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1.
A detailed characterization of the site is crucial to designing an efficient method of managing the risks associated with
tailings from abandoned mines. Therefore, samples collected from various depths within tailings in Guryong mine, Korea, were
analyzed for their chemical, physical and mineralogical characteristics. All samples of the Guryong tailings had acid-generating
potential. However, in the oxidation zone, the net acid generation (NAG) was low (30 kg H2SO4 t−1) although the acid neutralization potential (ANP) was less than zero. The ANP values in the unoxidation zone were higher
(> −56.0 kg CaCO3 t−1) than in the other zones. As a result, the amount of alkali ions that are needed to neutralize the acid needs to be considered.
In this experiment G3, G4 and G6 drill cores containing fine tailings particles near the unoxidation zone were observed to
contain calcite (CaCO3) with acid-neutralizing capacity. A low pH (2−4) in the oxidation zone of the tailings changed to a neutral pH in the unoxidation
zone of the tailings. These results suggest that the acid-neutralizing capacity of the tailings was controlled by particle
and mineral composition of tailings. 相似文献
2.
This paper presents results of a small scale study that utilized particle-tracking techniques to evaluate transport of river
water through an alluvial aquifer in a bank infiltration testing site in El Paso, Texas, USA. The particle-tracking survey
was used to better define filtration parameters. Several simulations were generated to allow visualization of the effects
of well placement and pumping rate on flow paths, travel time, the size of the pumping influence zone, and proportion of river-derived
water and groundwater mixing in the pumping well. Simulations indicate that migration of river water into the aquifer is generally
slow. Most water does not arrive at the well by the end of an 18-day pumping period at 0.54 m3/min pumping rate for a well located 18 m from the river. Forty-four percent of the water pumped from the well was river water.
The models provided important information needed to design appropriate sampling schedules for bank filtration practices and
ensured meeting adequate soil-retention times. The pumping rate has more effect on river water travel time than the location
of the pumping well from the river. The examples presented in this paper indicate that operating the pumping well at a doubled
distance from the river increased the time required for the water to travel to the well, but did not greatly change the capture
zone. 相似文献
3.
Spring and summer phytoplankton communities in the Chukchi and Eastern Beaufort Seas 总被引:2,自引:0,他引:2
Victoria Hill Glenn Cota Dean Stockwell 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3369
Phytoplankton pigments and size-fractionated biomass in the Chukchi and Beaufort Seas showed spatial and temporal variation during the spring and summer of 2002. Cluster analysis of pigment ratios revealed different assemblages over the shelf, slope and basin regions. In spring, phytoplankton with particle sizes greater than 5 μm, identified as diatoms and/or haptophytes, dominated over the shelf. Smaller (<5 μm) phytoplankton containing chlorophyll b, most likely prasinophytes, were more abundant over the slope and basin. Due to extensive ice cover at this time, phytoplankton experienced low irradiance, but nutrients were near maximal for the year. By summer, small prasinophytes and larger haptophytes and diatoms co-dominated in near-surface assemblages in largely ice-free waters when nitrate was mostly depleted. Deeper in the water column at 1–15% of the surface irradiance larger sized diatoms were still abundant in the upper nutricline. Phytoplankton from the shelf appeared to be advected through Barrow Canyon to the adjacent basin, explaining similar composition between the two areas in spring and summer. Off-shelf advection was much less pronounced for other slope and basin areas, which are influenced by the low-nutrient Beaufort gyre circulation, leading to a dominance of smaller prasinophytes and chlorophytes. The correlation of large-sized fucoxanthin containing phytoplankton with the higher primary production measurements shows promise for trophic status to be estimated using accessory pigment ratios. 相似文献
4.
Intense studies of upper and deep ocean processes were carried out in the Northwestern Indian Ocean (Arabian Sea) within the framework of JGOFS and related projects in order to improve our understanding of the marine carbon cycle and the ocean’s role as a reservoir for atmospheric CO2. The results show a pronounced monsoon-driven seasonality with enhanced organic carbon fluxes into the deep-sea during the SW Monsoon and during the early and late NE Monsoon north of 10°N. The productivity is mainly regulated by inputs of nutrients from subsurface waters into the euphotic zone via upwelling and mixed layer-deepening. Deep mixing introduces light limitation by carrying photoautotrophic organisms below the euphotic zone during the peak of the NE Monsoon. Nevertheless, deep mixing and strong upwelling during the SW Monsoon provide an ecological advantage for diatoms over other photoautotrophic organisms by increasing the silica concentrations in the euphotic zone. When silica concentrations fall below 2 μmol l−1, diatoms lose their dominance in the plankton community. During diatom-dominated blooms, the biological pathway of uptake of CO2 (the biological pump) appears to be more efficient than during blooms of other organisms, as indicated by organic carbon to carbonate carbon (rain) ratios. Due to the seasonal alternation of diatom and non-diatom dominated exports, spatial variations of the annual mean rain ratios are hardly discernible along the main JGOFS transect.Data-based estimates of the annual mean impact of the biological pump on the fCO2 in the surface water suggest that the biological pump reduces the increase of fCO2 in the surface water caused by intrusion of CO2-enriched subsurface water by 50–70%. The remaining 30 to 50% are attributed to CO2 emissions into the atmosphere. Rain ratios up to 60% higher in river-influenced areas off Pakistan and in the Bay of Bengal than in the open Arabian Sea imply that riverine silica inputs can further enhance the impact of the biological pump on the fCO2 in the surface water by supporting diatom blooms. Consequently, it is assumed that reduced river discharges caused by the damming of major rivers increase CO2 emission by lowering silica inputs to the Arabian Sea; this mechanism probably operates in other regions of the world ocean also. 相似文献
5.
Th sorption and export models in the water column: A review 总被引:2,自引:3,他引:2
Nicolas Savoye Claudia Benitez-Nelson Adrian B. Burd J. Kirk Cochran Matthew Charette Ken O. Buesseler George A. Jackson Matthieu Roy-Barman Sabine Schmidt Marc Elskens 《Marine Chemistry》2006,100(3-4):234
Over the past few decades, the radioisotope pair of 238U / 234Th has been widely and increasingly used to describe particle dynamics and particle export fluxes in a variety of aquatic systems. The present paper is one of five review articles dedicated to 234Th. It is focused on the models associated with 234Th whereas the companion papers (same issue) are focused on present and future methodologies and techniques (Rutgers van der Loeff et al.), C / 234Th ratios (Buesseler et al.), 234Th speciation (Santschi et al.) and present and future applications of 234Th [Waples, J.T., Benitez-Nelson, C.R., Savoye, N., Rutgers van der Loeff, M., Baskaran, M., Gustafsson, Ö., this issue. An Introduction to the application and future use of 234Th in aquatic systems. Marine Chemistry, FATE special issue]. In this paper, we review current 234Th scavenging models and discuss the relative importance of the non-steady state and physical terms associated with the most commonly used model to estimate 234Th flux. Based on this discussion we recommend that for future work the use of models should be accompanied by a discussion of the effect that model and data uncertainty have on the model results. We also suggest that future field work incorporate repeat occupations of sample sites on time scales of 1–4 weeks in order to evaluate steady state versus non-steady state estimates of 234Th export, especially during high flux events (> ca. 800 dpm m− 2 d− 1). Finally, knowledge of the physical oceanography of the study area is essential, particularly in ocean margins and in areas of established upwelling (e.g., Equatorial Pacific). These suggestions will greatly enhance the application of 234Th as a tracer of particle dynamics and flux in more complicated regimes. 相似文献
6.
Changing grading of soil: effect on critical states 总被引:6,自引:3,他引:3
Examples of situations are presented where the grading of a soil changes during its lifetime either by crushing of particles
leading to an increase of fine material or by slow transport of fine particles with seepage leading to a decrease of fine
material. Such grading changes influence the basic constitutive properties of the soil, in particular properties such as critical
states which are dependent on the available range of densities of packing. Discrete element modelling is used to show the
dependence of critical state conditions on grading and the way in which the particle assembly seeks out new critical state
conditions as the grading changes. 相似文献
7.
We study the aspect of unstable behavior (like strain localization bands) in elastic solids as a consequence of micro-fracturing.
A two-scale approach of computational homogenization is considered. The macroscopic behavior is investigated by finite element
computations on a unit cell. At the micro-level, we consider a granular structure with elastic grains. The inter-granular
boundaries are modeled with cohesive laws, friction and unilateral contact. We show that decohesion between grains gives rise
to macro-instabilities, indicated by the loss of ellipticity, typical for deformation localization bands. The relation between
the microscopic softening on inter-granular boundaries and the onset of macro-instabilities is studied through numerical examples.
The influence of the cohesive law and friction parameters is analyzed. For periodic distributions of granular structures,
we prove the loss of periodicity by failure and the corresponding size dependence effect in the homogenized response. We present
numerical examples of bifurcation of solutions for granular cell structures and of particular solutions specific to elementary
volumes with periodic cell distribution. Size dependence appears in the unstable regime and is strongly influenced by cohesion
and friction parameters. 相似文献
8.
We used transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to study magmatic crystals in the Ben
Lomond rhyolite lava dome, Taupo Volcanic Center, New Zealand. Using TEM and SEM to investigate the size distributions of
these crystals, we identified three size populations: microphenocrysts (>1.2 μm wide), microlites (>0.6 μm wide), and smaller
crystals (<0.6 μm wide) which we term "nanolites". The predominant mineral phases of the microlites and nanolites are augites,
pigeonites, and hypersthenes. The compositions and microstructures within these pyroxenes indicate disequilibrium crystallization
at approximately 850–900 °C and undercoolings as high as 300 °C from equilibrium crystallization temperatures. Complex microstructures
resulting from subsolidus reactions in augite and pigeonite are consistent with moderate cooling rates within the upper obsidian
layer of the Ben Lomond rhyolite dome. This study demonstrates the existence of sub-micron magmatic crystals in a rhyolite
and illustrates the potential of TEM to provide unique information about the crystallization and cooling histories of glassy
volcanic rocks.
Received: May 8, 1995 / Accepted: November 27, 1995 相似文献
9.
A. Ankilov A. Baklanov M. Colhoun K. -H. Enderle J. Gras Yu. Julanov D. Kaller A. Lindner A. A. Lushnikov R. Mavliev F. McGovern T. C. O'Connor J. Podzimek O. Preining G. P. Reischl R. Rudolf G. J. Sem W. W. Szymanski A. E. Vrtala P. E. Wagner W. Winklmayr V. Zagaynov 《Atmospheric Research》2002,62(3-4)
During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles. 相似文献
10.
Mass size distribution of the crustal elements (Al, Ca, Fe, Mg, Si, Ti), anthropogenic elements (Zn, Mn, Cr, Cu, K, P, Pb) and sea elements (Na, Cl) were obtained from measurements carried out with an inertial cascade impactor in Sfax. A fitting procedure by data inversion was applied to those data. This procedure yields accurate size distributions of aerosols in the diameter range 0.1–25 μm in two different sites. In a coastal industrial site, the mass distribution of the aerosol showed a bimodal structure; and in urban area, the lower particle mode cannot be observed. The elemental dry deposition flux was calculated as a function of particle size. The element flux size distribution increased rapidly with particle size. The modelling results indicate that the majority of the crustal and anthropogenic elements flux (>90%) was due to particles larger than 3 μm in diameter. 相似文献