全文获取类型
收费全文 | 628篇 |
免费 | 28篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 27篇 |
地球物理 | 211篇 |
地质学 | 219篇 |
海洋学 | 42篇 |
天文学 | 109篇 |
综合类 | 3篇 |
自然地理 | 38篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 21篇 |
2017年 | 18篇 |
2016年 | 45篇 |
2015年 | 27篇 |
2014年 | 27篇 |
2013年 | 35篇 |
2012年 | 30篇 |
2011年 | 46篇 |
2010年 | 28篇 |
2009年 | 35篇 |
2008年 | 36篇 |
2007年 | 14篇 |
2006年 | 24篇 |
2005年 | 18篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1987年 | 5篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1964年 | 2篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1961年 | 2篇 |
1954年 | 2篇 |
1952年 | 5篇 |
1951年 | 4篇 |
1950年 | 3篇 |
1949年 | 2篇 |
1948年 | 8篇 |
1941年 | 3篇 |
1940年 | 3篇 |
1939年 | 6篇 |
排序方式: 共有661条查询结果,搜索用时 15 毫秒
41.
This paper compares two generators of yearly water availabilities from sources located at multiple sites with regard to their ability to reproduce the characteristics of historical critical periods and to provide reliable results in terms of the return period of critical sequences of different length. The two models are a novel multi-site Markov mixture model explicitly accounting for drought occurrences and a multivariate ARMA. In the case of the multisite Markov mixture model parameter estimation is limited to a search in the parameter space guided by the value of parameter λ to show the sensitivity of the model to this parameter. Application to two of the longest time series of streamflows available in Sicily (Italy) shows that the models can provide quite different results in terms of estimated return periods of historic droughts, although they seem to perform more uniformly when it comes to simulate drought-related statistics such as drought length, severity and intensity. The role of parameter selection for the multisite Markov mixture model and of the marginal probability of generated flows in providing results consistent with the characteristics of the observed series is discussed. Both models are applied to the system of sources supplying the city of Palermo (Sicily) and its environs showing the applicability of the newly developed multisite Markov mixture model to medium-to-large scale water resources systems. 相似文献
42.
Carmela Freda Mario Gaeta Daniel B. Karner Fabrizio Marra Paul R. Renne Jacopo Taddeucci Piergiorgio Scarlato John N. Christensen Luigi Dallai 《Bulletin of Volcanology》2006,68(6):567-591
A comprehensive volcanological study of the Albano multiple maar (Alban Hills, Italy) using (i) 40Ar/39Ar geochronology of the most complete stratigraphic section and other proximal and distal outcrops and (ii) petrographic observations,
phase analyses of major and trace elements, and Sr and O isotopic analyses of the pyroclastic deposits shows that volcanic
activity at Albano was strongly discontinuous, with a first eruptive cycle at 69±1 ka producing at least two eruptions, and
a second cycle with two peaks at 39±1 and 36±1 ka producing at least four eruptions. Contrary to previous studies, we did
not find evidence of magmatic or hydromagmatic eruptions younger than 36±1 ka. The activity of Albano was fed by a new batch
of primary magma compositionally different from that of the older activity of the Alban Hills; moreover, the REE and 87Sr/86Sr data indicate that the Albano magma originated from an enriched metasomatized mantle. According to the modeled liquid line
of descent, this magma differentiated under the influence of magma/limestone wall rock interaction. Our detailed eruptive
and petrologic reconstruction of the Albano Maar evolution substantiates the dormant state of the Alban Hills Volcanic District.
Electronic Supplementary Material Supplementary material is available for this article at
Editorial responsibility: J. Donnelly-Nolan
An erratum to this article can be found at 相似文献
43.
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
44.
Mario Rabinowitz 《Astrophysics and Space Science》1998,262(4):391-410
Small, quiescent black holes can be considered as candidates for the missing dark matter of the universe, and as the core
energy source of ball lightning. By means of gravitational tunneling, unidirectional radiation is emitted from black holes
in a process much attenuated from that of Hawking radiation, P, which has proven elusive to detect. Gravitational tunneling
emission is similar to electric field emission of electrons from a metal in that a second body is involved which lowers the
barrier and gives the barrier a finite rather than infinite width. Hawking deals with a single isolated black hole. The radiated
power here is P ∝ e-2Δγ P, where e-2Δγ is the transmission probability.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
45.
Vincenzo Amico Giuseppe Impellizzeri Giovanna Oriente Mario Piattelli Sebastiano Sciuto Corrado Tringali 《Marine pollution bulletin》1979,10(10):282-284
Concentrations of chlorinated hydrocarbons (DDT and metabolites, PCBs, aldrin, dieldrin, HCB and BHCs) have been determined in the tissues of five species of marine animals sampled in selected areas of the central Mediterranean. 相似文献
46.
Vincenzo Amico Giovanna Oriente Mario Piattelli Corrado Tringali 《Marine pollution bulletin》1979,10(6):177-179
The levels of PCBs, DDT and BHC residues have been determined in thalli of 12 species of marine algae harvested along the east coast of Sicily. The results are discussed in comparison with those obtained earlier with animal species sampled in the same area. 相似文献
47.
Mario Bossolasco Guiseppe Cicconi Ignazio Dagnino Antonio Elena Giuseppe Flocchini 《Pure and Applied Geophysics》1965,62(1):207-214
Summary The relationship, already found by the authors, between sunspot numbers and the solar constant, as deduced from the highest global irradiance values at noon, is here reexamined and confirmed. Some attempts at explanation and further inferences are presented. 相似文献
48.
49.
Mario A. VESCONI Shawn P. WRIGHT Mauro SPAGNUOLO Robert JACOB Carlos CERRUTTI Luciana GARCIA Evangelina FERNANDEZ William A. CASSIDY 《Meteoritics & planetary science》2011,46(7):935-949
Abstract– More craters may be discovered in the future, but as it is currently known, the Campo del Cielo crater field is 18 km long by 4 km at its widest point. Such a distribution of craters suggests that the parent meteoroid entered and traversed the atmosphere at a very low angle relative to horizontal. The crater field contains at least 20 small craters produced by the larger fragments of the parent meteoroid. Four of these are explosion analog craters and the rest are penetration funnels. During four field seasons, we have constructed topographic and magnetic maps of four of the penetration funnels as found, and then dug trenches across them to learn their original structures and recover meteorites preserved within them. Structures of these penetration funnels indicate very low angles of impact, i.e., 9–16° relative to horizontal. This supports the idea that the parent meteoroid traversed the atmosphere at a low angle. Data given here for the four penetration funnels include projectile masses, lengths, widths, depths, and estimates of impact angles and azimuths. One of the penetration funnels described here (No. 6) can almost be classified as an explosion analog crater. 相似文献
50.
Martin SCHMIEDER Elmar BUCHNER Winfried H. SCHWARZ Mario TRIELOFF Philippe LAMBERT 《Meteoritics & planetary science》2010,45(8):1225-1242
Abstract– 40Ar/39Ar dating of potassium feldspar (primary spherulitic‐blocky and secondary idiomorphic K‐feldspar) separated from impact‐metamorphosed gneiss found near Videix in the western central part of the Rochechouart impact structure (NW Massif Central, France) yielded a Rhaetian combined age of 201 ± 2 Ma (2σ), indistinguishable within uncertainty from the age of the Triassic/Jurassic boundary. Ballen quartz intergrown with the primary K‐feldspar indicates post‐shock temperatures exceeding approximately 1000 °C that affected the precursor gneiss. Geochemically, both feldspar types represent essentially pure potassium end‐members. Apart from the approximately 15 km diameter impact deposit area, the youngest crystallization age known for basement rocks in this part of the Massif Central is approximately 300 Ma. No endogenic magmatic‐thermal events are known to have occurred later in this region. The K‐feldspar recrystallized from local feldspar melts and superimposed post‐shock hydrothermal crystallization, probably within some thousands of years after the impact. It is, therefore, suggested that the 40Ar/39Ar age for the Videix gneiss (as a potassic “impact metasomatite”) dates the Rochechouart impact, in consistence with evidence for K‐metasomatism in the Rochechouart impactites. The new age value is distinctly younger than the previously obtained Karnian–Norian age for Rochechouart and, thus, contradicts the Late Triassic multiple impact theory postulated some years ago. In agreement with the paleogeographic conditions in the western Tethys domain around the Triassic/Jurassic boundary, the near‐coastal to shallow marine Rochechouart impact is compatible with the formation of seismites and tsunami deposits in the latest Triassic of the British Isles and possible related deposits in other parts of Europe. 相似文献