全文获取类型
收费全文 | 777篇 |
免费 | 22篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 71篇 |
大气科学 | 44篇 |
地球物理 | 110篇 |
地质学 | 310篇 |
海洋学 | 23篇 |
天文学 | 219篇 |
综合类 | 5篇 |
自然地理 | 23篇 |
出版年
2022年 | 7篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 50篇 |
2017年 | 41篇 |
2016年 | 56篇 |
2015年 | 24篇 |
2014年 | 44篇 |
2013年 | 39篇 |
2012年 | 37篇 |
2011年 | 30篇 |
2010年 | 33篇 |
2009年 | 40篇 |
2008年 | 30篇 |
2007年 | 24篇 |
2006年 | 21篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 14篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有805条查询结果,搜索用时 15 毫秒
801.
The Ajanta caves are situated in Deccan Trap basalt and declared as one of the World Heritage Sites by UNESCO. The present study aims to investigate and understand the damage of caves and to protect the life of the visitors from the rockfall phenomenon at and around the caves. Information related to the detached rock mass/block was acquired by using Barton–Bandis model in Universal Distinct Element Code. Parameters for rockfall simulation were determined by rigorous field study and laboratory experiment and then calibrated some of the parameters by back analysis. RocFall 4.0 program has been used to calculate maximum bounce heights, total kinetic energies, and translational velocities of the falling blocks of different weights. The maximum bounce height varies from 14.0 to 19.0 m for the weight of the block size ranging from 500 to 2,000 kg, whereas the maximum velocity and maximum kinetic energy are 30.0 m/s and 917.66 kJ, respectively. Finally, the results of simulation have been used to find out the position of the barrier and its capacity to design the protection barrier. The barrier capacity was found to be 325 kJ for 2,000 kg of falling blocks at a height of 50.0 m. 相似文献
802.
MCT Zone of Alakhnanda valley is a major ductile shear zone in Garhwal Himalaya, which is characterised by different types
of mylonite rocks. On the basis of grain size and the percentage of matrix in the rock, zones comprising protomylonite, augen
mylonite, mylonite and ultramylonite have been identified. The study of microstructures, grain size and crystallographic preferred
orientation of quartz c-axis fabric reveals that the rocks of the MCT zone were deformed by a combination of intracrystalline creep (power law creep)
and grain boundary migration (sliding super plasticity). 相似文献
803.
One dimensional numerical model has been developed to predict the production of space charge and variations in other electrical
parameters within the low level stratiform type of cloud having very weak vertical motion. Non-linear coupled differential
equations which govern ion concentrations, charged and neutral droplet concentrations and electric field were used. Symmetry
has been observed in all the electrical parameters within the cloud. The magnitude of average positive ion concentrations
was observed to be high as compared to the negative ion concentrations, which is due to low scavenging rate of positive ions
than the negative ions, highly attributed to their mobilities. The rate of scavenging of ions affects the concentration of
charged droplets, which eventually influence the electric field and thus the space charge density within the cloud. Maximum
electric field (E
max) was observed at middle of the cloud whereas minimum was observed at both the edges of the cloud. Minimum electric field
(E
min) was found to be equal and constant (∼27 Vm−1) for any drop concentration. Net positive and negative space charges were observed at the top and bottom of the cloud, respectively.
The simulated results show some discrepancies to the natural condition, which are due to simulations made under some basic
assumptions and limitations and that will be incorporated in the future studies for natural cloud condition. 相似文献
804.
In this study, an attempt has been made to estimate land surface temperatures (LST) and spectral emissivities over a hard
rock terrain using multi-sensor satellite data. The study area, of about 6000 km2, is a part of Singhbhum-Orissa craton situated in the eastern part of India. TIR data from ASTER, MODIS and Landsat ETM+
have been used in the present study. Telatemp Model AG-42D Portable Infrared Thermometer was used for ground measurements
to validate the results derived from satellite (MODIS/ASTER) data. LSTs derived using Landsat ETM+ data of two different dates
have been compared with the satellite data (ASTER and MODIS) of those two dates. Various techniques, viz., temperature and
emissivity separation (TES) algorithm, gray body adjustment approach in TES algorithm, Split-Window algorithms and Single
Channel algorithm along with NDVI based emissivity approach have been used. LSTs derived from bands 31 and 32 of MODIS data
using Split-Window algorithms with higher viewing angle (50°) (LST1 and LST2) are found to have closer agreement with ground
temperature measurements (ground LST) over waterbody, Dalma forest and Simlipal forest, than that derived from ASTER data
(TES with AST 13). However, over agriculture land, there is some uncertainty and difference between the measured and the estimated
LSTs for both validation dates for all the derived LSTs. LST obtained using Single Channel algorithm with NDVI based emissivity
method in channel 13 of ASTER data has yielded closer agreement with ground measurements recorded over vegetation and mixed
lands of low spectral contrast. LST results obtained with TIR band 6 of Landsat ETM+ using Single Channel algorithm show close
agreement over Dalma forest, Simlipal forest and waterbody with LSTs obtained using MODIS and ASTER data for a different date.
Comparison of LSTs shows good agreement with ground measurements in thermally homogeneous area. However, results in agriculture
area with less homogeneity show difference of LST up to 2°C. The results of the present study indicate that continuous monitoring
of LST and emissivity can be undertaken with the aid of multi-sensor satellite data over a thermally homogeneous region. 相似文献
805.
The Pichavaram mangrove ecosystem is located between the Vellar and Coleroon Estuaries in south-eastern India. To document the spatial-depth-based variabilities in organic matter (OM) input and cycling, five sediment cores were collected. A comparative study was carried out of grain-size composition, pore water salinity, dissolved organic C (DOC), loss-on-ignition (LOI), elemental ratios (C/N and H/C), pigments (Chl a, Chl b, and total carotenoids), and humification indices. Sand is the major fraction in these cores ranging from 60% to 99% followed by silt and clay; cores from the estuarine margin have high sand content. In mangrove forests, pore-water DOC concentrations are high (32 ± 14 mg L−1), whereas salinity levels are low (50 ± 5.5‰). Likewise, LOI, organic C and N, and pigment concentrations are high in mangroves. OM is mainly derived from upstream terrestrial matter and/or mangrove litter, and marine OM. The humification indices do not vary significantly with depth because of rapid OM turnover. The bulk parameters indicate that the Vellar and Coleroon Estuaries are more affected by anthropogenic processes than mangrove forests. Finally, greater variability and sometimes lack of specific trends in bulk parameters implies that the 2004 tsunami caused extensive mixing in sediments. 相似文献