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91.
Frank J Millero 《Geochimica et cosmochimica acta》1985,49(2):547-553
The effect of ionic interactions of the major components of natural waters on the oxidation of Cu(I) and Fe(II) has been examined. The various ion pairs of these metals have been shown to have different rates of oxidation. For Fe(II), the chloride and sulfate ion pairs are not easily oxidized. The measured decrease in the rate constant at a fixed pH in chloride and sulfate solutions agrees very well with the values predicted. The effect of pH (6 to 8) on the oxidation of Fe(II) in water and seawater have been shown to follow the rate equation where k1 and k2 are the pseudo first order rate constants, β1 and β2 are the hydrolysis constants for Fe(OH)+ and Fe(OH)0. The value of αFE is the fraction of free Fe2+. The value of k1 (2.0 ±0.5 min?1) in water and seawater are similar within experimental error. The value of k2 (1.2 × 105 min?1) in seawater is 28% of its value in water in reasonable agreement with predictions using an ion pairing model.For the oxidation of Cu(I) a rate equation of the form was found where k0 (14.1 sec?1) and k1 (3.9 sec?1) are the pseudo first order rate constants for the oxidation of Cu+ and CuCl0, β1 is the formation constant for CuCl0 and αCu is the fraction of free Cu+. Thus, unlike the results for Fe(II), Cu(I) chloride complexes have measurable rates of oxidation. 相似文献
92.
Recognition that the cooling of the core is accomplished by conduction of heat into a thermal boundary layer (D″) at the base of the mantle, partly decouples calculations of the thermal histories of the core and mantle. Both are controlled by the temperature-dependent rheology of the mantle, but in different ways. Thermal parameters of the Earth are more tightly constrained than hitherto by demanding that they satisfy both core and mantle histories. We require evolution from an early state, in which the temperatures of the top of the core and the base of the mantle were both very close to the mantle solidus, to the present state in which a temperature increment, estimated to be ~ 800 K, has developed across D″. The thermal history is not very dependent upon the assumption of Newtonian or non-Newtonian mantle rheology. The thermal boundary layer at the base of the mantle (i.e., D″) developed within the first few hundred million years and the temperature increment across it is still increasing slowly. In our preferred model the present temperature at the top of the core is 3800 K and the mantle temperature, extrapolated to the core boundary without the thermal boundary layer, is 3000 K. The mantle solidus is 3860 K. These temperatures could be varied within quite wide limits without seriously affecting our conclusions. Core gravitational energy release is found to have been remarkably constant at ~ 3 × 1011 W. nearly 20% of the core heat flux, for the past 3 × 109 y, although the total terrestrial heat flux has decreased by a factor of 2 or 3 in that time. This gravitational energy can power the “chemical” dynamo in spite of a core heat flux that is less than that required by conduction down an adiabatic gradient in the outer core; part of the gravitational energy is used to redistribute the excess heat back into the core, leaving 1.8 × 1011 W to drive the dynamo. At no time was the dynamo thermally driven and the present radioactive heating in the core is negligibly small. The dynamo can persist indefinitely into the future; available power 1010 y from now is estimated to be 0.3 × 1011 W if linear mantle rheology is assumed or more if mantle rheology is non-linear. The assumption that the gravitational constant decreases with time imposes an implausible rate of decrease in dynamo energy. With conventional thermodynamics it also requires radiogenic heating of the mantle considerably in excess of the likely content of radioactive elements. 相似文献
93.
The spectrophotometric measurements of chloro complexes of lead in aqueous HCl, NaCl, MgCl2 and CaCl2 solutions at 25°C have been analyzed using Pitzer's specific interaction equations. Parameters for activity coefficients of the complexes PbCl+, PbCl20 and PbCl3? have been determined for the various media. Values of , and were obtained for the cumulative formation constants. []. These values are in reasonable agreement with literature data. The Pitzer parameters for the PbCl ion pairs in various media were used to calculate the speciation of Pb2+ in an artificial seawater solution. 相似文献
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96.
Deriving rules from activity diary data: A learning algorithm and results of computer experiments 总被引:1,自引:0,他引:1
Theo A. Arentze Frank Hofman Harry J.P. Timmermans 《Journal of Geographical Systems》2001,3(4):325-346
Activity-based models consider travel as a derived demand from the activities households need to conduct in space and time.
Over the last 15 years, computational or rule-based models of activity scheduling have gained increasing interest in time-geography
and transportation research. This paper argues that a lack of techniques for deriving rules from empirical data hinders the
further development of rule-based systems in this area. To overcome this problem, this paper develops and tests an algorithm
for inductively deriving rules from activity-diary data. The decision table formalism is used to exhaustively represent the
theoretically possible decision rules that individuals may use in sequencing a given set of activities. Actual activity patterns
of individuals are supplied to the system as examples. In an incremental learning process, the system progressively improves
on the selection of rules used for reproducing the examples. Computer experiments based on simulated data are performed to
fine-tune rule selection and rule value update functions. The results suggest that the system is effective and fairly robust
for parameter settings. It is concluded, therefore, that the proposed approach opens up possibilities to derive empirically
tested rule-based models of activity scheduling. Follow-up research will be concerned with testing the system on empirical
data.
Received: 31 January 2001 / Accepted: 13 September 2001 相似文献
97.
Hypothesized large-scale climatic extremes require verification from distantregions in order toconfirm the magnitude and timing of such events. Three of the most massivehypothesized volcanic events of the past two millennia, occurring in or aboutAD 536, 934 and1258, had profound climatic and demographic repercussions over much of Europe,the MiddleEast, and other areas, according to historical accounts recently described inStothers (1998, 1999,2000) as well as other research. Here we report on frost ring and otherdendrochronologicalevidence derived from a 1738-year tree-ring chronology from Mongolia andmillennial-scaletree-ring data from northern Siberia which demonstrate that these three eventsmay have alsoimpacted conditions in these distant regions. 相似文献
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Dispersion of the salt-marsh periwinkle Littoraria irrorata: Effects of water level,size, and season
This paper documents horizontal and vertical dispersion patterns of a Texas population of the saltmarsh periwinkle, Littoraria irrorata, over a 15-month period. The study was conducted within a tidal marsh on the Anahuac National Wildlife Refuge in Galveston Bay. Two mark-recapture experiments demonstrated that L. irrorata rarely move more than 2 m from their release point over long periods of time and do not home to individual Spartina plants. Adult L. irrorata forage farther away from the base of Spartina stalks at low tide than do juvenile snails. Remaining near the plant base may decrease both temperature and desiccation stress on juveniles. During warm months, L. irrorata climb grass stalks with tidal inundation and forage on the substratum at low tide. Snails are inactive and aggregate in detrital debris at the base of Spartina clumps during the winter. *** DIRECT SUPPORT *** A01BY058 00016 相似文献