全文获取类型
收费全文 | 304篇 |
免费 | 11篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 20篇 |
地球物理 | 59篇 |
地质学 | 110篇 |
海洋学 | 37篇 |
天文学 | 48篇 |
自然地理 | 38篇 |
出版年
2023年 | 1篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 21篇 |
2012年 | 6篇 |
2011年 | 17篇 |
2010年 | 7篇 |
2009年 | 19篇 |
2008年 | 21篇 |
2007年 | 12篇 |
2006年 | 9篇 |
2005年 | 7篇 |
2004年 | 20篇 |
2003年 | 14篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 13篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1974年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有319条查询结果,搜索用时 31 毫秒
31.
32.
The paper illustrates how spatially explicit forecasting of residential development can be undertaken and how it can be made
sensitive to policy instruments available to local and state governments. Predicted values in residential use based on a hedonic
analysis of residential property prices is found to have a significant effect on the hazard of development in a survival model
used to explain the likelihood that a farm or forest will be converted to residential use. Policy instruments are imbedded
in both the hedonic model of residential property values and a hazard model of parcel conversion, so as to test how effective
changes in policies can be at changing the pattern of land-use change. Some of the statistical and modeling obstacles that
impede progress on this spatially explicit modeling are also discussed. 相似文献
33.
This paper presents a task‐based and Semantic Web approach to find geospatial data. The purpose of the project is to improve data discovery and facilitate automatic retrieval of data sources. The work presented here helps create the beginnings of a Geospatial Semantic Web. The intent is to create a system that provides appropriate results to application users who search for data when facing tasks such as emergency response or planning activities. In our task‐based system, we formalize the relationships between types of tasks, including emergency response, and types of data sources needed for those tasks. Domain knowledge, including criteria describing data sources, is recorded in an ontology language. With the ontology, reasoning can be done to infer various types of information including which data sources meet specific criteria for use in particular tasks. The vision presented here is that in an emergency, for example, a user accesses a Web‐based application and selects the type of emergency and the geographic area. The application then returns the types and locations (URLs) of the specific geospatial data needed. We explore the abilities and limitations of the OWL Web Ontology Language along with other Semantic Web technologies for this purpose. 相似文献
34.
Nancy L. Ross 《Physics and Chemistry of Minerals》1998,25(8):597-602
The crystal structure of orthorhombic (Pbnm) ScAlO3 perovskite has been refined to 5 GPa using single-crystal X-ray diffraction. The compression of the structure if anisotropic
with β
a
=1.39(3)×10−3 GPa−1, β
b
=1.14(3)×10−3 GPa−1 and β
c
=1.84(3)×10−3 GPa−1. The isothermal bulk modulus of ScAlO3, K
T
, determined from fitting a Birch-Murnaghan equation of state (K
′
T
=4) to the volume compression data is 218(1) GPa. The interoctahedral angles to not vary significantly with pressure, and
the compression of the structure is entirely attributable to compression of the AlO6 octahedra. The compressibilities of the constituent AlO6 and ScO12 are well matched: βAl−O=1.6×10−3 GPa−1 and βSc−O=1.5×10−3 GPa−1. Therefore the distortion of the structure shows no significant change with increasing pressure.
Received: 18 August 1997 / Revised, accepted: 11 November 1997 相似文献
35.
36.
Origin of the Blue Ridge escarpment along the passive margin of Eastern North America 总被引:1,自引:0,他引:1
James A. Spotila Greg C. Bank Peter W. Reiners† Charles W. Naeser‡ Nancy D. Naeser‡ Bill S. Henika 《Basin Research》2004,16(1):41-63
The Blue Ridge escarpment is a rugged landform situated within the ancient Appalachian orogen. While similar in some respects to the great escarpments along other passive margins, which have evolved by erosion following rifting, its youthful topographic expression has inspired proposals of Cenozoic tectonic rejuvenation in eastern North America. To better understand the post‐orogenic and post‐rift geomorphic evolution of passive margins, we have examined the origin of this landform using low‐temperature thermochronometry and manipulation of topographic indices. Apatite (U–Th)/He and fission‐track analyses along transects across the escarpment reveal a younging trend towards the coast. This pattern is consistent with other great escarpments and fits with an interpretation of having evolved by prolonged erosion, without the requirement of tectonic rejuvenation. Measured ages are also comparable specifically to those measured along other great escarpments that are as much as 100 Myr younger. This suggests that erosional mechanisms that maintain rugged escarpments in the early post‐rift stages may remain active on ancient passive margins for prolonged periods. The precise erosional evolution of the escarpment is less clear, however, and several end‐member models can explain the data. Our preferred model, which fits with all data, involves a significant degree of erosional escarpment retreat in the Cenozoic. Although this suggests that early onset of topographic stability is not required of passive margin evolution, more data are required to better constrain the details of the escarpment's development. 相似文献
37.
Nancy S. Brickhouse 《Astrophysics and Space Science》2011,336(1):75-79
Young T Tauri stars exhibit strong solar-type magnetic activity, with extremely high temperature coronae and energetic flares.
In a few systems discovered with Chandra and XMM-Newton there is also evidence for X-ray emission produced by shocks associated
with magnetically channeled accretion. A recent 489 ksec Chandra HETG/ACIS-S observation of the classical T Tauri star TW
Hydrae has provided a wealth of spectroscopic diagnostics not available in lower signal-to-noise ratio observations. Using
line ratios for electron temperature, electron density, and column density we have found that the shock produced by the accelerating
material in the accretion stream behaves as predicted by standard theory. However, the properties of the post-shock plasma
differ substantially from the predictions of standard 1D shock models (Brickhouse et al. in Astrophys. J. 710:1835, 2010). The accretion process apparently heats the stellar atmosphere up to soft X-ray emitting temperatures, providing hot ions
to populate the magnetic corona, in loops, stellar wind, and/or jets. This gas is highly turbulent, as evidenced by non-thermal
line broadening. The observed properties of the accretion-fed corona should constrain theoretical models of an accretion-driven
dynamo. 相似文献
38.
We present a novel method of constructing streamlines to derive wind speeds within jovian vortices and demonstrate its application to Oval BA for 2001 pre-reddened Cassini flyby data, 2007 post-reddened New Horizons flyby data, and 1998 Galileo data of precursor Oval DE. Our method, while automated, attempts to combine the advantages of both automated and manual cloud tracking methods. The southern maximum wind speed of Oval BA does not show significant changes between these data sets to within our measurement uncertainty. The northern maximum does appear to have increased in strength during this time interval, which likely correlates with the oval’s return to a symmetric shape. We demonstrate how the use of closed streamlines can provide measurements of vorticity averaged over the encircled area with no a priori assumptions concerning oval shape. We find increased averaged interior vorticity between pre- and post-reddened Oval BA, with the precursor Oval DE occupying a middle value of vorticity between these two. 相似文献
39.
Jérôme Gattacceca Francis M. McCubbin Jeffrey N. Grossman Devin L. Schrader Nancy L. Chabot Massimo D'Orazio Cyrena Goodrich Ansgar Greshake Juliane Gross Katherine Helen Joy Mutsumi Komatsu Bingkui Miao 《Meteoritics & planetary science》2023,58(6):901-904
Meteoritical Bulletin 111 contains the 3094 meteorites approved by the Nomenclature Committee of the Meteoritical Society in 2022. It includes 11 falls (Antonin, Botohilitano, Cranfield, Golden, Great Salt Lake, Longde, Msied, Ponggo, Qiquanhu, Tiglit, Traspena), with 2533 ordinary chondrites, 165 HED, 123 carbonaceous chondrites (including 4 ungrouped), 82 lunar meteorites, 28 Rumuruti chondrites, 27 iron meteorites, 23 ureilites, 22 mesosiderites, 22 Martian meteorites, 21 primitive achondrites (one ungrouped), 17 ungrouped achondrites, 13 pallasites, 7 enstatite achondrites, 6 enstatite chondrites, and 5 angrites. Of the meteorites classified in 2022, 1787 were from Antarctica, 1078 from Africa, 180 from South America, 34 from Asia, 6 from North America, 4 from Europe, and 1 from Oceania. 相似文献
40.
A new locality bearing ichnofossils of the Cruziana Assemblage Zone-Ⅲ from the Mussoorie syncline,Lesser Himalaya,is located in rocks of Member-B of the Dhaulagiri Formation,Tal Group,exposed along the Maldewta-Chhimoli fresh road cut section.The site yielded ichnofossils Bergaueria perata,Cochlichnus anguineus,?Diplocraterion isp.,Dimorphichnus obliquus,diplichnitiform Cruziana bonariensis,Diplichnites gouldi,Glockeria isp.,Helminthopsis isp.,Monomorphichnus lineatus,Phycodes palmatum,Palaeophycus striatus,Planolites beverleyensis,Planolites montanus,Treptichnus cf.T.pedum,scratch marks and an undetermined worm impression.An Early Cambrian age (Cambrian Series 2) is assigned to the ichnofossil-bearing strata based on the stratigraphic position between the Drepanuroides and Palaeoolenus trilobite zones.A revised Cambrian ichnofossil zonation is presented for the Tal Group of the Mussoorie syncline.Together with their occurrence on rippled surfaces,and the lateral displacement of some trackways (due to current action),a sub-aqueous shallow-marine depositional setting is proposed for the rocks of Member-B. 相似文献