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891.
Cristina?PulidoEmail author Kaj?Sand-Jensen Esther?C.?H.?E.?T.?Lucassen Jan?G.?M.?Roelofs Klaus?P.?Brodersen Ole?Pedersen 《Aquatic Sciences - Research Across Boundaries》2012,74(2):351-360
Isoetids, as indicators of near-pristine softwater lakes, have a high priority in national and international (European Water
Directive Framework) assessments of ecological lake quality. Our main goal was to identify the most important environmental
factors that influence the composition of plant communities and specifically determine the presence and abundance of the isoetid
Lobelia dortmanna in NW European softwater lakes. Geographical position and composition of surface water, porewater, sediment and plant communities
were examined in 39 lakes in four regions (The Netherlands, Denmark, West Norway and East Norway) distributed over a 1,200-km
long distance. We confirmed that lake location was accompanied by significant changes in environmental variables between NW
European lakes. Lake location was the single most important determinant of vegetation composition and it had significant individual
contributions independent of the coupling to environmental variables. This influence of location was supported by a significant
decline of community similarity with geographical distance between pairs of lakes at regional, inter-regional and international
scales. Combining the geographical position with environmental variables for surface water, porewater and sediment significantly
improved prediction of vegetation composition. Specifically, the combination of latitude, surface water alkalinity, porewater
phosphate and redox potential offered the highest correlation (BIO ENV correlation 0.66) to vegetation composition. This complex
analysis can also account for high sediment variability in the littoral zone of individual lakes, by using site-specific physico-chemical
sediment factors, and offer better predictions of vegetation composition when lake water chemistry is relatively homogeneous
among lakes within regions. 相似文献
892.
Much attention has recently been devoted to the fate and effects of pharmaceuticals in the water cycle. Removal of antibiotics in effluents by photo‐treatment or biodegradation is a topic currently under discussion. Degradation and removal efficiencies of sulfisomidine (SUI) by photodegradation and aerobic biodegradability were studied. SUI behavior was monitored during photolysis and photocatalysis (catalyst titanium dioxide) using 150‐W medium‐pressure Hg lamp. Also an aerobic bacterial degradation test from the OECD series (closed bottle test (CBT, OECD 301 D)) was performed. The primary elimination of SUI was monitored. Structures of photo‐degradation products were assessed by chromatographic separation on a C18 column with ultraviolet detection at 270 nm and ion trap MS. The results demonstrate that SUI is not readily biodegradable in CBT. Photo catalysis was more is effective than photolysis. SUI underwent photodegradation and several SUI photoproducts were identified. Accordingly, the photodegradation pathway of SUI was postulated. When reaching the aquatic environment, SUI and its photo products can constitute a risk to the environment. 相似文献
893.
Malte Thoma Christoph Mayer Klaus Grosfeld 《Earth and Planetary Science Letters》2008,269(1-2):242-247
Subglacial lakes provide unique habitats, but the exact nature of physical and geochemical conditions are still a matter of debate and await direct sampling of water. Due to its isolation from external atmospheric forcing other environmental parameters influence the flow characteristics within the lake. In this study we use an improved treatment of the physical processes at the ice–water boundary interface to identify and quantify the impact of (1) the geothermal heat flux, (2) the heat flux from the lake into the ice, (3) the influence of the salinity of the lake water, and (4) the ice thickness on the size of the freezing area and the freeze/melt rates. We show that the modelled basal mass imbalance (that is the produced melt water minus the re-frozen water) depends on the geothermal heating as well as the heat flux into the ice. The circulation and the temperature distribution within subglacial Lake Vostok are rather stable against variations of geothermal heat flux, heat flux into the ice sheet, salinity of the lake, and small changes of the ice thickness above the lake. However, the flow regime for any subglacial lake with less than 2000 m ice thickness above, will be substantially different from those that experience higher pressures. This is because the buoyancy–temperature relationship reverses at this depth. 相似文献
894.
Klaus Regenauer-Lieb David A. Yuen Florian Fusseis 《Pure and Applied Geophysics》2009,166(10-11):1885-1908
The total rate of rock deformation results from competing deformation processes, including ductile and brittle mechanisms. Particular deformation styles arise from the dominance of certain mechanisms over others at different ambient conditions. Surprisingly, rates of deformation in naturally deformed rocks are found to cluster around two extremes, representing coseismic slip rates or viscous creep rates. Classical rock mechanics is traditionally used to interpret these instabilities. These approaches consider the principle of conservation of energy. We propose to go one step further and introduce a nonlinear far-from-equilibrium thermodynamic approach in which the central and explicit role of entropy controls instabilities. We also show how this quantity might be calculated for complex crustal systems. This approach provides strain-rate partitioning for natural deformation processes occurring at rates in the order of 10-3 to 10-9 s-1. We discuss these processes using examples of landslides and ice quakes or glacial surges. We will then illustrate how the mechanical mechanisms derived from these near-surface processes can be applied to deformation near the base of the seismogenic crust, especially to the phenomenon of slow earthquakes. 相似文献
895.
Relationships between porosity and hydraulic conductivity tend to be strongly scale- and site-dependent and are thus very difficult to establish. As a result, hydraulic conductivity distributions inferred from geophysically derived porosity models must be calibrated using some measurement of aquifer response. This type of calibration is potentially very valuable as it may allow for transport predictions within the considered hydrological unit at locations where only geophysical measurements are available, thus reducing the number of well tests required and thereby the costs of management and remediation. Here, we explore this concept through a series of numerical experiments. Considering the case of porosity characterization in saturated heterogeneous aquifers using crosshole ground-penetrating radar and borehole porosity log data, we use tracer test measurements to calibrate a relationship between porosity and hydraulic conductivity that allows the best prediction of the observed hydrological behavior. To examine the validity and effectiveness of the obtained relationship, we examine its performance at alternate locations not used in the calibration procedure. Our results indicate that this methodology allows us to obtain remarkably reliable hydrological predictions throughout the considered hydrological unit based on the geophysical data only. This was also found to be the case when significant uncertainty was considered in the underlying relationship between porosity and hydraulic conductivity. 相似文献
896.
It is well known that the neutral component of the local interstellar medium can effectively pass through the plasma interface ahead of the solar system and can penetrate deeply into the inner heliosphere. Here we present a newly-developed theoretical approach to describe the distribution function of LISM neutral hydrogen in the heliosphere, also taking into account time-dependent solar and interstellar boundary conditions. For this purpose we start from a Boltzmann-Vlasov equation, Fourier-transformed with respect to space and time coordinates, in connection with correspondingly transformed solar radiation forces and ionization rates, and then arrive at semi-analytic solutions for the transformed hydrogen velocity distribution function. As interstellar boundary conditions we allow for very general, non-Maxwellian and time-dependent distribution functions to account for the case that some LISM turbulence patterns or nonlinear wave-like shock structures pass over the solar system. We consider this theoretical approach to be an ideal instrument for the synoptic interpretation of huge data samples on interplanetary Ly- resonance glow intensities registered from different celestial directions over extended periods of time. In addition we feel that the theoretical approach presented here, when applied to interplanetary resonance glow data, may permit the detection of genuine fluctuations in the local interstellar medium. 相似文献
897.
Authors Index
Author Index Volume 56 相似文献898.
Andreas?M?llerEmail author Bas?J.?Hensen Richard?A.?Armstrong Klaus?Mezger Michel?Ballèvre 《Contributions to Mineralogy and Petrology》2003,145(4):406-423
The age of Proterozoic granulite facies metamorphism and deformation in the Strangways Metamorphic Complex (SMC) of central Australia is determined on zircon grown in syn-metamorphic and syn-deformational orthopyroxene-bearing, enderbitic, veins. SHRIMP zircon studies suggest that M 1–M 2 and the correlated periods of intense deformation (D 1–D 2) are part of a single tectonothermal event between 1,717±2 and 1,732±7 Ma. It is considered unlikely that the two metamorphic phases (M 1, M 2) suggested by earlier work represent separate events occurring within 10–25 Ma of each other. Previous higher estimates for the age of M 1 granulite metamorphism in the SMC (Early Strangways event at ca. 1,770 Ma) based on U–Pb zircon dating of granitic, intrusive rocks, are not believed to relate to the metamorphism, but to represent pre-metamorphic intrusion ages. Conventional multi-grain U–Pb monazite analyses on high-grade metasediments from three widely spaced localities in the western SMC yield 207Pb/ 235U ages between 1,728±11 and 1,712±2 Ma. The age range of the monazites corresponds to the SHRIMP zircon ages in the granulitic veins and is interpreted to record monazite growth (prograde in the metasedimentary rocks). The data imply a maximum time-span of 30 Ma for high-grade metamorphism and deformation in the SMC. There is, thus, no evidence for an extremely long period of continuous high-temperature conditions from 1,770 to ca. 1,720 Ma as previously proposed. The results firmly establish that the SMC has a very different high-grade metamorphic history than the neighbouring Harts Range, where upper amphibolite facies metamorphism in the Palaeozoic caused widespread growth or recrystallization of monazite. 相似文献
899.
Abstract— Based on optical microscopy and electron microprobe analysis of mafic minerals, four previously poorly described ordinary chondrites from Spain are classified. The classifications of Guareña (H6), Olmedilla de Alarcón (H5) and Reliegos (L5) are confirmed. Molina is reclassified as H5, based on new data. 相似文献
900.
Abstract— The Olton ordinary chondrites (two stones found in 1948) are H group, solar wind-bearing regolith breccias. The proximity of the recovery site to the Dimmitt strewnfield, and the similarity in texture, composition, noble gas contents and isotopic ratios to Dimmitt indicate that Olton is paired with Dimmitt. 相似文献