全文获取类型
收费全文 | 197篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 26篇 |
地球物理 | 48篇 |
地质学 | 69篇 |
海洋学 | 14篇 |
天文学 | 12篇 |
自然地理 | 32篇 |
出版年
2023年 | 3篇 |
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 26篇 |
2012年 | 10篇 |
2011年 | 8篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 11篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1961年 | 1篇 |
1946年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有210条查询结果,搜索用时 15 毫秒
201.
Within the period of our records, spills of vegetable oils at Vancouver harbour have caused greater losses of birds than spills of petroleum oils. Vegetable oils affect birds by feather wetting but do not exhibit odour and slick characteristics of petroleum oils. Because most vegetable oils are edible their potential danger to aquatic birds may go unnoticed; sites of storage and transhipment of vegetable oils may be overlooked in oil spill contingency planning. 相似文献
202.
Pavel Ya. Groisman Boris G. Sherstyukov Vyacheslav N. Razuvaev Richard W. Knight Jesse G. Enloe Nina S. Stroumentova Paul H. Whitfield Eirik Frland Inger Hannsen-Bauer Heikki Tuomenvirta Hans Aleksandersson Anna V. Mescherskaya Thomas R. Karl 《Global and Planetary Change》2007,56(3-4):371
Significant climatic changes over Northern Eurasia during the 20th century have been reflected in numerous variables of economic, social, and ecological interest, including the natural frequency of forest fires. For the former USSR, we are now using the Global Daily Climatology Network and a new Global Synoptic Data Network archive, GSDN, created jointly by U.S. National Climatic Data Center and Russian Research Institute for Hydrometeorological Information. Data from these archives (approximately 1500 of them having sufficiently long meteorological time series suitable for participation in our analyses) are employed to estimate systematic changes in indices used in the United States and Russia to assess potential forest fire danger. We use four indices: (1) Keetch–Byram Drought Index, (KBDI; this index was developed and widely used in the United States); (2) Nesterov, (3) Modified Nesterov, and (4) Zhdanko Indices (these indices were developed and widely used in Russia). Analyses show that after calibration, time series of the days with increased potential forest fire danger constructed using each of these three indices (a) are well correlated and (b) deliver similar conclusions about systematic changes in the weather conditions conducive to forest fires. Specifically, over the Eastern half of Northern Eurasia (Siberia and the Russian Far East) statistically significant increases in indices that characterize the weather conditions conducive to forest fires were found. These areas coincide with the areas of most significant warming during the past several decades south of the Arctic Circle. West of the Ural Mountains, the same indices show a steady decrease in the frequency of “dry weather summer days” during the past 60 yr. This study is corroborated with available statistics of forest fires and with observed changes in drought statistics in agricultural regions of Northern Eurasia. 相似文献
203.
The effectiveness of coastal management in developing countries is widely perceived to be inhibited by a lack of scientific data on the coastal zone. To try to fill this need for information, donors and big international non-governmental organizations are increasingly initiating large-scale, science-driven conservation programs, with the goal of creating and using management relevant transdisciplinary datasets. In Oceania, these programs are entering a context where local ecological knowledge is already informing existing community-based approaches to coastal management. This paper examines two large-scale programs in Fiji, the Marine Management Area Science initiative and the Vatu-i-Ra and Cakau Levu Reefs Seascape Project, and offers insight relevant to the planning and implementation of similar programs where local management systems are already in place. Research methods used to examine the programs included document analysis, direct observation, and semi-structured interviews with key stakeholders over multiple field visits to Fiji in 2009 and 2010. Results suggest that as donors, non-governmental organizations, and partners move forward in implementing these programs, there must be active steps taken to bridge boundaries between disciplines and among knowledge systems, evaluate the added value of science for all stakeholder groups, and build opportunities for datasets to be used after donor funding ends. 相似文献
204.
Empirical models for describing recent sedimentation rates in lakes distributed across broad spatial scales 总被引:1,自引:0,他引:1
Soren Brothers Jesse C. Vermaire Irene Gregory-Eaves 《Journal of Paleolimnology》2008,40(4):1003-1019
Over the last 20 years there has been a surge of interest in paleolimnology and as a result a large accumulation of lake sedimentation
records. This emerging archive has allowed us to develop empirical models to describe which variables explain significant
variation in sedimentation rates over the past ∼150 years across large spatial scales. We hypothesized that latitude would
be a significant explanatory variable of profundal zone lake sedimentation rates across a temperate to polar gradient. We
further hypothesized that along a more longitudinally-constrained dataset (i.e. east coast of North America), latitude would
explain a greater proportion of the variance. To test these hypotheses, we collated data from 125 natural, average-sized lakes
(with surface area <500 km2) by recording authors’ estimates of sedimentation rates (measured as mm/year) or by digitizing recent sediment profiles and
calculating sedimentation rates over the past ∼150 years. We found that, at both scales, latitude was the strongest predictor
of lake sedimentation rates (full dataset: r
2 = 0.28, P = 0.001, n = 125; east coast dataset: r
2 = 0.58, P < 0.001, n = 43). By conducting a multiple linear regression analysis, we found that 70% of the variance in sedimentation rates from
the east coast transect was explained by latitude and elevation alone. This latter model is of sufficient strength that it
is a robust predictive tool. Given that climate and land-use strongly co-vary with latitude and that both of these factors
have previously been shown to influence lake sedimentation rates, it appears that latitude is a surrogate measure for climate
and land-use changes. We also show support for land-use as an important variable influencing sedimentation rates by demonstrating
large increases in recent versus Holocene accumulation rates. These results indicate that it is possible to make generalizations
about sedimentation rates across broad spatial scales with even limited geographic data. 相似文献
205.
The Heath Steele massive sulphide deposit in northern New Brunswick lies conformably within a sedimentary-volcanic sequence of probable Ordovician age which has been metamorphosed to the greenschist stage. The dominant sulphide mineral is pyrite, and the main economic minerals are sphalerite, galena, and chalcopyrite; the general grade of the ore is 5% Zn, 2% Pb, and 1% Cu.The distribution of Pb and Zn in acid volcanic rocks stratigraphically above the massive sulphides is compared with the distribution in similar rocks stratigraphically below the sulphides. Whereas there are discernable differences in the populations, there is also considerable overlap between them. To enable individual samples to be classified, linear discriminant functions were calculated for the two groups; Pb and Zn were found to be the most useful variables to separate the two populations. The functions were then tested on hanging wall and footwall samples not used in computing the functions. A halo region, extending about 1,200 ft above the sulphides and 4,000 ft along the same stratigraphic horizon as the sulphides was outlined by samples classified as “hanging wall”. Beyond the halo zone there is no significant difference in the distribution of Pb and Zn between the hanging wall and footwall acid volcanic rocks.The results demonstrate that rocks at Heath Steele, which show no evidence of mineralogical alteration attributable to mineralization, have a trace element halo of considerable extent spatially associated with the sulphides. If similar halos can be shown to be a general feature of massive sulphide deposits, the technique described should have wide application for exploration for deeply buried deposits of this type. 相似文献
206.
Algorithms for GPS operation indoors and downtown 总被引:6,自引:0,他引:6
Nainesh Agarwal Julien Basch Paul Beckmann Piyush Bharti Scott Bloebaum Stefano Casadei Andrew Chou Per Enge Wungkum Fong Neesha Hathi Wallace Mann Anant Sahai Jesse Stone John Tsitsiklis Benjamin Van Roy 《GPS Solutions》2002,6(3):149-160
The proliferation of mobile devices and the emergence of wireless location-based services has generated consumer demand for
availability of GPS in urban and indoor environments. This demand calls for enhanced GPS algorithms that accommodate high
degrees of signal attenuation and multipath effects unique to the "urban channel." This paper overviews the market for location-based
services and discusses algorithmic innovations that address challenges posed by urban environments.
Electronic Publication 相似文献
207.
Jesse C. Ribot 《GeoJournal》1995,35(2):119-122
208.
Lirong Zhong Kirk Cantrell Alex Mitroshkov Jesse Shewell 《Environmental Earth Sciences》2014,71(9):4261-4272
Supercritical CO2 (scCO2) is a good solvent for organic compounds such as benzene, toluene, ethyl-benzene, and xylene (BTEX), phenols, and polycyclic aromatic hydrocarbons (PAHs). Monitoring results from geological carbon sequestration (GCS) field tests have shown that organic compounds are mobilized following CO2 injection. Such results have raised concerns regarding the potential for groundwater contamination by toxic organic compounds mobilized during GCS. Knowledge of the mobilization mechanism of organic compounds and their transport and fate in the subsurface is essential for assessing risks associated with GCS. Extraction tests using scCO2 and methylene chloride (CH2Cl2) were conducted to study the mobilization of volatile organic compounds (VOCs, including BTEX), the PAH naphthalene, and n-alkanes by scCO2 from representative reservoir rock and caprock obtained from depleted oil reservoirs and coal from an enhanced coal-bed methane recovery site. Results showed that the extent of mobilization for the organic compounds was a function of the source rock. In fate and transport sand column experiments, moisture content was found to have an important influence on the transport of the organic compounds. In dry sand columns the majority of the compounds were retained in the column except benzene and toluene. In wet sand columns the mobility of the BTEX was much higher than that of naphthalene. Based upon the results determined for the reservoir rock, caprock, and coal samples studied here, the risk to aquifers from contamination by organic compounds appears to be relatively low; however, further work is necessary to fully evaluate the risks. 相似文献
209.
Anitra E. Ingalls Kenia Whitehead Maxime C. Bridoux 《Geochimica et cosmochimica acta》2010,74(1):104-115
Diatom frustule-bound organic compounds presumably play an important role in biomineralization and constitute an important pool of organic matter preserved in diatom frustule-rich sediments. In this study, detailed analysis of diatom frustule-bound organic matter in opal-rich Southern Ocean plankton and sediments revealed for the first time the presence of low molecular weight, UV light absorbing compounds called mycosporine-like amino acids (MAAs). Chemically cleaned diatom frustule-derived biosilica was dissolved in HF, releasing bound or entrapped organic compounds that were subsequently characterized using liquid chromatography with UV-Vis and electrospray ionization mass spectrometry (LC/PDA/ESI-MS). Palythine ([M+H]+ = 245), porphyra-334 ([M+H]+ = 347) and shinorine ([M+H]+ = 333) were the most abundant MAAs detected in HF digests of plankton and sediment. Traces of asterina ([M+H]+ = 289), palythinol ([M+H]+ = 303) and palythinic acid ([M+H]+ = 329) were also detected. MAAs in cleaned HF digested frustules were up to two orders of magnitude more abundant than methanol extractable MAAs. MAAs are substituted with acid hydrolysable amino acid residues. Our results suggest that MAAs, and not proteins, could be responsible for the high proportion of the amino acids glycine and threonine found in hydrolysates of HF digested diatom-rich environmental samples. Total MAAs accounted for 3-27% of the carbon and 2-18% of total nitrogen in the frustules undergoing various chemical cleaning treatments. This is the first report of MAAs in close association with a mineral phase and we hypothesize that the mineral matrix could stabilize these compounds, thereby enhancing photoprotection against the harmful effects of UV light. The presence of frustule-bound MAAs in sediment cores further suggests the possibility that they could be used in compound-specific isotope analysis of diatom-bound organic matter and as indicators of past solar irradiance. 相似文献
210.
Dale Dominey-Howes Paula Dunbar Jesse Varner Maria Papathoma-Köhle 《Natural Hazards》2010,53(1):43-61
The Cascadia margin is capable of generating large magnitude seismic-tsunami. We use a 1:500 year tsunami hazard flood layer
produced during a probabilistic tsunami hazard assessment as the input to a pilot study of the vulnerability of residential and commercial buildings in Seaside, OR, USA. We map building
exposure, apply the Papathoma Tsunami Vulnerability Assessment Model to calculate building vulnerability and estimate probable maximum loss (PML) associated with a 1:500 year tsunami flood. Almost US$0.5 billion worth of buildings would be inundated, 95% of single
story residential and 23% of commercial buildings would be destroyed with PML’s exceeding US$0.5 billion worth of buildings would be inundated, 95% of single
story residential and 23% of commercial buildings would be destroyed with PML’s exceeding US116 million. These figures only
represent a tiny fraction of the total values of exposed assets and loss that would be associated with a Cascadia tsunami
impacting the NW Pacific coast. Not withstanding the various issues associated with our approach, this study represents the
first time that PML’s have ever been calculated for a Cascadia type tsunami, and these results have serious implications for
tsunami disaster risk management in the region. This method has the potential to be rolled out across the United States and
elsewhere for estimating building vulnerability and loss to tsunami. 相似文献