全文获取类型
收费全文 | 291篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 22篇 |
地球物理 | 102篇 |
地质学 | 124篇 |
海洋学 | 9篇 |
天文学 | 25篇 |
自然地理 | 14篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 11篇 |
2012年 | 9篇 |
2011年 | 12篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 3篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 14篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 12篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1978年 | 3篇 |
1973年 | 2篇 |
1959年 | 2篇 |
1954年 | 2篇 |
1940年 | 2篇 |
1936年 | 2篇 |
1935年 | 2篇 |
1933年 | 2篇 |
1931年 | 3篇 |
1930年 | 3篇 |
1928年 | 2篇 |
1926年 | 2篇 |
1925年 | 2篇 |
1924年 | 3篇 |
1916年 | 3篇 |
1914年 | 2篇 |
1912年 | 2篇 |
排序方式: 共有302条查询结果,搜索用时 15 毫秒
51.
52.
Tianyuan Zheng Xilai Zheng Huan Wang Jia Xin Bo Zhang Marc Walther 《Ground Water Monitoring & Remediation》2019,39(3):78-83
The oil content of oil-contaminated porous media is an important parameter for the assessment and remediation of oil pollution in soil and groundwater. However, an accurate measurement method is not available. In this study, we propose a new equation to calculate the oil content of water-bearing media based on traditional extraction–ultraviolet spectroscopy. Further, an improved experimental method was developed. The results indicate that the pure solid weight and oil content of oil-contaminated media can be accurately determined by introducing the oil drying loss coefficient (γ). The average relative errors of the improved method range from −0.14% to −0.96%. They are much smaller than errors of −4.49% to −10.97% of the original methods, indicating that the accuracy of measured oil content is enhanced. In addition, the accuracy of the new method does not depend on oil volatility and oil content. 相似文献
53.
We apply and evaluate a recent machine learning method for the automatic classification of seismic waveforms. The method relies on Dynamic Bayesian Networks (DBN) and supervised learning to improve the detection capabilities at 3C seismic stations. A time-frequency decomposition provides the basis for the required signal characteristics we need in order to derive the features defining typical “signal” and “noise” patterns. Each pattern class is modeled by a DBN, specifying the interrelationships of the derived features in the time-frequency plane. Subsequently, the models are trained using previously labeled segments of seismic data. The DBN models can now be compared against in order to determine the likelihood of new incoming seismic waveform segments to be either signal or noise. As the noise characteristics of seismic stations varies smoothly in time (seasonal variation as well as anthropogenic influence), we accommodate in our approach for a continuous adaptation of the DBN model that is associated with the noise class. Given the difficulty for obtaining a golden standard for real data (ground truth) the proof of concept and evaluation is shown by conducting experiments based on 3C seismic data from the International Monitoring Stations, BOSA and LPAZ. 相似文献
54.
Nawrass N. Ameen Nicole Klueglein Erwin Appel Eduard Petrovský Andreas Kappler Carsten Leven 《Studia Geophysica et Geodaetica》2014,58(3):442-460
We investigate magnetic phase (trans)formation in the presence of petroleum hydrocarbons and its relation to bacterial activity, in particular in the zone of remediation driven fluctuating water levels at a former military air base in the Czech Republic. In a previous study an increase of magnetite concentration from the groundwater table towards the top of the groundwater fluctuation zone (GWFZ) was reported, however with limited reliability as there was no control on small-scale effects. To recognize statistically significant magnetic signatures versus depth, we obtained multiple sediment cores from three locations in January 2011 and April 2012, penetrating the unsaturated zone, the GWFZ and the uppermost one meter below the groundwater level (~2.3 m depth at the time of sampling). Magnetic concentration variation versus depth was determined by measuring magnetic susceptibility (MS) and remanence parameters. Small-scale features were identified and eliminated by statistical processing of multiple cores. A trend of increasing MS values from the lowermost position of the groundwater table upward was verified and highest magnetic concentration was found at the top of the GWFZ. Magnetic mineralogy indicates that newly formed fine-grained magnetite in the single domain to small pseudo-single domain range is responsible for the MS enhancement confirming previous results. There is no correlation with the depth variation of hydrocarbon (HC) concentrations; however, total organic carbon is linked to MS and may represent a degradation product of HC that is bioavailable for microorganisms. Bacterial activity is likely responsible for magnetite formation as indicated by most probable number (MPN) results of iron-metabolizing bacteria. The comparison of our results with an earlier study conducted at the same site revealed that magnetic concentration clearly decreased since remediation was terminated in 2008, possibly due to dissolution of magnetite. 相似文献
55.
56.
Ida Damgaard Poul L. Bjerg Carsten S Jacobsen Aikaterini Tsitonaki Henriette Kerrn‐Jespersen Mette M. Broholm 《Ground Water Monitoring & Remediation》2013,33(1):48-61
At a low permeability clay till site contaminated with chlorinated ethenes (Gl. Kongevej, Denmark), enhanced reductive dechlorination (ERD) was applied by direct push injection of molasses and dechlorinating bacteria. The performance was investigated by long‐term groundwater monitoring, and after 4 years of remediation, the development of degradation in the clay till matrix was investigated by high‐resolution subsampling of intact cores. The formation of degradation products, the presence of specific degraders Dehalococcoides spp. with the vinyl chloride (VC) reductase gene vcrA, and the isotope fractionation of trichloroethene, cis‐dichloroethene (cis‐DCE), and VC showed that degradation of chlorinated ethenes occurred in the clay till matrix as well as in sand lenses, sand stringers, and fractures. Bioactive sections of up to 1.8 m had developed in the clay till matrix, but sections, where degradation was restricted to narrow zones around sand lenses and stringers, were also observed. After 4 years of remediation, an average mass reduction of 24% was estimated. Comparison of the results with model simulation scenarios indicate that a mass reduction of 85% can be obtained within approximately 50 years without further increase in the narrow reaction zones if no donor limitations occur at the site. Long‐term monitoring of the concentration of chlorinated ethenes in the underlying chalk aquifer revealed that the aquifer was affected by the more mobile degradation products cis‐DCE and VC generated during the remediation by ERD. 相似文献
57.
AbstractSmall dams fragment river landscapes, disrupting channel connectivity and impacting water quality and quantity. Although they impound volumetrically less total water than large dams, the ubiquity of small dams suggests their cumulative impacts could be significant. Documenting the distribution and characteristics of small dams is necessary to understanding and mitigating their impacts. In this study, we compare datasets of small dams in Oregon, compile a new comprehensive dataset, and document geographic variations in small dam distributions between different ecoregions. We used Oregon Water Resources Department dam and Oregon Department of Fish and Wildlife fish passage barrier datasets to compare dam heights and contributing drainage areas between different ecoregions. Over 61% of Oregon’s land area is above one or more small dam. We highlight the location of Oregon’s small dams at valley margins, transition zones between flat plains and mountains, and areas of high population density. Given the hidden nature of small dams, evaluation of small dam impacts using public imagery is not effective. However, knowledge of small dam distributions given their association with landforms can aid in finding unrecorded dams, assessing approaches for evaluating their geomorphic impacts, and informing their management. 相似文献
58.
Carsten W. Mueller Angelika KölblCarmen Hoeschen François HillionKatja Heister Anke M. HerrmannIngrid Kögel-Knabner 《Organic Geochemistry》2012,42(12):1476-1488
The specific features of the nano-scale secondary ion mass spectrometry (NanoSIMS) technology with the simultaneous analysis of up to seven ion species with high mass and lateral resolution enables us to perform multi-element and stable isotope measurements at the submicron scale. To elucidate the power of this technique, we performed an incubation experiment with soil particles of the fine silt and clay fractions (from an Albic Luvisol), with occluded particulate organic material and intact soil aggregates (from a Haplic Chernozem), using a 13C and 15N labelled amino acid mixture as tracer. Before and during 6-day incubation after the addition of the label, samples were consecutively prepared for NanoSIMS analysis. For this purpose, two different sample preparation techniques were developed: (i) wet deposition and (ii) the sectioning of epoxy resin embedded samples. Single soil particles (fine silt/clay fraction) showed an enrichment of 13C and 15N after label addition that decreased over time. On aggregates of particulate organic matter, re-aggregated during the 6-day incubation experiment, we could show a spatially heterogeneous enrichment of 13C and 15N on the particle surface. The enrichment in 15N demonstrated the diffusion of dissolved organic matter into intact soil aggregate interiors. The prospects of NanoSIMS for three dimensional studies of stable C and N isotopes in organo-mineral associations is demonstrated by the recorded depth profiles of the organic matter distribution on mineral particles. 相似文献
59.
by Tom Clemo Warren Barrash Edward C. Reboulet Timothy C. Johnson Carsten Leven 《Ground water》2009,47(4):515-525
This paper describes a combined field, laboratory, and numerical study of electromagnetic borehole flowmeter measurements acquired without the use of a packer or skirt to block bypass flow around the flowmeter. The most significant finding is that inflow through the wellbore screen changes the ratio of flow through the flowmeter to wellbore flow. Experiments reveal up to a factor of two differences in this ratio for conditions with and without inflow through the wellbore screen. Standard practice is to assume the ratio is constant. A numerical model has been developed to simulate the effect of inflow on the flowmeter. The model is formulated using momentum conservation within the borehole and around the flowmeter. The model is embedded in the MODFLOW-2000 ground water flow code. 相似文献
60.
by Ralf Köber Götz Hornbruch Carsten Leven Lars Tischer Jochen Großmann Peter Dietrich Holger Weiß Andreas Dahmke 《Ground water》2009,47(4):536-546
Most established methods to characterize aquifer structure and hydraulic conductivities of hydrostratigraphical units are not capable of delivering sufficient information in the spatial resolution that is desired for sophisticated numerical contaminant transport modeling and adapted remediation design. With hydraulic investigation methods based on the direct-push (DP) technology such as DP slug tests, DP injection logging, and the hydraulic profiling tool, it is possible to rapidly delineate hydrogeological structures and estimate their hydraulic conductivity in shallow unconsolidated aquifers without the need for wells. A combined application of these tools was used for the investigation of a contaminated German refinery site and for the setup of hydraulic aquifer models. The quality of DP investigation and the models was evaluated by comparisons of tracer transport simulations using these models and measured breakthroughs of two natural gradient tracer tests. Model scenarios considering the information of all tools together showed good reproduction of the measured breakthroughs, indicating the suitability of the approach and a minor impact of potential technical limitations. Using the DP slug tests alone yielded significantly higher deviations for the determined hydraulic conductivities compared to considering two or three of the tools. Realistic aquifer models developed on basis of such combined DP investigation approaches can help optimize remediation concepts or identify flow regimes for aquifers with a complex structure. 相似文献