全文获取类型
收费全文 | 304篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 24篇 |
地球物理 | 71篇 |
地质学 | 143篇 |
海洋学 | 20篇 |
天文学 | 47篇 |
综合类 | 2篇 |
自然地理 | 21篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 4篇 |
2018年 | 13篇 |
2017年 | 18篇 |
2016年 | 24篇 |
2015年 | 15篇 |
2014年 | 32篇 |
2013年 | 37篇 |
2012年 | 19篇 |
2011年 | 19篇 |
2010年 | 20篇 |
2009年 | 18篇 |
2008年 | 10篇 |
2007年 | 1篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1995年 | 2篇 |
1994年 | 8篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1968年 | 1篇 |
1962年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有334条查询结果,搜索用时 31 毫秒
251.
252.
Resistivity techniques have been used successfully to identify and delineate geothermal resources in Iceland. The most frequently used techniques include Schlumberger, central loop TEM and head-on profiling. Geothermal systems in Iceland are located both within and outsite the active volcanic regions. Outsite the active volcanic regions the temperature in the upper most kilometer of the geothermal systems is below 150° C whereas the temperature in the geothermal fields within the active volcanic regions exceeds 200° C. The resistivity of the rock in geothermal fields located outside the active volcanic regions ranges from about 10 m to some hundreds of m, and are characterized by considerably lower resistivity than of the surrounding rocks. Most of the geothermal systems within the active volcanic regions, show common resistivity structure with low resistivity of 1–5 m surrounding an inner core of higher resistivity. This increasing resistivity with depth is associated with a change in the conduction mechanism, from interface conduction to electrolyte conduction due to a change in alteration minerals at about 240° C. Examples of resistivity surveys of geothermal fields from both outsite and within the active volcanic regions are discussed. 相似文献
253.
We analyze the process of absorption which is produced under conditions of strong magnetic fields in the magnetosphere of a compact stellar source. The magnitude of the magnetic field lies in the range 1012-1013 Gauss, which are common values in modelling pulsars.Analyzing the first absorption lines (N = 0 toN 3) we arrive to the conclusions that the orientation of electron's spin does not change if it absorbs a photon. It means it maintains its orientation opposite to the external magnetic field after the absorption. For the fundamental line (N = 0 toN = 1) the dominant polarization of the photon is. For the next two transition lines (N = 0 toN = 2 andN = 0 toN = 3), the polarization is. In the case that the absorption lines belong to one of the first three transition lines, then the mean photon energy can be approached with the relation
=AN B and thus we get an error of 13.6% with respect to values obtained by the theoretical expression. Also we applied our absorption transition probabilities some known pulsar spectra and we determine which transition feature corresponds in their spectra.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9-13 November, 1992. 相似文献
254.
255.
256.
J. Haas P. Mioč J. Pamić B. Tomljenović P. Árkai A. Bérczi-Makk B. Koroknai S. Kovács E. Rálisch-Felgenhauer 《International Journal of Earth Sciences》2000,89(2):377-389
Due to the political boundaries between the Central European countries, on one hand, and the thick Tertiary cover in the
Pannonian Basin, on the other, the eastward continuation of the Alpine and Dinaridic units has been ambiguous and poorly documented.
Based on comparative analyses, the aim of the present paper is to define the pre-Tertiary structural units in the junction
area of the Alpine, Dinaridic, and Pannonian regions, in the SW part of the Pannonian Basin, and to draw conclusions on the
continuation of the Alpine and Dinaridic units. According to diagnostic characteristics of the Periadriatic Lineament system,
the Balaton Lineament system may be considered as its direct eastern continuation. North of the Periadriatic–Balaton Lineament
system, the Transdanubian Range Unit, due to its pre-Tertiary paleogeographic setting, shows mainly South Alpine facies relations;
however, its present structural position is identical to that of the Upper Austroalpine nappes. Between the Periadriatic–Balaton
and Zagreb–Zemplin Lineament systems heterogeneous structural units are juxtaposed, forming the Sava Composite Unit. In the
northern part of this composite unit non-metamorphosed nappes occur which can be considered the eastern continuation of the
South Alpine units. These nappes are overthrust onto Internal Dinaridic units in the Tertiary. The Zagreb–Zemplin (Mid-Hungarian)
Lineament separates the Sava Unit from the Tisza Unit showing close affinity to the Tethyan margin of the Eurasian plate during
the early stage of the Alpine evolution.
Received: 1 June 1999 / Accepted: 14 March 2000 相似文献
257.
Alex Martinez-Agirre Jesús Álvarez-Mozos Milutin Milenković Norbert Pfeifer Rafael Giménez José Manuel Valle Álvaro Rodríguez 《地球表面变化过程与地形》2020,45(3):605-621
The surface roughness of agricultural soils is mainly related to the type of tillage performed, typically consisting of oriented and random components. Traditionally, soil surface roughness (SSR) characterization has been difficult due to its high spatial variability and the sensitivity of roughness parameters to the characteristics of the instruments, including its measurement scale. Recent advances in surveying have greatly improved the spatial resolution, extent, and availability of surface elevation datasets. However, it is still unknown how new roughness measurements relates with the conventional roughness measurements such as 2D profiles acquired by laser profilometers. The objective of this study was to evaluate the suitability of Terrestrial Laser Scanner (TLS) and Structure from Motion (SfM) photogrammetry techniques for quantifying SSR over different agricultural soils. With this aim, an experiment was carried out in three plots (5 × 5 m) representing different roughness conditions, where TLS and SfM photogrammetry measurements were co-registered with 2D profiles obtained using a laser profilometer. Differences between new and conventional roughness measurement techniques were evaluated visually and quantitatively using regression analysis and comparing the values of six different roughness parameters. TLS and SfM photogrammetry measurements were further compared by evaluating multi-directional roughness parameters and analyzing corresponding Digital Elevation Models. The results obtained demonstrate the ability of both TLS and SfM photogrammetry techniques to measure 3D SSR over agricultural soils. However, profiles obtained with both techniques (especially SfM photogrammetry) showed a loss of high-frequency elevation information that affected the values of some parameters (e.g. initial slope of the autocorrelation function, peak frequency and tortuosity). Nevertheless, both TLS and SfM photogrammetry provide a massive amount of 3D information that enables a detailed analysis of surface roughness, which is relevant for multiple applications, such as those focused in hydrological and soil erosion processes and microwave scattering. © 2019 John Wiley & Sons, Ltd. 相似文献
258.
Study on the Chemical Character of Water Soluble Organic Compounds in Fine Atmospheric Aerosol at the Jungfraujoch 总被引:1,自引:0,他引:1
Zoltán Krivácsy András Gelencsér Gyula Kiss Ernő Mészáros Ágnes Molnár András Hoffer Tamás Mészáros Zsolt Sárvári Dóra Temesi Bálint Varga Urs Baltensperger Stephan Nyeki Ernest Weingartner 《Journal of Atmospheric Chemistry》2001,39(3):235-259
In this study the chemical nature of the bulk of water soluble organic compounds in fine atmospheric aerosol collected during summer 1998 at the Jungfraujoch, Switzerland (3580 m asl) is characterised. The mass concentration of water soluble organic substances was similar to those of major inorganic ions, and the water soluble organic matter was found to be composed of two main fractions: (i) highly polyconjugated, acidic compounds with a varying degree of hydrophobicity and (ii) slightly polyconjugated, neutral and very hydrophilic compounds. The contribution of both fractions to the total water soluble organic carbon was about 50%. Separation into individual components was impossible either by HPLC or capillary electrophoresis which indicates the presence of a high number of chemically similar but not identical species. Results obtained by ultrafiltration and HPLC-MS have shown that the molecular weights are of the order of several hundreds. Most of the protonation constants for the acidic compounds determined by capillary electrophoresis were in the range 104–107. 相似文献
259.
SPATIO‐TEMPORAL SPECIFICS OF HYDRO‐GEOMORPHIC PROCESSES IN HEADWATER PARTS OF MID‐MOUNTAINS RECONSTRUCTED BASED ON TREE‐RING DATA: A CASE STUDY FROM THE HRUBÝ JESENÍK MOUNTAINS (CZECH REPUBLIC)
下载免费PDF全文
![点击此处可从《Geografiska Annaler: Series A, Physical Geography》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Debris flows and debris floods cause frequent geomorphic hazards, even in the mid‐mountains of Central Europe. In the Hrubý Jeseník Mountains (Eastern Sudetes, Czech Republic), strong anthropogenic interventions have created specific conditions for erosion, transport and accumulation of material released by debris flow/flood events. We present a detailed spatio‐temporal reconstruction of the hydro‐geomorphic process activity in two adjacent sub‐catchments using dendrogeomorphic methods applied to the steep, narrow channels. An analysis of 172 sampled trees [Picea Abies (L.) Karst.] revealed 14 torrential events since 1943 in the Klepá?ský stream sub‐catchment and 11 events since 1897 in the Keprnický stream sub‐catchment. Identical events were identified in 1965, 1991, 1997, 2002 and 2010. The event return periods were comparable with return periods from the foothills of the European Alps. A higher frequency of events in the first sub‐catchment may be caused by the presence of a deep‐seated landslide, steeper slopes and a higher susceptibility to shallow slope deformations. Different spatial patterns of events were presented using the Kernel Density analysis in ArcMap 10.1. Clusters of affected trees in the valley floor during the last decades may be due to increased erosion below the check dams and increased accumulation above. The presence of check dams and slope stabilization works since the 1960s has mitigated the processes in several gullies, but due to the current non‐interventional management, the risk of their damage is increasing, particularly when increased activity is observed in the adjacent unprotected gullies. 相似文献
260.
Ágnes Novothny Manfred Frechen Erzsébet Horváth Matthias Krbetschek Sumiko Tsukamoto 《Quaternary Geochronology》2010,5(2-3):114-119
Anomalous fading of the infrared stimulated luminescence (IRSL) signal from the polymineral fine-grain and K-feldspar fractions of aeolian sediments from Hungary has been studied. The samples in this study have previously been dated using the multiple aliquot additive dose (MAAD) protocol to measure the IRSL signal. The IRSL measurements using MAAD were conducted ~4 weeks after the irradiation, making it difficult to assess to what extent these age estimates were affected by anomalous fading. In this study, equivalent doses were obtained using the single aliquot regenerative dose (SAR) protocol. The fading rate for each sample was calculated using the different IRSL components and different parts of the decay curve. For each sample, the middle part of the decay curve always showed a lower fading rate than the initial part of the decay curve. The difference between the fading rates for different parts of the decay curve was greater for the K-feldspars than for the polymineral fine grains. Fading corrected ages were calculated by integrating both the initial and the middle part of the decay curve. These ages were compared with optically stimulated luminescence (OSL) ages from quartz, infrared radiofluorescence (IR-RF) ages obtained from K-feldspars and also with independent ages, provided by radiocarbon dating of shells and charcoal, and uranium-series dating of travertine. 相似文献