全文获取类型
收费全文 | 239篇 |
免费 | 5篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 13篇 |
地球物理 | 53篇 |
地质学 | 96篇 |
海洋学 | 14篇 |
天文学 | 52篇 |
综合类 | 2篇 |
自然地理 | 16篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 11篇 |
2013年 | 21篇 |
2012年 | 14篇 |
2011年 | 13篇 |
2010年 | 14篇 |
2009年 | 17篇 |
2008年 | 13篇 |
2007年 | 9篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1991年 | 2篇 |
排序方式: 共有250条查询结果,搜索用时 93 毫秒
151.
L. N. Berdnikov M. A. Burlak O. V. Vozyakova A. V. Dodin S. A. Lamzin A. M. Tatarnikov 《Astrophysical Bulletin》2017,72(3):277-285
Having compared images of a jet of the young star RWAurA obtained with an interval of 21.3 yr, we have found that the outermost knots of the jet have emerged approximately 350 years ago. We come up with arguments that the jet itself has appeared at the same time, and intensive accretion onto the star has begun due to rearrangement of its protoplanetary disk structure caused by the tidal effect of the companion RWAur B. More precisely suppose that intensification of accretion is a response to changing conditions in the outer-disk regions which has followed after the sound wave, generated by these changes, has passed the disk in the radial direction. In our opinion difference in the parameters of blue and red lobes of the RWAurA jet is a result of the asymmetric distribution of the circumstellar matter above and below the disk due to companion’s passage. It was found from the analysis of the RWAur historical light curve that deep and long-term (Δt > 150 days) light attenuations of RWAurA observed after 2010 had no precedents in the previous 110 years.We also associate the change in the character of photometric variability of the star with the rearrangement of the structure of inner (r < 1 AU) regions of its protoplanetary disk, and discuss why these changes have begun only 350 years after the beginning of the active accretion phase. 相似文献
152.
Maiclaire K. Bolton Dmitry A. Storchak James Harris 《Physics of the Earth and Planetary Interiors》2006,158(1):27-45
The International Seismological Centre (ISC) publishes the definitive global bulletin of earthquake locations. In the ISC bulletin, we aim to obtain a free depth, but often this is not possible. Subsequently, the first option is to obtain a depth derived from depth phases. If depth phases are not available, we then use the reported depth from a reputable local agency. Finally, as a last resort, we set a default depth.In the past, common depths of 10, 33, or multiples of 50 km have been assigned. Assigning a more meaningful default depth, specific to a seismic region will increase the consistency of earthquake locations within the ISC bulletin and allow the ISC to publish better positions and magnitude estimates. It will also improve the association of reported secondary arrivals to corresponding seismic events.We aim to produce a global set of default depths, based on a typical depth for each area, from well-constrained events in the ISC bulletin or where depth could be constrained using a consistent set of depth phase arrivals provided by a number of different reporters.In certain areas, we must resort to using other assumptions. For these cases, we use a global crustal model (Crust2.0) to set default depths to half the thickness of the crust. 相似文献
153.
Evaluating Global Warming Potentials with historical temperature 总被引:1,自引:2,他引:1
Katsumasa Tanaka Brian C. O’Neill Dmitry Rokityanskiy Michael Obersteiner Richard S. J. Tol 《Climatic change》2009,96(4):443-466
Global Warming Potentials (GWPs) are evaluated with historical temperature by applying them to convert historical CH4 and N2O emissions to equivalent CO2 emissions. Our GWP analysis is based on an inverse estimation using the Aggregated Carbon Cycle, Atmospheric Chemistry, and
Climate Model (ACC2). We find that, for both CH4 and N2O, indices higher than the Kyoto GWPs (100-year time horizon) would reproduce better the historical temperature. The CH4 GWP provides a best fit to the historical temperature when it is calculated with a time horizon of 44 years. However, the
N2O GWP does not approximate well the historical temperature with any time horizon. We introduce a new exchange metric, TEMperature
Proxy index (TEMP), that is defined so that it provides a best fit to the temperature projection of a given period. By comparing
GWPs and TEMPs, we find that the inability of the N2O GWP to reproduce the historical temperature is caused by the GWP calculation methodology in IPCC using simplifying assumptions
for the background system dynamics and uncertain parameter estimations. Furthermore, our TEMP calculations demonstrate that
indices have to be progressively updated upon the acquisition of new measurements and/or the advancement of our understanding
of Earth system processes. 相似文献
154.
Thermochronological insights into the structural contact between the Tian Shan and Pamirs,Tajikistan
下载免费PDF全文
![点击此处可从《地学学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gilby Jepson Stijn Glorie Dmitry Konopelko Jack Gillespie Martin Danišík Noreen J. Evans Yunus Mamadjanov Alan S. Collins 《地学学报》2018,30(2):95-104
Multi‐method thermochronology along the Vakhsh‐Surkhob fault zone reveals the thermotectonic history of the South Tian Shan–Pamirs boundary. Apatite U/Pb analyses yield a consistent age of 251 ± 2 Ma, corresponding to cooling below ~550–350°C, related to the final closure of the Palaeo‐Asian Ocean and contemporaneous magmatism in the South Tian Shan. Zircon (U–Th–Sm)/He ages constrain cooling below ~180°C to the end of the Triassic (~200 Ma), likely related either to deformation induced by the Qiangtang collision or to the closure of the Rushan Ocean. Apatite fission track thermochronology reveals two low‐temperature (<120°C) thermal events at ~25 Ma and ~10 Ma, which may be correlated with tectonic activity at the distant southern Eurasian margin. The late Miocene cooling is confirmed by apatite (U–Th–Sm)/He data and marks the onset of mountain building within the South Tian Shan that is ongoing today. 相似文献
155.
Milan Chytrý Michal Horsk Jií Danihelka Nikolai Ermakov Dmitry A. German Michal Hjek Petra Hjkov Martin Ko
í Svatava Kubeov Pavel Lustyk Jeffrey C. Nekola Vra Pavelkov i
nkov Zdenka Preislerov Philipp Resl Milan Valachovi
《Boreas: An International Journal of Quaternary Research》2019,48(1):36-56
Steppe‐tundra is considered to have been a dominant ecosystem across northern Eurasia during the Last Glacial Maximum. As the fossil record is insufficient for understanding the ecology of this vanished ecosystem, modern analogues have been sought, especially in Beringia. However, Beringian ecosystems are probably not the best analogues for more southern variants of the full‐glacial steppe‐tundra because they lack many plant and animal species of temperate steppes found in the full‐glacial fossil record from various areas of Europe and Siberia. We present new data on flora, land snails and mammals and characterize the ecology of a close modern analogue of the full‐glacial steppe‐tundra ecosystem in the southeastern Russian Altai Mountains, southern Siberia. The Altaian steppe‐tundra is a landscape mosaic of different habitat types including steppe, mesic and wet grasslands, shrubby tundra, riparian scrub, and patches of open woodland at moister sites. Habitat distribution, species diversity, primary productivity and nutrient content in plant biomass reflect precipitation patterns across a broader area and the topography‐dependent distribution of soil moisture across smaller landscape sections. Plant and snail species considered as glacial relicts occur in most habitats of the Altaian steppe‐tundra, but snails avoid the driest types of steppe. A diverse community of mammals, including many species typical of the full‐glacial ecosystems, also occurs there. Insights from the Altaian steppe‐tundra suggest that the full‐glacial steppe‐tundra was a heterogeneous mosaic of different habitats depending on landscape‐scale moisture gradients. Primary productivity of this habitat mosaic combined with shallow snow cover that facilitated winter grazing was sufficient to sustain rich communities of large herbivores. 相似文献
156.
We have analyzed our long-term (1995–2008) JHKLM photometry for three variable RV Tau supergiants. It follows from this analysis that: the amplitude of the JHK brightness variations is approximately the same, 0
m
. 9–1
m
, for the three stars; a negative linear trend is noticeable in the variations of the mean J brightness for AC Her; and the mean J brightness of R Sct and V Vul remained constant. The observed J brightness fluctuations in the supergiants are shown to be consistent either only with the temperature pulsations (AC Her
and V Vul) or with the temperature and radial pulsations (R Sct). We have detected long-term pulsations in the J brightness and J-H color variations of the supergiants with the following characteristic time scales: ∼1500 days (AC Her), ∼3500 days (R Sct),
and ∼800 and ∼1500 days (V Vul). Our search for a periodic component in the infrared brightness variations of the three stars
has revealed periods that differ from those obtained from optical observations. We show that relatively hot dust shells (T
d ∼ 700–800 K) exist around the supergiants under study; the densest and most massive shell was observed for V Vul. The ranges
of optical-depth variations for the dust shells were τ(1.25 μm) ≈ 0.04–0.10 (AC Her), ≈0.02–0.12 (R Sct), and ≈0.18–0.32 (V Vul). The spectral types in the infrared varied over
narrower ranges than those that followed from optical observations of these stars. 相似文献
157.
I. A. Tararin S. I. Dril G. P. Sandimirova Z. G. Badredinov S. A. Tatarnikov T. A. Vladimirova 《Doklady Earth Sciences》2010,431(1):356-360
Metamorphic units of the Khavyven Highland that crop out in the northern portion of the Khavyven Uplift of the basement structures
of the Central Kamchatka Trough are formed by rocks of the Khavyven Formation, which are metamorphosed in the green-schist
facies. The formation comprises two strata: the lower part that consists of amphibole-micaceous ± garnet, epidote-micaceous
± garnet crystalline schists, and micaceous ± garnet quartzite schists has a total thickness of some 500 m, and the upper
part, which is formed by epidote-amphibole and phengite-amphibole green schists and overlying epidote-amphibole-micaceous
quartzites, with a visible thickness of some 750 m. The isotopic ratios of Sr, Nd, and Pb were determined in the examined
rocks of the Khavyven Formation for the first time. The high 87Sr/86Sr and low 143Nd/144Nd ratios and the high K/La, Ba/Th, Th/Ta, and La/Nb ratios in combination with a deep Ta-Nb minimum indicate that the original
volcanites of the crystalline schists of the lower rock mass had a subduction nature. The green schist of the upper rock mass,
whose composition corresponds to that of spilitic basalts, have elevated 87Sr/86Sr and 143Nd/144Nd ratios, thus combining indications of depleted melts of the N-MORB and E-MORB types and those of subduction melts, which
explains the deep Ta-Nb minimum and the low (La/Yb)
N
ratios. The isotopic signatures of lead in rocks of the lower and the upper strata are similar. The composition points of
the crystalline schists and the green schists are located near the trend of isotopic evolution of lead in the depleted mantle,
which indicates that the rocks are closely related to this mantle source. 相似文献
158.
The paper is devoted to the upscaling method appropriate for single-phase flow in media with discontinuous permeability distribution.
The suggested algorithm is a modification of the iterative adaptive local–global upscaling developed by Chen and coauthors.
The key feature of this method is a consistency between local and coarse global calculated characteristics. In this work,
we apply a modified procedure to determine the boundary conditions used in the local fine-scale computation. To increase the
accuracy of these boundary conditions on each iteration, we involve an additional preliminary step based on the results of
coarse scale calculations from the previous iteration. Numerical tests show an essential improvement of the accuracy of upscaled
flow rates for most of the realizations of statistical permeability distribution. Although the developed method is universal,
its efficiency increases with increasing of permeability contrast. 相似文献
159.
A. A. Tatarnikova A. M. Tatarnikov V. F. Esipov E. A. Kolotilov 《Astronomy Letters》2009,35(3):182-194
We present the results of our spectroscopic and photometric observations of the classical symbiotic star V1413 Aql in 2003–2007, which cover the transition phase of its hot component from activity to quiescence. Various quiescence criteria for the hot component of the system are analyzed. Judging by its photometric characteristics, the system had not yet returned to quiescence by 2007, although a fairly strong He II λ4686 Å line observed previously during quiescence in 1993 appeared in its spectrum. We model the continuum energy distribution for V1413 Aql based on a standard three-component model and a model with an accretion disk. Analysis of the forbidden [O III] and [Ne III] lines shows that the neon abundance in V1413 Aql may be enhanced with respect to the oxygen abundance. The cool component of V1413 Aql has been found to be a variable M5-type red giant, with the variability amplitude at λ = 7500 Å being at least 2 m . 相似文献
160.
We present an analysis of the poorly studied UV spectra of the symbiotic Nova PU Vul taken in 1991–1996. The continuum spectral
energy distribution during that period (the nebular phase) can be reproduced by the standard model, which includes radiation
from the hot component and nebula, in contrast to spectra observed in the 1980s, when the hot component of PU Vul was in its
“supergiant” stage. The hot component’s temperature gradually increased from74 000 K (1991) to 100 000 K (1996), and the evolution
of this component reflected by the Hertzsprung-Russell diagram corresponds to theoretical models describing the evolution
of a thermonuclear outburst in the envelope of a white dwarf. Based on our analysis of UV observations of the eclipse in 1993–1994,
we estimate the size of the cool component to have been at least 285R⊙. This confirms earlier suggestions that the cool component of PU Vul belongs to luminosity class II (bright giants) or I
(supergiants), rather than class III (normal giants). Our analysis of Rayleigh scattering of the hot component’s radiation
on atomic hydrogen in the extended atmosphere of the cool component suggests that the mass-loss rate of the cool component
of PU Vul is variable. 相似文献