全文获取类型
收费全文 | 1973篇 |
免费 | 86篇 |
国内免费 | 34篇 |
专业分类
测绘学 | 42篇 |
大气科学 | 203篇 |
地球物理 | 450篇 |
地质学 | 670篇 |
海洋学 | 160篇 |
天文学 | 375篇 |
综合类 | 5篇 |
自然地理 | 188篇 |
出版年
2022年 | 9篇 |
2021年 | 32篇 |
2020年 | 36篇 |
2019年 | 24篇 |
2018年 | 54篇 |
2017年 | 45篇 |
2016年 | 77篇 |
2015年 | 53篇 |
2014年 | 75篇 |
2013年 | 124篇 |
2012年 | 74篇 |
2011年 | 116篇 |
2010年 | 98篇 |
2009年 | 116篇 |
2008年 | 97篇 |
2007年 | 115篇 |
2006年 | 114篇 |
2005年 | 75篇 |
2004年 | 73篇 |
2003年 | 60篇 |
2002年 | 66篇 |
2001年 | 44篇 |
2000年 | 34篇 |
1999年 | 48篇 |
1998年 | 32篇 |
1997年 | 22篇 |
1996年 | 22篇 |
1995年 | 20篇 |
1994年 | 14篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 8篇 |
1987年 | 16篇 |
1986年 | 22篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 16篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有2093条查询结果,搜索用时 15 毫秒
1.
2.
Andrew J. Westphal Christopher Snead Janet Borg Eric Quirico Pierre‐Ivan Raynal Michael E. Zolensky Gianluca Ferrini Luigi Colangeli Pasquale Palumbo 《Meteoritics & planetary science》2002,37(6):855-865
Abstract— It has now been about a decade since the first demonstrations that hypervelocity particles could be captured, partially intact, in aerogel collectors. But the initial promise of a bonanza of partially‐intact extraterrestrial particles, collected in space, has yet to materialize. One of the difficulties that investigators have encountered is that the location, extraction, handling and analysis of very small (10 μm and less) grains, which constitute the vast majority of the captured particles, is challenging and burdensome. Furthermore, current extraction techniques tend to be destructive over large areas of the collectors. Here we describe our efforts to alleviate some of these difficulties. We have learned how to rapidly and efficiently locate captured particles in aerogel collectors, using an automated microscopic scanning system originally developed for experimental nuclear astrophysics. We have learned how to precisely excavate small access tunnels and trenches using an automated micromanipulator and glass microneedles as tools. These excavations are only destructive to the collector in a very small area—this feature may be particularly important for excavations in the precious Stardust collectors. Using actuatable silicon microtweezers, we have learned how to extract and store “naked” particles—essentially free of aerogel—as small as 3 μm in size. We have also developed a technique for extracting particles, along with their terminal tracks, still embedded in small cubical aerogel blocks. We have developed a novel method for storing very small particles in etched nuclear tracks. We have applied these techniques to the extraction and storage of grains captured in aerogel collectors (Particle Impact Experiment, Orbital Debris Collector Experiment, Comet‐99) in low Earth orbit. 相似文献
3.
Transport by southeastern rivers has insignificant influence on the lead concentration of southeastern shelf waters. If the rate of mobilization and transport of lead by these rivers is representative of uncontaminated fluvial transport during the Pleistocene, only about 5% of the prehistoric output of lead to the North Atlantic can be accounted for by river input.Lead concentrations in southeastern shelf waters are similar to those of North Atlantic Water from the upper 1000 m, which is probably similar to the intrusion source water for the shelf. Atmospheric inputs to the shelf of the same magnitude as observed for the Western North Atlantic are difficult to reconcile given the residence time of shelf waters and their lead concentration unless the rate of loss of lead to shelf sediments is about the same as the atmospheric flux. 相似文献
4.
Optimal deflection of NEOs en route of collision with the Earth 总被引:1,自引:0,他引:1
Recently, a method for the n-body analysis of the velocity change required to deflect a hazardous near-Earth object (NEO) was presented by Carusi et al. [Carusi, A., Valsecchi, G.B., D'Abramo, G., Boattini A., 2002. Icarus 159, 417-422]. We extent this method in order to optimize the velocity change vector instead of its along-track magnitude. From an application of both methods to a fictitious NEO we find Carusi's parallel approach to be reasonable for phases of unperturbed two-body motion. But, for orbit phases inhering third-body perturbations, i.e., for planetary close approaches or prior to a collision, the results obtained from the new method show the radial component of deflection impulse to play a major role. We show that a fivefold greater efficiency can be achieved by a deflection impulse being non-parallel to orbital velocity. The new method is applied to two possible 99942 Apophis impact trajectories in order to provide constraints for future Apophis deflection mission analysis. 相似文献
5.
6.
7.
Veined lithologies are formed by fracturing and sealing processes, with the veins representing former fluid conduits through the rock. Although detailed fieldwork and numerical simulations have provided a better understanding of vein growth, few studies have attempted to seal fractures and generate veins experimentally. In this pilot study, we subjected fractured quartzite to temperature gradients of 45–125 °C under hydrothermal conditions in a static fluid, with the aim of precipitating secondary quartz in the cooler portions of the fracture. Results show that secondary quartz precipitates due to the imposed temperature gradient, causing the initial fracture to seal locally. Although no systematic sealing pattern was observed along the fracture, samples subjected to higher temperatures exhibit a smaller fracture width and appear to have reacted more extensively. Electron microprobe mapping visualizes the spatial distribution of secondary quartz, which contains elevated concentrations of aluminium. 相似文献
8.
9.
Sarah Church Peter Ade James Bock Melanie Bowden John Carlstrom Ken Ganga Walter Gear James Hinderks Wayne Hu Brian Keating John Kovac Andrew Lange Eric Leitch Olivier Mallie Simon Melhuish Anthony Murphy Ben Rusholme Creidhe OSullivan Lucio Piccirillo Clem Pryke Andy Taylor Keith Thompson 《New Astronomy Reviews》2003,47(11-12):1083
QUEST on DASI is a ground-based, high-sensitivity, high-resolution (ℓmax2500) experiment designed to map CMB polarization at 100 and 150 GHz and to measure the power spectra from E-modes, B-modes from lensing of the CMB, and B-modes from primordial gravitational waves. The experiment comprises a 2.6 m Cassegrain optical system, equipped with an array of 62 polarization-sensitive bolometers (PSBs), located at the South Pole. The instrument is designed to minimize systematic effects; features include differencing of pairs of orthogonal PSBs within a single feed, a rotatable achromatic waveplate, and axisymmetric rotatable optics. In addition the South Pole location allows both repeatable and highly controlled observations. QUEST on DASI will commence operation in early 2005. 相似文献
10.
Ralph D. Lorenz 《Meteoritics & planetary science》2004,39(4):617-623
Abstract— A model for an impact ejecta landform peculiar to Saturn's moon Titan is presented. Expansion of the ejecta plume from moderate‐sized craters is constrained by Titan's thick atmosphere. Much of the plume is collimated along the incoming bolide's trajectory, as was observed for plumes from impacts on Jupiter of P/Shoemaker‐Levy‐9, but is retained as a linear, diagonal ejecta cloud, unlike on Venus where the plume “blows out.” On Titan, the blowout is suppressed because the vertically‐extended atmosphere requires a long wake to reach the vacuum of space, and the modest impact velocities mean plume expansion along the wake is slow enough to allow the wake to close off. Beyond the immediate ejecta blanket around the crater, distal ejecta is released into the atmosphere from an oblique line source: this material is winnowed by the zonal wind field to form streaks, with coarse radar‐bright particles transported less far than fine radar‐dark material. Thus, the ejecta form two distinct streaks faintly reminiscent of dual comet tails, a sharply W‐E radar‐dark one, and a less swept and sometimes comma‐shaped radar‐bright one. 相似文献