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241.
A highly diverse assemblage of mammal and other continental vertebrate fossils is reported in recent years from Vastan lignite
mine (21°25′47″ N; 73°07′30″ E). Its importance in testing palaeobiogeographic hypothesis of mammalian dispersal in to or
out of India has necessitated a definite age of the sequence. Nummulites burdigalensis is the only age diagnostic foraminifer in the section. This species is widespread in the Indian sedimentary basins and used
to mark Early Eocene strata. In the present study two subspecies of Nummulites burdigalensis, viz., Nummulites burdigalensis burdigalensis and Nummulites burdigalensis kuepperi, are distinguished which led to further biostratigraphic refinement. Their concurrence in the section implies basal Cuisian
age and shallow benthic zone SBZ 10 (most likely the lower part). The examination of this species from Kutch indicates the
occurrence of evolutionarily advanced subspecies Nummulites burdigalensis cantabricus of middle Cuisian age (SBZ 11). Contrary to some recent reports, the study rules out the occurrence of N. globulus or any other Ilerdian foraminifer from the mine section. 相似文献
242.
Identification of seismic events from continuously recorded seismic data in real-time through a Digital Seismic Data Recording
system is a difficult task. Despite the vast amount of research in this field, the signal processing and event parameters
discrimination algorithms have not yet fully come of age. Presently, we have a wide spectrum of trigger algorithms, ranging
from a very simple amplitude threshold type to the sophisticated ones based on pattern recognition approaches. Some of the
other approaches use adaptive technique and neural network methods. Researchers are continuously making efforts for the development
of algorithms using various techniques, which produce minimum false trigger. Some approaches have been reported which are
accurate for detecting first phase of events and take minimum possible computational time. In this paper several approaches
for detecting event signals in background noise are presented and their precision evaluation is discussed. 相似文献
243.
Shivani Shah B. M. Rao Prashant Kumar P. K. Pal 《Journal of Earth System Science》2010,119(6):775-781
Since the beginning of the summer monsoon 2009, experimental mesoscale weather forecasts in real time are being generated
using WRF model by the Meteorology and Oceanography Group at the Space Applications Centre (ISRO) and are disseminated through
MOSDAC () to various users. To begin with, the 12 h, 24 h and 48 h forecasts for the western India region are made available. A study
is undertaken to comprehensively assess the cloudiness prediction performance of WRF model. The evaluations have been made
over the three months period during monsoon 2009. INSAT cloud imagery data has been used as a reference for these evaluations.
The verification strategy includes computation of various skill scores. It is seen that probability of detection (POD) of
cloud is 84% and the false alarm rate (FAR) is around 18%. It is hoped that this assessment will provide information on the
use of these forecasts in various applications. 相似文献
244.
Distribution of arsenic and mercury in subtropical coastal beachrock,Gulf of Mannar,India 总被引:1,自引:0,他引:1
J Dajkumar Sahayam N Chandrasekar S Krishna Kumar G Victor Rajamanickam 《Journal of Earth System Science》2010,119(1):129-135
An assessment of coastal pollution was made on the basis of trace element concentrations (arsenic — As, mercury — Hg) in the
Gulf of Mannar. The beachrock samples were collected along the coastal tracts between Rameswaram and Kanyakumari. The samples
were dried and digested to determine the As and Hg using atomic absorption spectrophotometer (AAS-air-acetylene and nitrous
oxide method). The As and Hg accumulation status of the beachrock was assessed using geo-accumulation index values (I
geo). The accumulation of As and Hg in the beachrock ranges from 2.75 to 20.72 μg g−1 and from 0.06 to 0.31 μg g−1, respectively. The As and Hg concentrations in the beachrocks are compared with crustal average values and average of other
region sediments. The possible source of the contamination is from atmospheric deposition and anthropogenic activities. 相似文献
245.
Variations in long term wind speed during different decades in Arabian Sea and Bay of Bengal 总被引:1,自引:0,他引:1
A study has been carried out by comparing the extreme wind speeds estimated based on NCEP/NCAR reanalysis data for 100 years
return period using Fischer Tippet-1 (commonly known as Gumbel) and Weibull distributions for three locations (off Goa, Visakhapatnam
and Machilipatnam) in the north Indian Ocean. The wind dataset for Goa is compared with that from ERA-40 data. For higher
wind speeds (12–20m s−1), NCEP wind speed has higher percentage of occurrence than that of ERA-40. Analysis has shown slight upward trend in the
annual maximum wind for location off Machilipatnam with an increase of 1.2 cm s−1 per year and a decreasing trend of −1.3 cm s−1 per year in the case of Goa. The Weibull distribution with shape parameter 2 fits the annual maximum wind data better than
FT-1 distribution. 相似文献
246.
R. T. Ratheesh Kumar Tanmay K. Maji Rajesh R. Nair 《Journal of Earth System Science》2010,119(5):717-730
Indian Ocean subduction zone is one of the most active plate margins of the globe as evident from its vast record of great
magnitude earthquake and tsunami events. We use Bouguer admittance (Morlet isostatic response function) in Sumatra-Java subduction
zones comprising both the subduction and over-riding plates to determine the lithospheric mechanical strength variations.
We determine effective elastic thickness (T
e
) for five oceanic windows (size 990 × 990 km2) by analyzing the admittance using Bouguer gravity and bathymetry data. The results show bimodal T
e
values < 20 km for Sumatra and 20−40 km for Java. The lower bimodal values obtained for Sumatra appears to correlate well
with the zones of historical seismicity. This is in sharp contrast with Java subduction zone, which shows higher T
e
values (20–40 km) and apparently associated with low magnitude earthquakes. We suggest a strong and wide interseismic coupling
for Sumatra between the subducting and over-riding plates, and deeper mantle contributing to low strength, shallow focus —
high magnitude seismicity and vice versa for Java, leading to their seismogenic zonation. 相似文献
247.
Extreme climate and weather events are increasingly being recognized as key aspects of climate change. Pre-monsoon season
(March–May) is the hottest part of the year over almost the entire South Asian region, in which hot weather extremes including
heat waves are recurring natural hazards having serious societal impacts, particularly on human health. In the present paper,
recent trends in extreme temperature events for the pre-monsoon season have been studied using daily data on maximum and minimum
temperatures over a well-distributed network of 121 stations for the period 1970–2005. For this purpose, time series of extreme
temperature events have been constructed for India as a whole and seven homogeneous regions, viz., Western Himalaya (WH),
Northwest (NW), Northeast (NE), North Central (NC), East coast (EC), West coast (WC) and Interior Peninsula (IP). 相似文献
248.
This paper presents the computation of time series of the 22 July 2007 M 4.9 Kharsali earthquake. It occurred close to the Main Central Thrust (MCT) where seismic gap exists. The main shock and
17 aftershocks were located by closely spaced eleven seismograph stations in a network that involved VSAT based real-time
seismic monitoring. The largest aftershock of M 3.5 and other aftershocks occurred within a small volume of 4 × 4 km horizontal extent and between depths of 10 and 14 km.
The values of seismic moment (M
∘) determined using P-wave spectra and Brune’s model based on f
2 spectral shape ranges from 1018 to 1023 dyne-cm. The initial aftershocks occurred at greater depth compared to the later aftershocks. The time series of ground motion
have been computed for recording sites using geometric ray theory and Green’s function approach. The method for computing
time series consists in integrating the far-field contributions of Green’s function for a number of distributed point source.
The generated waveforms have been compared with the observed ones. It has been inferred that the Kharsali earthquake occurred
due to a northerly dipping low angle thrust fault at a depth of 14 km taking strike N279°E, dip 14° and rake 117°. There are
two regions on the fault surface which have larger slip amplitudes (asperities) and the rupture which has been considered
as circular in nature initiated from the asperity at a greater depth shifting gradually upwards. The two asperities cover
only 10% of the total area of the causative fault plane. However, detailed seismic imaging of these two asperities can be
corroborated with structural heterogeneities associated with causative fault to understand how seismogenesis is influenced
by strong or weak structural barriers in the region. 相似文献
249.
In the middle of 2007, a severe flood affected the People’s Republic of Bangladesh. This is a natural disaster that takes
people’s lives, destroys livestock, infrastructures and communication systems and, damages crops and fish ponds. Despite many
adverse impacts, the flood situation is an accepted phenomenon to the citizens of Bangladesh, due to the immense increase
of soil fertility due to the flood, plus, the recharge of aquifer, ecosystem and fish. The flood of 2007 was the 5th major
flood of the last 20 years when more than thirty-five percent of the area of the country was inundated with flood water. As
in the past, the flood of 2007 had its own significance. The geography of the country contains a floodplain delta of three
major river basins: the Ganges, the Brahmaputra and the Meghna (GBM). The mean monthly rainfall plot from the TRMM satellite
data has shown that for both the Meghna and Brahmaputra basins, the rainfall was higher during July 2007 than any other months
of the last 2 years. This excess rainfall had accumulated in the Brahmaputra and Meghna rivers and carried downstream to Bangladesh.
This was the main cause of the flooding in 2007. The first crossing above the danger level of the river waters was observed
at Durgapur station of the Someswari and at Sunamganj station of the Surma on the nineteenth of July, 2007 inside Bangladesh.
In terms of magnitude of the peak and duration of the flood, the Brahmaputra was higher in 2007 than during 2004. However,
the Ganges river water level never crossed the danger level during flood of 2007. The Meghna was lower during the flood peak
for the duration of the flood in 2007. The year–to-year variability in both the magnitude and duration of the flood suggests
changes in rainfall and landuse pattern of the catchment. 相似文献
250.
Jagadish Prasad Sahoo Pradip Kumar Pradhan 《Geotechnical and Geological Engineering》2010,28(6):889-897
An experimental investigation was undertaken to study the effects of lime-stabilized soil-cushion on the strength behavior
of expansive soil. In the present investigation, a series of laboratory tests (Unconfined compression tests and CBR tests)
were conducted on both expansive soil alone and expansive soil cushioned with lime-stabilized non-expansive cohesive soil.
Lime contents of 2, 4, 6, 8 and 10% by dry weight of cohesive non-swelling soil was used in the stabilized soil cushion. Both
expansive soil and lime stabilized soil cushion were compacted to Standard Proctor’s optimum condition with thickness ratio
2:1. Tests on cushioned expansive soils were conducted at different curing and soaking periods i.e., 7, 14, 28 and 56 days.
The test results revealed that maximum increase in strength was achieved after 14 days of curing or soaking period with 8%
of lime content. 相似文献