全文获取类型
收费全文 | 347篇 |
免费 | 10篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 22篇 |
地球物理 | 81篇 |
地质学 | 127篇 |
海洋学 | 16篇 |
天文学 | 61篇 |
自然地理 | 43篇 |
出版年
2022年 | 2篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 24篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 15篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1971年 | 3篇 |
1968年 | 2篇 |
1895年 | 1篇 |
排序方式: 共有357条查询结果,搜索用时 234 毫秒
121.
Matthew S. M. Bolton Britta J. L. Jensen Kristi Wallace Nore Praet David Fortin Darrell Kaufman Marc De Batist 《第四纪科学杂志》2020,35(1-2):81-92
Glass composition-based correlations of volcanic ash (tephra) traditionally rely on extensive manual plotting. Many previous statistical methods for testing correlations are limited by using geochemical means, masking diagnostic variability. We suggest that machine learning classifiers can expedite correlation, quickly narrowing the list of likely candidates using well-trained models. Eruptives from Alaska's Aleutian Arc-Alaska Peninsula and Wrangell volcanic field were used as a test environment for 11 supervised classification algorithms, trained on nearly 2000 electron probe microanalysis measurements of glass major oxides, representing 10 volcanic sources. Artificial neural networks and random forests were consistently among the top-performing learners (accuracy and kappa > 0.96). Their combination as an average ensemble effectively improves their performance. Using this combined model on tephras from Eklutna Lake, south-central Alaska, showed that predictions match traditional methods and can speed correlation. Although classifiers are useful tools, they should aid expert analysis, not replace it. The Eklutna Lake tephras are mostly from Redoubt Volcano. Besides tephras from known Holocene-active sources, Holocene tephra geochemically consistent with Pleistocene Emmons Lake Volcanic Center (Dawson tephra), but from a yet unknown source, is evident. These tephras are mostly anchored by a highly resolved varved chronology and represent new important regional stratigraphic markers. 相似文献
122.
ArcGIS to Unity: a design pipeline for creation of 3D terrain in serious egames for geology
下载免费PDF全文
![点击此处可从《Geology Today》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Annabeth Robinson Clare E. Gordon Jacqueline Houghton Geoffrey E. Lloyd Daniel J. Morgan 《Geology Today》2015,31(6):237-240
One of the key challenges during the development of the Virtual World Project ‘egame environment’ discussed in this issue was the creation of the digital virtual landscape from an original 2002 base map of a field area. In this [online] paper we will walk through the design pipeline that was developed by the virtual worlds project team, and discuss some of the issues that were discovered when translating from a 2D map to a 3D environment using available software, for others interested in replicating this work. 相似文献
123.
124.
Sara R. Heap Qian Gong Tony Hull Jeffrey Kruk Lloyd Purves 《Astrophysics and Space Science》2014,354(1):211-214
One of the key goals of NASA’s astrophysics program is to answer the question: How did galaxies evolve into the spirals and elliptical galaxies that we see today? We describe a space mission concept called Galaxy Evolution Spectroscopic Explorer (GESE) to address this question by making a large spectroscopic survey of galaxies at a redshift, z~1 (look-back time of ~8 billion years). GESE is a 1.5-m space telescope with an ultraviolet (UV) multi-object slit spectrograph that can obtain spectra of hundreds of galaxies per exposure. The spectrograph covers the spectral range, 0.2–0.4 μm at a spectral resolving power, R~500. This observed spectral range corresponds to 0.1–0.2 μm as emitted by a galaxy at a redshift, z=1. The mission concept takes advantage of two new technological advances: (1) light-weighted, wide-field telescope mirrors, and (2) the Next-Generation MicroShutter Array (NG-MSA) to be used as a slit generator in the multi-object slit spectrograph. 相似文献
125.
N. Kameswara Rao B. N. Ashoka C. Lloyd C. D. Pike D. J. Stickland 《Journal of Astrophysics and Astronomy》1990,11(4):445-460
A new radial velocity study has been made of the highly eccentric, early-type binary BD -1° 1004 using spectra from the Kavalur
Observatory. All available archival material has also been reexamined. An attempt has been made to correct for line ‘dragging’
by the secondary spectrum to improve the fit of the observed data to the orbital solutions. It is found that an earlier suggestion
of apsidal regression is still possible although ω is probably constant within the errors. There remain problems and inconsistencies
with other orbital elements, in particular K1 and γ 相似文献
126.
127.
J.V. Narlikar D. Lloyd N.C. Wickramasinghe M.J. Harris M.P. Turner S. Al-Mufti M.K. Wallis M. Wainwright P. Rajaratnam S. Shivaji G.S.N. Reddy S. Ramadurai F. Hoyle 《Astrophysics and Space Science》2003,285(2):555-562
The results of biological studies of a cryosampler flown with a balloon, in which air samples were collected at altitudes
ranging from 20 to 41 km, well above the Tropopause over Hyderabad, are described. In the analysis carried out in Cardiff,
voltage-sensitive dyes that could detect the presence of viable cells were used on these air-samples. Clumps of viable cells
were found to be present in samples collected at all the altitudes. The images obtained from electron microscopy are consistent
with the above finding. Reference is also made to another paper presented at this conference describing the identification
of bacterial species in the sample carried out in Sheffield. Counter arguments are discussed against the criticism that the
detected cells and microorganisms (in the samples collected above the local tropopause at 16 km) are due to terrestrial contamination.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
128.
129.
The formation of methylamine (CH3NH2) in the upper troposphere and lower stratosphere of Jupiter is investigated. Translationally hot hydrogen atoms are produced in the photolysis of ammonia, phosphine, and acetylene which react with methane to produce methyl (CH3) radicals; the latter recombine with NH2 to form CH3NH2. Also, methane is catalytically dissociated to CH3 + H by the species C2 and C2H produced in the photolysis of acetylene. It is shown that the combined production of CH3NH2 and subsequent photolysis to HCN is unlikely to account for the HCN observed near Jupiter's tropopause. Recombination of NH2 and C2H5N followed by photolysis to HCN is the preferred path. Production of C2H6 by these two processes is negligible in comparison to the downward flux of C2H6 from the Lyman α photolysis region of CH4. An upper limit column density on CH3PH2 is estimated to be ~1013 cm?2 as compared to 1015 cm?2 for CH3NH2. Hot H atoms account for a negligible fraction of the total ortho-para conversion by the reaction H + H2 相似文献
130.
A new approach is demonstrated that permits a reliable estimate of specific yield using published values of the van Genuchten water retention parameters and effective grain sizes and the measured effective grain sizes of soil samples. The specific yield distribution of the soil texture was computed using the published values of the van Genuchten parameters. The specific yield values and the published values of effective grain sizes were then used to construct a specific yield–effective grain size curve, which estimates the ‘point’ specific yield of the soil samples. Applying the central limit theorem, the point specific yields could be transformed into an ‘areal’ specific yield for a study area. Compared with other commonly used approaches, the present procedure requires relatively low computational efforts and readily obtainable data. It is cost effective and does not depend on soil texture classification. More importantly, it incorporates the depth to water table and the variations in grain sizes inherent in natural soil conditions in the estimation. The approach developed was applied for estimating the specific yield of an unconfined sandy aquifer created by land reclamation in the equatorial region. The values obtained were compared with field measurements and the typical ranges of specific yield from the literature. Instead of a single estimate of the specific yield, the method yields a confidence interval with a high confidence level of 95% and with a narrower range than the typical ranges from the literature. In addition, the estimated values are close to the field measurements; hence, the procedure provides a cost‐effective alternative to field measurement. The applicability of the present approach could be extended to sites with heterogeneity in the horizontal direction. Nevertheless, the applicability of the present approach for layered soil profiles requires further evaluations. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献