全文获取类型
收费全文 | 5609篇 |
免费 | 276篇 |
国内免费 | 44篇 |
专业分类
测绘学 | 155篇 |
大气科学 | 400篇 |
地球物理 | 2106篇 |
地质学 | 1837篇 |
海洋学 | 410篇 |
天文学 | 722篇 |
综合类 | 28篇 |
自然地理 | 271篇 |
出版年
2022年 | 38篇 |
2021年 | 112篇 |
2020年 | 108篇 |
2019年 | 79篇 |
2018年 | 227篇 |
2017年 | 220篇 |
2016年 | 335篇 |
2015年 | 251篇 |
2014年 | 286篇 |
2013年 | 371篇 |
2012年 | 311篇 |
2011年 | 311篇 |
2010年 | 264篇 |
2009年 | 289篇 |
2008年 | 238篇 |
2007年 | 215篇 |
2006年 | 173篇 |
2005年 | 146篇 |
2004年 | 167篇 |
2003年 | 124篇 |
2002年 | 80篇 |
2001年 | 99篇 |
2000年 | 76篇 |
1999年 | 64篇 |
1998年 | 84篇 |
1997年 | 70篇 |
1996年 | 49篇 |
1995年 | 40篇 |
1994年 | 56篇 |
1993年 | 43篇 |
1992年 | 46篇 |
1991年 | 39篇 |
1990年 | 57篇 |
1989年 | 41篇 |
1988年 | 33篇 |
1987年 | 34篇 |
1986年 | 41篇 |
1984年 | 42篇 |
1983年 | 37篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 27篇 |
1979年 | 27篇 |
1978年 | 32篇 |
1977年 | 30篇 |
1976年 | 28篇 |
1975年 | 31篇 |
1974年 | 35篇 |
1973年 | 33篇 |
1971年 | 41篇 |
排序方式: 共有5929条查询结果,搜索用时 15 毫秒
941.
IUPA: a tool for the evaluation of the general usefulness of practices for adaptation to climate change and variability 总被引:1,自引:0,他引:1
P. Debels C. Szlafsztein P. Aldunce C. Neri Y. Carvajal M. Quintero-Angel A. Celis A. Bezanilla D. Martínez 《Natural Hazards》2009,50(2):211-233
A prototype multi-purpose index is proposed for use in the evaluation of practices for adaptation to climate variability and
change. The Index of Usefulness of Practices for Adaptation (IUPA) allows the user to assign weights and scores to a set of
user-defined evaluation criteria. Individual criterion scores are aggregated into a final index value. Both the final value
and the individual parameter scores provide useful information for improved decision making in the context of climate change.
An innovative aspect of IUPA is that guidance is given to the user through the inclusion of recommendations on evaluation
criteria and criterion-specific weight factors. These have been defined by a panel of experts from the Latin-American and
Caribbean Region (LAC). Application of the index is demonstrated for an existing adaptation practice from the Coquimbo Region,
Chile. The IUPA tool is recommended for use in the evaluation of adaptation practices in their design, implementation and
post-implementation phase. It is practical for a quick first assessment or when limited financial resources are available,
making the tool especially useful for practitioners in the developing world. The index is flexible both from the perspective
of its construction and use. Additional expert opinions can easily be included in the future versions of the tool. 相似文献
942.
Implications of geomorphological research for recent and prehistoric avalanches and related hazards at Huascaran,Peru 总被引:2,自引:0,他引:2
Detailed research of superficial deposits below the northern peak of Huascaran (Cordillera Blanca) provides new information
on the limits of a paleo-avalanche originating from this mountain. Geomorphological mapping of the sediments identified glacial
deposits, deposits from historical rock-debris avalanches and huge boulders from a paleo-avalanche. Schmidt Hammer rock-hardness
tests were used to distinguish between the several generations of rock-debris avalanches, but largely failed to distinguish
between the much older moraine and the paleo-avalanche sediments. Thus, only the field geomorphological mapping proved to
be reliable for identifying the limits of the paleo-avalanche. The limits identified as granite boulders deposited over volcanic
rocks were found to extend 30 m further up the opposite valley slope than previously had been mapped. This larger extent implies
a greater volume and/or greater mobility for the prehistoric event. 相似文献
943.
On the eastern extremity of the Jiaodong peninsula, China, shoshonitic magmas have been injected into the supracrustal rocks of the Sulu ultra-high pressure (UHP) terrane during the crustal exhumation phase. These granitoids (collectively termed the Shidao igneous complex or Jiazishan alkaline complex) show geochemical and isotopic signatures of an enriched subcontinental lithospheric mantle and intruded soon after the subducted Yangtze crust had reached peak metamorphic pressure conditions (240–220 Ma). We have applied various geochronometers to an alkali-gabbro sample from the Jiazishan pluton and the results allow reconstruction of the Triassic-to-present thermal history. Initial rapid cooling of the gabbro at crustal depths is indicated by the close agreement between the Sm-Nd mineral isochron age (228?±?36 Ma) and the Rb-Sr biotite age (207?±?1) Ma. This interpretation is confirmed by previously published U-Pb zircon ages (225–209 Ma), and 40Ar/39Ar amphibole and K-feldspar ages (~214 Ma) from the Jiazishan syenites. A titanite fission-track age of 166?±?8 Ma (closure temperature range 285–240°C) records widespread Jurassic magmatism in the Jiaodong peninsula, indicating that the gabbro reached upper crustal levels before it was reheated by nearby Jurassic plutons. A subsequent cooling and reheating event is indicated by an apatite fission-track age of 106?±?6 Ma which coincides with the emplacement of the adjacent Weideshan pluton (108?±?2 Ma) and postdates a period of regional lithospheric thinning beneath eastern China. A period of slow cooling (or thermal stability) from late Cretaceous to early Tertiary, documented by an apatite (U-Th)/He age of 39?±?5 Ma, was followed by a final stage of more enhanced cooling since the late Eocene. Results of this work imply that the eastern Sulu terrane has experienced a complex cooling and reheating history. Our data are consistent with a model of initial rapid cooling (sudden exhumation) of the UHP terrane, driven by the release of buoyancy forces, followed by two progressively slower cooling intervals (both after renewed crustal reheating) during the Jurassic and Cretaceous. 相似文献
944.
M. Jamrozy D. Kozieł-Wierzbowska S. Zoła A. Kuźmicz J. Machalski 《Journal of Astrophysics and Astronomy》2011,32(4):467-470
J1159+5820 is an extended radio galaxy with a quite unusual morphology, featuring two pairs of radio lobes. Such sources,
called double–double radio galaxies, constitute a very rare class of extragalactic radio sources. Furthermore, the extended
radio structure of this source shows an X-shape form. According to a much likely scenario, such a morphology is due to interrupting
nuclear activity in its central active galactic nucleus. Interestingly, the host of this source is a near-distance bright
galaxy named CGCG 292-057, which is clearly disturbed, with tidal features and shells as plausible signs of a recent merger. 相似文献
945.
María Jos Salas 《Geological Journal》2011,46(6):637-650
The ostracod fauna from the Floian (Lower Ordovician) strata of the Cordillera Oriental, Argentina (Acoite Formation) are documented. One new genus Acoitella and four species are recognized, two of which are new (Nanopsis victoria sp. nov. and Conchoprimitia frequens sp. nov.). The diversity of the Early Ordovician ostracod faunas of the Central Andean Basin is evaluated. Compared with other regions, the ostracod diversity, at generic and specific level, of the Cordillera Oriental was comparatively high during the Tremadocian (nine species recorded) and comparatively low during the Floian (four species recorded). The taxonomic composition of the fauna is similar during the entire Early Ordovician of the Cordillera Oriental, where it displays a high percentage of soanellids. The Floian assemblages are characterized by the dominance of the eridostracan C. frequens sp. nov. with a high percentage of nondimorphic palaeocopids: Nanopsis and two genera of the Soanellidae family (Saltite and Acoitella gen nov.). An ostracod shell bed is described and interpreted to be a parautochthonous assemblage, as a result of transport within the same habitat. The composition of the fauna, with the presence of Saltite and Nanopsis, shows significant affinities with East Gondwana. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
946.
Javier Alcántara-Carrió Silvia Albarracín Isabel Montoya Montes Germán Flor-Blanco Ángela Fontán Bouzas Jorge Rey Salgado 《Geo-Marine Letters》2013,33(2-3):209-216
The objective of this study is to document and interpret a recently discovered carbonate-cemented coastal barrier on the inner shelf of the Gulf of Valencia (western Mediterranean Sea). The coastal barrier was identified in a high-resolution digital bathymetric model based on a cartographic survey of the study area using a multibeam echosounder. Moreover, radiocarbon dating and petrographic analyses were performed on a rock sample recovered from the seabed. The data reveal the submerged coastal barrier to be approx. 1.7 km wide and 70 km long, and incised by channels of various dimensions. Aligned more or less parallel to the modern coastline, it is interpreted as corresponding to the shoreline of a former sea-level stillstand. The barrier and lagoon system became stranded above sea level in the course of a subsequent forced regression, which also caused the incision of the river courses. Age dating of the cemented rock suggests that the fossil coastal barrier most probably formed during the prolonged Tyrrhenian (Eemian) sea-level highstand, induration taking place by carbonate cementation at the contact between freshwater and seawater (beach-rock formation). The fact that the fossil barrier is today submerged below modern sea level is explained by the sustained subsidence affecting the region. 相似文献
947.
Automatic tracing of the foot of the continental slope 总被引:1,自引:0,他引:1
The UNCLOS III (Article 76, Section 4(b)) defines the foot of the continental slope as the point of maximum change in the gradient at its base. It is impossible to locate so defined afoot and thus to trace the foot‐line objectively by eye. In this study we show a method designed automatically to detect and trace the foot‐line of the continental slope from an irregular array of bathymetrical data. Our algorithm first transforms the bathymetric surface to a maximum curvature surface. On this new surface, the foot‐line corresponds to one of the ridges; instead of tracing the foot‐line on the bathymetric surface, we now can trace the ridges on the maximum curvature surface. The tracing of the ridges can be done automatically and objectively and the foot‐line is identified as being one of these ridges. We devote particular attention to the case when the ridge‐line is not defined, i.e., to the case when the point of maximum gradient change becomes a region of maximum gradient change. 相似文献
948.
Susana Bolhão Muiños James R. Hein Martin Frank José Hipólito Monteiro Luís Gaspar Tracey Conrad 《Marine Georesources & Geotechnology》2013,31(1):40-70
Eighteen deep-sea ferromanganese crusts (Fe-Mn crusts) from 10 seamounts in the northeast Atlantic were studied. Samples were recovered from water depths of ~1,200 to ~4,600 m from seamounts near Madeira, the Canary and Azores islands, and one sample from the western Mediterranean Sea. The mineralogical and chemical compositions of the samples indicate that the crusts are typical continental margin, hydrogenetic Fe-Mn crusts. The Fe-Mn crusts exhibit a Co + Cu + Ni maximum of 0.96 wt%. Platinum-group element contents analyzed for five samples showed Pt contents from 153 to 512 ppb. The resource potential of Fe-Mn crusts within and adjacent to the Portuguese Exclusive Economic Zone (EEZ) is evaluated to be comparable to that of crusts in the central Pacific, indicating that these Atlantic deposits may be an important future resource. 相似文献
949.
The calcarean sponge Paraleucilla magna is classified as being an invasive species on the Mediterranean Sea, where it causes economic damages to mollusc farms. On the Brazilian coast, this species is considered to be cryptogenic, and information on its ecology is scarce. The same is true for Sycettusa hastifera, another calcarean sponge with a worldwide distribution. Data on the ecology of these species could help in elucidating their potential to become a threat if they are found to be exotic species in Brazil. In the present work, we studied habitat selection, growth and mortality of early juveniles of P. magna and habitat selection of S. hastifera in a Marine Reserve from Southeastern Brazil, where these species are abundant in the benthic community. Granite plates were used for habitat selection analysis, varying in substrate inclination (vertical and horizontal) and exposure to light and hydrodynamism (exposed and sheltered). To analyse the growth and mortality rates, sponges were mapped and then measured once a week for 10 weeks. If a monitored sponge was not found in the following week, it was considered to be dead. Our results showed that, although P. magna and S. hastifera are capable of inhabiting substrates exposed to different environmental conditions, they showed habitat preferences. Growth of the juveniles of P. magna seemed not to have damaged any neighbouring invertebrates. The mortality of juveniles of this species was higher during the first 2 weeks of life but its causes could not be elucidated. 相似文献
950.
Assessment of the effects of a marine urban outfall discharge on caged mussels using chemical and biomarker analysis 总被引:1,自引:0,他引:1
de los Ríos A Juanes JA Ortiz-Zarragoitia M López de Alda M Barceló D Cajaraville MP 《Marine pollution bulletin》2012,64(3):563-573
To assess the presence of endocrine disruptors in treated marine outfall discharges and their possible effects, mussels (Mytilus galloprovincialis) were caged in the environmental mixing zone of the outfall of the Santander sanitation system and in one control area. After 30, 60 and 90 days, samples were collected to perform chemical analyses (metals, anionic surfactants, alkylphenols, bisphenol A, phthalates and estrogenic hormones), biomarkers of general stress (lysosomal membrane stability-LMS, histopathology) and biomarkers of endocrine disruption (vitellogenin-like proteins and gonad index). There were no significant differences between outfall and control sites on contaminant levels, except for 4-tert-octylphenol which was higher in the outfall site. Bacteriological counts were higher in the outfall area. No relevant differences in biomarkers were detected between treated and control mussels. A significant reduction in LMS occurred in both groups after 90 days caging, indicating a stress situation possibly related to caging or to post-spawning reproductive state. 相似文献