全文获取类型
收费全文 | 332篇 |
免费 | 8篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 12篇 |
地球物理 | 102篇 |
地质学 | 108篇 |
海洋学 | 22篇 |
天文学 | 57篇 |
综合类 | 3篇 |
自然地理 | 37篇 |
出版年
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 11篇 |
2013年 | 11篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 12篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 20篇 |
2006年 | 9篇 |
2005年 | 20篇 |
2004年 | 7篇 |
2003年 | 12篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1973年 | 5篇 |
1969年 | 1篇 |
1968年 | 3篇 |
排序方式: 共有347条查询结果,搜索用时 0 毫秒
51.
Ulf Sderlund Sten-ke Elming Richard E. Ernst Don Schissel 《Precambrian Research》2006,150(3-4):136-152
The Central Scandinavian Dolerite Group (CSDG) occurs in five separate complexes in central Sweden and SW Finland. U–Pb baddeleyite ages of dolerite dikes and sills fall into three age intervals: 1264–1271 (the Dalarna complex), 1256–1259 (the Västerbotten-Ulvö-Satakunta complexes) and 1247 Ma (the Jämtland complex). Timing and spatial distribution of CSDG are unlike expressions of the voluminous and short-lived magmatism which characterises plume-associated large igneous provinces (LIPs). Protracted mafic magmatism in association with mantle plume tail (hotspot) activity beneath the Fennoscandian lithosphere or discrete events of extension behind an active margin (subduction) are considered more plausible tectonic settings. Both settings are consistent with timing, relative magma volumes between complexes and vertical ascent of individual magma pulses through the crust, as inferred from seismic sections [Korja, A., Heikkinen, P., Aaro, S., 2001. Crustal structure of the northern Baltic Sea palaeorift. Teconophysics 331, 341–358]. In the hotspot model, the lack of a linear track of intrusions can be explained by an almost stationary position of Fennoscandia relative to the hotspot, in agreement with palaeomagnetic data [Elming, S.-Å., Mattsson, H., 2001. Post Jotnian basic intrusion in the Fennoscandian Shield, and the break up of Baltica from Laurentia: a palaeomagnetic and AMS study. Precambrian Res. 108, 215–236]). Together with geological evidence, dolerite sill complexes and dike swarms in Labrador (Canada), S Greenland and central Scandinavia in the range 1234–1284 Ma are best explained by long-lived subduction along a continuous Laurentia-Baltica margin preceding Rodinia formation. There is no support for the hypothesis that CSDG was fed by magma derived from a distal mantle plume located between Baltica and Greenland and, hence, for rifting between the cratons at 1.26 Ga.The epsilon-Hf in various members of the CSDG varies between 4.7 and 10.3, which are overall higher than both older and younger Mesoproterozoic mafic intrusions in central Fennoscandia. Magma generated from a hotspot mantle source that was mixed to highly variable degrees with an enriched subcontinental lithospheric mantle could account for the wide range in Hf isotope composition. In the course of Hf isotope development work during this project we have analysed four fragments of the Geostandard 91500 reference zircon and after evaluating the existing ICPMS and TIMS data we calculate a mean 176Hf/177Hf value of 0.282303 ± 0.000003 (2σ). 相似文献
52.
Water samples were collected from 18 natural springs within the West Fork of the Obey River watershed. Overton County, Tennessee,
to determine if groundwater was adversely affected by runoff from abandoned surface coal mines Six springs were found to be
affected severely and deemed unfit as a source of potable water Water quality of the remaining springs was essentially unaffected
it appeared that proximity to surface mines, elevation at the outflow, and geology of the surrounding strata determined the
quality of the groundwater
The unit is jointly supported by Tennessee Technological University, the Tennessee Wildlife Resource Agency, and the US. Fish
and Wildlife Service 相似文献
53.
We report here on the observation and offline detection of the meteotsunami off the New Jersey coast on June 13, 2013, using coastal radar systems and tide gauges. This work extends the previous observations of tsunamis originating in Japan and Indonesia. The radars observed the meteotsunami 23 km offshore, 47 min before it arrived at the coast. Subsequent observations showed it moving onshore. The neighboring tide gauge height reading provides confirmation of the radar observations near the shore. 相似文献
54.
55.
Following the statistical analyses of long‐term rainfall‐runoff records from research basins in humid temperate latitudes, Hewlett and co‐workers extended the global challenge to disprove their findings that rainfall intensity was non‐significant. This paper responds to Hewlett's challenge as no preceding analyses have involved forested basins in a tropical cyclone‐prone area. Based on a 7 year rainfall‐runoff record, quickflow (QF), peak flow (QP) and quickflow response ratios (QRR) were regressed as dependent variables against rainfall parameters (intensity, Pi, amount, P), storm duration, D and antecedent flow, I. These data sets were categorised into total streamflow (Q) classes and stratified into three seasons, (monsoon, post‐monsoon and dry) for forested and cleared catchments. Where rainfall variable collinearity met acceptable levels, the addition of Pi to regression models including P, D, I contributed up to 9% and 66% of the respective variations in quickflow and peak flow. For the highest Q storm classes (monsoon), Pi alone accounted for up to 67% and 91% of the variation in QF and QP respectively and was the dominant influence on QP for all seasons. The very high rainfall intensities experienced in the monsoon season is a causal factor why these results differ from those of other research drainage basins. Surprisingly, Pi continued to have a significant influence on QF for dry season classes when less‐intense rainfall occurs. Further the results were similar for both catchments across all seasons. P was the dominant independent variable affecting QF above a threshold Q of 50 mm (monsoon), as rainfall contributes directly to saturation overland flow and return flow under saturated conditions. Further although QRR increased with increasing Q for each season, the regression results for that parameter were poor possibly due to the non‐linearity of the rainfall‐runoff relationship. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
56.
Engineering projects that require deformation monitoring frequently utilize geodetic sensors to measure displacements of target
points located in the deformation zone. In situations where control stations and targets are separated by a kilometer or more,
GPS can offer higher precision position updates at more frequent intervals than can normally be achieved using total station
technology. For large-scale deformation projects requiring the highest precision, it is therefore advisable to use a combination
of the two sensors. In response to the need for high precision, continuous GPS position updates in harsh deformation monitoring
environments, a software has been developed that employs triple-differenced carrier-phase measurements in a delayed-state
Kalman filter. Two data sets were analyzed to test the capabilities of the software. In the first test, a GPS antenna was
displaced using a translation stage to mimic slow deformation. In the second test, data collected at a large open pit mine
were processed. It was shown that the delayed-state Kalman filter developed could detect millimeter-level displacements of
a GPS antenna. The actual precision attained depends upon the amount of process noise infused at each epoch to accommodate
the antenna displacements. Higher process noise values result in quicker detection times, but at the same time increase the
noise in the solutions. A slow, 25 mm displacement was detected within 30 min of the full displacement with sigma values in
E, N and U of ±10 mm or better. The same displacement could also be detected in less than 5 h with sigma values in E, N and U of ±5 mm or better. The software works best for detecting long period deformations (e.g., 20 mm per day or less) for which
sigma values of 1–2 mm are attained in all three solution components. It was also shown that the triple-differenced carrier-phase
observation can be used to significantly reduce the effects of residual tropospheric delay that would normally plague double-differenced
observations in harsh GPS environments.
相似文献
Don KimEmail: |
57.
Giovanni Tecchio Marco Donà Francesca da Porto 《Bulletin of Earthquake Engineering》2016,14(11):3099-3124
Masonry arch bridges are crucial elements in the railway transportation network throughout Europe. Although significant advances in seismic risk assessment of various bridge types have been made by developing fragility curves of generalized classes of structures, there are no comparable tools for masonry arch structures. In this context, this paper presents the construction of seismic fragility curves of single-span masonry bridges according to the limit analysis method. An iterative procedure is implemented to define the capacity curve of the equivalent single degree of freedom system through non-linear kinematic analysis. The process involves determination of the collapse mechanism, calculation of the limit load multiplier, and definition of the thrust line. The intrinsic variability of the seismic action is incorporated with the use of different sets of elastic spectra compatible with EC 8 Type-1 spectrum for various types of soil, with peak ground acceleration varying over the range 0.05–1.5 g. The fragility curves of the generalized classes of single-span masonry bridges are finally obtained from the effective ranges of the main geometric and material parameters affecting arch bridge capacity. 相似文献
58.
Don D. Eisenhour 《Meteoritics & planetary science》1996,31(2):243-248
Abstract— A method is described for correcting thin-section-derived chondrule sizes for three common sources of bias: (1) the non-equatorial sectioning of chondrules, (2) the non-zero thickness of thin sections, and (3) the unequal probability of sectioning different size chondrules. Application of the correction procedure to chondrule data from CO chondrites results in a reduction of mean and median chondrule diameters, an increase in minimum diameters, and transforms nearly log-normal distributions to distributions that conform to a Weibull probability function. The Weibull-function form of CO chondrule size distributions is similar to the form of chondrule distributions in ordinary chondrites obtained by disaggregation analyses. 相似文献
59.
This study investigates the sulfur and oxygen isotope fractionations of dissimilatory sulfate reduction and works to reconcile the relationships between the oxygen and sulfur isotopic and elemental systems. We report results of experiments with natural populations of sulfate-reducing bacteria using sediment and seawater from a marine lagoon at Fællestrand on the northern shore of the island of Fyn, Denmark. The experiments yielded relatively large magnitude sulfur isotope fractionations for dissimilatory sulfate reduction (up to approximately 45‰ for 34S/32S) with higher δ18O accompanying higher δ34S, similar to that observed in previous studies. The seawater used in the experiments was spiked by addition of 17O-labeled water and the 17O content of residual sulfate was found to depend on the fraction of sulfate reduced in the experiments. The 17O data provides evidence for recycling of sulfur from metabolic intermediates and for an 18O/16O fractionation of ∼25-30‰ for dissimilatory sulfate reduction. The close correlation between the 17O data and the sulfur isotope data suggests that isotopic exchange between cell water and external water (reactor water) was rapid under experimental conditions. The molar ratio of oxygen exchange to sulfate reduction was found to be about 2.5. This value is slightly lower than observed in studies of natural ecosystems [e.g., Wortmann U. G., Chernyavsky B., Bernasconi S. M., Brunner B., Böttcher M. E. and Swart P. K. (2007) Oxygen isotope biogeochemistry of pore water sulfate in the deep biosphere: dominance of isotope exchange reactions with ambient water during microbial sulfate reduction (ODP Site 1130). Geochim. Cosmochim. Acta71, 4221-4232]. Using recent models of sulfur isotope fractionations we find that our combined sulfur and oxygen isotopic data places constraints on the proportion of sulfate recycled to the medium (78-96%), the proportion of sulfur intermediate sulfite that was recycled by way of APS to sulfate and released back to the external sulfate pool (∼70%), and also that a fraction of the sulfur intermediates between sulfite and sulfide were recycled to sulfate. These parameters can be constrained because of the independent information provided by δ18O, δ34S, δ17O labels, and Δ33S. 相似文献
60.
采矿业已经而且还将继续在宜兴山区经济发展中发挥举足轻重的作用,但目前 对矿产资源的开发利用方式将严重阻碍宜兴市山区采矿业的可持续发展,在分析其存在的主 要问题的基础上提出了一些积极的对策. 相似文献