全文获取类型
收费全文 | 1231篇 |
免费 | 50篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 74篇 |
地球物理 | 350篇 |
地质学 | 428篇 |
海洋学 | 139篇 |
天文学 | 183篇 |
综合类 | 3篇 |
自然地理 | 81篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 23篇 |
2020年 | 37篇 |
2019年 | 33篇 |
2018年 | 47篇 |
2017年 | 52篇 |
2016年 | 64篇 |
2015年 | 42篇 |
2014年 | 65篇 |
2013年 | 85篇 |
2012年 | 51篇 |
2011年 | 73篇 |
2010年 | 74篇 |
2009年 | 78篇 |
2008年 | 77篇 |
2007年 | 55篇 |
2006年 | 58篇 |
2005年 | 42篇 |
2004年 | 38篇 |
2003年 | 30篇 |
2002年 | 31篇 |
2001年 | 19篇 |
2000年 | 18篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 15篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1971年 | 3篇 |
1970年 | 5篇 |
1963年 | 4篇 |
排序方式: 共有1290条查询结果,搜索用时 15 毫秒
91.
Late Pleistocene–Holocene environments in Valle Carbajal, Tierra del Fuego, Argentina 总被引:1,自引:0,他引:1
Ana María Borromei Andrea Coronato Mirta Quattrocchio Jorge Rabassa Silvia Grill Claudio Roig 《Journal of South American Earth Sciences》2007,23(4):321-335
The authors discuss Late Pleistocene–Holocene depositional environments in one of the Fuegian Andes valleys on the basis of palynological, geomorphological, and sedimentological analyses from two sites located near the Beagle Channel. The results obtained at these localities reinforce and refine the Late Pleistocene–Holocene climatic pattern previously recorded there. A colder period, associated with the Younger Dryas stadial event, is suggested by low Nothofagus pollen frequency, and communities of grass, low scrub, and shrub heath expanded into the low/middle slopes (10,310 14C yr BP). By ca. 9500 14C yr BP, warmer and drier conditions occurred, as evidenced by the development of open-grown vegetation in the valley floors (pollen zone O-3), followed by the expansion of open Nothofagus woodland (pollen zone O-2) in the middle Holocene. The milder climate subsequently changed, as indicated by the spreading of the closed forest and mire (pollen zone O-1), to more humid and cooler conditions during the last ca. 5000 yr BP. 相似文献
92.
Jos María Viramonte Raúl Alberto Becchio Jos Germn Viramonte Marcio Martins Pimentel Roberto Donato Martino 《Journal of South American Earth Sciences》2007,24(2-4):167-183
New field, petrological, geochemical, and geochronological data (U–Pb and Sm–Nd) for Ordovician rock units in the southeastern Puna, NW Argentina, indicate two lithostratigraphic units at the eastern–northeastern border of salar Centenario: (1) a bimodal volcanosedimentary sequence affected by low- to medium-grade metamorphism, comprising metasediments associated with basic and felsic metavolcanic rocks, dated 485 ± 5 Ma, and (2) a plutonic unit composed of syenogranites to quartz-rich leucogranites with U–Pb zircon ages between 462 ± 7 and 475 ± 5 Ma. Felsic metavolcanic and plutonic rocks are peraluminous and show similar geochemical differentiation trends. They also have similar Sm–Nd isotopic compositions (TDM model ages of 1.54–1.78 Ga; εNd(T) values ranging from −3.2 to −7.5) that suggest a common origin and derivation of the original magmas from older (Meso-Paleoproterozoic?) continental crust. Mafic rocks show εNd(T) ranging from +2.3 to +2.5, indicating a depleted mantle source. The data presented here, combined with those in the literature, suggest Ordovician magmatism mainly recycles preexisting crust with minor additions of juvenile mantle-derived material. 相似文献
93.
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
94.
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
95.
Alberto Berretti 《Planetary and Space Science》1998,46(11-12)
We review some results about the analytic structure of Lindstedt series for some complex analytic dynamical systems: in particular, we consider Hamiltonian maps (like the standard map and its generalizations), the semi-standard map and Siegel's problem of the linearization of germs of holomorphic diffeomorphisms of (
,0). The analytic structure of those series can be studied numerically using Padé approximants, and one can show the existence of natural boundaries for real, diophantine values of the rotation number; by complexifying the rotation number, we show how these natural boundaries arise from the accumulation of singularities due to resonances, providing a new intuitive insight into the mechanism of the break-down of invariant KAM curves. Moreover, we study the Lindstedt series at resonances, i.e. for rational values of the rotation number, by suitably rescaling to 0 the value of the perturbative parameter, and a simple analytic structure emerges. Finally, we present some proofs for the simplest models and relate these results to renormalization ideas. 相似文献
96.
97.
Jorge A. Mendiguren 《Pure and Applied Geophysics》1980,118(2):1192-1208
It is shown, through numerical experiments, that the effect of ignoring ellipticity and rotation of the earth when inverting free oscillation data in moment tensor studies, is to introduce spurious spectral components in the solution. For numerical simulation of the data conditions of the 1970 deep Colombian event the spurious part has isotropic and deviatoric components, besides a distortion in the phase spectra which may lead to artificial precursive source in the solution. The magnitude of the artificial isotropic component is of the order of 10% of the real source moment tensor, depending on the data set used in the inversion. Measuring the excitation of each mode at each station using the technique of integrating over the spectral peaks does not cancel completely the effect of multiplet splitting, in particular that splitting due to rotation of the earth. The effect of lateral heterogeneities was simulated by introducing arbitrary splitting parameters which produced scattering in the eigenperiods compatible with those observed. For that splitting the inversion rendered additional isotropic components.We conclude that the observed implosive precursor the the 1970 Colombian event could have been artificially introduced by ignoring rotation, ellipticity and lateral heterogeneities of the earth.A procedure to invert free oscillation data for an elliptical rotating earth is proposed. It could be applied to a laterally inhomogeneous earth if the excitation for that model could be computed. Its application to real data for the deep Colombian event indicates that we will need to improve our knowledge on the effect of rotation, ellipticity, lateral heterogeneities and anelasticity on free oscillation and their excitation in order to solve accurately for the six components of the moment tensor independently. 相似文献
98.
Luciano Sbriz Margarita R. Aquino Natividad M. Alberto de rodriguez Scott W. Fowler Jose L. Sericano 《Marine pollution bulletin》1998,36(12):971-979
Bivalves (Crassostrea rizhophorae, Isognomon alatus, Codakia orbicularis Linné, and Tellina fausta) and sediment samples collected from 12 locations along the Dominican Republic coastline were used to assess the degree of nearshore contamination by selected chlorinated hydrocarbons and heavy metals. Concentrations of total chlordanes, DDTs and PCBs ranged from 0.51 to 7.47 ng/g, < MDL to 30.9 ng/g and 11.3 to 82.3 ng/g, and from < MDL to 1.73 ng/g, 0.21 to 12.5 ng/g and 0.46 to 41.9 ng/g in bivalves and surface sediments, respectively. The concentration ranges of predominantly anthropogenic Cu, Pb and Zn were 3.08–866 μg/g, 0.08–1.46 μg/g and 22.9–4380 μg/g in bivalve soft parts and 1.01–111 mg/g, 0.420–134 μg/g and 1.96–277 μg/g in surface sediments, respectively. Mercury concentrations ranged from 0.290 to 7.02 μg/g and from 0.096 to 0.565 μg/g in both matrices. The relatively high Hg concentrations found in bivalves from two stations in Bahia Samana, near to a known source of past Hg contamination in the sediments, require a more in-depth survey of the area. In general the concentrations of selected chlorinated hydrocarbons and trace metals, compared with those reported for the same matrices in the Caribbean and west Atlantic coastal areas, show at present the existence of only very localized contamination problems in the Dominican Republic. 相似文献
99.
The paper presents an analysis of 17 long annual maximum series (AMS) of flood flows for Swiss Alpine basins, aimed at checking the presence of changes in the frequency regime of annual maxima. We apply Pettitt's change point test, the nonparametric sign test and Sen's test on trends. We also apply a parametric goodness‐of‐fit test for assessing the suitability of distributions estimated on the basis of annual maxima collected up to a certain year for describing the frequency regime of later observations. For a number of series the tests yield consistent indications for significant changes in the frequency regime of annual maxima and increasing trends in the intensity of annual maximum discharges. In most cases, these changes cannot be explained by anthropogenic causes only (e.g. streamflow regulation, construction of dams). Instead, we observe a statistically significant relationship between the year of change and the elevation of the catchment outlet. This evidence is consistent with the findings of recent studies that explain increasing discharges in alpine catchments with an increase in the temperature controlling the portion of mountain catchments above the freezing point. Finally, we analyse the differences in return periods (RPs) estimated for a given flood flow on the basis of recent and past observations. For a large number of the study AMS, we observe that, on average, the 100‐year flood for past observations corresponds to a RP of approximately 10 to 30 years on the basis of more recent observation. From a complementary perspective, we also notice that estimated RP‐year flood (i.e. flood quantile (FQ) associated with RP) increases on average by approximately 20% for the study area, irrespectively of the RP. Practical implications of the observed changes are illustrated and discussed in the paper. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
100.
Philippe Vernant Abdelali Fadil Taoufik Mourabit Driss Ouazar Achraf Koulali Jose Martin Davila Jorge Garate Simon McClusky Robert Reilinger 《Journal of Geodynamics》2010,49(3-4):123-129
We present GPS observations in Morocco and adjacent areas of Spain from 15 continuous (CGPS) and 31 survey-mode (SGPS) sites extending from the stable part of the Nubian plate to central Spain. We determine a robust velocity field for the W Mediterranean that we use to constrain models for the Iberia-Nubia plate boundary. South of the High Atlas Mountain system, GPS motions are consistent with Nubia plate motions from prior geodetic studies. We constrain shortening in the Atlas system to <1.5 mm/yr, 95% confidence level. North of the Atlas Mountains, the GPS velocities indicate Nubia motion with respect to Eurasia, but also a component of motion normal to the direction of Nubia-Eurasia motion, consisting of southward translation of the Rif Mountains in N Morocco at rates exceeding 5 mm/yr. This southward motion appears to be directly related to Miocene opening of the Alboran Sea. The Betic Mountain system north of the Alboran Sea is characterized by WNW motion with respect to Eurasia at ~1–2 mm/yr, paralleling Nubia-Eurasia relative motion. In addition, sites located in the Betics north of the southerly moving Rif Mountains also indicate a component of southerly motion with respect to Eurasia. We interpret this as indicating that deformation associated with Nubia-Eurasia plate motion extends into the southern Betics, but also that the Betic system may be affected by the same processes that are causing southward motion of the Rif Mountains south of the Alboran Sea. Kinematic modeling indicates that plate boundary geometries that include a boundary through the Straits of Gibraltar are most compatible with the component of motion in the direction of relative plate motion, but that two additional blocks (Alboran-Rif block, Betic Mountain block), independent of both Nubia and Eurasia are needed to account for the motions of the Rif and Betic Mountains normal to the direction of relative plate motion. We speculate that the southward motions of the Alboran-Rif and Betic blocks may be related to mantle flow, possibly induced by southward rollback of the subducted Nubian plate beneath the Alboran Sea and Rif Mountains. 相似文献