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491.
M. C. Ramadevi B. T. Ravishankar Abhilash R. Sarwade S. Vaishali Nirmal Kumar Iyer Anuj Nandi V. Girish Vivek Kumar Agarwal Blessy Elizabeth Baby Mohammed Hasan S. Seetha Dipankar Bhattacharya 《Journal of Astrophysics and Astronomy》2018,39(1):11
Scanning Sky Monitor (SSM) onboard AstroSat is an X-ray sky monitor in the energy range 2.5–10 keV. SSM scans the sky for X-ray transient sources in this energy range of interest. If an X-ray transient source is detected in outburst by SSM, the information will be provided to the astronomical community for follow-up observations to do a detailed study of the source in various other bands. SSM instrument, since its power-ON in orbit, has observed a number of X-ray sources. This paper discusses observations of few X-ray transients by SSM. The flux reported by SSM for few sources during its Performance Verification phase (PV phase) is studied and the results are discussed. 相似文献
492.
Local vs. Regional Groundwater Flow Delineation from Stable Isotopes at Western North America Springs 下载免费PDF全文
The recharge location for many springs is unknown because they can be sourced from proximal, shallow, atmospheric sources or long‐traveled, deep, regional aquifers. The stable isotope (18O and 2H) geochemistry of springs water can provide cost‐effective indications of relative flow path distance without the expense of drilling boreholes, conducting geophysical studies, or building groundwater flow models. Locally sourced springs generally have an isotopic signature similar to local precipitation for that region and elevation. Springs with a very different isotopic composition than local meteoric inputs likely have non‐local recharge, representing a regional source. We tested this local vs. regional flow derived hypothesis with data from a new, large springs isotopic database from studies across Western North America in Arizona, Nevada, and Alberta. The combination of location‐specific precipitation data with stable isotopic groundwater data provides an effective method for flow path determination at springs. We found springs in Arizona issue from a mix of regional and local recharge sources. These springs have a weak elevation trend across 1588 m of elevation where higher elevation springs are only slightly more depleted than low elevation springs with a δ18O variation of 5.9‰. Springs sampled in Nevada showed a strong elevation‐isotope relationship with high‐elevation sites discharging depleted waters and lower elevation springs issuing enriched waters; only a 2.6‰ difference exists in 18O values over an elevation range of more than 1500 m. Alberta's springs are mostly sourced from local flow systems and show a moderate elevation trend of 1200 m, but the largest range in δ18O, 7.1‰. 相似文献
493.
Samuel V. Panno Walton R. Kelly John Scott Wei Zheng Rachel E. McNeish Nancy Holm Timothy J. Hoellein Elizabeth L. Baranski 《Ground water》2019,57(2):189-196
Groundwater in karst aquifers constitutes about 25% of drinking water sources globally. Karst aquifers are open systems, susceptible to contamination by surface-borne pollutants. In this study, springs and wells from two karst aquifers in Illinois, USA, were found to contain microplastics and other anthropogenic contaminants. All microplastics were fibers, with a maximum concentration of 15.2 particles/L. The presence of microplastic was consistent with other parameters, including phosphate, chloride and triclosan, suggesting septic effluent as a source. More studies are needed on microplastic sources, abundance, and impacts on karst ecosystems. 相似文献
494.
Konstantinos Papadopoulos Elizabeth Vintzileou Ioannis N. Psycharis 《地震工程与结构动力学》2019,48(13):1432-1450
This paper presents a numerical study of the response to earthquake actions of eight ancient Greek multidrum columns, which were chosen as representative of a broad spectrum of the ancient columns preserved to date. The study was conducted using the FE software Abaqus, in three steps. At first, the software efficiency to predict the rocking response of dry-stone structures was verified. Afterwards, various numerical models of one typical ancient multidrum column were seismically excited. Records of four real earthquakes differing in frequency content were used for the excitation of the models. Each column model was different from the others at least in one geometric or modeling parameter. Although the examined parameters affected the numerical results, their variation did not alter significantly the overall behavior of the column. In the last step of the study, numerical models of eight columns were seismically excited using four seismic records. In these analyses, among the simulation approaches tested in the second step, the simpler one was adopted. On the basis of the numerical results, conclusions were drawn regarding the seismic resistance of the columns and its correlation with the dynamic characteristics of the columns (size, slenderness, and frequency parameter) and with the basic intensity measures and frequency content indicator of the seismic motions (PHA, PHV, PHD, and Tg). Thus, criteria of seismic collapse for the multidrum columns are proposed, which can be used for the approximate assessment of the seismic vulnerability of free-standing ancient columns, provided that the columns are in good preservation state. 相似文献
495.
Christopher M. Stevenson Elizabeth Knaus James J. Mazer John K. Bates 《Geoarchaeology》1993,8(5):371-384
Users of the obsidian hydration dating method have routinely assumed that artifacts which originate from the same geological flow will be of the same chemical composition and thus hydrate at the same rate under equivalent conditions of temperature and relative humidity. Recent laboratory experimentation into the hydration process has shown that the intrinsic water content of the glass is the dominant factor in establishing the rate of hydration. Water content determinations on a large suite of samples from numerous prehistoric quarries within the Coso volcanic field, California, indicated that water content values, and thus hydration rate, varied significantly on a within flow basis. It is recommended that water determinations be made on individual artifacts prior to obsidian hydration dating. © 1993 John Wiley & Sons, Inc. 相似文献
496.
Soils‐based evidence derived from thin section micromorphology is used to explore contrasts in pre‐Hispanic and Hispanic arable land management practices associated with raised fields in an inter‐Andean valley of Ecuador. Differences in textural pedofeature characteristics suggest that, where they are found in the same locality, camellón systems were more intensively manured and cultivated than wachu systems. Both, however, were more intensively managed than traditional Hispanic arable fields. The importance of the camellón in pre‐Hispanic agriculture is emphasized by soils‐based evidence that highlights the efforts made to clear these fields of volcanic ash after the Quilotoa eruption of ca. A.D. 1280. This research suggests that, in an andosol context, pre‐Hispanic and Hispanic arable land management practices leave relict and fossil soil micromorphology features that can be used to interpret land use intensities. © 2002 Wiley Periodicals, Inc. 相似文献
497.
Elizabeth L. Podowski Tom S. Moore Kevin A. Zelnio George W. Luther III Charles R. Fisher 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):2041-2056
Hydrothermal vent environments are characterized by large gradients of toxic chemicals and high temperatures, which play a significant role in defining species’ distributions. We used high-resolution imagery and spatially explicit in-situ physico-chemical measurements analyzed within a Geographic Information System (GIS) in order to characterize the spatial relations among different groups of megafauna, temperature, and chemistry within two discrete vent communities (40 and 50 m2) on the Eastern Lau Spreading Center (ELSC). Chemical (sulfide and O2 concentrations) and temperature data were obtained from approximately 75 different locations within each community using in-situ instruments. All data were integrated into a GIS, which served as a visualization tool and enabled the data to be analyzed in a spatial context. Our results confirm the importance of abiotic variables in defining the distributions of some fauna and elucidate several biological associations that are consistent between the two communities. The provannid snail, Alviniconcha spp., appears to actively avoid temperatures above 32–46 °C and/or sulfide concentrations exceeding approximately 260 μM. Slightly higher average sulfide concentrations and temperatures were measured among aggregations of Ifremeria nautilei compared to aggregations of the mussel Bathymodiolus brevior; however, the presence of mixed aggregations of the two species indicates an overlap in requirements. The brachyuran crab, Austinograea spp., was consistently observed directly on symbiont-containing species, particularly Alviniconcha spp. The solitary snail, Eosipho desbruyeresi, was rarely observed on biological substrata, but was often (60% of its population at the most active site) within 5 cm of symbiont-containing fauna, indicating a tolerance and preference for proximity to areas of high productivity. Densities and coverage of species differed substantially between the two communities despite high species overlap. Symbiont-containing species covered much larger areas at the more hydrothermally active site, ABE1, while shrimp and anemones occurred in relatively higher densities within the less-active site, TM1. This is the first study to thoroughly characterize realized distributions of megafauna at vent sites along the ELSC. 相似文献
498.
Narcisa Gabriela Pricope Lin Cassidy Andrea Elizabeth Gaughan Jonathan David Salerno Forrest Robert Stevens Joel Hartter 《社会与自然资源》2020,33(3):418-431
AbstractConducting research on coupled social-ecological systems (SESs) presents inherent challenges, such as coordination across disparate disciplines or integrating across multiple scales and levels of governance. To overcome these common challenges, we propose that structuring the research design itself according to SES principles provides for integrative execution of SES science. First, starting with pilot work, human and natural science researchers should work as a team to identify and access multi-level entry points (i.e. points of direct engagement) within the system, relative to the spatiotemporal scales under investigation. Second, teams should implement an adaptive process that begins with the proposed research design and uses shared experiences from pilot work to refine protocols prior to subsequent data collection. We provide examples of multi-level and multi-scale entry points, and show that adaptive management of research design through coordinated iteration allows for better research integration and applicable outcomes. 相似文献
499.
500.
Sansom Garett T. Thompson Courtney Sansom Lindsay Fawkes Leanne Boerlin Elizabeth 《Natural Hazards》2022,111(3):2809-2818
Natural Hazards - Natural and anthropogenic hazards are increasingly becoming commonplace due to climate change and population pressures. The state of Texas is particularly vulnerable to these... 相似文献