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51.
Abstract. Nematocytes are the specialized stinging cells of cnidarians. So far, Pelagia noctiluca (Cnidaria, Scyphozoa) nematocytes have never been isolated. Taking in account the notable increase in the population of Pelagia noctiluca ("blooming") in the Strait of Messina in 1999, we performed preliminary studies on the applicability of two different methods for isolating nematocytes from tentacles and mouth arms: a chemical method, namely SCN treatment, and a physical one, namely heat dissociation. These approaches have already been employed to isolate nematocytes from Aiptasia diaphana (Anthozoa). Membrane integrity was assessed by the cytological Trypan blue test. To evaluate cell viability, the capacity to regulate cell volume was investigated under 35 % hyposmotic shock by image computer processing of sagittal sections. The results show that heat dissociation is unsuitable to isolate nematocytes because the cell membrane was damaged as revealed by cytological test. On the other hand, SCN treatment yields 90% anatomically intact, isolated nematocytes from tentacles, but not from mouth arms. Nematocytes isolated by SCN exhibit volume regulation mechanisms (RVD). These results are compared with those described in Aiptasia diaphana (Anthozoa), which lives in a different habitat. 相似文献
52.
H. A. Loaiciga R. B. Leipnik P. F. Hudak M. A. Marino 《Stochastic Hydrology and Hydraulics》1994,8(1):1-17
Assuming that the ln hydraulic conductivity in an aquifer is mathematically approximated by a spatial deterministic surface, or trend, plus a stationary random noise, we treat the problem of finding what the effective hydraulic conductivity of that aquifer is. This problem is tackled by spectral methods applied to a type of diffusion equation of groundwater flow, together with suitable coordinate transformations. Analytical (exact) solutions in terms of elementary functions are presented for one- and three-dimensional finite and infinite domains. Stability criteria are obtained for the solutions, in terms of a critical parameter, that turns out to involve the product of correlation scale and trend gradient. For the case of finite and symmetrical domains, additional provisions to insure the stability of numerical calculations of effective hydraulic conductivity are provided. Effective hydraulic conductivity is an important property, with potential applications in the calibrations of groundwater and transport numerical models. 相似文献
53.
Loaiciga H. A. Leipnik R. B. Hudak P. F. Marino M. A. 《Stochastic Environmental Research and Risk Assessment (SERRA)》1994,8(1):1-17
Assuming that the ln hydraulic conductivity in an aquifer is mathematically approximated by a spatial deterministic surface, or trend, plus a stationary random noise, we treat the problem of finding what the effective hydraulic conductivity of that aquifer is. This problem is tackled by spectral methods applied to a type of diffusion equation of groundwater flow, together with suitable coordinate transformations. Analytical (exact) solutions in terms of elementary functions are presented for one- and three-dimensional finite and infinite domains. Stability criteria are obtained for the solutions, in terms of a critical parameter, that turns out to involve the product of correlation scale and trend gradient. For the case of finite and symmetrical domains, additional provisions to insure the stability of numerical calculations of effective hydraulic conductivity are provided. Effective hydraulic conductivity is an important property, with potential applications in the calibrations of groundwater and transport numerical models. 相似文献
54.
PhotoelectricUBV photometry of the long period southern eclipsing binary system W Cru gathered over an 18-mo period in 1984–1985 is presented and examined.The light curve is characterized by continuous Beta Lyrae-like variation: unexpected in such a long period (198.5 days) system; together with peculiar irregularities, of the order of 0.1 mag (or more inU) and time-scales of a few days.A high mass model (total mass 70M
) could be made to be roughly consistent with the data, though alternative models of much lower mass are also possible, and may turn out to be preferable, in terms of goodness-of-fit, as well as for theoretical reasons. The low mass models would require, though, the more massive component to be unseen (as now generally supposed for Lyrae itself).The photometry alone, or even combined with a known spectroscopic mass-function, seems unlikely to be able to furnish a single definitive solution, and more guidelines from reliable theoretical expectation may prove helpful in interpreting the data. 相似文献
55.
Alana Hanson Roxanne Johnson Cathleen Wigand Autumn Oczkowski Earl Davey Erin Markham 《Estuaries and Coasts》2016,39(5):1376-1385
Coastal wetlands, well recognized for their ecosystem services, have faced many threats throughout the USA and elsewhere. While managers require good information on the net impact of these combined stressors on wetlands, little such information exists. We conducted a 4-month mesocosm study to analyze the multiple stressor effects of precipitation changes, sea level rise, and eutrophication on the salt marsh plant Spartina alterniflora. Pots containing plants in an organic soil matrix were positioned in tanks and received Narragansett Bay (RI, USA) water. The study simulated three precipitation levels (ambient daily rain, biweekly storm, and drought), three levels of tidal inundations (high (15 cm below mean high water (MHW)), mean (MHW), and low (15 cm above MHW)), and two nutrient enrichment levels (unenriched and nutrient-enriched bay water). Our results demonstrate that storm and drought stressors led to significantly less above- and belowground biomass than those in ambient rain conditions. Plants that were flooded at high inundation had less belowground biomass, fine roots, and shoots. Nutrients had no detectable effect on aboveground biomass, but the enriched pots had higher stem counts and more fine roots than unenriched pots, in addition to greater CO2 emission rates; however, the unenriched pots had significantly more coarse roots and rhizomes, which help to build peat in organogenic marshes. These results suggest that multiple stressors of altered precipitation, sea level rise, and nutrient enrichment would lead to reduced marsh sustainability. 相似文献
56.
Shao Weizeng Jiang Xingwei Nunziata Ferdinando Marino Armando Yang Zhehao Zhang Youguang Corcione Valeria 《Ocean Dynamics》2020,70(11):1397-1407
Ocean Dynamics - In this study, synthetic aperture radar (SAR) imaging of waves across ocean fronts was investigated using C-band Sentinel-1 VV-polarized SAR imagery collected over the Yangtze and... 相似文献
57.
58.
D. Bettoni P. Mazzei R. Rampazzo A. Marino G. Galletta L. M. Buson 《Astrophysics and Space Science》2014,354(1):83-88
The Galaxy Evolution Explorer (GALEX) detected ultraviolet emission in about 50 % of multi-spin early-type galaxies (ETGs), suggesting the occurrence of a recent rejuvenation episode connected to the formation of these kinematical features. With the aim at investigating the complex evolutionary scenario leading to the formation of counter rotating ETGs (CR-ETGs) we use our Smooth Particle Hydrodynamic (SPH) code with chemo-photometric implementation. We discuss here the UV evolutionary path of two CR-ETGs, NGC 3593 and NGC 5173, concurrently best fitting their global observed properties, i.e., morphology, dynamics, as well as their total B-band absolute magnitude and spectral energy distribution (SED) extended over three orders of magnitude in wavelength. These simulations correspond to our predictions about the target evolution which we follow in the color-magnitude diagram (CMD), near-UV (NUV) versus r-band absolute magnitude, as a powerful diagnostic tool to emphasize rejuvenation episodes. 相似文献
59.
60.
Estuaries exhibit a large range in their responses to nitrogen loadings determined in part by characteristics of the driver, such as magnitude and frequency, but also by such intrinsic characteristics as physical/chemical factors (e.g., depth, volume, hypsometry, salinity, turbidity) and biological factors (e.g., nature of ecological communities, trophic interactions). To address the richness of estuarine response to driver variables, the aim ultimately is to establish a simple estuarine classification scheme, beginning with a river-dominated subset of estuarine systems and focusing on the role of water residence time in the estuary. Residence time (or flushing time) is related to other drivers (streamflow, nutrient, and sediment loads) and drives much of the biological response of estuaries because of flushing effects on plankton, temperature, nutrients, and light. Toward this goal, nutrient–phytoplankton–zooplankton (NPZ) models have been used to examine a range of subjects including effects of nutrient limitation and zooplankton predation on phytoplankton dynamics and fish predation. This class of model can admit a wide range of behavior, including multiple steady-states and oscillatory behavior. The NPZ equations include terms for nutrient recycling, phytoplankton settling, benthic regeneration, and zooplankton mortality. Analysis of the equations suggests that both the nature of nitrogen loading (i.e., whether it is correlated with discharge or independent of it) and residence time are critical in determining the steady-state response of the system. 相似文献