全文获取类型
收费全文 | 342篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 11篇 |
地球物理 | 111篇 |
地质学 | 140篇 |
海洋学 | 37篇 |
天文学 | 39篇 |
综合类 | 1篇 |
自然地理 | 17篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 17篇 |
2017年 | 20篇 |
2016年 | 17篇 |
2015年 | 25篇 |
2014年 | 21篇 |
2013年 | 20篇 |
2012年 | 22篇 |
2011年 | 25篇 |
2010年 | 27篇 |
2009年 | 18篇 |
2008年 | 31篇 |
2007年 | 20篇 |
2006年 | 4篇 |
2005年 | 15篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有360条查询结果,搜索用时 31 毫秒
321.
Roberto Ambrosini Pietro Bolli Claudio Bortolotti Francesco Gaudiomonte Filippo Messina Mauro Roma 《Experimental Astronomy》2010,27(3):121-130
Apart from externally generated Radio Frequency Interference (RFI), the occurrence of self-interference is a major concern
at any modern radio telescope site. Antenna servo motor controllers, data acquisition processors, and fast computing capabilities
operate very close to extremely sensitive and wideband radio astronomical receivers. In this paper, we present a set of measurements
of the RFI level generated by a cluster of computers that will be installed at the site of the Sardinia Radio Telescope (SRT).
The measured levels are compared to Recommendation ITU-R RA.769-2, which gives the threshold levels for interference detrimental
to radio astronomy observations. Our analysis shows that, with proper shielding of the noisiest devices, it will be possible
to preserve the present excellent RFI conditions of the SRT site. 相似文献
322.
Rapid estimation of ground-shaking maps for seismic emergency management in the Campania Region of southern Italy 总被引:1,自引:1,他引:0
Vincenzo Convertito Raffaella De Matteis Luciana Cantore Aldo Zollo Giovanni Iannaccone Mauro Caccavale 《Natural Hazards》2010,52(1):97-115
Strong ground-shaking mapping soon after a moderate-to-large earthquake is crucial to recognize the areas that have suffered
the largest damage and losses. These maps have a fundamental role for emergency services, loss estimation and planning of
emergency actions by the Civil Protection Authorities. This is particularly important for areas with high seismic risk levels,
such as the Campania-Lucania Region in southern Italy. Taking advantage of the Irpinia Seismic Network (ISNet), a recently
installed dense and wide dynamic seismic network, we have developed a procedure for rapid estimation of ground-shaking maps
after moderate-to-large earthquakes (GRSmap). This uses an optimal data gridding scheme designed to account for bi-dimensional
features of strong ground-motion fields, such as directivity, radiation patterns and focal mechanisms, to which most damage
can be correlated. The basis of the mapping technique is a triangulation procedure to locally correct predicted data at the
triangle barycentres where their vertices correspond to seismic stations. The method has been tested off-line using a simulated
M 6.6 earthquake located at the centre of ISNet and applied to data of the 23 November 1980 Irpina M 6.9 earthquake recorded by a sparse network. This has highlighted its ability to predict peak ground-motion parameters of
large magnitude earthquakes with respect to the attenuation relationships. 相似文献
323.
The Le Castella marine terrace is the smallest and youngest terrace of the Crotone area (southern Italy), and formed after a rapid marine ingression due to a glacio-eustatic rise outpacing the regional uplift of the area. The most prominent feature of the terrace deposits is a seaward-accreting clinoform about 10 m thick, inferred to be formed during forced regressive conditions. This prograding body is mostly composed of bioclastic material, and shows an internal complexity consisting of alternating oblique and sigmoid elementary units inferred to be produced mainly by changes of accommodation development. Foreset avalancing was due to sediment accumulation by gravity-flow processes, while topsets were characterized by the migration of medium- to large-scale dunes showing a unimodal palaeocurrent pattern, oblique with respect to the dip direction of the large-scale clinoform foresets. The Le Castella clinoform starts to develop from a topographic step on the basement due to tectonics, which also controlled the palaeoshoreline trend.The recognized stratigraphic and facies architectures, the palaeocurrent pattern, and the inferred palaeogeographic setting during deposition, all suggest that the Le Castella clinoform is an example of spit system attached to the mainland and accreted due to longshore transport. The present example contributes to establish criteria allowing the recognition of ancient spit systems, which still are poorly known and rarely documented in the pre-Quaternary geological record. 相似文献
324.
Poiano is the largest karst spring of the Emilia Romagna region (northern Italy). It drains an aquifer of unique properties composed of anhydrite with halite lenses at depth and gypsum at the surface (both with high NaCl content). Hydrogeological research has been undertaken using automatically recorded hourly data on temperature, electrical conductivity, and water level. Water feeding the Poiano spring is restricted within the gypsum/anhydrite outcrop between the Lucola, Sologno and Secchia rivers. Karstification in the Upper Secchia Valley only concerns the gypsum rocks mainly present along the border and in the shallower parts of the sulfate outcrop and does not appear to occur at depth. Data strongly support the hypothesis that the salt content in the spring water derives from active halokinetic movements. For the first time, the fundamental hydrogeological importance of the anhydrite part inside the sulfate rocks is demonstrated. If gypsum prevails over anhydrite the karst drainage network can extend deep into the rocks following a network of fractures and fissures. Instead, if in the deep parts of the aquifer anhydrite prevails over gypsum, the karst evolution cannot take place at depth and the structure of the underground drainage paths only follows near-surface paths in gypsum. 相似文献
325.
E. Caffau A. Koch L. Sbordone P. Sartoretti C.J. Hansen F. Royer N. Leclerc P. Bonifacio N. Christlieb H.‐G. Ludwig E.K. Grebel R.S. de Jong C. Chiappini J. Walcher S. Mignot S. Feltzing M. Cohen I. Minchev A. Helmi T. Piffl E. Depagne O. Schnurr 《Astronomische Nachrichten》2013,334(3):197-216
In preparation for future, large‐scale, multi‐object, high‐resolution spectroscopic surveys of the Galaxy, we present a series of tests of the precision in radial velocity and chemical abundances that any such project can achieve at a 4 m class telescope. We briefly discuss a number of science cases that aim at studying the chemo‐dynamical history of the major Galactic components (bulge, thin and thick disks, and halo) – either as a follow‐up to the Gaia mission or on their own merits. Based on a large grid of synthetic spectra that cover the full range in stellar parameters of typical survey targets, we devise an optimal wavelength range and argue for a moderately high‐resolution spectrograph. As a result, the kinematic precision is not limited by any of these factors, but will practically only suffer from systematic effects, easily reaching uncertainties <1km s–1. Under realistic survey conditions (namely, considering stars brighter than r = 16 mag with reasonable exposure times) we prefer an ideal resolving power of R ∼20 000 on average, for an overall wavelength range (with a common two‐arm spectrograph design) of [395;456.5] nm and [587;673] nm. We show for the first time on a general basis that it is possible to measure chemical abundance ratios to better than 0.1 dex for many species (Fe, Mg, Si, Ca, Ti, Na, Al, V, Cr, Mn, Co, Ni, Y, Ba, Nd, Eu) and to an accuracy of about 0.2 dex for other species such as Zr, La, and Sr. While our feasibility study was explicitly carried out for the 4MOST facility, the results can be readily applied to and used for any other conceptual design study for high‐resolution spectrographs. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
326.
D. Majaess L. Sturch C. Moni Bidin M. Soto W. Gieren R. Cohen F. Mauro D. Geisler C. Bonatto J. Borissova D. Minniti D. Turner D. Lane B. Madore G. Carraro L. Berdnikov 《Astrophysics and Space Science》2013,347(1):61-70
Cepheids are key to establishing the cosmic distance scale. Therefore it’s important to assess the viability of QZ Nor, V340 Nor, and GU Nor as calibrators for Leavitt’s law via their purported membership in the open cluster NGC 6067. The following suite of evidence confirms that QZ Nor and V340 Nor are members of NGC 6067, whereas GU Nor likely lies in the foreground: (i) existing radial velocities for QZ Nor and V340 Nor agree with that established for the cluster ( $-39.4\pm0.2(\sigma_{\bar {x}}) \pm1.2 (\sigma)~\mbox{km/s}$ ) to within 1 km/s, whereas GU Nor exhibits a markedly smaller value; (ii) a steep velocity-distance gradient characterizes the sight-line toward NGC 6067, thus implying that objects sharing common velocities are nearly equidistant; (iii) a radial profile constructed for NGC 6067 indicates that QZ Nor is within the cluster bounds, despite being 20′ from the cluster center; (iv) new BVJH photometry for NGC 6067 confirms the cluster lies d=1.75±0.10 kpc distant, a result that matches Wesenheit distances computed for QZ Nor/V340 Nor using the Benedict et al. (Astron. J. 133:1810, 2007, HST parallaxes) calibration. QZ Nor is a cluster Cepheid that should be employed as a calibrator for the cosmic distance scale. 相似文献
327.
The magnitude and even direction of recent Antarctic climate change is still debated because the paucity of long and complete
instrumental data records. While along Antarctic Peninsula a strong warming coupled with large retreat of glaciers occurred,
in continental Antarctica a cooling was recently detected. Here, the first existing permafrost data set longer than 10 years
recorded in continental Antarctica is presented. Since 1997 summer ground surface temperature showed a strong warming trend
(0.31°C per year) although the air temperature was almost stable. The summer ground surface temperature increase seemed to
be influenced mainly by the increase of the total summer radiation as confirmed also by the increase of the summer thawing
degree days. In the same period the active layer exhibited a thickening trend (1 cm per year) comparable with the thickening
rates observed in several Arctic locations where air warming occurred. At all the investigated depths permafrost exhibited
an increase of mean annual temperature of approximately 0.1°C per year. The dichotomy between active layer thickness and air
temperature trends can produce large unexepected and unmodelled impacts on ecosystems and CO2 balance. 相似文献
328.
Up‐to‐date and accurate digital elevation models (DEMs) are essential for many applications such as numerical modeling of mass movements or mapping of terrain changes. Today the Federal Department of Topography, swisstopo, provides Digital Terrain Models (DTMs) and Digital Surface Models (DSMs) derived from airborne LiDAR data with a high spatial resolution of 2 m covering the entire area of Switzerland below an elevation of 2000 m a.s.l.. However, above an elevation of 2000 m a.s.l., which is typical for high‐alpine terrain, the best product available is the a DTM with a spatial resolution of 25 m. This spatial resolution is insufficient for many applications in complex terrain. In this study, we investigate the quality of DSMs derived from opto‐electronic scanner data (ADS80; acquired in autumn 2010) using photogrammetric image correlation techniques based on the multispectral nadir and backward looking sensor data. As reference, we take a high precision airborne LiDAR data set with a spatial resolution of ca. 0.5 m, acquired in late summer 2010, covering the Grabengufer/Dorfbach catchment near Randa, VS. We find the deviations between the two datasets are surprisingly low. In terrain with inclination angles of less than 30° the RMSE is below 0.5 m. In extremely steep terrain of more than 50° the RMSE goes up to 2 m and outliers increase significantly. We also find dependencies of the deviations on illumination conditions and ground cover classes. Finally we discuss advantages and disadvantages of the different data acquisition methods. 相似文献
329.
Mauro de Melo Júnior Leonardo K. Miyashita Naira J. Silva Salvador A. Gaeta Rubens M. Lopes 《Marine Ecology》2013,34(3):363-372
We investigated the reproductive biology of the planktonic harpacticoid copepod Euterpina acutifrons, including morphometric data, egg production rates (EPR) and viability, and weight‐specific egg production. Experiments were carried out during 1 year in an inner‐shelf area off Ubatuba (SE Brazil), a site seasonally influenced by bottom intrusions of the relatively cold and nutrient‐rich South Atlantic Central Water (SACW). We hypothesized that E. acutifrons attain higher reproductive rates when SACW penetrates in this region. Live females were incubated individually in cell culture plates during two periods of 24 h each, under controlled temperature and light conditions. Euterpina acutifrons carried on average 16.9 ± 6.9 eggs·sac?1, ranging between 10.8 ± 5.7 and 30.8 ± 7.4 eggs·sac?1. Estimated EPRs ranged from 6.3 ± 3.4 to 13.6 ± 4.2 eggs·female?1·day?1, with mean weight‐specific egg production rates of 0.06 ± 0.04 and 0.17 ± 0.08 per day. Euterpina acutifrons was not directly influenced by SACW intrusions, but body length and clutch size were positively related to temperature and chlorophyll content. Egg hatching time was clearly dependent on water temperature, as a 2 °C increase resulted in a decrease of 15 h in egg hatching time. This shows that even a small variation in temperature may considerably affect E. acutifrons population dynamics. Reproductive traits of this pelagic harpacticoid seem, therefore, to be controlled by the trade‐offs between increased food supply and the metabolic demands at low temperatures associated with SACW bottom intrusions toward this coastal area. 相似文献
330.
E. Caffau R. Faraggiana H.‐G. Ludwig P. Bonifacio M. Steffen 《Astronomische Nachrichten》2011,332(2):128-139
Zirconium (Zr), together with strontium and yttrium, is an important element in the understanding of the Galactic nucleosynthesis. In fact, the triad Sr‐Y‐Zr constitutes the first peak of s‐process elements. Despite its general relevance not many studies of the solar abundance of Zr were conducted. We derive the zirconium abundance in the solar photosphere with the same CO5BOLD hydrodynamical model of the solar atmosphere that we previously used to investigate the abundances of C‐N‐O. We review the zirconium lines available in the observed solar spectra and select a sample of lines to determine the zirconium abundance, considering lines of neutral and singly ionised zirconium. We apply different line profile fitting strategies for a reliable analysis of Zr lines that are blended by lines of other elements. The abundance obtained from lines of neutral zirconium is very uncertain because these lines are commonly blended and weak in the solar spectrum. However, we believe that some lines of ionised zirconium are reliable abundance indicators. Restricting the set to Zr II lines, from the CO5BOLD 3D model atmosphere we derive A (Zr) = 2.62 ± 0.06, where the quoted error is the RMS line‐to‐line scatter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献