全文获取类型
收费全文 | 571篇 |
免费 | 29篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 41篇 |
大气科学 | 59篇 |
地球物理 | 186篇 |
地质学 | 181篇 |
海洋学 | 27篇 |
天文学 | 57篇 |
综合类 | 3篇 |
自然地理 | 51篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 8篇 |
2020年 | 15篇 |
2019年 | 10篇 |
2018年 | 16篇 |
2017年 | 15篇 |
2016年 | 25篇 |
2015年 | 21篇 |
2014年 | 20篇 |
2013年 | 38篇 |
2012年 | 30篇 |
2011年 | 27篇 |
2010年 | 22篇 |
2009年 | 41篇 |
2008年 | 24篇 |
2007年 | 29篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 18篇 |
2003年 | 18篇 |
2002年 | 16篇 |
2001年 | 16篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 1篇 |
排序方式: 共有605条查询结果,搜索用时 15 毫秒
291.
292.
Abstract The first numerical age determinations from radiocarbon dating establish the chronology of glacial events in Redes Natural Park (Cantabrian Mountain, NW Spain). A core drilled in an ice-dammed deposit provided a minimum age of 28 990 ± 230 years BP for the maximum glacial expansion (phase I). Another core from a cirque bottom-fill provided organic sediment with 20 640 ± 300 years BP, a minimum age for the first glacial retreat (phase II). Radiometric dating of proglacial deposits interpreted as synchronous with the last glacial maximum phase in neighbouring Cornelia basin (Picos de Europa), yield ages of 40 480 ± 820 years BP. The chronological data presented in this work are consistent with the model of glacier evolution established in the Pyrénées, with a glacial maximum phase for the last glacial period older than 18 ka. © 2002 Éditions scientifiques et médicales Elsevier SAS. AU rights reserved. 相似文献
293.
Gregory J. Holk T. Kurtis Kyser Don Chipley Eric E. Hiatt Jim Marlatt 《Journal of Geochemical Exploration》2003,80(2-3):297-320
Lead isotope ratios and associated trace element concentrations (U, Th and Pb) extracted by partial-leaching with 2% nitric acid from Proterozoic sandstones and basement rocks reveal much about the fluid evolution of sedimentary basins hosting unconformity-type uranium deposits. In addition, these techniques have great potential as a guide for exploration of uranium and other types of deposits in basins of any age. Isotope ratios of Pb in Proterozoic sandstones from basins known to contain high-grade uranium deposits are radiogenic at key geological localities and settings distal to known mineralization and particularly in altered zones proximal to mineralization. Sandstones completely cemented by quartz overgrowths typically have non-radiogenic Pb isotope ratios, indicating early closure of porosity and isolation of these rocks from later fluid events. Alternatively, the unconformity served as both a source of uranium and radiogenic Pb as well as an avenue for late-stage (<250–900 Ma) fluid flow. The mafic volcanic units, which are relatively reducing lithologies and therefore have removed uranium from basinal brines, have uranium-supported radiogenic Pb isotope ratios. Comparison of 238U/206Pb and 206Pb/204Pb ratios is useful in determining the timing and nature of U and Pb migration before, during and after mineralization in these basins. This comparison can be used to delineate the presence of radiogenic Pb isotope ratios that are not internally supported by uranium and thorium in rocks, eventually providing the explorationist with geochemical vectors that point toward sites of high potential for economic uranium mineralization. 相似文献
294.
青藏高原地区的大气浑浊度特征 总被引:3,自引:0,他引:3
本文通过比较Angstrom大气浑浊度系数的各种计算方法,得出了适合青藏高原地区的大气浑浊度系数的计算方法。据此利用1982年8月至1983年7月青藏高原地区部分观测站的太阳直接辐射资料计算了大气浑浊度系数,分析了它的变化特征。同时利用常规气象要素拟合得出了计算大气浑浊度系数的经验公式,计算和分析了青藏高原地区大气浑浊度系数的时间和空间分布。 相似文献
295.
Lucia Plank Andreas Hellerschmied Jamie McCallum Johannes Böhm Jim Lovell 《Journal of Geodesy》2017,91(7):867-880
The possibility of observing satellites with the very long baseline interferometry (VLBI) technique has been discussed for several years in the geodetic community, with observations of either existing satellites of the global navigation satellite systems or of satellites dedicated to realise a space tie. Such observations were carried out using the Australian telescopes in Hobart and Ceduna which, for the first time, integrated all the necessary steps: planning the observations (automated scheduling), correlation of the data and the generation of a series of time delay observables suitable for a subsequent geodetic analysis. We report on the development of new and the adaptation of existing routines for observing and data processing, focusing on technology development. The aim was to use methods that are routinely used in geodetic VLBI. A series of test experiments of up to six hours duration was performed, allowing to improve the observations from session to session and revealing new problems still to be solved. The newly developed procedures and programs now enable more observations. Further development assumed, this bears the prospect of being directly applied to the observation of dedicated space-tie satellites. 相似文献
296.
Joseph A. Stewart Steven J. Christopher John R. Kucklick Louise Bordier Thomas B. Chalk Arnaud Dapoigny Eric Douville Gavin L. Foster William R. Gray Rosanna Greenop Marcus Gutjahr Freya Hemsing Michael J. Henehan Philip Holdship Yu‐Te Hsieh Ana Kolevica Yen‐Po Lin Elaine M. Mawbey James W. B. Rae Laura F. Robinson Rachael Shuttleworth Chen‐Feng You Shuang Zhang Russell D. Day 《Geostandards and Geoanalytical Research》2021,45(1):77-96
The boron isotopic ratio of 11B/10B (δ11BSRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ11BSRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ11BSRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca < 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes. 相似文献
297.
A large assemblage of salmon bones excavated 50 yr ago from an ∼10,000-yr-old archaeological site near The Dalles, Oregon, USA, has been the primary evidence that early native people along the Columbia River subsisted on salmon. Recent debate about the human role in creating the deposit prompted excavation of additional deposits and analysis of archaeologic, geologic, and hydrologic conditions at the site. Results indicate an anthropogenic source for most of the salmonid remains, which have associated radiocarbon dates indicating that the site was occupied as long ago as 9300 cal yr B.P. The abundance of salmon bone indicates that salmon was a major food item and suggests that migratory salmonids had well-established spawning populations in some parts of the Columbia Basin by 9300-8200 yr ago. 相似文献
298.
Paul V. Burger James J. Papike Charles K. Shearer Jim M. Karner 《Geochimica et cosmochimica acta》2009,73(11):3248-318
Growth zoning in jarosite, an Fe3+-bearing sulfate mineral, can generally be characterized by variation of Na+ for K+ in the crystallographic A site or by Al3+ for Fe3+ in the octahedral (B) site. Growth zoning in a sample from Post Pit, NV, however, is more complicated than has been observed in other jarosite samples examined in this study and by previous work, and is characterized by varying Ba, Sr, P, and As. In this sample, these elements define a coupled substitution in which Ba2+ and Sr2+ substitute for K+ in the crystallographic A site, and are balanced by the substitution of P5+ and As5+ for S6+ in the tetrahedral (X) site. The Post Pit sample also exhibits a high concentration of V, which does not appear to participate in the aforementioned coupled substitution. Analysis of mineral stoichiometry and charge balance reveal that V is likely tetravalent, and represents a charge excess in the B site. The occurrence of V-bearing goethite in this sample records fluctuating fluid pH, resulting in the alternating stability of jarosite and goethite. Measurement of the REEs in jarosite by SIMS, indicate that Ce is trivalent in the Post Pit sample; reduced relative to Ce4+ found in the remainder of the sample suite. The presence of V4+ and Ce3+ indicate that the Post Pit sample was deposited in a less oxidizing environment than the remainder of the sample suite. This study illustrates how jarosite crystal chemistry can be used to place relative constraints on fluid conditions (pH, Eh, chemistry, etc.) in the terrestrial environment, and characterizes possible major and trace element coupled substitutions into the jarosite crystal structure. Furthermore, this study provides a framework for future studies to examine mineral-fluid partition coefficients (D values) which may place more absolute constraints on fluid chemistry in the jarosite depositional environment. 相似文献
299.
IGS Earth Rotation Parameters 总被引:1,自引:0,他引:1
Since its official start in January 1994, the International GPS Service (IGS) has been distributing, as part of its product
combination, two distinct Earth rotation parameter (ERP) series: the IGS Rapid series and the IGS Final series. Initially,
the IGS Rapid ERP values were interpolations of the International Earth Rotation Service (IERS) Bulletin A, whereas the IGS
Final ERP series was based on the IERS Bulletin B. Since June 1996, the IGS has been generating its own Final ERP series consistent
with the IGS combined orbit products and based on weighted means of individual IGS analysis center (AC) solutions. At first,
only the polar motion (PM) coordinates and their rates were combined. Length of Day (LOD) and Universal Time (UT) solutions,
also based on separate weighted mean combinations, followed in March 1997. Currently, the IGS Rapid and Final combinations
are produced and made available within 17 hours and 11 days, respectively, after the last observation. Both IGS and the best
AC series are consistent and precise at the 0.1-milliarcsecond (mas) level for PM and at about 30 μs for LOD. Biases in some
AC solutions may exceed these consistency levels. Comparisons of both IGS ERP series with external standards, such as the
IERS multitechnique Bulletins and atmospheric angular momentum series, confirm the estimated precisions. ? 1999 John Wiley
& Sons, Inc. 相似文献
300.