全文获取类型
收费全文 | 2337篇 |
免费 | 112篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 81篇 |
大气科学 | 231篇 |
地球物理 | 628篇 |
地质学 | 826篇 |
海洋学 | 199篇 |
天文学 | 283篇 |
综合类 | 46篇 |
自然地理 | 162篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 14篇 |
2021年 | 39篇 |
2020年 | 41篇 |
2019年 | 47篇 |
2018年 | 275篇 |
2017年 | 169篇 |
2016年 | 110篇 |
2015年 | 61篇 |
2014年 | 114篇 |
2013年 | 123篇 |
2012年 | 55篇 |
2011年 | 325篇 |
2010年 | 118篇 |
2009年 | 137篇 |
2008年 | 97篇 |
2007年 | 78篇 |
2006年 | 87篇 |
2005年 | 75篇 |
2004年 | 66篇 |
2003年 | 72篇 |
2002年 | 44篇 |
2001年 | 28篇 |
2000年 | 28篇 |
1999年 | 19篇 |
1998年 | 27篇 |
1997年 | 22篇 |
1996年 | 24篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1970年 | 2篇 |
1965年 | 4篇 |
1962年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有2456条查询结果,搜索用时 31 毫秒
151.
The evolution of pore-water and the composition of solid phases in the vadose zone of pyritic tailings was studied by means of unsaturated column experiments. Several columns of water-saturated mine tailings were dried during 125 days under controlled laboratory conditions. The columns were dismantled at four successive drying stages and the evolution of pore-water, mineralogy, water content and temperature was characterized.Sulfide and aluminosilicate minerals present in the waste dissolved, releasing sulfate and other solutes (mainly Fe, Zn, Cu, Al, Mg and Ca) to the pore-water. Evaporation caused a crust of efflorescent, water-soluble sulfates to develop over the complete top surface of the columns and into the pores of the underlying waste material. This crust, which has also been identified in the field, changed the hydraulic properties of the tailings and produced a decrease in the evaporation rate of the columns. Moreover, these water-soluble precipitates (mainly rozenite, szomolnokite, halotrichite, hexahydrite, mirabilite and gypsum) acted as temporary sinks for Cd, Pb, Co and Ni, which could be released to the surface run-off or the groundwaters during rainfall events under field conditions.Pore-water evolution was determined not only by geochemical processes (dissolution of sulfides and aluminosilicates, precipitation of secondary phases) but also by thermal and hydraulic processes. Progressive dilution was observed in the lower part of the columns. Dilution was caused by the thermally driven vapor flux from the top of the column to its colder bottom and subsequent condensation therein. This process, which may also occur in tailings under sub-arid climate, played a key role on the evolution of pore-water with increasing drying. 相似文献
152.
Jean-Franois Pastre Agns Gauthier Sbastien Nomade Paul Orth Ana Andrieu Franck Goupille Herv Guillou Stphane Kunesch Stphane Scaillet Paul Randall Renne 《Comptes Rendus Geoscience》2007,339(16):987-997
The Alleret maar (Massif Central, France) provides a long lacustrine sequence (40.6 m) attributed to the early Middle Pleistocene. Sediment, pollen and diatoms analysis of its upper part (AL2 core, 14.6 m) indicates two temperate phases marked by high lake levels, forest development and vegetation expansion. They are separated by a cold period during which lake level drops, coarse sediment input increases and steppic and xerophilous plants develop. Pollen data suggests that this sequence belongs to the upper part of the Cromerian complex. These results are in agreement with the 557 ± 3 ka (±12 ka, including all errors) 40Ar/39Ar age obtained from an interbedded tephra layer emitted by the Mont-Dore/Sancy strato-volcano and establish that this sequence probably covers the MIS 15 substages. 相似文献
153.
Andrs Folguera Antonio Introcaso Mario Gimnez Francisco Ruiz Patricia Martinez Cynthia Tunstall Ezequiel García Morabito Víctor A. Ramos 《Tectonophysics》2007,439(1-4):129-147
The western retroarc of the Southern Andes between 38° and 40° S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4–3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Expected crustal thickness at these latitudes is around 38 km, whereas in this part of the retroarc the thickness is less than 32 km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath the South American plate, which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 Ma. Gravimetric studies show that the upper plate did not react homogeneously to slab steepening, but ancient sutures and lithospheric discontinuities deeply buried under Mesozoic to Cenozoic sequences in the retroarc were locally reactivated. These processes resulted in an asthenospheric anomaly that correlates at the surface with the area of Pliocene to Quaternary doming, widespread extension and three radial troughs. Two of the troughs have accommodated substantial amounts of extension, but the third was probably aborted at an early stage. Moreover, the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly, and their age distribution, may indicate minor migration of the asthenospheric anomaly between 4 and 2 Ma through the western South American plate. 相似文献
154.
Graciela Salinas de Salmuni Inés Velasco Mirta Fresina Alberto L. Flores 《GeoJournal》2007,70(4):273-279
Much of the central-western region of Argentina, where San Juan Province is located, experiences arid to semi-arid climatic
conditions with low average annual rainfall accompanied by substantial evapotranspiration. Consequently, a viable crop industry
depends to a large extent upon irrigation from major river systems. Increasing demand for water in the lower basin of the
San Juan River is emphasizing the need for more accurate estimates of water used for irrigation. Since the water demand for
a particular crop is very closely related to crop area, monitoring the area of crop under irrigation is considered a proxy
for the amount of water used. Landsat 5 imagery for the growing season, field data and aerial photographs were used to evaluate
crop area. 相似文献
155.
Vulnerability assessment in a volcanic risk evaluation in Central Mexico through a multi-criteria-GIS approach 总被引:1,自引:1,他引:1
José Fernando Aceves-Quesada Jesús Díaz-Salgado Jorge López-Blanco 《Natural Hazards》2007,40(2):339-356
The Valley of Toluca is a major industrial and agricultural area in Central Mexico, especially the City of Toluca, the capital
of The State of Mexico. The Nevado de Toluca volcano is located to the southwest of The Toluca Basin. Results obtained from
the vulnerability assessment phase of the study area (5,040 km2 and 42 municipalities) are presented here as a part of a comprehensive volcanic risk assessment of The Toluca Basin. Information
has been gathered and processed at a municipal level including thematic maps at 1:250,000 scale. A database has been built,
classified and analyzed within a GIS environment; additionally, a Multi-Criteria Evaluation (MCE) approach was applied as
an aid for the decision-making process. Cartographic results were five vulnerability maps: (1) Total Population, (2) Land
Use/Cover, (3) Infrastructure, (4) Economic Units and (5) Total Vulnerability. Our main results suggest that the Toluca and
Tianguistenco urban and industrial areas, to the north and northeast of The Valley of Toluca, are the most vulnerable areas,
for their high concentration of population, infrastructure, economic activity, and exposure to volcanic events. 相似文献
156.
Angel F. Nieto-Samaniego María de Jesús Paulina Olmos-Moya Gilles Levresse Susana A. Alaniz-Alvarez Fanis Abdullin Alexis del Pilar-Martínez 《International Geology Review》2020,62(3):311-319
ABSTRACTThe Mesa Central of Mexico (MC) is an elevated plateau located 2000 m above sea level in central Mexico, where intrusions outcrop that register the history of exhumation-erosion occurring during the Late Cretaceous-Paleogene. The tectonic history of the region records formation of the Late Cretaceous-Paleogene ‘Mexican orogen’; this was followed by extension of the entire region and several plutons were then exhumed. The age and magnitude of the crustal uplift and erosion occurring during exhumation has not been addressed to date. Therefore, this study reports the crystallization and cooling ages of two plutons, the Tesorera Granodiorite and the Comanja Granite, and estimates their emplacement depths. Based on these data, the exhumation age of the Tesorera Granodiorite is estimated to be between ~73 Ma and ~63 Ma at an exhumation rate of ~528 m/m. y. and that of the Comanja Granite is 52 Ma and 48 Ma at an exhumation rate of ~2500 m/m. y. Exhumation-erosion event of the Tesorera Granodiorite was located on the trace of the San Luis-Tepehuanes Fault System and that of the Comanja Granite on the a trace of the El Bajío Fault System. Furthermore, the high exhumation rate in the Comanja Granite suggests that gravitational collapse played an important role during exhumation. 相似文献
157.
158.
F. Francés 《Stochastic Hydrology and Hydraulics》1998,12(4):267-283
Due to the social and economic implications, flood frequency analysis must be done with the highest precision. For this reason,
the most suitable statistical model must be selected, and the maximum amount of information must be used. Floods in Mediterranean
rivers can be produced by two different mechanisms, which forces the use of a non-traditional distribution like the TCEV.
The information can be increased by using additional non-systematic data, or with a regional analysis, or both. Through the
statistical gain concept, it has been shown that in most cases the use of additional non-systematic information can decrease
the quantile estimation error in about 50%. In a regional analysis, the␣benefit of additional information in one station,
is propagated to the rest of␣the␣stations with only a small decrease with respect to the at-site equivalent analysis. 相似文献
159.
Jesús Gallego 《Astrophysics and Space Science》1998,263(1-4):1-14
The evolution of the Star Formation Rate (SFR) density of the Universe as a function of look-back time is a fundamental parameter
in order to understand the formation and evolution of galaxies. The current picture, only outlined in the last years, is that
the global SFR density has dropped by about an order of magnitude from a redshift of z∼1.5 to the current value at z=0. Because
these SFR density studies are now extended to the whole range in redshift, it becomes mandatory to combine data from different
SFR tracers. At low redshifts, optical emission lines are the most widely used. Using Hα as current-SFR tracer, the Universidad
Complutense de Madrid (UCM) Survey provided the first estimation of the global SFR density in the Local Universe. The Hα flux
in emission is directly related to the number of ionizing photons and, modulo IMF, to the total mass of stars formed. Metallic
lines like [OII]λ3727 and [OIII]λ5007 are affected by metallicity and excitation. Beyond redshifts z∼0.4, Hα is not observable
in the optical and [OII]λ3727 or UV luminosities have to be used. The UCM galaxy sample has been used to obtain a calibration
between [OII]λ3727 luminosity and SFR specially suitable for the different types of star-forming galaxies found by deep spectroscopic
surveys in redshifts up to z∼1.5. These calibrations, when applied to recent deep redshift surveys confirm the drop of the
SFR density of the Universe since z∼1 previously infered in the UV. However, the fundamental parameter that determines galactic
evolution is mass, not luminosity. The mass function for local star-forming galaxies is critical for any future comparison
with other galaxy populations of different evolutionary status. Hα velocity-widths for UCM galaxies indicate that besides
a small fraction of 1010-1011 M⊙ starburst nuclei spirals, the majority have dynamical masses in the ∼109 M⊙ range. A comparison with published data for faint blue galaxies suggests that star-forming galaxies at z∼1 would have SFR
per unit mass and burst strengths similar to those at z=0, but being intrinsically more massive.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
160.
Yves Grosdidier Anthony F.J. Moffat Agnès Acker 《Astrophysics and Space Science》1998,260(1-2):181-184
We present HST-WFPC2/Hα deep images of the ejected nebula M1-67. Our data suggest that M1-67 is the imprint of a previous,
slow LBV wind ejected from the central star WR124, now a WN8 star. We find evidence that the LBV wind is highly variableand anisotropic. Some dense, persisting clumps have possibly been ejected directly from the stellar surface.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献