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131.
The Schmidt hammer is a useful tool applied by geomorphologists to measure rock strength in field conditions. The essence of field application is to obtain a sufficiently large dataset of individual rebound values, which yields a meaningful numerical value of mean strength. Although there is general agreement that a certain minimum sample size is required to proceed with the statistics, the choice of size (i.e. number of individual impacts) was usually intuitive and arbitrary. In this paper we show a simple statistical method, based on the two‐sample Student's t‐test, to objectively estimate the minimum number of rebound measurements. We present the results as (1) the ‘mean’ and ‘median’ solutions, each providing a single estimate value, and (2) the empirical probability distribution of such estimates based on many field samples. Schmidt hammer data for 14 lithologies, 13–81 samples for each, with each sample consisting of 40 individual readings, have been evaluated, assuming different significance levels. The principal recommendations are: (1) the recommended minimum sample size for weak and moderately strong rock is 25; (2) a sample size of 15 is sufficient for sandstones and shales; (3) strong and coarse rocks require 30 readings at a site; (4) the minimum sample size may be reduced by one‐third if the context of research allows for higher significance level for test statistics. Interpretations based on less than 10 readings from a site should definitely be avoided. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
132.
Wojciech Walkusz Slawek Kwasniewski Stig Falk-Petersen Haakon Hop Vigdis Tverberg Piotr Wieczorek & Jan Marcin Weslawski 《Polar research》2009,28(2):254-281
Seasonal changes in the zooplankton composition of the glacially influenced Kongsfjorden, Svalbard (79°N, 12°E), and its adjacent shelf were studied in 2002. Samples were collected in the spring, summer and autumn in stratified hauls (according to hydrographic characteristics), by means of a 0.180-mm Multi Plankton Sampler. A strong front between the open sea and the fjord waters was observed during the spring, preventing water mass exchange, but was not observed later in the season. The considerable seasonal changes in zooplankton abundance were related to the seasonal variation in hydrographical regime. The total zooplankton abundance during the spring (40–2010 individuals m−3 ) was much lower than in the summer and autumn (410–10 560 individuals m−3 ). The main factors shaping the zooplankton community in the fjord include: the presence of a local front, advection, the flow pattern and the decreasing depth of the basin in the inner fjord. Presumably these factors regulate the gross pattern of zooplankton density and distribution, and override the importance of biological processes. This study increased our understanding of seasonal processes in fjords, particularly with regard to the strong seasonal variability in the Arctic. 相似文献
133.
Giuseppe Leto Marián Jakubík Tomáš Paulech Luboš Neslušan Piotr A. Dybczyński 《Earth, Moon, and Planets》2009,105(2-4):263-266
We simulate the formation of the Oort cloud (OC) till the age of 2 Gyr starting from an initial disc of planetesimals made by 10 038 test particles. The results on the outer part of the distant comet reservoir are reported by Neslu?an et al. (this issue). Here we deal with the evolution of the population and structure at 2 Gyr of the complementary inner part of the Oort cloud. The dynamical evolution of the massless test particles was followed via the numerical integration of their orbits. We considered the perturbations produced by four giant planets assuming they have their current orbits and masses, as well as the perturbations caused by the Galactic tide and passing stars. The efficiency of the formation of inner OC is found to be very low: only about 1.1% of all considered particles ended in this part of the OC. At 2 Gyr, the dynamics of the inner cloud is mainly governed by the dominant z-term of the Galactic tide. The number density of the bodies is proportional to the heliocentric distance, r, as r ?3.53. The directional distribution of orbits is still strongly inhomogeneous. There are large empty regions in the space angles around the Galactic Equator points with the galactic longitude 90 and 270° (non-rotating frame), or there are only few bodies having the ecliptical latitude higher than +60° or lower than 60°. A strong concentration of objects at the Ecliptic is apparent up to ≈1,000 AU, with a possible—but still not proved—extension to ≈1,500 AU. Beyond r ≈ 6,000 AU, bodies directly above and below the Sun, with respect to the Ecliptic, are absent. 相似文献
134.
Tadeusz Jan Jopek Christiane Froeschlé Robert Gonczi Piotr A. Dybczyński 《Earth, Moon, and Planets》2008,102(1-4):53-58
We present the results of an extensive study of the Tunguska Cosmic Body (TCB) origin on dynamical grounds. To identify the
TCB parent, or a plausible candidate, we applied the well-known concept of dynamical similarity whereby we have compared the
geocentric and heliocentric dynamical parameters of a selected set of the Near Earth Objects (NEOs) and TCB particles. First,
we made use the idea of Kresak by comparing geocentric coordinates of the TCB radiant with those of the NEOs. Second, we studied
the long-term dynamical evolution of all NEOs and TCB particles searching for similarities between their heliocentric orbits.
As a general result, we observed many more similar cases and a different pattern of the high orbital similarity among the
TCB particles and the asteroid orbits than we did for comets. 相似文献
135.
The paper attempts to answer the following key question: how will a city′s world rank change in the face of crisis in its main economic sector? Crisis is defined here as a decline in financial performance in the given sector, which leads to the decline of its constituent firms and corporations on the world economic scene. The World Economic Center Index(WECI) has been created in order to rank cities based on the value of their resident corporations by sector and show their level of stability upon the removal of the most important sector. This provides information on the potential of each analyzed city as well as on its advanced features or area of specialization. Research has shown that nearly half the World Economic Centers are dominated by the financial and materials sectors of the economy. Different sectors dominate different regions of the world. For example, consumer staples and materials were dominant in North America, while information technology and financials were dominant in Europe. In Asia, several sectors tend to dominate the economy. Research has shown that the ability of a principal economic sector to resist economic crisis largely depends on the strength of the command and control function of a city. Finally, a high globalization level of a city is a key determinant of its susceptibility to economic crisis. 相似文献
136.
A New Subfamily of Aphids (Hemiptera,Aphidomorpha) from the Early Cretaceous Lebanese Amber with a Description of the Oldest Apterous Morphs 总被引:1,自引:1,他引:0
<正>Aphids are marked by their high polymorphism,but species reported from the Early Cretaceous are known only from alate morphs.The discovery of an apterous adult morph in Lebanese amber and a larva of the same species are very important for the understanding of both the morphological and biological evolution of this insect group at the very early stage of development.Gondvanoaphis estephani new subfamily,new genus and species of the recent aphids family Thelaxidae is described.The characters of the new genus in respect to other genera placed in Thelaxidae are reviewed.The palaeoecological and palaeogeographical data concerning Gondvanoaphis new genus are also discussed. 相似文献
137.
Study of litter influence on magnetic susceptibility measurements of urban forest topsoils using the MS2D sensor 总被引:1,自引:1,他引:0
Jarosław Zawadzki Piotr Fabijańczyk Tadeusz Magiera Zygmunt Strzyszcz 《Environmental Earth Sciences》2010,61(2):223-230
Field magnetometry is fast and convenient method used to detect areas contaminated by technogenic magnetic particles and potentially
polluted with heavy metals. Frequently, measurements of soil magnetic susceptibility (κ) are carried out with MS2D Bartington
sensor, which penetration range equals 10 cm, although 90% of the total signal is detected from a depth of up to 6 cm. Thick
uppermost organic soil layers may significantly influence on the measured κ because the penetration range may be not large
enough to cover the layers where the most of anthropogenic contaminants are cumulated. The aim of the study was to investigate
on how the removal of the litter improves the MS2D measurements of soil pollution. Accordingly, the correlations between κ
values measured on the successively removed overlying soil sub-horizons were investigated. Measurements were performed at
15 sites located in different forest in the Upper Silesian Industrial Area, Poland. The results showed that the litter removal
enabled the MS2D to measure the κ more related to the anthropogenic pollution, and did not affect the measuring variance. 相似文献
138.
Pece V.?GorsevskiEmail author Paul E.?Gessler Piotr?Jankowski 《Journal of Geographical Systems》2003,5(3):223-251
A robust method for spatial prediction of landslide hazard in roaded and roadless areas of forest is described. The method is based on assigning digital terrain attributes into continuous landform classes. The continuous landform classification is achieved by applying a fuzzy k-means approach to a watershed scale area before the classification is extrapolated to a broader region. The extrapolated fuzzy landform classes and datasets of road-related and non road-related landslides are then combined in a geographic information system (GIS) for the exploration of predictive correlations and model development. In particular, a Bayesian probabilistic modeling approach is illustrated using a case study of the Clearwater National Forest (CNF) in central Idaho, which experienced significant and widespread landslide events in recent years. The computed landslide hazard potential is presented on probabilistic maps for roaded and roadless areas. The maps can be used as a decision support tool in forest planning involving the maintenance, obliteration or development of new forest roads in steep mountainous terrain. 相似文献
139.
Piotr Flin 《Astrophysics and Space Science》1982,86(2):493-495
The mean density of matter, as estimated from deep optical samples of galaxies, is too low to close the Universe. However, some additional considerations do not exclude such a possibility. 相似文献
140.
Piotr Lubiski Andrzej A. Zdziarski 《Monthly notices of the Royal Astronomical Society》2001,323(2):L37-L42
We study properties of Fe K lines of a large sample of Seyfert 1s observed by ASCA . Fits with power laws and Gaussian lines yield the average linewidth and equivalent width of 0.22±0.03 keV and 0.13±0.01 keV, respectively. Thus, the typical lines are weak and narrow. We then obtain the average line profile of all our spectra, and find it to consist of a narrow core and blue and red wings, with the red wing being much weaker than that of e.g. MCG −6-30-15. We obtain three average spectra of Seyferts grouped according to the hardness, and find the equivalent width of the core (originating in a remote medium) to be ≃50 eV in all three cases. The wings are well fitted by a broad line from a disc with strong relativistic effects. Its equivalent width correlates with the slope, increasing from ∼70 eV for the hardest spectrum to ∼120 eV for the softest one. The inner disc radius decreases correspondingly from ∼40 to ∼10 gravitational radii, and the fitted disc inclination is ∼45°. The obtained correlation between the slope and the strength of the broad Fe K line is found to be consistent with the previously found correlation of the slope and Compton reflection. 相似文献