全文获取类型
收费全文 | 244篇 |
免费 | 20篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 14篇 |
地球物理 | 60篇 |
地质学 | 49篇 |
海洋学 | 14篇 |
天文学 | 84篇 |
综合类 | 1篇 |
自然地理 | 27篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 8篇 |
2012年 | 10篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 20篇 |
2005年 | 13篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有265条查询结果,搜索用时 15 毫秒
101.
Giorgio Matt Enrico Costa Marco Feroci Tomaso Belloni Marco Tavani 《New Astronomy Reviews》1998,42(9-10)
Results from a BeppoSAX observational campaign on GRS 1915+105, performed in October/November 1996, are presented. The source was observed 10 times (nine 10 ksec snapshots, one 100 ksec long observation). The broad band spectral analysis reveals a complex spectrum, including Compton reflection and an iron emission line, probably originating from a relativistic disc. 相似文献
102.
A.Comastri C.Vignali M.Cappi G.Matt R.Audano H.Awaki S.Ueno 《Monthly notices of the Royal Astronomical Society》1998,295(2):443-450
We present results of the ASCA observation of the Seyfert 2 galaxy NGC 4507. The 0.5–10 keV spectrum is rather complex and consists of several components: (i) a hard X-ray power law heavily absorbed by a column density of about 3-1023 cm−2 , (ii) a narrow Fe Kα line at 6.4 keV, (iii) soft continuum emission well above the extrapolation of the absorbed hard power law and (iv) a narrow emission line at ∼0.9 keV. The line energy, consistent with highly ionized neon (Ne IX ), may indicate that the soft X-ray emission is derived from a combination of resonant scattering and fluorescence in a photoionized gas. Some contribution to the soft X-ray spectrum from thermal emission, as a blend of Fe L lines, by a starburst component in the host galaxy cannot be ruled out with the present data. 相似文献
103.
Modeling multiaquifer wells with MODFLOW 总被引:3,自引:0,他引:3
Multiaquifer wells, i.e., wells that are open across more than one aquifer, can have a profound effect on the hydraulics of a ground water system. These wells change the physical system by establishing direct hydraulic links between otherwise isolated strata. Several methods are available to simulate multiaquifer wells in the context of comprehensive ground water flow simulators. In this paper, we review four methods to represent multiaquifer wells with the widely used code MODFLOW. These methods include a specialized code developed, but never formally released, by the U.S. Geological Survey (USGS), the Multi-Aquifer Well (MAW1) Package. An expanded implementation of the techniques in the MAW1 Package has been incorporated in the Multi-Node Well Package released recently by the USGS (Halford and Hanson 2002). We examine the performance of the methods in the context of a benchmarking study against the analytical solutions of Papadopulos (1966) and Sokol (1963). Our results demonstrate that results obtained with the MAW1 Package closely match exact solutions for pumping and nonpumping conditions, using both coarse and refined grids. 相似文献
104.
105.
The Gemini Telescopes are being built to exploit the splendid infrared sites of Mauna Kea in Hawaii and Cerro Pachon in Chile. Both telescopes are being designed to deliver 0.1 arcsecond images at 2.2 m to the focal plane. This image size includes all tracking and enclosure effects. To exploit the superb infrared characteristics of the sites and telescopes we will require a new generation of IR instruments which will challenge both instrument designers and infrared array technologies. 相似文献
106.
Zhiguo Long Matt Duckham Sanjiang Li Steven Schockaert 《International journal of geographical information science》2016,30(6):1072-1094
This paper develops a new mechanism to efficiently compute and compactly store qualitative spatial relations between spatial objects, focusing on topological and directional relations for large datasets of region objects. The central idea is to use minimum bounding rectangles (MBRs) to approximately represent region objects with arbitrary shape and complexity and only store spatial relations that cannot be unambiguously inferred from the relations of corresponding MBRs. We demonstrate, both in theory and practice, that our approach requires considerably less construction time and storage space, and can answer queries more efficiently than the state-of-the-art methods. 相似文献
107.
Erik O. D. Sevre Monica D. Christiansen Matt Broten Shuo M. Wang David A. Yuen 《Visual Geosciences》2008,13(1):125-132
The Sony PlayStation 3 (PS3) offers the computational power of a parallel processor at low cost, which makes it a great starter
unit for development in parallel programming. To explore the capabilities of the unit, we took a simple ray tracing program
and extended it to render triangulated height field data across the PS3’s 6 synergistic processing units (SPUs). We also implemented
the heat averaging equation as a precursor to CFD analysis on the PS3. In our studies, we found the Cell engine in the PS3
to be a powerful machine, however great care must be taken while developing because its unique platform calls for many levels
of optimization to ensure efficiency.
For insight on early work done on modern stream computing and GPU processing look up the Merrimac project and Pat Hanrahan. 相似文献
108.
Matt T. Trentman 《Journal of Atmospheric Chemistry》2018,75(4):399-410
Changes in the frequency of precipitation as a result of a changing climate, as well as anthropogenic induced deposition of nitrogen (N), both have the potential to alter grassland productivity and diversity. Central U.S. weather patterns are dominated by three major air mass trajectories including regional sources from the Gulf of Mexico (marine tropical, Mt), the Pacific Northwest (mild pacific, mP), and the Desert Southwest (continental tropical, Ct). In this work, the Hybrid Single Particle Lagrangian Integrated Trajectory model was used to determine trends in the proportion of precipitation events from these air mass sources from 1983 to 2006 relative to Konza Prairie Biological Station (KPBS), KS. The annual volume-weighted mean (VWM) concentrations and wet deposition of a variety of precipitation dissolved solutes were linked to source regions north or south of KPBS. The proportion of precipitation events from Mt significantly increased, while the proportion of events from Ct and mP decreased significantly over the study period. The annual VWM concentrations of most solutes were typically higher from precipitation sourced to the north of KPBS. However, wet deposition of four ecologically relevant solutes (NH4+, NO3?, H+, and SO4?2) was higher from events from the southern region, likely due to higher precipitation amounts. The proportion of reduced N increased significantly over the study period but was not affected by source region despite the higher use of fertilizers for agriculture in the northern source region. Given the location of this site relative to three dominant air mass paths, future shifts in these patterns will likely impact wet nutrient deposition. 相似文献
109.
110.
P. O. Petrucci G. Ponti G. Matt L. Maraschi J. Malzac M. Mouchet C. Boisson A. Longinotti K. Nandra P. Ferrando G. Henri 《Astronomische Nachrichten》2006,327(10):1043-1046
Mkn 841 has been observed during 3 different periods (January 2001, January 2005 and July 2005) by XMM‐Newton for a total cumulated exposure time of ∼108 ks. We present in this paper a broad band spectral analysis of the complete EPIC‐pn data sets. These observations confirm the presence of the strong soft excess and complex iron line profile known to be present in this source since a long time. They also reveal their extreme and puzzling spectral and temporal behaviors. Indeed, the 0.5–2 keV soft X‐ray flux decreases by a factor 3 between 2001 and 2005 and the line shape appears to be a mixed of broad and narrow components, both variable but on different timescales. The broad‐band 0.5–10 keV spectra are well described by a model including a primary power law continuum, a blurred photoionized reflection and a narrow iron line, the blurred reflection fitting self‐consistently the soft excess and the broad line component. The origin and nature of the narrow component is unclear. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献