全文获取类型
收费全文 | 628篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 51篇 |
地球物理 | 165篇 |
地质学 | 194篇 |
海洋学 | 67篇 |
天文学 | 108篇 |
综合类 | 2篇 |
自然地理 | 47篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 30篇 |
2016年 | 32篇 |
2015年 | 22篇 |
2014年 | 31篇 |
2013年 | 35篇 |
2012年 | 29篇 |
2011年 | 38篇 |
2010年 | 38篇 |
2009年 | 31篇 |
2008年 | 37篇 |
2007年 | 29篇 |
2006年 | 31篇 |
2005年 | 24篇 |
2004年 | 21篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1963年 | 4篇 |
1961年 | 2篇 |
1940年 | 2篇 |
排序方式: 共有651条查询结果,搜索用时 125 毫秒
141.
Gaseous nitric acid and ammonia were sampled with annular denuders at a forest savannah site from April to December 1987. The analysis of the extract was made spectrophotometrically and by a selective electrode for NO3
– and NH4
+, respectively. Higher concentrations were observed during the vegetation burning period at the end of the dry season. In the studied savannah area, large soil emissions of NO occur during the rainy season, although very low concentrations of HNO3 (0.035 ppb) and also of particulate NO3
– (0.43 g m-3) were observed; it is likely that NOx are lost by fast vertical transport to the upper troposphere. During the nonburning period, the average concentration of NH3 was 2.7 ppb, which is much lower than values given in the literature for the tropical America atmosphere. The concentrations of HNO3 and NH3 were always below the values needed to produce ammonium nitrate aerosols. 相似文献
142.
As urbanization progresses, more realistic methods are required to analyze the urban microclimate. However, given the complexity and computational cost of numerical models, the effects of realistic representations should be evaluated to identify the level of detail required for an accurate analysis. We consider the realistic representation of surface heating in an idealized three-dimensional urban configuration, and evaluate the spatial variability of flow statistics (mean flow and turbulent fluxes) in urban streets. Large-eddy simulations coupled with an urban energy balance model are employed, and the heating distribution of urban surfaces is parametrized using sets of horizontal and vertical Richardson numbers, characterizing thermal stratification and heating orientation with respect to the wind direction. For all studied conditions, the thermal field is strongly affected by the orientation of heating with respect to the airflow. The modification of airflow by the horizontal heating is also pronounced for strongly unstable conditions. The formation of the canyon vortices is affected by the three-dimensional heating distribution in both spanwise and streamwise street canyons, such that the secondary vortex is seen adjacent to the windward wall. For the dispersion field, however, the overall heating of urban surfaces, and more importantly, the vertical temperature gradient, dominate the distribution of concentration and the removal of pollutants from the building canyon. Accordingly, the spatial variability of concentration is not significantly affected by the detailed heating distribution. The analysis is extended to assess the effects of three-dimensional surface heating on turbulent transfer. Quadrant analysis reveals that the differential heating also affects the dominance of ejection and sweep events and the efficiency of turbulent transfer (exuberance) within the street canyon and at the roof level, while the vertical variation of these parameters is less dependent on the detailed heating of urban facets. 相似文献
143.
Neo-deterministic definition of seismic input for residential seismically isolated buildings 总被引:1,自引:1,他引:0
Elisa Zuccolo Franco Vaccari Antonella Peresan Alberto Dusi Alessandro Martelli Giuliano F. Panza 《Engineering Geology》2008,101(3-4):89-95
This paper deals with the neo-deterministic definition of the seismic input in the municipality of Nimis (Italy), aimed at the design of residential seismically isolated buildings. The seismic input is defined by the computation of realistic synthetic seismograms considering different levels of detail for the earthquake source, both for a bedrock model and taking into account the specific site conditions. The horizontal response spectrum, calculated in the centre of the municipality by modelling the most dangerous source, advises against the construction of a building with a fixed base, but it is compatible with the seismic isolation, and it has been, therefore, used for the design of a residential seismically isolated building. The maximum displacement for the isolation system has been estimated about 17 cm, a value much lower than that provided by the code design response spectrum (28 cm). The importance of the realistic modelling, which permits the generalization of empirical observations by means of, physically sound, theoretical considerations, is evident, as it allows for the optimisation of the structural design with respect to the site of interest. 相似文献
144.
GPS Solutions - Correctly fixing carrier phase integer ambiguities is a prerequisite to achieve high-precision positioning solutions from global navigation satellite system (GNSS). However, for the... 相似文献
145.
Andres Simón-Moral Jose Luis Santiago Alberto Martilli 《Boundary-Layer Meteorology》2017,163(1):103-121
A Reynolds-averaged Navier–Stokes microscale model is used for the simulation of the effect of unstable thermal stratification on the flow within an aligned configuration of building-like cubes as used in Santiago et al. (Urban Clim 9:115–133, 2014). The spatially-averaged results show increased dispersive fluxes, turbulent length scales and sectional drag coefficient. An extension of K-theory is presented to parametrize the sum of the turbulent and dispersive fluxes, and the length scale and drag coefficient increases are parametrized as functions of the ratio of buoyant and inertial forces. This approach improves the results of urban canopy parametrization simulations inside and above the urban canyon and represents the first attempt to account for the dispersive fluxes and the effect of solar radiation on the flow. 相似文献
146.
We describe texture, mineralogy and whole-rock composition of cognate monzonite sub-volcanic clasts within debris flow deposits
related to the 5000 years catastrophic phreatomagmatic eruption probably linked to the Sciara del Fuoco sector collapse. The
debris flows are at the top of accretionary lapilli-rich ash deposits overlying potassic (KS, shoshonites) lavas of the Neostromboli
period. The monzonites are inferred to be crystallized in situ, at low P, at the side walls and/or roof margins of a shallow magma chamber and to be cogenetic with the KS Neostromboli
extrusives. They can be considered "ideal orthocumulates" since they approximately retain a bulk liquid composition and possibly
represent "slowly cooled equivalents" of their KS shoshonite host rock. The "closure temperature" of final solidification
of the monzonite lithic suite was estimated through ternary-feldspar geothermobarometry, plagioclase–K-feldspar and K-feldspar–biotite
equilibria and is in the range of 750–790 °C with a maximum –logfO2 around 15.1–15.3. The estimated pressure of crystallization is <0.5 kbar. Potassic lavas and dikes, previously emplaced during
the Neostromboli period, also resemble the monzonites in both major trace elements and mineral chemistry. The cogenetic relationship
between KS Neostromboli extrusives and the monzonite host-rock magma from which the sub-volcanic clasts were derived is clear
evidence that a shallow magma chamber existed between the caldera collapse of the Vancori period and the Sciara del Fuoco
sector collapse (i.e. between 13 000 and 5000 years). The monzonite clasts were derived from crystallization at very shallow
depth (ca. 1 km) and strongly support the hypothesis of violent decompression of the shallow magmatic plumbing system during
the Sciara del Fuoco sector collapse. Climax of the regressive landslide event, with maximum disruption of the chamber walls,
took place during emplacement of the debris flows, i.e. during the late stage of the Neostromboli phreatomagmatic eruption.
Received: 15 September 1996 / Accepted: 5 May 1997 相似文献
147.
148.
Scraping and extirpating: two strategies to induce recovery of diseased Gorgonia ventalina sea fans 下载免费PDF全文
Claudia Patricia Ruiz‐Diaz Carlos Toledo‐Hernández Alex E. Mercado‐Molina Alberto M. Sabat 《Marine Ecology》2016,37(2):336-343
Coral diseases are currently playing a major role in the worldwide decline in coral reef integrity. One of the coral species most afflicted by disease in the Caribbean, and which has been the focus of much research, is the sea fan Gorgonia ventalina. There is, however, very little information regarding the capacity of sea fans to recover after being infected. The aim of this study was to compare the rehabilitation capacity of G. ventalina after diseased‐induced lesions were eliminated either by scraping or extirpating the affected area. Scraping consisted of removing any organisms overgrowing the axial skeleton from the diseased area as well as the purple tissue bordering these overgrowths using metal bristle brushes. Extirpation consisted of cutting the diseased area, including the surrounding purpled tissue, using scissors. The number of scraped colonies that fully or partially rehabilitated after being manipulated and the rates at which the sea fans whose lesions were scrapped grew back healthy tissue were compared among: (i) colonies that inhabited two sites with contrasting environmental conditions; (ii) colonies of different sizes and (iii) colonies with different ratios of area of legions to total colony area (LA/CA). Both strategies proved to be very successful in eliminating lesions from sea fans. In the case of scraping, over 51% of the colonies recovered between 80% and 100% of the lost tissue within 16 months. The number of colonies that recovered from scraping was similar among sites and among colony sizes, but differed significantly depending on the relative amount of lesion to colony area (LA/CA). When lesions were extirpated, lesions did not reappear in any of the colonies. We conclude that lesion scraping is useful for eliminating relatively small lesions (i.e. LA/CA < 10%), as these are likely to recover in a shorter period of time, whereas for relatively large lesions (LA/CA ≥ 10%) it is more appropriate to extirpate the lesion. 相似文献
149.
Alberto C. Montefinale T. W. Zawidzki Henry M. Papée 《Pure and Applied Geophysics》1963,54(1):190-195
Summary Deviations from a law previously established, which correlates the precipitable water vapour values in a vertical column of air over a measuring station with the latter's temperature and altitude, are reduced by multiple regression analysis, and implications are discussed.Contribution of the «Centro Nucleazione Aerosoli» of the National Research Council of Italy, Via Vettore 4 (Monte Sacro)Roma. 相似文献
150.
Summary Rates of release of nitrous oxide, from monodisperse fractions of activated alumina, are measured at room temperature and atmospheric pressure. The values obtained follow a simple first-order law with respect to the gas adsorbed, the relative parameters depending strongly on the size of the particulates examined (5 to 50 micron). 相似文献