全文获取类型
收费全文 | 2585篇 |
免费 | 41篇 |
国内免费 | 27篇 |
专业分类
测绘学 | 245篇 |
大气科学 | 163篇 |
地球物理 | 526篇 |
地质学 | 911篇 |
海洋学 | 59篇 |
天文学 | 627篇 |
综合类 | 21篇 |
自然地理 | 101篇 |
出版年
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 34篇 |
2019年 | 29篇 |
2018年 | 138篇 |
2017年 | 111篇 |
2016年 | 151篇 |
2015年 | 76篇 |
2014年 | 130篇 |
2013年 | 150篇 |
2012年 | 105篇 |
2011年 | 115篇 |
2010年 | 98篇 |
2009年 | 110篇 |
2008年 | 88篇 |
2007年 | 62篇 |
2006年 | 59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2653条查询结果,搜索用时 15 毫秒
991.
Natural Resources Research - In mineral exploration, geophysical inversion is a common mathematical tool to obtain reliable information on subsurface density properties based on gravity... 相似文献
992.
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
993.
The Biot linearized theory of fluid saturated porous materials is used to study the plane strain deformation of a two-phase
medium consisting of a homogeneous, isotropic, poroelastic half-space in welded contact with a homogeneous, isotropic, perfectly
elastic half-space caused by a two-dimensional source in the elastic half-space. The integral expressions for the displacements
and stresses in the two half-spaces in welded contact are obtained from the corresponding expressions for an unbounded elastic
medium by applying suitable boundary conditions at the interface. The case of a long dip-slip fault is discussed in detail.
The integrals for this source are solved analytically for two limiting cases: (i) undrained conditions in the high frequency
limit, and (ii) steady state drained conditions as the frequency approaches zero. It has been verified that the solution for
the drained case (ω → 0) coincides with the known elastic solution. The drained and undrained displacements and stresses are compared graphically.
Diffusion of the pore pressure with time is also studied. 相似文献
994.
Climate change adds another dimension of challenges to the growth and sustainability of Indian agriculture. The growing exposure to livelihood shocks from climate variability/change and limited resource base of the rural community to adapt has reinforced the need to mainstream climate adaptation planning into developmental landscape. However, a better understanding of micro-level perceptions is imperative for effective and informed planning at the macro-level. In this paper, the grass-root level perspectives on climate change impacts and adaptation decisions were elicited at farm level in the Moga district of Punjab and Mahbubnagar district of Telangana, India. The farmers opined that the climatic variability impacts more than the long-term climate change. They observed change in the quantum, onset and distribution of rainfall, rise in minimum as well as maximum temperature levels, decline in crop yield and ground water depletion. The key socio-economic effects of climate change included decline in farm income, farm unemployment, rural migration and increased indebtedness among farmers. In order to cope with climate variability and change thereon, farmers resorted to adaptation strategies such as use of crop varieties of suitable duration, water conservation techniques, crop insurance and participation in non-farm activities and employment guarantee schemes. Farmers’ adaptation to changing climate was constrained by several technological, socio-economic and institutional barriers. These include limited knowledge on the costs–benefits of adaptation, lack of access to and knowledge of adaptation technologies, lack of financial resources and limited information on weather. Besides, lack of access to input markets, inadequate farm labour and smaller farm size were the other constraints. Further, on the basis of the grass-root elicitation a ‘Need-Based Adaptation’ planning incorporating farmers’ perceptions on climate change impacts, constraints in the adoption of adaptation strategies and plausible adaptation options were linked with the most suitable ongoing programmatic interventions of the Government of India. The study concluded that micro-level needs and constraints for various adaptation strategies and interventions should be an integral part of the programme development, implementation and evaluation in the entire developmental paradigm. 相似文献
995.
Application of the time-predictable model in Peninsular India for future seismic hazard assessment 总被引:1,自引:0,他引:1
It has been the belief among Earth scientists that the Peninsular Shield is aseismic, as the region attained stability long
ago. However, the earthquake at Koyna (10 December 1967), Bhadrachalam (13 April 1969), Broach (23 March 1970), Hyderabad
(30 June 1983), Khillari (30 September 1993), Jabalpur (22 May 1997), Gujarat (26 January 2001), and additional ones of smaller
magnitudes, altered this concept. This area has experienced many widely distributed shallow earthquakes, some of them having
large magnitudes. It is now widely accepted that seismic activity still continues with moderate events. Therefore, a need
has arisen to take into consideration recent seismological data to assess the future seismic status of Peninsular India. Earthquake
generation model has been studied to develop the statistical relations with surface wave magnitude (M
S
≥ 4.5). Five seismogenic sources showing clustering of earthquakes and including at least three main shocks of magnitude
4.5 ≤ M
S
≤ 6.5 giving two repeat times, have been identified. It is mainly based on the so-called “regional time-predictable model”.
For the considered region it is observed that the time interval between two consecutive main shocks depends on the preceding
main shock magnitude (M
p
) not on the following main shocks magnitude M
f
suggesting the validity of time predictable model in the region. 相似文献
996.
Ashok Kumar Rakesh Kumar Arun K. Singh Sahendra Ram Pradeep K. Singh Rajendra Singh 《Arabian Journal of Geosciences》2017,10(18):411
Underground extraction of total thickness of a thick coal seam in single lift by bord and pillar method increases pillar height during retreat. Field studies found that the increase in pillar height affects the depillaring operation adversely, especially, during caving of the strong/massive roof strata. Dilution in strength due to the increased pillar height caused catastrophic failure of barrier pillars and goaf overriding. This warrants a systematic study of pillar strength variation for the different heights of pillar. A review of different pillar strength estimation approaches for an analysis of the dilution in strength of the heightened pillar suggested that numerical modelling provides a better option for such a systematic study. Accordingly, investigations are conducted on simulated models in laboratory adopting a recognised numerical modelling procedure. The observed nature of variations in pillar strengths with the increase in its height in the numerical models and empirical formula is found to be matched. But a mismatch is found between the strength values of the two approaches with an increase in height of the pillar. Considering validity of the empirical formulation in Indian coalfields, a relationship is developed to incorporate a correction in the strength values of the numerical models. The suggested correction on the basis of this simple study of the pillar strength variation would be helpful for the use of the established simulation tool during the depillaring of a thick coal seam. 相似文献
997.
In this paper, we analyze the TEC data for April 2013 observed at Agra station, India (geogr. lat. 27.2° N, long. 78° E) to examine the effect of earthquake of magnitude M = 7.8 which occurred on 16 April 2013 at Pakistan–Iran border region. We process the TEC data using the s statistical criterion to find out anomalous variation in TEC data. We also study the VLF propagation signal from NPM, Hawaii (21.42° N, 158° W), which is monitored at the same station (Agra station) in the light of this earthquake as well as solar flares. The nighttime fluctuation method is used to analyze the VLF data for the period of ±5 days from the day of earthquake (11–21 April 2013). The anomalous enhancements and depletions are found in TEC data on 1–9 days before the occurrence of event. 相似文献
998.
Global structure of the Madden-Julian Oscillations during two recent contrasting summer monsoon seasons over India 总被引:1,自引:0,他引:1
A. D. Vernekar V. Thapliyal R. H. Kripalani S. V. Singh B. Kirtman 《Meteorology and Atmospheric Physics》1993,52(1-2):37-47
Summary The global nature of the Madden-Julian Oscillations (MJOs) have been investigated by applying a frequency filter to daily data for the summer monsoon months (June to September) during two contrasting years—1987, a deficient monsoon year and 1988, an excess monsoon year. Several meteorological parameters at five levels in the troposphere have been examined. Regions with large amplitude of these oscillations are isolated for each year. The results indicate that the global spatial distribution of these oscillations is more in a deficient year than in an excess year, in particular over the Indian subcontinent and the EI Niño Southern Oscillation (ENSO) regions. The principal modes of variability during these two years have been investigated through Empirical Orthogonal Functions (EOFs). The first two eigenmodes of 850 hPa zonal wind explain nearly 50% of the variance. The dipole type of structure between the Indian and the Pacific region is more apparent in 1987 than in 1988. Time-longitude cross sections of the filtered zonal wind over the equatorial regions clearly show that eastward propagation is detected in 1987, but is virtually absent in 1988. It is also seen that the 30–60 day filtered winds are stronger during the monsoon of 1987 than in 1988. 相似文献
999.
Shiv Mohan Singh Kumar Avinash Parmanand Sharma Ravindra Uttam Mulik Ajay Kumar Upadhyay Rasik Ravindra 《地学前缘(英文版)》2017,8(6):1339-1347
Cryoconite samples were collected from two different climatic domains i.e., the Sutri Dhaka glacier, western Himalaya India and Svalbard glaciers, the Spitsbergen, Arctic, to understand the elemental source and elemental deposition patterns. The data of geochemical analysis suggest that the Himalayan cryoconite samples accumulate higher concentrations as compared to the cryoconite samples of the Arctic glaciers. The concentration of lithophile elements (Cs, Li, Rb and U) was recorded higher in the cryoconite holes of the Himalayas, especially, in the lower to the higher parts of the glacier, whereas, lower concentrations were recorded in the Arctic samples. Chalcophile elements in the Himalayan cryoconites are enriched in As and Bi while the Arctic cryoconite samples show a higher concentration of Bi, Pb and As. The higher concentrations are responsible for influencing the ecosystem and in human health related issues. Siderophile elements (Co, Fe, Mn and Ni) show high concentrations in the Himalayan samples, whereas, the Arctic samples show minor variations and low elemental concentration in these elements, respectively. In addition, a few elements, such as Ag, Mg, and Ca show higher concentration in the Himalayan glacier samples. Ca also occurs in high concentrations in Arctic glacier samples. R-mode factor analysis of the Himalayas (Arctic) samples indicate that the elements are distributed in four (three) factors, explaining 89% (90%) of the variance in their elemental distribution. The Factor 1 suggests statistically significant positive loadings for most of the lithophile, chalcophile and siderophile elements of the “Himalayan” and the Arctic cryoconite samples. The sample-wise factor score distribution shows a considerable variation in the sampling locations along the glaciers of both the regions. Factors 2 and 3, demonstrate insignificant loading for most of the elements, except statistically significant positive loading in some of the elements of the both, Himalayan and Arctic “cryoconites”. The higher elemental concentration in the cryoconites of the Himalayan region may be an indicator of the natural processes and/or attributed to the rapid industrialization in the Asian countries. 相似文献
1000.
Chemometric analysis to infer hydro-geochemical processes in a semi-arid region of India 总被引:1,自引:0,他引:1
Chander Kumar Singh Satyanarayan Shashtri Kumari Rina Saumitra Mukherjee 《Arabian Journal of Geosciences》2013,6(8):2915-2932
Groundwater exploitation in Punjab has increased in last few decades due to rapid increase in industrialization, population, crop production, and erratic monsoon. In the present study, groundwater samples from 29 locations were collected and analyzed for almost all major anions, cations, and heavy metals. The analyzed parameters formed the attribute database for statistical analysis. The study approach included multivariate statistical analysis of hydro-chemical data to identify hydro-geochemical processes occurring in the study area and its relation to groundwater quality. The principal component analysis produced seven significant factors that explained nearly 77 % of the cumulative variance. Factor 1 explained nearly 22.05 % of dataset with variables loading indicating mineralization of geological component of soil. Trilinear plot and other graphical methods were also used to identify chemical facies of groundwater and geochemical processes occurring in study area. The water type in the study area is of Na/K–Mg–HCO3 type. It was found that the general hydro-geochemistry of groundwater in the study area dominated is by the processes such as carbonate/silicate weathering, ion-exchange, and dissolution. Thus, statistical methods can prove to be an effective tool understanding hydro-geochemistry of a region along with conventional graphical methods. 相似文献