal depths are about 2?C10?km and shocks are accompanied by blast-like subterranean sounds. The epicenter (21.09?N 70.45E, focal depth: 5?km from location program, 3?km from MTS) of the October 20, 2011 mainshock occurred about 12-km WNW of Talala town or 8-km SSW of the 2007?M w 5.0 earthquake epicenter. The epicentral trends deciphered from local earthquake data indicate two ENE trends (Narmada trend) for about 50?km length and a conjugate 15-km-long NNW trend (Aravali trend). The focal mechanisms by moment-tensor analysis of full wave forms of two 2007 events of Mw 4.8 and 5.0 and the 2011 event of Mw 5.1 indicate rupture along either of the two trends. The ENE trends follow a gravity low between the gravity highs of Girnar mounts. Seismic reflections also indicate a fault in the area named Girnar Fault. Most of Saurashtra region including the Talala area is covered by Deccan Trap Basalt forming plateaus and conical ridges. There is no major fault within Saurashtra Peninsula though it is believed to have major faults along the boundaries that are non-seismic. The intensity of the October 20, 2011 Talala earthquake is estimated to be 6.5 in MM scale while isoseismals of 6, 5, and 4 and felt distance give Mw 5.1 based on Johnston??s 1994 empirical regressions. The source parameters of the 2011 Talala earthquake are estimated using data from 14 broadband seismograph stations. Estimated seismic moment, moment magnitude, stress drop, corner frequency, and source radius are found to be 1016.6 N-m, 5.1, 1.6?MPa, 1.3?Hz, and 2,300?m, respectively. The b and p values are obtained to be low, being 0.67 and 0.71, respectively. PGA of 35?cm/sec2 is noted and the decay rate of acceleration has been estimated from strong motion data recorded at 5 stations with epicentral distances ranging from 32 to 200?km. 相似文献
825.
B. K. Rastogi Sandeep Kumar Aggrawal Nagabhushan Rao Pallabee Choudhury 《Natural Hazards》2013,65(2):1085-1107
Paper describes triggered seismicity to 200?km distance and for a decade due to the 2001 M w7.7 Bhuj earthquake. The Kachchh region is seismically one of the most active intraplate regions of the World due to the occurrence of two large earthquakes 1819 (M w7.8) and 2001 (M w7.7). Though, it has high hazard but was known to have low seismicity in view of the occurrence of fewer smaller shocks. However, the status seems to have changed after 2001. Besides the strong aftershock activity for over a decade, seismicity has spread to nearby faults in Kachchh peninsula and at several places southward for 200?km distance in Saurashtra peninsula. Beyond the rupture zone of the 2001 Bhuj earthquake, more than 40 mainshocks of M w?~?3?C5 have occurred at 20 different locations, which is unusual. The increased seismicity is inferred to be caused by stress perturbation due to the 2001 Bhuj earthquake by viscoelastic process. In Saurashtra, over and above the viscoelastic stress increase, the transient stress increase by water table rise in monsoons seems to be affecting the timing of mainshocks and associated sequences of earthquakes. 相似文献
826.
Sudhakar M. Rao T. Thyagaraj P. Raghuveer Rao 《Geotechnical and Geological Engineering》2013,31(4):1399-1404
Compacted expansive clays swell due to crystalline swelling and osmotic/double layer swelling mechanisms. Crystalline swelling is driven by adsorption of water molecules at clay particle surfaces that occurs at inter-layer separations of 10–22 Å. Diffuse double layer swelling occurs at inter-layer separations >22 Å. The tendency of compacted clay to develop osmotic or double layer swelling reduces with increase in solute concentration in bulk solution. This study examines the consequence of increase in solute concentration in bulk solution on the relative magnitudes of the two swelling modes. The objective is achieved by inundating compacted expansive clay specimens with distilled water and sodium chloride solutions in free-swell oedometer tests and comparing the experimental swell with predictions from Van’t Hoff equation. The results of the study indicate that swell potential of compacted expansive clay specimens wetted with relatively saline (0.4, 1 and 4 M sodium chloride) solutions are satisfied by crystalline swelling alone. Comparatively, compacted clay specimens inundated with less saline solutions (0.005–0.1 M sodium chloride) require both crystalline and osmotic swelling to satiate the swell potential. 相似文献
827.
Assessment of trace element contamination in soils around Chinnaeru River Basin, Nalgonda District, India 总被引:1,自引:1,他引:0
G. Machender Ratnakar Dhakate G. Tamma Rao G. Loukya M. N. Reddy 《Environmental Earth Sciences》2013,70(3):1021-1037
Concentrations of trace elements such as As, Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, V, Y, Zn and Zr were studied in soils to understand metal contamination due to agriculture and geogenic activities in Chinnaeru River Basin, Nalgonda District, India. This area is affected by the geogenic fluoride contamination. The contamination of the soils was assessed on the basis of geoaccumulation index, enrichment factor (EF), contamination factor and degree of contamination. Forty-four soil samples were collected from the agricultural field from the study area from top 10–50 cm layer of soil. Soil samples were analyzed for trace elements using X-ray fluorescence spectrometer. Data revealed that soils in the study area are significantly contaminated, showing high level of toxic elements than normal distribution. The ranges of concentration of Ba (370–1,710 mg/kg), Cr (8.7–543 mg/kg), Cu (7.7–96.6 mg/kg), Ni (5.4–168 mg/kg), Rb (29.6–223 mg/kg), Sr (134–438 mg/kg), Zr (141.2–8,232 mg/kg) and Zn (29–478 mg/kg). The concentration of other elements was similar to the levels in the earth’s crust or pointed to metal depletion in the soil (EF < 1). The high EFs for some trace elements obtained in soil samples show that there is a considerable heavy metal pollution, which could be due to excessive use of fertilizers and pesticides used for agricultural or may be due to natural geogenic processes in the area. Comparative study has been made with other soil-polluted heavy metal areas and its mobility in soil and groundwater has been discussed. A contamination site poses significant environmental hazards for terrestrial and aquatic ecosystems. They are important sources of pollution and may result in ecotoxicological effects on terrestrial, groundwater and aquatic ecosystems. 相似文献
828.
Assessment of groundwater inflows into Kuteshwar Limestone Mines through flow modeling study, Madhya Pradesh, India 总被引:1,自引:0,他引:1
The development of limestone mining activities in Katni, Madhya Pradesh becomes necessary to increase the depth of exploration to produce ore. Increase in the exploration depth means that mining pits were subjected to water inrush. A hydrological and a hydrogeological model for the Katni area have been developed using USGS flow code, MODFLOW 2000. Collected GIS-based information was synthesized in a finite difference numerical model. The regional steady flow was calibrated under pre-development conditions assuming an equivalent porous medium approach. Water budget calculations show that the total groundwater flow into the aquifer system due to interaction with river amounts to 14,783 m3/day. Infiltration from precipitation provides 1,600 m3/day of the groundwater supply, while 1,446 m3/day comes from lateral inflow and the remaining. The inflows into mine pit area amounts to 15,725 m3/day. Although the karstic nature of the limestone aquifer the equivalent porous medium flow model is appropriate to represent hydraulic heads and recharge/discharge relationships on a regional scale. The results of this study can be used to predict the required amounts of pumping and the possible locations to dewater the groundwater in the mining pits. 相似文献
829.
We have investigated the effects of Compton broadening due to electron scattering in an expanding stellar atmospheres. The line transfer equation is solved by including the second approximation of Edmonds (Astrophys. J. 119:58, 1954) which is due to Compton broadening and obtained the line profiles in (1) plane parallel (PP) (2) spherical (SS) atmospheres. The effect on spectral line formation is studied for different parameters like (a) optical depths (b) densities (c) frequencies (d) temperatures (e) thickness of the atmosphere and (f) expanding velocities. Various combination of the above parameters are used in computing the line profiles observed at infinity. Line profiles are compared for the above said parameters. It is noticed that the expansion of the gases in the atmosphere produces P-Cygni type profiles and at higher optical depths the line profiles change from emission to absorption with their line centers shifting to blue side in the expanding atmospheres. 相似文献
830.
A sensitivity analysis of the parameterizations of vertical mixing and radiative fluxes on the seasonal evolution of Lake Erie's thermal structure is performed using the Massachusetts Institute of Technology general circulation model (MITgcm) and the General Estuarine Transport Model (GETM). The models have the same horizontal resolution and are forced with observed meteorological data from April to October of 2002 and 2008. For turbid waters like Lake Erie, the three-band model for the parameterization of downward shortwave radiation produces more accurate temperatures in the thermocline and less error in simulating the mixed-layer depths than the widely used two-band model. Although the two models differ in vertical and horizontal mixing, numerical methods, and vertical discretization, they produced qualitatively comparable results. Comparison with observations shows that the models can reproduce the time evolution of the lake temperature reasonably well. The MITgcm and the GETM with the Mellor-Yamada level 2.5 (MY2.5) closure produce a deeper mixed layer than observed at a station located in the eastern basin, causing large errors in simulating the temperature in the thermocline while the GETM, using a turbulence scheme called “gen,” reproduces a mixed layer in better agreement with observations. The mixed-layer obtained with the k-ε closure is between those obtained with gen and MY2.5. The error in simulating the mixed-layer depths and the thermocline temperature at a station located in the central basin using the gen closure and the GETM was about 2°C lower than that obtained by the K-Profile Parameterization mixing scheme of the MITgcm. The models simulated a lake-wide anticyclonic circulation occupying the southwest part of the central basin but showed distinct differences in simulating gyres in the northwestern part of the central basin and in the eastern basin of the lake. The signature of a basin-scale Poincaré wave observed in the current data is also well represented by the two models. 相似文献