全文获取类型
收费全文 | 319篇 |
免费 | 3篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 37篇 |
地球物理 | 67篇 |
地质学 | 114篇 |
海洋学 | 27篇 |
天文学 | 58篇 |
自然地理 | 14篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2020年 | 10篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 5篇 |
2013年 | 25篇 |
2012年 | 18篇 |
2011年 | 12篇 |
2010年 | 13篇 |
2009年 | 13篇 |
2008年 | 19篇 |
2007年 | 22篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有322条查询结果,搜索用时 15 毫秒
81.
The magnetic field in an axisymmetric pore is current free and can be represented by a flux tube with a magnetic potential of the formAJ
0(kr)e
-kz. For a given magnetic flux the field in this pore model is uniquely defined if the magnetic pressure balances the gas pressure at two levels. For models with fluxes of 0.5–3.0 × 1020 mx the surface radius varies from 1100–2700 km (diameters of 3–8 arc-sec) and the Wilson depression is estimated at 200 km. As the flux increases, the field becomes nearly horizontal at the edge of the pore and eventually a penumbra is formed. The distinction between pores and sunspots is investigated; the critical flux is about 1020 Mx, corresponding to a radius of 1500 km.Visitor, as a member of the High Altitude Observatory Solar Project, at Sacramento Peak Observatory, Sunspot, N.M., U.S.A. 相似文献
82.
83.
A procedure is presented for designing Kalman filters to measure linear and angular ship motion parameters using realistic models of the ship motion dynamics. The design is based on the state space modeling of ship motion dynamics. The designed filters exhibited significant accuracy improvement (order of magnitude) over filters which do not model ship dynamics. The sensitivity of the filter mechanization to mismodeling of dynamics is investigated. Bounding filter design techniques are used to minimize the effects of mismodeling. The particular measurement system investigated consisted of linear and angular accelerometers in a strapdown mode. The design techniques are also applicable to inertial instruments in a stable inertial platform mode. 相似文献
84.
Helioseismological sound-speed profiles severely constrain possible deviations from standard solar models, allowing us to derive new limits on anomalous solar energy losses by the Primakoff emission of axions. For an axion-photon coupling gay 5 × 10−10 GeV−1, the solar model is almost indistinguishable from the standard case, while gay 10 × 10−10 GeV−1 is probably excluded, corresponding to an axion luminosity of about 0.20 L. This constraint on gay is much weaker than the well-known globular-cluster limit, but about a factor of 3 more restrictive than previous solar limits. Our result is primarily of interest to the large number of current or proposed search experiments for solar axions because our limit defines the maximum gay for which it is self-consistent to use a standard solar model to calculate the axion luminosity. 相似文献
85.
Abstract— The potential hazard of a meteorite impact in the ocean is controversial with respect to the destructive power of generated large ocean waves (tsunamis). We used numerical modeling of hypervelocity impact to investigate the generation mechanism and the characteristics of the resulting waves up to a distance of 100–150 projectile radii. The wave signal is primarily controlled by the ratio between projectile diameter and water depth, and can be roughly classified into deep‐water and shallow‐water impacts. In the latter, the collapse of the crater rim results in a wave signal similar to solitary waves, which propagate and decay in agreement with shallow‐water wave theory. The much more likely scenario for an asteroid impact on Earth is a relatively small body (much smaller than the water depth) striking the deep sea. In this case, the collapse of the transient crater results in a significantly different and much more complex wave signal that is characterized by strong nonlinear behavior. We found that such waves decay much more rapidly than previously assumed and cannot be treated as long waves. For this reason, the shallow‐water theory is not applicable for the computation of wave propagation, and more complex models (full solution of the Boussinesq equations) are required. 相似文献
86.
Jörn Parplies Andreas Lücke Heinz Vos Jens Mingram Martina Stebich Ulrich Radtke Jingtai Han Gerhard H. Schleser 《Journal of Paleolimnology》2008,40(1):471-487
Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ15N) and stable organic carbon isotope (δ13Corg) ratios were continuously analysed on a high resolution sediment profile from Lake Sihailongwan (SHL), covering the time
span between 16,500 and 9,500 years BP. Strong variations of the investigated proxy parameters are attributed to great climatic
fluctuations during the investigated time period. Variations in organic carbon isotope ratios and the ratio of TOC/TN (C/N
ratio) are discussed with respect to changing proportions of different organic matter (OM) sources to bulk sedimentary OM.
Phases of high TOC content, high TN content, depleted δ13Corg values and high δ15N values are interpreted as times with increased productivity of lacustrine algae in relation to input of terrigenous organic
matter. Two distinct phases of enriched nitrogen isotope ratios from 14,200 to 13,700 and 11,550 to 11,050 years BP point
towards a reduced phytoplankton discrimination against 15N due to a diminished dissolved inorganic nitrogen pool. The combination of geochemical (TOC, TN, C/N ratio) and isotopic
(δ13Corg, δ15N) proxy parameters points to a division of climate development into four stages. A cold and dry stage before 14,200 years
BP, a warm optimum stage with high phytoplankton productivity from 14,200 to 12,450 BP, a colder and drier stage from 12,450
to 11,600 BP and a stage of climatic amelioration with high variability in TOC and TN contents after 11,600 BP. These results
are discussed in relation to monsoon variability and Northern Hemisphere climate development of the late glacial. 相似文献
87.
Kahlenberg Volker Mayerl Michael Jean-Philippe Schmidmair Daniela Krüger Hannes Tribus Martina 《Mineralogy and Petrology》2018,112(2):219-228
Mineralogy and Petrology - In the course of an exploratory study on the quaternary system Na2O-K2O-CaO-SiO2 single crystals of the first anhydrous sodium potassium calcium silicate have been... 相似文献
88.
Martina Flörke Ellen Kynast Ilona Bärlund Stephanie Eisner Florian Wimmer Joseph Alcamo 《Global Environmental Change》2013,23(1):144-156
To enhance global water use assessment, the WaterGAP3 model was improved for back-calculating domestic, manufacturing and thermoelectric water uses until 1950 for 177 countries. Model simulations were carried-out on a national scale to estimate water withdrawals and consumption as well as cooling water required for industrial processes and electricity production. Additionally, the amount of treated and untreated wastewater as generated by the domestic and manufacturing sectors was modeled. In the view of data availability, model simulations are based on key socio-economic driving forces and thermal electricity production. Technological change rates were derived from statistical records in order to consider developments in water use efficiency, which turned out to have a crucial role in water use dynamics. Simulated domestic and industrial water uses increased from ca. 300 km3 in 1950 to 1345 km3 in 2010, 12% of which were consumed and 88% of which were discharged back into freshwater bodies. The amount of domestic and manufacturing wastewater increased considerably over the last decade, but only half of it was untreated. The downscaling of the untreated wastewater volume to river basin scale indicates a matter of concern in East and Southeast Asia, Northern Africa, and Eastern and Southern Europe. In order to reach the Millennium Development Goals, securing water supply and the reduction of untreated wastewater discharges should be amongst the priority actions to be undertaken. Population growth and increased prosperity have led to increasing water demands. However, societal and political transformation processes as well as policy regulations resulting in new water-saving technologies and improvements counteract this development by slowing down and even reducing global domestic and industrial water uses. 相似文献
89.
M. Breger M. Hareter M. Endl R. Kuschnig W.W. Weiss J.M. Matthews D.B. Guenther A.F.J. Moffat J.F. Rowe S.M. Rucinski D. Sasselov 《Astronomische Nachrichten》2012,333(2):131-137
The Praesepe cluster contains a number of δ Sct and γ Dor pulsators. Asteroseismology of cluster stars is simplified by the common distance, age and stellar abundances. Since asteroseismology requires a large number of known frequencies, the small pulsation amplitudes of these stars require space satellite campaigns. The present study utilizes photometric MOST satellite measurements in order to determine the pulsation frequencies of two evolved (EP Cnc, BT Cnc) and two main‐sequence (BS Cnc, HD 73872) δ Sct stars in the Praesepe cluster. The frequency analysis of the 2008 and 2009 data detected up to 34 frequencies per star with most amplitudes in the submillimag range. In BS Cnc, two modes showed strong amplitude variability between 2008 and 2009. The frequencies ranged from 0.76 to 41.7 cd–1. After considering the different evolutionary states and mean stellar densities of these four stars, the differences and large ranges in frequency remain (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
90.