全文获取类型
收费全文 | 722篇 |
免费 | 34篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 37篇 |
地球物理 | 206篇 |
地质学 | 285篇 |
海洋学 | 84篇 |
天文学 | 84篇 |
综合类 | 3篇 |
自然地理 | 36篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 35篇 |
2017年 | 26篇 |
2016年 | 37篇 |
2015年 | 25篇 |
2014年 | 26篇 |
2013年 | 61篇 |
2012年 | 45篇 |
2011年 | 54篇 |
2010年 | 44篇 |
2009年 | 48篇 |
2008年 | 20篇 |
2007年 | 35篇 |
2006年 | 28篇 |
2005年 | 31篇 |
2004年 | 16篇 |
2003年 | 19篇 |
2002年 | 27篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 14篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有764条查询结果,搜索用时 62 毫秒
91.
92.
Carvalho S Gaspar MB Moura A Vale C Antunes P Gil O da Fonseca LC Falcão M 《Marine pollution bulletin》2006,52(11):1414-1424
This study reports the longitudinal distribution of sediment properties, including inorganic and organic contaminants, and the structure of the benthic community in Obidos lagoon, a coastal system permanently connected to the sea and with negligible freshwater sources. Sediments from the upper to central lagoon consist of fine particles (91%) and from the lower lagoon of sands (94%). Chemical composition is strongly correlated to the percentage of fine particles. Contamination is relatively low in those sediments suggesting the effect of diffuse sources. The increase in organic matter content from down- to upstream areas was associated with the dominance of opportunistic species, while sensitive and indifferent species to organic enrichment were mainly associated to the clean sandy downstream area. The marine biotic index (AMBI) was suitable for the discrimination of the biological and environmental gradients in the Obidos lagoon and was highly related with the gradient of organic matter content in this system. 相似文献
93.
Maria Dolores Frías Roberto Mínguez Jose Manuel Gutiérrez Fernando J. Méndez 《Climatic change》2012,113(2):371-392
This paper analyzes changes of maximum temperatures in Europe, which are evaluated using two state-of-the-art regional climate models from the EU ENSEMBLES project. Extremes are expressed in terms of return values using a time-dependent generalized extreme value (GEV) model fitted to monthly maxima. Unlike the standard GEV method, this approach allows analyzing return periods at different time scales (monthly, seasonal, annual, etc). The study focuses on the end of the 20th century (1961?C2000), used as a calibration/validation period, and assesses the changes projected for the period 2061?C2100 considering the A1B emission scenario. The performance of the regional models is evaluated for each season of the calibration period against the high-resolution gridded E-OBS dataset, showing a similar South-North gradient with larger values over the Mediterranean basin. The inter-RCM changes in the bias pattern with respect to the E-OBS are larger than the bias resulting from a change in the boundary conditions from ERA-40 to ECHAM5 20c3m. The maximum temperature response to increased green house gases, as projected by the A1B scenario, is consistent for both RCMs. Under that scenario, results indicate that the increments for extremes (e.g. 40-year return values) will be two or three times higher than those for the mean seasonal temperatures, particularly during Spring and Summer in Southern Europe. 相似文献
94.
The United Nations Framework on Climate Change (UNFCCC), at its thirteenth meeting in 2005 (COP-11), agreed to start a work program to explore a range of policy approaches and positive incentives for Reducing Emissions from Deforestation and Degradation (REDD). This process was further encouraged in the 2007 COP-13 with the explicit consideration of REDD activities as a means to enhance mitigation action by developing countries in the future. This paper outlines the context of this ongoing political process by reviewing the science indicating that land-use change is a key contributor of greenhouse emissions globally and the assumptions that REDD activities may be competitive—in terms of cost effectiveness—in comparison to other mitigation options. The paper then examines REDD proposals submitted by Parties before COP-13 and identifies key economic, technological, methodological and institutional challenges associated with their implementation. These proposals are discussed in the light of major drivers of deforestation and ongoing efforts to address deforestation. This reveals another set of challenges which, if not taken into account, may undermine REDD effectiveness. The paper aims to aid the policy process and contribute to the best possible design of a REDD framework under the future climate regime. 相似文献
95.
Masakazu Yoshimori Christoph C. Raible Thomas F. Stocker Manuel Renold 《Climate Dynamics》2010,34(1):101-121
The significance of the Atlantic meridional overturning circulation (MOC) for regional and hemispheric climate change requires
a complete understanding using fully coupled climate models. Here we present a persistent, decadal oscillation in a coupled
atmosphere–ocean general circulation model. While the present study is limited by the lack of comparisons with paleo-proxy
records, the purpose is to reveal a new theoretically interesting solution found in the fully-coupled climate model. The model
exhibits two multi-century-long stable states with one dominated by decadal MOC oscillations. The oscillations involve an
interaction between anomalous advective transport of salt and surface density in the North Atlantic subpolar gyre. Their time
scale is fundamentally determined by the advection. In addition, there is a link between the MOC oscillations and North Atlantic
Oscillation (NAO)-like sea level pressure anomalies. The analysis suggests an interaction between the NAO and an anomalous
subpolar gyre circulation in which sea ice near and south of the Labrador Sea plays an important role in generating a large
local thermal anomaly and a meridional temperature gradient. The latter induces a positive feedback via synoptic eddy activity
in the atmosphere. In addition, the oscillation only appears when the Nordic Sea is completely covered by sea ice in winter,
and deep convection is active only near the Irminger Sea. Such conditions are provided by a substantially colder North Atlantic
climate than today. 相似文献
96.
97.
Edwin GNOS Silvio LORENZETTI Otto EUGSTER A. J. Timothy JULL Beda A. HOFMANN Ali Al‐KATHIRI Manuel EGGIMANN 《Meteoritics & planetary science》2009,44(3):375-387
Abstract— The recently discovered Jiddat al Harasis (JaH) 073 strewn field is the largest found so far in the Sultanate of Oman, covering an area of 19 × 6 km. The 3463 single stones collected range in weight from 52.2 kg down to <1 g (total weight 600.8 kg) and show a pronounced mass sorting. The strewn field shape can be approximated by a NW‐SE‐oriented ellipsoid, indicating an atmospheric entry from SE at a low angle relative to the surface. The meteorite belongs to the L6 ordinary chondrite group and shows S4 average shock grade. Smaller stones generally show a higher weathering grade resulting in a spread from W2 and W4. Enhanced weathering of the stones causing fragmentation after the fall is observed in sandy depressions. Five 14C measurements on stones of variable size and weathering grade yielded 14C from 3.8 to 49.9 dpm/kg. Three samples give a 14C/ 10Be age consistent with about 14.4 ka. For two samples the cosmogenic, trapped, and radiogenic noble gases were measured. The ratio of the 4He and 40Ar gas retention ages of 0.29 ± 0.10 and that of the 3He and 21Ne cosmic ray exposure ages of 0.36 ± 0.08 Ma indicate that JaH 073 experienced a complex exposure history and lost 4He and 40Ar due to a major collision. Fragmentation statistics indicate a single major atmospheric disruption and an originally relatively spherical shape of the object. Assuming the material collected represents the majority of fallen mass, and 90–99% of the original weight was lost by ablation, the pre‐atmospheric minimum radius of the meteoroid with density 3.4 g cm?3would have been at least 75 cm. 相似文献
98.
Chemical and chronologic complexity in the convecting upper mantle: Evidence from the Taitao ophiolite, southern Chile 总被引:1,自引:0,他引:1
Ruth F. Schulte Manuel Schilling Ryo Anma James Farquhar Mary F. Horan Tsuyoshi Komiya Philip M. Piccoli Lynnette Pitcher Richard J. Walker 《Geochimica et cosmochimica acta》2009,73(19):5793-5819
Exposure of the ca. 6 Ma Taitao ophiolite, Chile, located 50 km south of the Chile Triple Junction, allows detailed chemical and isotopic study of rocks that were recently extracted from the depleted mantle source of mid-ocean ridge basalts (DMM). Ultramafic and mafic rocks are examined for isotopic (Os, Sr, Nd, and O), and major and trace element compositions, including the highly siderophile elements (HSE). Taitao peridotites have compositions indicative of variable extents of partial melting and melt extraction. Low δ18O values for most whole rock samples suggest some open-system, high-temperature water–rock interaction, most likely during serpentinization, but relict olivine grains have δ18O values consistent with primary mantle values. Most of the peridotites analyzed for Nd–Sr isotopes have compositions consistent with estimates for the modern DMM, although several samples are characterized by 87Sr/86Sr and 143Nd/144Nd indicative of crustal contamination, most likely via interactions with seawater. The peridotites have initial 187Os/188Os ratios that range widely from 0.1168 to 0.1288 (γOs = −8.0 to +1.1), averaging 0.1239 (γOs = −2.4), which is comparable to the average for modern abyssal peridotites. A negative correlation between the Mg# of relict olivine grains and Os isotopic compositions of whole rock peridotites suggests that the Os isotopic compositions reflect primary mantle Re/Os fractionation produced by variable extents of partial melting at approximately 1.6 Ga. Recent re-melting at or near the spatially associated Chile Ridge further modified these rocks, and Re, and minor Pt and Pd were subsequently added back into some rocks by late-stage melt–rock or fluid–rock interactions.In contrast to the peridotites, approximately half of the mafic rocks examined have whole rock δ18O values within the range of mantle compositions, and their Nd and Sr isotopic compositions are all generally within the range of modern DMM. These rocks have initial 187Os/188Os ratios, calculated for 6 Ma, that range from 0.126 (γOs = −1) to as high as 0.561 (γOs = +342). The Os isotopic systematics of each of these rocks may reflect derivation from mixed lithologies that include the peridotites, but may also include pyroxenites with considerably more radiogenic Os than the peridotites. This observation supports the view that suprachondritic Os present in MORB derives from mixed mantle source lithologies, accounting for some of the worldwide dichotomy in 187Os/188Os between MORB and abyssal peridotites.The collective results of this study suggest that this >500 km3 block of the mantle underwent at least two stages of melting. The first stage occurred at 1.6 Ga, after which the block remained isolated and unmixed within the DMM. A final stage of melting recently occurred at or near the Chile Ridge, resulting in the production of at least some of the mafic rocks. Convective stirring of this mantle domain during a >1 Ga period was remarkably inefficient, at least with regard to Os isotopes. 相似文献
99.
Dionisis Katsikopoulos Ángeles Fernández-González Manuel Prieto 《Geochimica et cosmochimica acta》2009,73(20):6147-455
The enthalpy of mixing of the calcite-rhodochrosite (Ca,Mn)CO3 solid solution was determined at 25 °C from calorimetric measurements of the enthalpy of precipitation of solids with different compositions. A detailed study of the broadening of powder X-ray diffraction peaks shows that most of the precipitates are compositionally homogeneous. All the experimental enthalpy of mixing (ΔHm) values are positive and fit reasonably well (R2 = 0.86) to a Guggenheim function of three terms:
100.
Jürgen Oberst Valéry Lainey Christophe Le Poncin-Lafitte Veronique Dehant Pascal Rosenblatt Stephan Ulamec Jens Biele J?rn Spurmann Ralph Kahle Volker Klein Ulrich Schreiber Anja Schlicht Nicolas Rambaux Philippe Laurent Beno?t Noyelles Bernard Foulon Alexander Zakharov Leonid Gurvits Denis Uchaev Scott Murchie Cheryl Reed Slava G. Turyshev Jesus Gil Mariella Graziano Konrad Willner Kai Wickhusen Andreas Pasewaldt Marita W?hlisch Harald Hoffmann 《Experimental Astronomy》2012,34(2):243-271
GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame. 相似文献