全文获取类型
收费全文 | 2586篇 |
免费 | 48篇 |
国内免费 | 28篇 |
专业分类
测绘学 | 245篇 |
大气科学 | 163篇 |
地球物理 | 530篇 |
地质学 | 914篇 |
海洋学 | 59篇 |
天文学 | 627篇 |
综合类 | 21篇 |
自然地理 | 103篇 |
出版年
2022年 | 23篇 |
2021年 | 30篇 |
2020年 | 35篇 |
2019年 | 29篇 |
2018年 | 138篇 |
2017年 | 113篇 |
2016年 | 151篇 |
2015年 | 76篇 |
2014年 | 131篇 |
2013年 | 150篇 |
2012年 | 107篇 |
2011年 | 115篇 |
2010年 | 98篇 |
2009年 | 111篇 |
2008年 | 88篇 |
2007年 | 62篇 |
2006年 | 60篇 |
2005年 | 56篇 |
2004年 | 32篇 |
2003年 | 41篇 |
2002年 | 54篇 |
2001年 | 36篇 |
2000年 | 39篇 |
1999年 | 44篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 27篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 31篇 |
1991年 | 40篇 |
1990年 | 28篇 |
1989年 | 41篇 |
1988年 | 48篇 |
1987年 | 52篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 61篇 |
1983年 | 58篇 |
1982年 | 34篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1976年 | 12篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1972年 | 14篇 |
1971年 | 10篇 |
排序方式: 共有2662条查询结果,搜索用时 20 毫秒
961.
The morphometric analysis of river basin helps to explore the interrelationship between hydraulic parameters and geomorphologic characteristics. The study has been conducted in the Upper Tons basin of Northern Foreland of Peninsular India. The river basin has been characterized using the topographical maps, CARTOSAT satellite image integrated using the GIS techniques. The drainage density analysis indicates lower values in the north-eastern regions and thus these regions can be categorized as better ground water potential zone. There are in total 10 sub-watersheds which have been delineated; SW-4 has maximum drainage density (4.75), stream frequency (5.61) and drainage texture (26.64) followed by SW-6–10. The prioritized sub-watershed numbers SW-4 and SW-6–10 need conservation practices because of their high erodibility and run-off. SW-1–3 and SW-5 regions have better permeable bed rocks and hence good for water harvesting. The areal parameter indicates elongated shape of basin and moderate to steeper ground slope. The results are supported by extensive field survey. This study can be applied for soil and water management, as well as disaster prevention from similar type of drainage basins. 相似文献
962.
Sudhir Kumar Singh Prosper Basommi Laari Sk. Mustak Prashant K. Srivastava Szilárd Szabó 《国际地球制图》2013,28(11):1202-1222
AbstractAn integrated Markov Chain and Cellular Automata modelling (CA MARKOV), multicriteria evaluation techniques have been applied to produce transition probability. The unsupervised method was employed to classify the satellite images of year 1985, 1995, 2005 and 2015 to meet the magnitude of LULC change. Results showing the spatial pattern of the sub-basin is largely influenced by the biophysical and socio-economic drivers leading to growth of agricultural lands and built-up area in the basin. Simulated plausible future LULC changes for 2025 which is based on a CA MARKOV that integrates Markovian transition probabilities computed from satellite-derived LULC maps and a CA contiguity spatial filter (5 × 5). Further, the fragmentation analysis was performed to check the fragmentation scenario in the year 2025. The result for year 2025 with reasonably good accuracy will be useful to the planners, policy- and decision-makers. 相似文献
963.
Akshay O. Jain Tejaskumar Thaker Ashish Chaurasia Parth Patel Anupam Kumar Singh 《国际地球制图》2013,28(11):1237-1256
AbstractShuttle Radar Topography Mission (SRTM-GL1), Advanced Space Borne Thermal Emission and Reflection Radiometer- Global DEM (GDEM-V2), recently released Advanced Land Observing Satellite (‘DAICHI’) DEM (AW3D30) and Indian National Cartosat-1 DEM v3 (CartoDEM-V3.1) provide free topographic data at a 30-m resolution for Indian peninsula. In this research study, the vertical accuracy of DEM is evaluated for above data-sets and compared with high accuracy dual frequency GNSS of a millimetre accuracy. The extensive field investigation is carried out using a stratified random fast static DGPS survey for collecting 117 high accuracy ground control points in a predominantly agriculture catchment. Further, the effect of land cover, slope and low-lying coastal zone on DEM vertical accuracy was also analysed and presented in this study. 相似文献
964.
Similarity solutions are obtained for one-dimensional adiabatic flow behind a magnetogasdynamic cylindrical shock wave propagating in a rotating non-ideal gas in presence of an azimuthal magnetic field. The density of the medium ahead of the shock is assumed to be constant. In order to obtain the similarity solutions the angular velocity of the ambient medium is assumed to be obeying a power law and to be decreasing as the distance from the axis increases. It is found that the similarity solutions exist, in both the cases, when the initial magnetic field is constant or obeying a power law. The effects of an increase in the value of the index for variation of angular velocity of the ambient medium, in the value of the parameter of the non-idealness of the gas and in the strength of the initial magnetic field are obtained. 相似文献
965.
In the Himalayan regions, precipitation-runoff relationships are amongst the most complex hydrological phenomena, due to
varying topography and basin characteristics. In this study, different artificial neural networks (ANNs) algorithms were used to
simulate daily runoff at three discharge measuring sites in the Himalayan Kosi River Basin, India, using various combinations
of precipitation-runoff data as input variables. The data used for this study was collected for the monsoon period (June to October)
during the years of 2005 to 2009. ANNs were trained using different training algorithms, learning rates, length of data
and number of hidden neurons. A comprehensive multi-criteria validation test for precipitation-runoff modeling has been undertaken
to evaluate model performance and test its validity for generating scenarios. Global statistics have demonstrated that
the multilayer perceptron with three hidden layers (MLP-3) is the best ANN for basin comparisons with other MLP networks
and Radial Basis Functions (RBF). Furthermore, non-parametric tests also illustrate that the MLP-3 network is the best network
to reproduce the mean and variance of observed runoff. The performance of ANNs was demonstrated for flows during
the monsoon season, having different soil moisture conditions during period from June to October. 相似文献
966.
967.
Anthropogenic arsenic menace in Delhi Yamuna Flood Plains 总被引:2,自引:1,他引:1
Chandra S. Dubey Bhupendra K. Mishra Dericks P. Shukla Ravindra P. Singh M. Tajbakhsh Purushottam Sakhare 《Environmental Earth Sciences》2012,65(1):131-139
Arsenic, one of the most poisonous chemical elements, was analyzed in the waters of the host of the 2010 Commonwealth Games,
i.e., New Delhi. The study revealed shocking outcomes with arsenic concentrations well beyond the safe limits set by WHO,
and a maximum concentration up to 180 ppb was found in the groundwater. Analysis of around 120 water samples collected extensively
along the Yamuna Flood Plain showed that more than 55% had arsenic contamination beyond the WHO limit of 10 ppb. The maximum
value of arsenic in coal and fly ash from Rajghat coal-based thermal power plant contained 200 and 3,200 ppb, respectively.
Moreover, the ore petrography of coal samples shows the presence of arsenopyrite mineral. Maximum concentration of arsenic
contamination is found within a 5-km radius from power plants. In the perspective of Delhi, arsenic contamination is purely
anthropogenic due to coal-based thermal power plants, which had already shown toxic arsenic, fluorine and China-type coal
effects. The presence of such power plants in coal field locations, e.g., West Bengal and Bangladesh, could release the arsenic
due to combustion in superthermal power plants, thus accentuating the arsenic concentration besides the natural arsenic coming
from the foreland basins of the Himalaya in Indian sub-continent. 相似文献
968.
A data-driven approach for analyzing dynamics of tide–aquifer interaction in coastal aquifer systems
Analysis of tidal effects on aquifer systems plays an important role in coastal aquifer management owing to various hydrological,
engineering and environmental problems in coastal areas. Using the real-world data of unconfined and confined aquifers, a
data-driven approach is presented in this study for the analysis of tide–aquifer interaction in coastal aquifers. Six analytical
tide–aquifer interaction models were selected which take into account the effects of vertical beach, sloping beach, tidal
loading, aquifer leakage, outlet capping, and combined leakage and outlet capping on tide-induced groundwater fluctuations.
The tide–aquifer interaction datasets were obtained from the Konan groundwater basin (unconfined aquifer) of Japan and the
Dridrate groundwater basin (confined aquifer) of Morocco. The analysis of the results obtained by the sloping beach model
revealed that for a given beach slope, the amplitude of groundwater level increases with an increase in aquifer diffusivity
and a decrease in aquifer thickness. However, no significant effect of beach slope was observed in this study at unconfined
sites for all the datasets. The influence of tidal loading was found to be considerably less for all the three confined sites.
Further, the analysis of the results of the leakage model indicated that with an increase in leakage into the aquifer, the
amplitude of groundwater level as well as the phase shift (time lag) decreases. Of all the confined and unconfined datasets,
only two confined sites were found to be affected by outlet capping. Overall, it is concluded that the coastal beach bordering
the Konan basin is not significantly sloping, the contribution of tidal loading to tide-induced groundwater fluctuations in
the Dridrate aquifer is not appreciable, and that the aquifer leakage and outlet capping do not exist at the unconfined sites
under investigation. 相似文献
969.
Stability of slope will always a problem due to its geodynamic nature of Himalayan region. The area investigated belongs to
the Lower Siwalik formation, which is prone to failure due to presence of various weak planes or structures present in the
rock mass. Frequent landslides causing loss of life, property, disturbance of morphological, surface and subsurface water
flow pattern. A huge landslide in the Amiyan area occurred in 1999 and blocked the Gaula River which caused loss of agricultural
land and other properties as well as waterlogged upstream side. The debris of Amiyan slope contains soil and sandstones of
various types. This article deals with instability analysis of slopes of the Amiyan area, near Kathgodam, Nainital, Uttarakhand.
This area experiences a number of local as well as regional slides. Extensive field surveys have been carried out to understand
the geological detail. Laboratory experiments have been conducted to determine the various physicomechanical properties of
rock mass. These properties have been used as input parameters for the numerical simulation. A number of researchers have
used two-dimensional numerical models to simulate the slide area. Three-dimensional slope stability studies provide a better
understanding of the mechanism of failure as well as zone of influence. The computed deformations and stress distribution,
along the failure surface, have been compared with the field measurements and found to be in good agreement with field observations.
In this case, finite difference method has been applied on the stability analysis of Amiyan slope. The study indicates that
the slope is vulnerable and needs proper protection. 相似文献
970.
Glacial lakes and glacial lake outburst flood in a Himalayan basin using remote sensing and GIS 总被引:1,自引:0,他引:1
Sanjay K. Jain Anil K. Lohani R. D. Singh Anju Chaudhary L. N. Thakural 《Natural Hazards》2012,62(3):887-899
Glacial hazards relate to hazards associated with glaciers and glacial lakes in high mountain areas and their impacts downstream. The climatic change/variability in recent decades has made considerable impacts on the glacier life cycle in the Himalayan region. As a result, many big glaciers melted, forming a large number of glacial lakes. Due to an increase in the rate at which ice and snow melted, the accumulation of water in these lakes started increasing. Sudden discharge of large volumes of water with debris from these lakes potentially causes glacial lake outburst floods (GLOFs) in valleys downstream. Outbursts from glacier lakes have repeatedly caused the loss of human lives as well as severe damage to local infrastructure. Monitoring of the glacial lakes and extent of GLOF impact along the downstream can be made quickly and precisely using remote sensing technique. A number of hydroelectric projects in India are being planned in the Himalayan regions. It has become necessary for the project planners and designers to account for the GLOF also along with the design flood for deciding the spillway capacity of projects. The present study deals with the estimation of GLOF for a river basin located in the Garwhal Himalaya, India. IRS LISSIII data of the years 2004, 2006 and 2008 have been used for glacial lake mapping, and a total of 91 lakes have been found in the year 2008, and out of these, 45 lakes are having area more than 0.01?km2. All the lakes have been investigated for vulnerability for potential bursting, and it was found that no lake is vulnerable from GLOF point of view. The area of biggest lake is 0.193, 0.199 and 0.203?km2 in the years 2004, 2006 and 2008, respectively. Although no lake is potentially hazardous, GLOF study has been carried out for the biggest lake using MIKE 11 software. A flood of 100-year return period has been considered in addition to GLOF. The flood peak at catchment outlet comes out to be 993.74, 1,184.0 and 1,295.58 cumec due to GLOF; 3,274.74, 3,465.0 and 3,576.58 cumec due to GLOF; and 100-year return flood together considering breach width of 40, 60 and 80?m, respectively. 相似文献