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851.
The process of upwelling/sinking and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. Further,precipitation and monsoonal floods, apart from the marine meteorological parameters, are expected to influence the sea level fluctuations along the coast. This study comprises determining the sea level from the various parameters together with the pure wind stress forcing, which is compared with the observed cycle. However, it is found that there is considerable difference between the computations and observations. This suggests that the sea level is dependent not just on the local forcing alone, but also on the induced background circulation as well. For example, the sea level changes along the east coast of India, particularly the northern region, are more sensitive to freshwater discharge from various rivers joining the Bay of Bengal. This is due to more frequently occurring pre- and postmonsoon cyclonic storms and the associated surges in the Bay of Bengal as compared to the Arabian Sea. Hence the salinity effects are particularly important in the coastal waters off the east coast of India during monsoon months (June-September). For the west coast of India, however, it is expected that the large-scale coastal circulation may play a role in determining sea level changes in addition to other forcings. The salinity effects are negligible along the west coast in the absence of any major river systems that join the Arabian Sea. The local advection currents caused by the offshore directed freshwater discharge from various estuaries joining the coastal bay also seemed to influence the sea level. In order to elucidate the essential dynamics involved and to study the effect of the remote forcing, a three-dimensional baroclinic, nonlinear numerical model is used with appropriate open boundary conditions. The local effect of the current has been incorporated in the west coast model by means of opening a channel at Cochin through which the rainwater is carried away to the model ocean. The low saline plume, cascading from north along the east cost of India, has been incorporated in the east coast model through a proper forcing applied at the northern boundary of the model. With the inclusion of these remote forcings in the models, the disagreement between the simulations and the observations is minimized. 相似文献
852.
Abstract In the field of ocean engineering, anchors are used for several purposes. This article studies the behavior of a helical anchor embedded in soft marine clay under vertical repetitive loading. Helical anchors are simple steel shafts to which one or more helical plates are attached at regular intervals. The tests are conducted on a model helical anchor installed in a soft marine clay bed prepared in a test tank. Repetitive loading is applied using a pneumatic loading arrangement. Different cyclic load ratios and time periods are adopted. In each test, after the application of repetitive loading, poststatic‐pullout tests are conducted to observe the effect of repetitive loading on anchor behavior. From the test results, it is found that, up to a cyclic load ratio of 55%, there is no reduction in capacity. Instead, there seems to be a marginal increase in capacity and reduction in displacement. The reasons for this behavior are explained in terms of induced changes in strength and deformation behavior of marine clay under repetitive load. However, at higher cyclic load ratios, there seems to be reduction in pullout capacity of the anchor, and the reason for this is explained in terms of strain criteria. From this investigation, it can be concluded that the deep anchor is more suitable to a marine environment than a shallow anchor. 相似文献
853.
854.
Uplifted crust in parts of western India 总被引:1,自引:0,他引:1
H. C. Tewari G. Surya Prakasa Rao B. Rajendra Prasad 《Journal of the Geological Society of India》2009,73(4):479-488
During northward movement of the Indian sub-continent, after its breakup from the Gondwanaland in the Late Cretaceous, the
western part of India traversed over the Reunion plume. The Saurashtra peninsula and the Cambay Basin are two important geological
regions in this part. Two and half dimensional density models, based on the crustal seismic structure, were generated to establish
a relationship between these two regions. These models indicate that the crust is 32–33 km thick in the eastern Saurashtra
and the northern part of the Cambay Basin. The shallower crust is in a triangular region formed by the extension of the western
limb of the Proterozoic Aravalli trend in Saurashtra, its eastern limb and the Narmada fault in the south. Compared to 36–37
km thick crust to the west and 38–40 km to the east of this region the crust in the above triangular region is uplifted by
4 to 6 km. This uplift took place either after the deposition of Mesozoic sediments or was concomitant with the rise of Reunion
plume prior to the extrusion of the Deccan volcanics as the region was close to the axis of the plume. 相似文献
855.
Track prediction of very severe cyclone ‘Nargis’ using high resolution weather research forecasting (WRF) model 总被引:1,自引:0,他引:1
The recent very severe cyclonic storm (VSCS) ‘Nargis’ over the Bay of Bengal caused widespread destruction over Myanmar after
hitting the coast on 2 May 2008. The real time forecasting of the VSCS ‘Nargis’ was a very difficult task as it did not follow
the normal westerly/northwesterly track. In the present study, a detailed diagnostic analysis of the system ‘Nargis’ is carried
out initially to investigate the features associated with this unusual movement and subsequently the real time forecast of
VSCS ‘Nargis’ using high resolution advanced version weather research forecasting (WRF) model is presented. The advanced research
WRF model was run for 72 h at 27 km and 20 km resolutions with 28, 29, 30 April and 1 May as the initial conditions. The diagnostic
study indicates that the recurvature of the system ‘Nargis’ was mainly associated with:
The real time track forecast using the WRF model run at 27 km and 20 km resolution based on the initial conditions of 28 April
(when the system was only 550 km away from the Indian coast) indicated that the system had a northeasterly forecast track
and was not expected to cross the Indian coast. Similarly, based on 29 April initial condition the system showed east/east-northeasterly
movement towards the Myanmar coast. The east/east-northeasterly movement of the ‘Nargis’ was persisting in the forecast based
on 30 April and 1 May initial conditions with respective landfall errors of 85 km and 50 km with 27 km resolution, which reduces
to 30 km and 40 km respectively with 20 km resolution, however, with a landfall time delay of about 10 h. Improvement of mean
forecast errors at different forecast hours is noticed in WRF model run at higher resolution compared to that run at lower
resolution. Thus, it is very clear that the advanced version WRF model had captured movement of the system reasonably well
almost 3 days in advance. Consistence with the diagnostic analysis the WRF model forecast also indicates southerly/southwesterly
strong steering wind at 200 hPa level and maximum pressure fall to the east of the system. 相似文献
• | upper level southerly/southwesterly steering wind at 200 hPa level associated with anticyclonic circulation over southeastern sector of the centre of the system |
• | higher SST (29°C or more) with higher positive anomalies over the region to the northeast of the cyclone centre, and |
• | large negative 24 h pressure changes and large vorticity maximum to the east of the system. |
856.
George Mathew Archana Nair T. K. Gundu Rao Kanchan Pande 《Journal of Earth System Science》2009,118(4):391-404
Thermal infrared spectroscopy is a powerful technique for the compositional analysis of geological materials. The spectral
feature in the mid-IR region is diagnostic of the mineralogy and spectral signatures of mixtures of minerals that add linearly,
and therefore, can be used as an important tool to determine the mineralogy of rocks in the laboratory and remotely for planetary
exploration. The greatest challenge in the emission measurement lies in the measurement of the weak thermal photons emitted
from geological materials in a laboratory setup, and accurately records the temperature of the rock sample. The present work
pertains to the details of a new Thermal Emission Spectrometer (TES) laboratory that has been developed under the ISRO Planetary
Science and Exploration (PLANEX) programme, for emission related mineralogical investigations of planetary surfaces. The focus
of the paper is on the acquisition and calibration technique for obtaining emissivity, and the deconvolution procedure to
obtain the modal abundances of the thermal emission spectra in the range of 6–25 μm using Fourier Transform Infrared (FTIR)
spectroscopy. The basic technique is adopted from the work of Ruff et al (1997). This laboratory at the Department of Earth Sciences, IIT-Bombay is currently developing pure end mineral library
of mineral particulates (<65 μm), and adding new end members to the existing ASU spectral library. The paper argues the need
for considering Lunar Orbiter Thermal Emission Spectrometer (LOTES) for future Indian Moon mission programme (Chandrayan-II)
to determine evidences of varied lithologies on the lunar surface. 相似文献
857.
858.
Natural radioactivity measurements in beach sand along southern coast of Orissa,eastern India 总被引:1,自引:1,他引:0
The beach placer deposits in the southern coastal Orissa, India may have significant levels of radiation due to the presence
of Th and U bearing minerals such as monazite and zircon. In this study, Gopalpur and Rushikulya beach regions were selected
to study the ambient radiation environment. The average activity concentrations of radioactive elements such as 232Th, 238U and 40K of beach sand samples were measured by γ-ray spectrometry using a HPGe detector, and found to be much higher than the internationally
accepted values. The cross plots of eTh/eU and eTh/K inferred that the sand samples of Gopalpur and Rushikulya beach placer
deposit were deposited in leached uranium and an oxidising environment. The absorbed γ dose rate levels of the study areas
are similar to other monazite sand-bearing HBRAs of southern and southwestern coastal regions of India and of world. Different
radiation hazard indices were estimated for the present study area and were found to be much higher than the internationally
accepted values. Hence, Gopalpur and Rushikulya beach placer region can be considered as a high background radiation area
and a potential zone for radiogenic heavy mineral exploration. 相似文献
859.
Transfer of moisture through the unsaturated zone in the tropical forest using the neutron probe 总被引:1,自引:1,他引:0
A. T. Fouépé M.Sc. L. Kengni Ph.D. V. V. S. Gurunadha Rao Ph.D. J. R. Ndam Ph.D. 《International Journal of Environmental Science and Technology》2009,6(3):379-388
Knowledge of moisture content is crucial in assessing spatial and temporal movement of water through the unsaturated zone. Moisture storage is also important for monitoring the soil water balance and for validation of water balance models. The purpose of this work was to determine and analyse moisture content profiles at point locations in the unsaturated zone of a lateritic soil around Nsimi, south of Cameroon. Neutron probe has been connected to a set of tensiometers in an area of 60 ha. A comparative study between a site covered with vegetation and a site uncovered was conducted to assess the influence of vegetation in the process of moisture transfers. The results showed that the spatial distribution of moisture profiles varied according to the site and the texture of the soil, with in general increasing of moisture from the surface horizon toward the deeper layers. The mean values of moisture varied fromθm = 0,397 cm3/cm3 on barren site, against 0 = 0,429 cm3/cm3 in vegetation. Values of suction were generally strong in surface and at depth, but weak in the intermediate layers. 相似文献
860.
Xiaoxu Sun Jiansheng Chen Hongbing Tan Wenbo Rao Yongsen Wang Xiaoyan Liu Zhiguo Su 《中国地球化学学报》2009,28(4):351-357
In this study, with the method of vacuum extraction, two evaporative processes of soil water and free water under equilibrium
condition were simulated. For each sample, water vapor was condensed by liquid nitrogen and was collected in four time intervals.
From the analysis of hydrogen and oxygen isotopic compositions of the water collected at different times, it was discovered
that the isotope fractionation of soil water also follows the mode, which is just the same as the evaporative process of free
water. The relationship between the stable hydrogen and oxygen isotopes in residual water showed that the simulative evaporation
line was close to the global meteoric water line (GMWL) under the equilibrium condition at about 20°C. Comparison of the two
types of evaporative processes indicated that the isotope fractionation and evaporation velocity of soil water were only slightly
modified by the Van der Waals force. 相似文献