全文获取类型
收费全文 | 507篇 |
免费 | 14篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 19篇 |
地球物理 | 84篇 |
地质学 | 157篇 |
海洋学 | 36篇 |
天文学 | 96篇 |
综合类 | 2篇 |
自然地理 | 119篇 |
出版年
2021年 | 4篇 |
2020年 | 7篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 20篇 |
2012年 | 14篇 |
2011年 | 21篇 |
2010年 | 14篇 |
2009年 | 22篇 |
2008年 | 27篇 |
2007年 | 24篇 |
2006年 | 27篇 |
2005年 | 16篇 |
2004年 | 20篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 12篇 |
1999年 | 23篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 10篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1978年 | 2篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1970年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有525条查询结果,搜索用时 218 毫秒
81.
82.
83.
B. W. Stappers B. M. Gaensler † S. Johnston 《Monthly notices of the Royal Astronomical Society》1999,308(3):609-617
Using the Australia Telescope Compact Array (ATCA) we have imaged the fields around five promising pulsar candidates to search for radio pulsar wind nebulae (PWNe). We have used the ATCA in its pulsar-gating mode; this enables an image to be formed containing only off-pulse visibilities, thereby dramatically improving the sensitivity to any underlying PWN. Data from the Molonglo Observatory Synthesis Telescope were also used to provide sensitivity on larger spatial scales. This survey found a faint new PWN around PSR B0906−49; here we report on non-detections of PWNe towards PSRs B1046−58, B1055−52, B1610−50 and J1105−6107. Our radio observations of the field around PSR B1055−52 argue against previous claims of an extended X-ray and radio PWN associated with the pulsar. If these pulsars power unseen, compact radio PWNe, upper limits on the radio flux indicate that a fraction of less than 10−6 of their spin-down energy is used to power this emission. Alternatively, PSRs B1046−58 and B1610−50 may have relativistic winds similar to other young pulsars and the unseen PWN may be resolved and fainter than our surface brightness sensitivity threshold. We can then determine upper limits on the local interstellar medium (ISM) density of 2.2×10−3 and 1×10−2 cm−3 , respectively. Furthermore, we derive the spatial velocities of these pulsars to be ∼450 km s−1 and thus rule out the association of PSR B1610−50 with supernova remnant (SNR) G332.4+00.1 (Kes 32). Strong limits on the ratio of unpulsed to pulsed emission are also determined for three pulsars. 相似文献
84.
Helen M. Johnston Robert Fender Kinwah Wu 《Monthly notices of the Royal Astronomical Society》1999,308(2):415-423
We present new optical and infrared (IR) observations of Cir X-1 taken near apastron. Both sets of spectra show asymmetric emission lines. Archival optical observations show that an asymmetric H α emission line has been in evidence for the past 20 years, although the shape of the line has changed significantly. We present an eccentric ( e ∼0.7–0.9) low-mass binary model, where the system consists of a neutron star orbiting around a (sub)giant companion star of 3–5 M⊙ . We suggest that the broad components of the emission lines arise in a high-velocity, optically thick flow near the neutron star, while the narrow components of the optical and the IR lines arise near the companion star and a heated ejecta shell surrounding the binary respectively. In this model, the velocity of the narrow component reflects the space velocity of the binary; the implied radial velocity (+430 km s−1 after correcting for Galactic rotation) is the highest velocity known for an X-ray binary. 相似文献
85.
An Intercomparison of NO2 and OClO Measurements at Arrival Heights, Antarctica during Austral Spring 1996 总被引:2,自引:0,他引:2
R. W. Sanders S. Solomon K. Kreher P. V. Johnston 《Journal of Atmospheric Chemistry》1999,33(3):283-298
For several years NO2 and OClO, two species important to understanding ozone destruction in the Antarctic stratosphere, have been measured at Arrival Heights, Antarctica by two groups: New Zealand's National Institute of Water and Atmospheric Research (NIWA) and the NOAA Aeronomy Laboratory in Boulder, Colorado. Using data independently collected by these two groups during the Austral spring of 1996, it is shown that the two data sets are in extremely close agreement. Besides offering validation of the instrumentation and analysis techniques of both groups, this result provides confidence in the more complete history of these species gained by combining the two data sets. 相似文献
86.
Assessment of the LandStar Real-Time DGPS Service under Several Operational Conditions 总被引:1,自引:0,他引:1
LandStar is a differential global positioning service (DGPS) that provides 24-h real-time positioning for various applications
on land, water, and air in North America, Australia, New Zealand, Europe, and Africa. Its focus is on real-time applications
requiring a submeter positioning capability such as agriculture, forestry, Geospatial Information Systems (GIS), survey/mapping,
and land/vehicular navigation. LandStar uses a Wide Area Network of reference stations to derive DGPS corrections to model
the variation of GPS error sources over a large area. These model parameters are used by the Virtual Reference Station processors
to calculate standard corrections that are available for all predefined locations in the network. The corrections are transmitted
to the user by L-band satellite communication in the standard RTCM SC104 DGPS correction format. This article investigates
the performance of the LandStar Mk III system under various operational conditions and assesses its performance in both static
and kinematic modes. Four field tests were conducted during 12 months that tested the sysem in clear static and kinematic
conditions as well as suboptimal environments associated with low and heavy foliage conditions. Both the accuracy and availability
of the system under these conditions is investigated, with an emphasis on whether the above variables are caused by the LandStar
system differential corrections, the GPS measurements, or a combination of both. ? 1999 John Wiley & Sons, Inc. 相似文献
87.
88.
J. D. Johnston 《Mineralium Deposita》1999,34(5-6):571-598
The Irish carbonate-hosted base metal deposits have long been an enigmatic subclass of deposit. Some of the Irish deposits
(Harberton Bridge, Allenwood) are clearly epigenetic, hosted in breccia pipes and have close affinities to Mississippi Valley-type
deposits. Others, are characterised by stratabound and sometimes stratiform mineralisation (Abbeytown, Navan), while a third
group is associated closely with concordant dolomitic breccias and cavity fill mineralisation at the base of carbonate mud
mounds (Lisheen, Ballinalack). When the stratigraphic and textural evidence is reviewed, it is apparent that all of the base
metal mineralisation occurred in already compacted sediments. Hence, mineralisation probably occurred at depths of at least
several 100 m depth below the sea bed. The mineralisation occurred either during transtensional Lower Carboniferous basin
development, or subsequently, during the onset of Variscan shortening. Fluids may have been derived from dewatering of Variscan-driven
deformation to the south of the carbonate platform, with fluid flow through major fracture zones and basal clastic aquifers.
Alternatively, high heat flow produced by Lower Carboniferous extension may have driven the mineralising system. Syn-genetic
models are extremely difficult to sustain. 相似文献
89.
Evaluating a process‐based model for use in streambank stabilization: insights on the Bank Stability and Toe Erosion Model (BSTEM)
下载免费PDF全文
![点击此处可从《地球表面变化过程与地形》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kate Klavon Garey Fox Lucie Guertault Eddy Langendoen Holly Enlow Ron Miller Anish Khanal 《地球表面变化过程与地形》2017,42(1):191-213
Streambank retreat is a complex cyclical process involving subaerial processes, fluvial erosion, seepage erosion, and geotechnical failures and is driven by several soil properties that themselves are temporally and spatially variable. Therefore, it can be extremely challenging to predict and model the erosion and consequent retreat of streambanks. However, modeling streambank retreat has many important applications, including the design and assessment of mitigation strategies for stream revitalization and stabilization. In order to highlight the current complexities of modeling streambank retreat and to suggest future research areas, this paper reviewed one of the most comprehensive streambank retreat models available, the Bank Stability and Toe Erosion Model (BSTEM), which has recently been integrated with several popular hydrodynamic and sediment transport models including the Hydrologic Engineering Center's River Analysis System (HEC‐RAS). The objectives of this paper were to: (i) comprehensively review studies that have utilized BSTEM and report their findings, (ii) address the limitations of the model so that it can be applied appropriately in its current form, and (iii) suggest directions of research that will help make the model a more useful tool in future applications. The paper includes an extensive overview of peer reviewed studies to guide future users of BSTEM. The review demonstrated that the model needs further testing and evaluation outside of the central United States. Also, further development is needed in terms of accounting for spatial and temporal variability in geotechnical and fluvial erodibility parameters, incorporating subaerial processes, and accounting for the influence of riparian vegetation on streambank pore‐water pressure dynamics, applied shear stress, and erodibility parameters. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
90.
Michael J. Hollaway Keith J. Beven Clare Mc W. H. Benskin Adrian L. Collins Robert Evans Peter D. Falloon Kirsty J. Forber Kevin M. Hiscock Ron Kahana Christopher J. A. Macleod Mary C. Ockenden Martha L. Villamizar Catherine Wearing Paul J. A. Withers Jian G. Zhou Nicholas J. Barber Philip M. Haygarth 《水文研究》2018,32(17):2779-2787
River discharge and nutrient measurements are subject to aleatory and epistemic uncertainties. In this study, we present a novel method for estimating these uncertainties in colocated discharge and phosphorus (P) measurements. The “voting point”‐based method constrains the derived stage‐discharge rating curve both on the fit to available gaugings and to the catchment water balance. This helps reduce the uncertainty beyond the range of available gaugings and during out of bank situations. In the example presented here, for the top 5% of flows, uncertainties are shown to be 139% using a traditional power law fit, compared with 40% when using our updated “voting point” method. Furthermore, the method is extended to in situ and lab analysed nutrient concentration data pairings, with lower uncertainties (81%) shown for high concentrations (top 5%) than when a traditional regression is applied (102%). Overall, for both discharge and nutrient data, the method presented goes some way to accounting for epistemic uncertainties associated with nonstationary physical characteristics of the monitoring site. 相似文献