全文获取类型
收费全文 | 347篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 31篇 |
地球物理 | 135篇 |
地质学 | 95篇 |
海洋学 | 29篇 |
天文学 | 40篇 |
自然地理 | 20篇 |
出版年
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 19篇 |
2013年 | 17篇 |
2012年 | 12篇 |
2011年 | 22篇 |
2010年 | 24篇 |
2009年 | 30篇 |
2008年 | 15篇 |
2007年 | 14篇 |
2006年 | 14篇 |
2005年 | 21篇 |
2004年 | 5篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有363条查询结果,搜索用时 297 毫秒
291.
Small Purge Method to Sample Vapor from Groundwater Monitoring Wells Screened Across the Water Table
下载免费PDF全文
![点击此处可从《Ground Water Monitoring & Remediation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Groundwater monitoring wells are present at most hydrocarbon release sites that are being assessed for cleanup. If screened across the vadose zone, these wells provide an opportunity to collect vapor samples that can be used in the evaluation of vapor movement and biodegradation processes occurring at such sites. This paper presents a low purge volume method (modified after that developed by the U.S. EPA) for sampling vapor from monitoring wells that is easy to implement and can provide an assessment of the soil gas total petroleum hydrocarbon (TPH) and O2 concentrations at the base of the vadose zone. As a result, the small purge method allows for sampling of vapor from monitoring wells to support petroleum vapor intrusion (PVI) risk assessment. The small purge volume method was field tested at the Hal's service station site in Green River, Utah. This site is well‐known for numerous soil gas measurements containing high O2 and high TPH vapor concentrations in the same samples which is inconsistent with well‐accepted biodegradation models for the vapor pathway. Using the low purge volume method, monitoring wells were sampled over, upgradient, and downgradient of the light nonaqueous phase liquid (LNAPL) footprint. Results from our testing at Hal's show that vapor from monitoring wells over LNAPL contained very low O2 and high TPH concentrations. In contrast, vapor from monitoring wells not over LNAPL contained high O2 and low TPH concentrations. The results of this study show that a low purge volume method is consistent with biodegradation models especially for sampling at sites where low permeability soils exist in and around a LNAPL source zone. 相似文献
292.
A rural subdivision in south central Wisconsin was instrumented with monitoring wells and lysimeters before, during, and after its construction to examine the impacts of the unsewered subdivision on groundwater quality and quantity. Prior to construction, the 78-acre (32 ha) site was farmland. Sixteen homes were constructed beginning in 2003. Initial monitoring from 2002 to 2005 showed that groundwater beneath the site had been impacted by previous agricultural use, with nitrate-N values as high as 30 mg/L and some detections of the herbicide atrazine. Our 12-year study shows that the transition from agricultural to residential land use has changed groundwater quality in both negative and positive ways. Although groundwater elevations showed typical seasonal fluctuations each year, there were no measurable changes in groundwater levels or general flow directions during the 12-year study period. Chloride values increased in many wells, possibly as a result of road salting or water softener discharge. Nitrate concentrations varied spatially and temporally over the study period, with some initial concentrations substantially above the drinking water standard. In some wells, nitrate and atrazine levels have declined substantially since agriculture ceased. However, atrazine was still present at trace concentrations throughout the site in 2014. Wastewater tracers show there are small but detectable impacts from septic effluent on groundwater quality. Particle traces based on a groundwater flow model are consistent with the hypothesis that septic leachate has impacted groundwater quality. 相似文献
293.
In order to enable greater accuracy in the determination of the mass discharge of gas and water-gas ratios (WGR) in groundwater from springs, we have developed a field-deployable instrument using commercially available components to independently measure the gas and water mass flow rates in springs with bubbling mixed-phase flow. Collecting and measuring the free gas phase will allow for further compositional analysis that may be useful in improving gas-derived parameters such as recharge temperature and age, as well as quantification of methanogenesis and flux of crustal/mantle gasses. By installing a phase separator at the spring discharge, a thermal mass flow sensor is utilized to measure the gas flow rate (ebullition + flux) generated from a spring. The water flow rate is determined by a standard weir. Field performance of the device was tested on a spring discharging from the Arbuckle-Simpson aquifer near the town of Connerville in south-central Oklahoma, USA. 相似文献
294.
This paper describes a set of MATLAB functions currently being developed for Space Based Augmentation System (SBAS) availability
analysis. This toolset includes simulation algorithms that are constantly being developed and updated by various working groups.
This set of functions is intended for use as a fast, accurate, and highly customizable experimental test bed for algorithm
development. A user-friendly interface has also been developed for the tool. It is open source and can be downloaded from
the Stanford GPS Research Laboratory web site (). Therefore, it provides a common ground for different working groups to compare their results. This paper demonstrates the
utility of this toolset by analyzing the SBAS service volume models for the Conterminous United States. The paper describes
the functionality provided within the software, and shows an example set of contour plots which are the means for investigating
how different algorithms and parameters impact availability. 相似文献
295.
Evaluating weather observations and the Climate Forecast System Reanalysis as inputs for hydrologic modelling in the tropics
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Daniel A. Auerbach Zachary M. Easton M. Todd Walter Alexander S. Flecker Daniel R. Fuka 《水文研究》2016,30(19):3466-3477
Correctly representing weather is critical to hydrological modelling, but scarce or poor quality observations can often compromise model accuracy. Reanalysis datasets may help to address this basic challenge. The Climate Forecast System Reanalysis (CFSR) dataset provides continuous, globally available records, and CFSR data have produced satisfactory hydrological model performance in some temperate and monsoonal locations. However, the use of CFSR for hydrological modelling in tropical and semi‐tropical basins has not been adequately evaluated. Taking advantage of exceptionally high rainfall station density in the catchments of the Rio Grande de Loiza above San Juan, Puerto Rico, we compared model performance based on CFSR records with that based on publicly available weather stations in the Global Historical Climate Network (GHCN, n = 21) and on a dataset of rainfall records maintained by the United States Geological Survey Caribbean Water Science Center (USGS, n = 24). For an implementation of the Soil and Water Assessment Tool (SWAT) with subbasins defined at 11 streamflow gages, uncalibrated measures of Nash–Sutcliffe efficiency (NSE) were >0 at 8 of 11 gages using USGS precipitation data for daily simulations over the period 1998–2012, but were <0 using GHCN weather station records (8 of 11) and CFSR reanalysis data (9 of 11). Autocalibration of individual SWAT models for each of the 11 basins against each of the available weather datasets yielded NSE values > 0 using all precipitation inputs, including CFSR. However, the ground weather station closest to the geographic basin centre produced the highest NSE values in only 5 of 11 cases. The spatially interpolated CFSR data performed as well or better than single ground observations made further than 20–30 km, and sometimes better than individual weather stations <10 km from the basin centroid. In addition to demonstrating the need to evaluate available weather inputs, this research reinforces the value of CFSR data as a means to supplement ground records and consistently determine a baseline for hydrologic model performance. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
296.
Sinem Yavuz Roman Pevzner Sofya Popik Konstantin Tertyshnikov Todd Wood Michelle C. Robertson Julia Correa Barry Freifeld 《Geophysical Prospecting》2022,70(1):108-120
Time-lapse seismic is one of the main methods for monitoring changes in reservoir conditions caused by production or injection of fluids. One approach to time-lapse seismic is through permanent reservoir monitoring, whereby seismic sources and/or receivers are permanently deployed. Permanent reservoir monitoring can offer a more cost-effective and environmentally friendly solution than traditional campaign-based surveys that rely on temporarily deployed equipment while facilitating more frequent measurements. At the CO2CRC Otway Project, surface orbital vibrators were coupled to a buried geophone array to form a permanent reservoir monitoring system. These are fixed position seismic sources that provide both P and S waves using induction motor-driven eccentric masses. After an initial injection of CO2 in February 2016, five months of continuous seismic data were acquired, and reflection imaging was used to assess the system performance. Analysis of the data showed the effects of weather variations on the near-surface conditions and the sweep signatures of surface orbital vibrators. Data processing flows of the continuous data was adapted from Vibroseis four-dimensional data processing flows. Ground roll proved a significant challenge to data processing. In addition, variations in the surface wave pattern were linked to major rainfall events. For the appraisal of surface orbital vibrators in imaging, a Vibroseis four-dimensional monitor survey data with similar geometry was also processed. Surface orbital vibrators are observed to be reliable sources with a potential to provide a repeatable signal, especially if the ground roll should fall outside the target window of interest. To guide future permanent reservoir monitoring applications, a repeatability analysis was performed for the various key data processing steps. 相似文献
297.
298.
299.
Organic farmers are a prime clientele for climate services by virtue of their social profile and vulnerability of produce to climate extremes. The study draws on an online survey and in-depth interviews with organic farmers in Georgia (United States). It shows that organic farmers access and act on climate information in ways that reflect their emphasis on diversified and flexible systems. They favor a pluralistic knowledge base that integrates scientific expertise with place-based experience and intuitive understandings. Their management style combines information at multiple temporal scales and draws on a range of technical and social resources. Translating climate forecasts into usable science for organic farming requires attention to the identities, commitments, and relationships that define the organic farming community. 相似文献
300.
The dispersion of fibrous amphiboles by glacial processes in the area surrounding Libby,Montana, USA
William H. Langer Bradley S. Van Gosen Gregory P. Meeker David T. Adams Todd M. Hoefen 《Environmental Earth Sciences》2011,64(1):157-168
Mining operations began at a world-class vermiculite deposit at Vermiculite Mountain near Libby, Montana, circa 1920 and ended
in 1990. Fibrous and asbestiform amphiboles intergrown with vermiculite ore are suspected to be a causative factor in an abnormally
high number of cases of respiratory diseases in former mine and mill workers, and in residents of Libby. The question addressed
in this report is whether some of the amphibole from Vermiculite Mountain could have been dispersed by Pleistocene glacial
processes rather than by human activity after vermiculite mining began. The history of Pinedale glaciation in the Libby area
provides a framework for estimating the presence and distribution of asbestiform amphiboles derived from Vermiculite Mountain
and found in naturally occurring sediments of Glacial Lake Kootenai that underlie the Libby Valley area. There were two situations
where sediments derived from Vermiculite Mountain were deposited into Glacial Lake Kootenai: (1) as lake-bottom sediments
derived from meltwater flowing down Rainy Creek when the valley south of Vermiculite Mountain was free of ice but active ice
still covered Vermiculite Mountain; and (2) as lake-bottom sediments eroded from the Rainy Creek outwash and re-deposited
during a re-advance of the Purcell Trench Glacier lobe near Moyie Springs, Idaho. 相似文献