全文获取类型
收费全文 | 1769篇 |
免费 | 92篇 |
国内免费 | 96篇 |
专业分类
测绘学 | 65篇 |
大气科学 | 125篇 |
地球物理 | 342篇 |
地质学 | 1054篇 |
海洋学 | 120篇 |
天文学 | 131篇 |
综合类 | 23篇 |
自然地理 | 97篇 |
出版年
2023年 | 12篇 |
2022年 | 25篇 |
2021年 | 53篇 |
2020年 | 60篇 |
2019年 | 43篇 |
2018年 | 137篇 |
2017年 | 132篇 |
2016年 | 119篇 |
2015年 | 78篇 |
2014年 | 130篇 |
2013年 | 203篇 |
2012年 | 85篇 |
2011年 | 118篇 |
2010年 | 89篇 |
2009年 | 99篇 |
2008年 | 67篇 |
2007年 | 44篇 |
2006年 | 57篇 |
2005年 | 48篇 |
2004年 | 42篇 |
2003年 | 40篇 |
2002年 | 59篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 12篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
排序方式: 共有1957条查询结果,搜索用时 15 毫秒
41.
Accidental spills of hydrocarbons, such as Light Non-Aqueous Phase Liquids (LNAPLs), are one of the most common sources of subsurface contamination. Migration of LNAPL in a porous medium is influenced by various factors such as the number of fluids present in the unsaturated/saturated zones and the proportion of pores occupied by each fluid. The results for relationship between matric suction and degree of saturation are presented in this paper for water–air, water–LNAPL and LNAPL–air systems in a sand. A simple and reliable setup using Buchner funnel was designed to obtain these relations. It was found that the relationship between matric suction head and degree of saturation is hysteretic for all the fluid systems (water–air, water–LNAPL and LNAPL–air). Furthermore, the amount of hysteresis depended upon the fluid system, with the maximum hysteresis occurring for water–air system. The results suggest that the amount of trapped air depends upon the reversal degree of saturation from drying to wetting. 相似文献
42.
Ben Page 《Geoforum》2003,34(4):483-498
In 1991 the people of the town of Kumbo in Northwest Cameroon expelled the national water corporation from town by force. They claimed to be retrieving a network that the community rightfully owned and they began to run the system along community lines. The paper tells the story of that water supply twice. First it reproduces the popular accounts that circulated in the 1990s that emphasize the role played by the community in the development and operation of the water supply and portray recent events as a triumph of community management. Then it retells the story using archive evidence that puts a quite different light on some of the events. It is argued that the emphasis on community management has a tendency to obscure other important aspects of the story, for example its political context and consequences. It is suggested that the widespread admiration for any initiative that is community based often results in an uncritical analysis of this form of development project. In this case the commodification of water accelerates after the community has wrested control of this public service from the state. 相似文献
43.
44.
Geochemistry and petrogenesis of Sikait leucogranite, Egypt: an example of S-type granite in a metapelitic sequence 总被引:1,自引:0,他引:1
The Sikait leucogranite (SLG) is a body of porphyritic garnet granite intruded a metapelitic sequence and interlayered orthogneisses.
Multiple deformation and low- to medium-grade metamorphism of the sequence was closely associated with pluton emplacement.
Textural features of the SLG indicate that subsolidus plastic deformation was induced during the extensive thrusting. The
granite is strongly peraluminous, alkali-rich and HFS (high field-strength) elements-depleted with low contents of REE, all
facts that substantiate the geochemical characteristics of S-type granites.
The geologic and geochemical features are consistent with a dehydration melting model of the hosted metapelites to generate
the peraluminous SLG. However, geochemical modelling of trace elements and REEs suggest that the anatectic partial melt was
subsequently affected by fractional crystallization of feldspars. This could explain much of the chemical attributes of SLG.
Received: 20 September 1994 / Accepted: 2 August 1996 相似文献
45.
In this work we have tried to detect and collect later phases associated with the Moho discontinuity and use them to study the lateral variations of the crustal thickness in southwest (SW) Japan. We first compute synthetic seismograms for local earthquakes taking into account the focal mechanism solutions estimated from first motion polarity data. Then we compare the synthetics with the observed waveforms to detect the major later phases in seismograms of shallow crustal earthquakes in SW Japan. Taking the advantage of the high quality and great quantity of Hi-net waveform data now available throughout the entire Japan Islands, we have detected 1659 Moho-reflected phases (PmP and SmS) from shallow events in SW Japan. We estimated the crustal thickness in the study area using travel time differences between these later phases and the first P and S arrivals. Our results show that the Moho is deep in Chubu district and becomes shallower along the coastlines of the Japan Sea and the Pacific Ocean. A thinner crust appears in Osaka Bay and Awajii Island where the 1995 Kobe earthquake (M7.2) occurred. 相似文献
46.
In this study, a capillary barrier system was designed and tested for an arid land environment. To simulate arid land conditions
of high temperature and sub-irrigation systems, the barrier was subjected to thermal and hydraulic gradients in opposite directions;
to test the barrier system under these severe conditions, an experimental apparatus was designed and fabricated. The multilayer
capillary barrier consisted of three layers made of silica sand, a mixture of sand and bentonite in equal portions, and a
mixture of clay (25%) and aggregate (75%). Several one dimensional coupled heat and moisture tests were performed. Temperature
variations along the thickness of the barrier were recorded as a function of time, and at the end of each test, the barrier
was sliced into small sections, for the determination of volumetric water content as a function of distance from the heat
source. The experimental results were discussed in view of the barrier's intended purpose of its ability to store moisture
for long time durations.
Coupled heat and moisture flow equations were developed and solved numerically via a finite difference method. Diffusivity
parameters were calculated by using experimental results, a numerical model, and Powell's conjugate directions method of nonlinear
optimization. The model was calibrated and the results were discussed. Good agreement between calculated and experimental
results was obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
47.
Sami Khomsi Mourad Bédir M. Ghazi Ben Jemia Hédi Zouari 《Comptes Rendus Geoscience》2004,336(15):1401-1408
Structural interpretations of newly acquired seismic lines in northeastern Tunisia allow us to highlight a new thrust front for the Atlasic range of Tunisia, in contrast to the previously Zaghouan fault thrust Dorsale zone. This new thrust front takes place on weakness tectonic zones, materialized by inherited faults anchored on the pre-Triassic basement. This front seems to be a paleogeographic trend controlling structural style and basin fill with a synsedimentary activity. The front is expressed by reverse faults, thrust faults, back thrusting, and decollement structures. To cite this article: S. Khomsi et al., C. R. Geoscience 336 (2004). 相似文献
48.
Kiichiro Kawamura Takahiro Hosono Huda Mohamed Allawati Yujiro Ogawa Hidetsugu Taniguchi 《Island Arc》2005,14(4):564-570
Abstract Magnetic susceptibility and the anisotropy of magnetic susceptibility were measured on an 800-cm-thick succession of cumulate gabbro in the Sadm area of the Oman ophiolite. The section contained three distinct cumulate units. The susceptibility tends to decrease upward in each from a melanocratic layer (several tens of centimeters thick) to a leucocratic layer (a few meters thick). The susceptibility decreases in accordance with the decreasing number of magnetite grains, which are the alteration product mainly of olivine minerals. This suggests the cyclic downward accumulation of olivine in the cumulate gabbro. The apparent strain deduced from the patterns of magnetic and grain fabrics was the result mostly of simple shear, so that the layering of gabbro is understood to be formed primarily by a crystal cumulus process followed by simple shear deformation. 相似文献
49.
Mohamed Chaker Raddadi Annie Arnaud Vanneau Grard Poupeau Elisabeth Carrio-Schaffhauser Hubert Arnaud Alice Rivera 《Comptes Rendus Geoscience》2005,337(16):96
High gamma-radioactivity in carbonates is usually ascribed to uranium of detrital minerals and organic matter, and to thorium and potassium of clays. The present study based on Urgonian marls and marly limestones (France) shows that some of the most radioactive values correspond instead to some ‘pure’ limestones. These peaks are generally associated with a sequence boundary or a maximum flooding surface. Low-level γ-spectrometry and ICP–MS analyses show that although high radioactivities are mostly associated with uranium, there is no obvious correlation between uranium enrichment and lithology. Also, correlation between high radioactivity and argillaceous beds might not be systematic. To cite this article: M.C. Raddadi et al., C. R. Geoscience 337 (2005). 相似文献
50.
Rouaida Trabelsi Moncef Zaïri Habib Smida Hamed Ben Dhia 《Comptes Rendus Geoscience》2005,337(5):515-524
The intensive agricultural and economic activities induce the increase of the risk of groundwater quality degradation through high groundwater pumping rates. The salinization and contamination are the main sources of this pollution, especially in coastal aquifers. The explanation of the origin of salinity for the shallow aquifer of Northern Sahel of Sfax was analysed by a chemical study of the groundwater main compounds. The partitioning of groundwaters into homogenous groups is undertaken by graphical techniques, including a Stiff pattern diagram, an expanded Durov diagram and several binary diagrams. The study indicates the presence of various salinization processes. In the recharge area, salinization is the result of dissolution/precipitation of the aquifer formation material (group I). The irrigation water return and the intensive pumping have been identified as major sources of salinization in the south by direct cation exchange and mixing reactions (groups II and III). The anomaly of high groundwater salinity observed near the Hazeg zone was explained by the presence of a seawater intrusion in this area. This hypothesis is related to the high chloride concentration, to the presence of inverse cation exchange reactions (group IV), and to the piezometric level inferior to sea level. To cite this article: R. Trabelsi et al., C. R. Geoscience 337 (2005). 相似文献