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721.
In the present work, we built a mathematical model of polychlorinated biphenyl (PCB) bioaccumulation in Perna viridis, namely, a one-compartment model with a time dependent incorporation rate R (μg g−1 lipid per ppb water per day), with positive substrate cooperativity as the underlying physical mechanism. The temporal change of the PCB concentration Q (μg g−1 lipid) in the soft tissues of the mussel depends on the competition of the input rate RW and the output rate kQ, where W is the concentration of PCB in water (ppb water) and k is the elimination rate (per day). From our experimental data, k=0.181±0.017 d−1. The critical concentration in water Wc for positive substrate cooperativity was found to be 2.4 ppb. Below Wc, R is a constant. For a water concentration of 0.5 ppb Aroclor 1254, R=24.0±2.4 μg g−1 lipid ppb−1 d−1. Above Wc, positive substrate cooperativity comes into effect and R becomes a function of time and dependent on the concentration Q in a form R=γQ/(Q+δ). This is the case for a water concentration of 5 ppb Aroclor 1254, where γ=15.1 μg g−1 lipid ppb−1 d1 and δ≈200 μg g−1 lipid. From this model, the uptake is exponentially increasing when the PCB concentration in the mussel is small compared to 200 μg g−1 lipid, and hyperbolically increasing when the concentration is large compared to 200 μg g−1 lipid, which are consistent with the experimental data. The model is useful for understanding the true processes taking place during the bioaccumulation and for risk assessment with higher confidence. Future experimental data which challenge the present model are anticipated and in fact desirable for improvement and perfection of the model. 相似文献
722.
Products and mechanisms for the gas-phase reactions of NO3 radicals with CH2=CHCl, CH2=CCl2, CHCl=CCl2,cis-CHCl=CHCl andtrans-CHCl=CHCl in air have been studied. The experiments were carried out at 295±2 K and 740±5 Torr in a 480-L Teflon-coated reaction chamber and at 295±2 K and 760±5 Torr in a 250-L stainless steel reactor. NO3 was generated by the thermal dissociation of N2O5. Experiments with15NO3 and CD2CDCl have also been performed. The initially formed nitrate peroxynitrates decay into carbonyl compounds, nitrates, HCl and ClNO2. In adidtion, there are indications of nitrooxy acid chlorides being produced. The reactions with CH2=CCl2 and CHCl=CCl2 are more complex due to release of chlorine atoms which eventually lead to formation of chloroacid chlorides.A general reaction mechanism is proposed and the observed concentration-time profiles of reactants and products are simulated for each compound. The rate constants for the initial step of NO3 addition to the chloroethenes are determined as: (2.6±0.5, 9.4±0.9, 2.0±0.4 and 1.4±0.4) × 10–16 cm3 molecule–1 s–1 for CH2=CHCl, CH2=CCl2, CHCl=CCl2 andcis-CHCl=CHCl, respectively. 相似文献
723.
This paper records sedimentary data which indicate that at least part of the Wilsons River floodplain, on the margins of the subtropical rainforest known as the 'Big Scrub', has a long and certainly pre-European history of relative treelessness. Despite a general presumption that this lowland subtropical region was completely forested prior to European settlement, recent historical research has indicated that certain areas were naturally open. While the historical information is clear, the data reported here-a fossil pollen record and one radiocarbon date- reinforces that information for one type of locality, providing an initial indication of time depth. 相似文献
724.
An inexpensive Pull-Up Shallow Water Seismometer (PUSS) has been designed and built to conduct long range seismic refraction experiments in the North Sea and the continental shelf around Britain, with the particular goal of studying the crustal and lithospheric structure under the epeirogenic basin of the North Sea. Signals from a gimbal-mounted 3-component geophone and a hydrophone are frequency modulated and mixed with clock and flutter correction signals before being recorded on a standard speed cassette tape recorder, with one hour of recording time. A 100 hour programmable timer allows the interval between the time of reset of the clock and each shot window of optional 5 or 10 min duration, to be preselected. The PUSS is launched and recovered using a pull-up technique originally developed for current meters. The replay system is also described.In May 1976 sea trials of 5 PUSSes were conducted along a 200 km refraction line in the North Sea. The encouraging performance of the equipment resulted in the decision to build a further 10 units and to proceed with a 400 km refraction line planned for the summer of 1977. 相似文献
725.
A minor generalization of the theory of random walk is used as a basis for a model of ocean current flow. The model is then applied in a computer simulation of drifter motion. The results of simulation indicate that the geometry of a coastline can have significant impact on the distribution of drifter landings. 相似文献
726.
Features of coastal upwelling regions that determine net air-sea CO<Subscript>2</Subscript> flux 总被引:1,自引:0,他引:1
Debby Ianson Richard A. Feely Christopher L. Sabine Lauren W. Juranek 《Journal of Oceanography》2009,65(5):677-687
The influence of the coastal ocean on global net annual air-sea CO2 fluxes remains uncertain. However, it is well known that air-sea pCO2 disequilibria can be large (ocean pCO2 ranging from ∼400 μatm above atmospheric saturation to ∼250 μatm below) in eastern boundary currents, and it has been hypothesized
that these regions may be an appreciable net carbon sink. In addition it has been shown that the high productivity in these
regions (responsible for the exceptionally low surface pCO2) can cause nutrients and inorganic carbon to become more concentrated in the lower layer of the water column over the shelf
relative to adjacent open ocean waters of the same density. This paper explores the potential role of the winter season in
determining the net annual CO2 flux in temperate zone eastern boundary currents, using the results from a box model. The model is parameterized and forced
to represent the northernmost part of the upwelling region on the North American Pacific coast. Model results are compared
to the few summer data that exist in that region. The model is also used to determine the effect that upwelling and downwelling
strength have on the net annual CO2 flux. Results show that downwelling may play an important role in limiting the amount of CO2 outgassing that occurs during winter. Finally data from three distinct regions on the Pacific coast are compared to highlight
the importance of upwelling and downwelling strength in determining carbon fluxes in eastern boundary currents and to suggest
that other features, such as shelf width, are likely to be important. 相似文献
727.
728.
729.
W. Mörikofer F. Steinhauser K. Cehak H. Steinhäusser 《Theoretical and Applied Climatology》1959,10(1):154-164
Ohne Zusammenfassung 相似文献
730.
Basalt at Sassafras was erupted in the Middle Eocene. The K‐Ar ages average 45.3 ± 4.9 Ma on whole rock and 48.4 ± 1.9 Ma on plagioclase. The basalt is not limited to a plateau capping, but extends 150 m down into adjacent valleys. Comparison with nearby Eocene basalts shows that there was in excess of 250 m of local relief in the central Shoalhaven valley by the Early Tertiary. The basalts were extruded at high elevation, and denudation of the coastal margin of the upland was already well advanced. Post‐basaltic denudation has been very slow, and the Early Tertiary landscape is well preserved. 相似文献