全文获取类型
收费全文 | 24451篇 |
免费 | 171篇 |
国内免费 | 919篇 |
专业分类
测绘学 | 1410篇 |
大气科学 | 1977篇 |
地球物理 | 4502篇 |
地质学 | 11629篇 |
海洋学 | 1004篇 |
天文学 | 1631篇 |
综合类 | 2161篇 |
自然地理 | 1227篇 |
出版年
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 4762篇 |
2017年 | 4037篇 |
2016年 | 2578篇 |
2015年 | 235篇 |
2014年 | 86篇 |
2013年 | 28篇 |
2012年 | 990篇 |
2011年 | 2732篇 |
2010年 | 2017篇 |
2009年 | 2311篇 |
2008年 | 1893篇 |
2007年 | 2363篇 |
2006年 | 55篇 |
2005年 | 195篇 |
2004年 | 402篇 |
2003年 | 410篇 |
2002年 | 250篇 |
2001年 | 50篇 |
2000年 | 55篇 |
1999年 | 17篇 |
1998年 | 21篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1976年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Manish P. Kale Shirish A. Ravan P. S. Roy Sarnam Singh 《Journal of the Indian Society of Remote Sensing》2009,37(3):457-471
Satellite remote sensing is a proven tool for mapping landuse patterns and estimating vegetation biomass/carbon. Present study
aims at estimating the potential of forests of Radhanagari WLS (Western Ghats, India) to sequester the atmospheric carbon-di-oxide,
using ground based observations coupled with satellite remote sensing. The study area was stratified for dominant forest types
based on the structure and composition of vegetation and elevation variations. Permanent sample plots were laid down in these
homogeneous vegetation strata (HVS) to make different observations during time 1 and time 2. Carbon sequestration by plantations
was also studied and compared with natural forests. Species and area-specific biomass equations were used for estimating carbon
pool and sequestration. Among natural forests ‘mixed moist deciduous’ forests exhibited highest sequestration rate (8%), whereas,
plantation as obvious had a comparatively higher sequestration rate than natural forests (20.27%). Total carbon sequestration
by forests of the Radhanagari WLS between 2004 and 2006 is 78742.09 tons. Eligible land for reforestation activity under clean
development mechanism (CDM) of Kyoto Protocol was identified using satellite remote sensing using 1989 and 2005 datasets and
it was observed that the potential land that can be used for reforestation activity is 10080 ha. 相似文献
182.
Georges Balmino 《Journal of Geodesy》2009,83(10):989-995
We have applied efficient methods for computing variances and covariances of functions of a global gravity field model expanded
in spherical harmonics, using the full variance–covariance matrix of the coefficients. Examples are given with recent models
derived from GRACE (up to degree and order 150), and with simulated GOCE derived solutions (up to degree and order 200). 相似文献
183.
Lars E. Sjöberg 《Journal of Geodesy》2009,83(10):967-972
The topographic bias is defined as the error/bias committed by continuing the external gravity field inside the topographic
masses by a harmonic function. We study the topographic bias given by a digital terrain model defined by a spherical template,
and we show that the topographic bias is given only by the potential of an inner-zone cap, and it equals the bias of the Bouguer
shell, independent of the size of the cap. Then we study the effect on the real Earth by decomposing its topography into a
template, and we show also in this case that the topographic bias is that of the Bouguer shell, independent of the shape of
the terrain. Finally, we show that the topographic potential of the terrain at the geoid can be determined to any precision
by a Taylor expansion outside the Earth’s surface. The last statement is demonstrated by a Taylor expansion to fourth order. 相似文献
184.
Long term shoreline oscillation and changes of Cauvery delta coastline inferred from satellite imageries 总被引:2,自引:0,他引:2
R. Sathyanarayan Sridhar K. Elangovan P. K. Suresh 《Journal of the Indian Society of Remote Sensing》2009,37(1):79-88
Coastal zone is highly volatile ecosystem which is always in adjustments. Loss of shore line will cause severe impact on human
life and as well as their properties. Remote sensing is a reliable technique to study the historical shoreline changes. Therefore
in this paper long term shoreline oscillations of Cauvery delta shorelines at Poompuhar, Tharangambadi and Nagapattinam were
studied using satellite imageries and the same was physically observed at the above three locations with the help of reference
pillars and compared mutually. It was observed that the shoreline at Poompuhar is under accretion at the rate of 1.79m/ year
and other shoreline stretches at Tharangambadi and Nagapattinam were under erosion at 0.4888m/ year and 0.4985m/ year respectively.
It was also observed that the remote sensing study qualitatively matches with the physical observation for all the three coastal
stretches of the study area. 相似文献
185.
Many regions around the world require improved gravimetric data bases to support very accurate geoid modeling for the modernization
of height systems using GPS. We present a simple yet effective method to assess gravity data requirements, particularly the
necessary resolution, for a desired precision in geoid computation. The approach is based on simulating high-resolution gravimetry
using a topography-correlated model that is adjusted to be consistent with an existing network of gravity data. Analysis of
these adjusted, simulated data through Stokes’s integral indicates where existing gravity data must be supplemented by new
surveys in order to achieve an acceptable level of omission error in the geoid undulation. The simulated model can equally
be used to analyze commission error, as well as model error and data inconsistencies to a limited extent. The proposed method
is applied to South Korea and shows clearly where existing gravity data are too scarce for precise geoid computation. 相似文献
186.
Nidhi Nagabhatla R. Wickramasuriya S. N. Prasad 《Journal of the Indian Society of Remote Sensing》2009,37(3):443-455
The present study investigates the potential of readily available and easily accessible global data sets to understand regional/local
level interactions in wetland systems. The biogeographical zones of India were used a base-frame to select three sites. The
study well fits the interests of National Wetland Committee of India to investigate and document fundamental information on
wetland extent/distribution. The national partnership with SACON represents this interest. SACON commenced the inland wetland
inventory module at national scale using geospatial data, although the provincial scale analysis is underway. In addition,
the global irrigated area mapping (GIAM-IWMI) project generated multi-scalar spatial outputs for irrigated/rain-fed areas.
With the existing information base, a multi-level geospatial analysis using Arc GIS algorithmic modelling was used to derive
comprehensive appraisal of wetland systems complementing the data from GIAM and SACON. It was observed that the overlap between
the two layers was 58 percent for Gujarat and 10 percent in Tamil Nadu. In Krishna basin the wetland’s cover 1.04 million
hectare excluding the rice agro-ecosystem. The difference in the biogeography of the case sites governs the gradient of information
derived from both data layers. Additionally, the global lakes and wetlands database (GLWD) database added thematic information
on coastal wetlands. In summary we describe the cross-scaling the global data layers to compliment the regional/national level
monitoring assignments. 相似文献
187.
Assessment of groundwater potential zones using GIS technique 总被引:1,自引:0,他引:1
A case study was conducted to find out the groundwater potential zones in Kattakulathur block, Tamil Nadu, India with an aerial
extent of 360.60 km2. The thematic maps such as geology, geomorphology, soil hydrological group, land use / land cover and drainage map were prepared
for the study area. The Digital Elevation Model (DEM) has been generated from the 10 m interval contour lines (which is derived
from SOI, Toposheet 1:25000 scale) and obtained the slope (%) of the study area. The groundwater potential zones were obtained
by overlaying all the thematic maps in terms of weighted overlay methods using the spatial analysis tool in ArcGIS 9.2. During
weighted overlay analysis, the ranking has been given for each individual parameter of each thematic map and weights were
assigned according to the influence such as soil −25%, geomorphology − 25%, land use/land cover −25%, slope − 15%, lineament
− 5% and drainage / streams − 5% and find out the potential zones in terms of good, moderate and poor zones with the area
of 49.70 km2, 261.61 km2 and 46.04 km2 respectively. The potential zone wise study area was overlaid with village boundary map and the village wise groundwater
potential zones with three categories such as good, moderate and poor zones were obtained. This GIS based output result was
validated by conducting field survey by randomly selecting wells in different villages using GPS instruments. The coordinates
of each well location were obtained by GPS and plotted in the GIS platform and it was clearly shown that the well coordinates
were exactly seated with the classified zones. 相似文献
188.
Reshu Agarwal Rakesh Gupta J. K. Garg 《Journal of the Indian Society of Remote Sensing》2009,37(3):473-481
A three-step hierarchical Semi Automated Empirical Methane Emission Model (SEMEM) has been used to estimate methane emission
from wetlands and waterlogged areas in India using Moderate Resolution Imagine Spectroradiometer (MODIS) sensor data onboard
Terra satellite. Wetland Surface Temperature (WST), methane emission fluxes and wetland extent have been incorporated as parameters
in order to model the methane emission. Analysis of monthly MODIS data covering the whole of India from November 2004 to April
2006 was carried out and monthly methane emissions have been estimated. Interpolation techniques were adopted to fill the
data gaps due to cloudy conditions during the monsoon period. AutoRegressive Integrated Moving Average (ARIMA) model has been
fitted to estimate the emitted methane for the months of May 2006 to August 2006 using SPSS software. 相似文献
189.
190.
Ben K. H. Soon Steve Scheding Hyung-Kuen Lee Hung-Kyu Lee Hugh Durrant-Whyte 《GPS Solutions》2008,12(4):261-271
This paper presents a simple and effective approach that incorporates single-frequency, L1 time-differenced GPS carrier phase
(TDCP) measurements without the need of ambiguity resolution techniques and the complexity to accommodate the delayed-state
terms. Static trial results are included to illustrate the stochastic characteristics and effectiveness of the TDCP measurements
in controlling position error growth. The formulation of the TDCP observation model is also described in a 17-state tightly-coupled
GPS/INS iterative, extended Kalman filter (IEKF) approach. Preliminary land vehicle trial results are also presented to illustrate
the effectiveness of the TDCP which provides sub-meter positional accuracies when operating for more than 10 min. 相似文献