全文获取类型
收费全文 | 426篇 |
免费 | 3篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 15篇 |
地球物理 | 97篇 |
地质学 | 126篇 |
海洋学 | 28篇 |
天文学 | 90篇 |
综合类 | 7篇 |
自然地理 | 58篇 |
出版年
2023年 | 2篇 |
2021年 | 7篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 30篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 19篇 |
2009年 | 35篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 16篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 4篇 |
排序方式: 共有435条查询结果,搜索用时 0 毫秒
431.
Jason W. Barnes Lawrence Lemke Rick Foch Christopher P. McKay Ross A. Beyer Jani Radebaugh David H. Atkinson Ralph D. Lorenz Stéphane Le Mouélic Sebastien Rodriguez Jay Gundlach Francesco Giannini Sean Bain F. Michael Flasar Terry Hurford Carrie M. Anderson Jon Merrison Máté ádámkovics Simon A. Kattenhorn Jonathan Mitchell Devon M. Burr Anthony Colaprete Emily Schaller A. James Friedson Kenneth S. Edgett Angioletta Coradini Alberto Adriani Kunio M. Sayanagi Michael J. Malaska David Morabito Kim Reh 《Experimental Astronomy》2012,33(1):55-127
We describe a mission concept for a stand-alone Titan airplane mission: Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR). With independent delivery and direct-to-Earth communications, AVIATR could contribute to Titan science either alone or as part of a sustained Titan Exploration Program. As a focused mission, AVIATR as we have envisioned it would concentrate on the science that an airplane can do best: exploration of Titan??s global diversity. We focus on surface geology/hydrology and lower-atmospheric structure and dynamics. With a carefully chosen set of seven instruments??2 near-IR cameras, 1 near-IR spectrometer, a RADAR altimeter, an atmospheric structure suite, a haze sensor, and a raindrop detector??AVIATR could accomplish a significant subset of the scientific objectives of the aerial element of flagship studies. The AVIATR spacecraft stack is composed of a Space Vehicle (SV) for cruise, an Entry Vehicle (EV) for entry and descent, and the Air Vehicle (AV) to fly in Titan??s atmosphere. Using an Earth-Jupiter gravity assist trajectory delivers the spacecraft to Titan in 7.5 years, after which the AVIATR AV would operate for a 1-Earth-year nominal mission. We propose a novel ??gravity battery?? climb-then-glide strategy to store energy for optimal use during telecommunications sessions. We would optimize our science by using the flexibility of the airplane platform, generating context data and stereo pairs by flying and banking the AV instead of using gimbaled cameras. AVIATR would climb up to 14?km altitude and descend down to 3.5?km altitude once per Earth day, allowing for repeated atmospheric structure and wind measurements all over the globe. An initial Team-X run at JPL priced the AVIATR mission at FY10 $715M based on the rules stipulated in the recent Discovery announcement of opportunity. Hence we find that a standalone Titan airplane mission can achieve important science building on Cassini??s discoveries and can likely do so within a New Frontiers budget. 相似文献
432.
Seth S. Haines Jay E. Diffendorfer Laurie Balistrieri Byron Berger Troy Cook Don DeAngelis Holly Doremus Donald L. Gautier Tanya Gallegos Margot Gerritsen Elisabeth Graffy Sarah Hawkins Kathleen M. Johnson Jordan Macknick Peter McMahon Tim Modde Brenda Pierce John H. Schuenemeyer Darius Semmens Benjamin Simon Jason Taylor Katie Walton-Day 《Natural Resources Research》2014,23(1):3-17
Natural resource planning at all scales demands methods for assessing the impacts of resource development and use, and in particular it requires standardized methods that yield robust and unbiased results. Building from existing probabilistic methods for assessing the volumes of energy and mineral resources, we provide an algorithm for consistent, reproducible, quantitative assessment of resource development impacts. The approach combines probabilistic input data with Monte Carlo statistical methods to determine probabilistic outputs that convey the uncertainties inherent in the data. For example, one can utilize our algorithm to combine data from a natural gas resource assessment with maps of sage grouse leks and piñon-juniper woodlands in the same area to estimate possible future habitat impacts due to possible future gas development. As another example: one could combine geochemical data and maps of lynx habitat with data from a mineral deposit assessment in the same area to determine possible future mining impacts on water resources and lynx habitat. The approach can be applied to a broad range of positive and negative resource development impacts, such as water quantity or quality, economic benefits, or air quality, limited only by the availability of necessary input data and quantified relationships among geologic resources, development alternatives, and impacts. The framework enables quantitative evaluation of the trade-offs inherent in resource management decision-making, including cumulative impacts, to address societal concerns and policy aspects of resource development. 相似文献
433.
Lynn Abramson Sue Wirick Cindy Lee Chris Jacobsen Jay A. Brandes 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1369-1380
Diatoms play a significant role in the global carbon cycle through their role in biogenic silica production and the transport of organic matter to the seafloor. Recent work has shown that silicified diatom frustules contain a significant amount of organic matter, and that the proportion of diatom-bound organic matter increases with depth in the water column and sediments. Here, we investigate the association between organic matter and the mineral phase. We used a combination of scanning transmission X-ray microscopy (STXM) and carbon X-ray absorption near-edge structure (XANES) spectroscopy to characterize the distribution and composition of organic matter in frustules of the diatom Cylindrotheca closterium and a biomimetic silica gel. To our knowledge, this study represents the first successful attempt to simultaneously image and obtain chemical information about the organic matter within a diatom frustule using X-ray spectromicroscopy near the carbon edge. Organic carbon, most likely protein, was distributed throughout the frustules and was not removed by harsh chemical treatment. The physical structure of the frustules appeared to be related to the chemical composition of this organic matter, with aromatic or unsaturated carbon being concentrated in the most intricately patterned regions of the frustule. A similar physical and chemical structure was observed in a biomimetic silica gel precipitated spontaneously with polylysine. These results are consistent with the theory that organic constituents of diatom frustules direct silica precipitation and become incorporated within the silica matrix as it forms. The relationship between organic matter composition and silica morphology, the failure of harsh chemical treatments to remove this organic matter, and the spontaneous nature of the co-precipitation of silica and organic matter indicate some chemical interaction between the siliceous and organic components of diatom frustules. Frustule-bound organic matter should therefore be protected from decomposition in the water column or diagenetic alteration in sediments unless the frustule dissolves. 相似文献
434.
Jay T. Bergstralh 《Icarus》1973,19(4):499-506
The Lorentz half-width αL, of the fine-structure components of the methane 3v3R-branch in the Jovian spectrum has been measured from photoelectric observations of the singlet R(1). A value of αL = 0.088?0.011+0.015Å, or 0.072?0.009+0.009 cm?1, has been found. Curves of growth for the 3v3R-branch manifolds have been calculated, using the measured value of αL and assuming a reflecting-layer atmosphere. The Walker-Hayes (1967) equivalent widths have been reanalyzed for rotational temperature and methane abundance. The half-width derived here is significantly different from a similar measurement made by C. B. Farmer (1969). The source of the discrepancy remains obscure. 相似文献
435.
Resin‐impregnated sediment blocks are a by‐product of micromorphological sample processing. These blocks can be further studied using a variety of destructive, nondestructive, and minimally destructive geochemical techniques. X‐ray fluorescence microanalyses conducted on sediment blocks yield semiquantitative major and trace elemental abundances that can be used to generate compositional maps, and to illustrate compositional change within or between archaeological strata and features. Sediment blocks can also be drilled to obtain small sediment samples for stable oxygen and carbon isotopic analyses. Both elemental and isotopic analyses can be conducted in conjunction with micromorphological analyses to yield a holistic picture of archaeological sediment composition, source, and depositional processes. The integration of micromorphological, compositional, and isotopic analyses is used here to aid in the differentiation of calcareous ash and lime plasters from the Neolithic site of Asıklı Höyük, Turkey. 相似文献