全文获取类型
收费全文 | 1759篇 |
免费 | 83篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 48篇 |
大气科学 | 123篇 |
地球物理 | 462篇 |
地质学 | 706篇 |
海洋学 | 227篇 |
天文学 | 157篇 |
综合类 | 12篇 |
自然地理 | 117篇 |
出版年
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 38篇 |
2020年 | 38篇 |
2019年 | 41篇 |
2018年 | 70篇 |
2017年 | 81篇 |
2016年 | 97篇 |
2015年 | 83篇 |
2014年 | 90篇 |
2013年 | 106篇 |
2012年 | 93篇 |
2011年 | 130篇 |
2010年 | 99篇 |
2009年 | 125篇 |
2008年 | 109篇 |
2007年 | 87篇 |
2006年 | 74篇 |
2005年 | 59篇 |
2004年 | 70篇 |
2003年 | 48篇 |
2002年 | 32篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 12篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有1852条查询结果,搜索用时 15 毫秒
101.
102.
Recent drilling and sampling of hydrothermal fluids from Long Valley permit an accurate characterization of chemical concentrations and equilibrium conditions in the hydrothermal reservoir. Hydrothermal fluids are thermodynamically saturated with secondary quartz, calcite, and pyrite but are in disequilibrium with respect to aqueous sulfide-sulfate speciation. Hydrothermal fluids are enriched in 18O by approximately 1‰ relative to recharge waters. 18O and Cl concentrations in well cuttings and core from high-temperature zones of the reservoir are extensively depleted relative to fresh rhyolitic tuff compositions. Approximately 80% of the Li and 50% of the B are retained in the altered reservoir rock. Cl mass balance and open-system 18O fractionation models produce similar water-rock ratios of between 1.0 and 2.5 kg kg−1. These water-rock ratios coupled with estimates of reservoir porosity and density produce a minimum fluid residence time of 1.3 ka. The low fluid Cl concentrations in Long Valley correlate with corresponding low rock concentrations. Mass balance calculations indicate that leaching of these reservoir rocks accounts for Cl losses during hydrothermal activity over the last 40 ka. 相似文献
103.
Maria Nikkarinen Eeva Kallio Pekka Lestinen Matti Ayrs 《Journal of Geochemical Exploration》1984,21(1-3)
The variation of Cu and Zn contents with grain size was studied in the size fractions: 2000-500 μm, 500-64 μm, 64-2 μm and minus 2 μm. The fixation to different minerals was investigated in the 500-64 μm and minus 64 μm fractions with microscope, microprobe, electron microscope and X-ray diffraction after heavy-liquid separation.The distribution of Cu and Zn between the four size fractions is very similar in all target areas. The contents tend to be highest in the minus 2 μm fraction, and to decrease with increasing grain size except for an increase in the coarsest material. This feature is typical in mineralized areas with till having anomalously high Cu and Zn contents.The anomalous Cu and Zn in the till of Talvivaara are mainly fixed to chalcopyrite and sphalerite, respectively, which indicates that the main part of the material originates from fresh bedrock and that postglacial alterations are slight. In the till of Outokumpu and Maaselkä sulphides are rare. We assume that in Outokumpu the reason for this is the postglacial weathering of sulphides and that in Maaselkä a great deal of till derives from highly weathered, sulphide-poor, preglacial regolith. In both target areas Cu in till seems to fix to limonite and also to clay minerals, particularly in Maaselkä. Zinc seems mainly to be hosted by limonite in Outokumpu. 相似文献
104.
105.
106.
107.
108.
Refraction effects of optical beams are generally caused by an inhomogeneous propagation medium and are a major source of systematic errors in the precise optical determination of angles and distances in the atmospheric surface layer. In this contribution a method for deriving vertical temperature and refractive index gradients from optical scintillation is presented. Knowledge of these gradients is required for the compensation of atmospherically induced errors for highly precise terrestrial geodetic measurements, like direct transfer and levelling. The advantage of the present optical method is, that temperature and refractive index gradients can be derived as line-averaged values over the propagation path, which is not possible by meteorological point measurements. Field observations have been carried out with a displaced-beam scintillometer over flat terrain and under different atmospheric conditions in order to verify this method. The experiments show, that this method allows to derive accurate correction values for precise terrestrial geodetic measurements. 相似文献
109.
Studia Geophysica et Geodaetica - Den Gegenstand der Untersuchung bildete der ideale, zweidimensionale Filter mit der Übertragungsfunktion gleich 1 in einem Kreisgebiet, dessen Mittelpunkt... 相似文献
110.
A technique to improve the empirical mode decomposition in the Hilbert-Huang transform 总被引:2,自引:0,他引:2
The Hilbert-based time-frequency analysis has promising capacity to reveal the time-variant behaviors of a system. To admit
well-behaved Hilbert transforms, component decomposition of signals must be performed beforehand. This was first systematically
implemented by the empirical mode decomposition (EMD) in the Hilbert-Huang transform, which can provide a time-frequency representation
of the signals. The EMD, however, has limitations in distinguishing different components in narrowband signals commonly found
in free-decay vibration signals. In this study, a technique for decomposing components in narrowband signals based on waves’
beating phenomena is proposed to improve the EMD, in which the time scale structure of the signal is unveiled by the Hilbert
transform as a result of wave beating, the order of component extraction is reversed from that in the EMD and the end effect
is confined. The proposed technique is verified by performing the component decomposition of a simulated signal and a free
decay signal actually measured in an instrumented bridge structure. In addition, the adaptability of the technique to time-variant
dynamic systems is demonstrated with a simulated time-variant MDOF system. 相似文献