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排序方式: 共有428条查询结果,搜索用时 62 毫秒
381.
Dipl.-Biol. Meinhard Simon Prof. Dr. Max M. Tilzer 《Aquatic Sciences - Research Across Boundaries》1982,44(2):263-275
The breakdown of autumnal phytoplankton was studied in Lake Constance by combining chemical seston analyses, bacterial counts
and scanning electron microscopy. High algal biomass was associated with low numbers of free-living bacteria. The degradation
of algae occurred in two phases: First, dissolved material was released leading to growth of free-living bacteria. Thereafter,
bacteria attached to the decaying particles and decomposed them until highly refractory material was left behind. Attached
bacteria always comprised less than 25% of total bacteria. Dead organic seston exceeded microbial biomass by a factor of 4–10.
Pheopigments increased in senescent and dying algal cells relative to chlorophyll. Therefore, pheopigment fractions were used
as a relative index of algal decay. 相似文献
382.
Max Wyss 《Pure and Applied Geophysics》1997,149(1):3-16
This review summarizes the result of the second round of nominations for the IASPEI Preliminary List of Significant Precursors. Currently this List contains five cases of precursors: (1) foreshocks, (2) preshocks, (3) seismic quiescence before major aftershocks, (4) radon decrease in ground water, and (5) ground water level increase. A list of four cases that could not be accepted nor rejected by the panels reviewing them contains three on crustal deformations and one on seismic quiescence. In the second round 10 nominations were evaluated, nine new ones and one which had been considered previously. Two were accepted for the List, two were placed in the category of undecided cases. To date, a total of 40 nominations have been evaluated by IASPEI. For 37 of these the nominations, the mail reviews, the panel opinions, and, where supplied, the author's reply were published. This evaluation process remains active throughout the International Decade for Natural Hazards Reduction. Additional nominations are invited.The IASPEI Sub-commission on Earthquake Prediction does not guarantee that precursors accepted for the List can be used for earthquake prediction, nor does rejection of a nomination mean that the particular method could never become useful for prediction. However, the List, as well as the interchanges between authors and reviewers, allow us to gauge the state-of-the-art in earthquake prediction research. It is clear that we do not have an earthquake prediction capability, because the manner in which to use the few precursors on the List for predictions is not known. It also appears that many of the results thought to be conclusive by the authors, may not command the respect of the seismological research community at large. A more quantitative approach to data analysis, the use of rigorous statistical techniques, and high quality, long-term data sets are needed to make progress in earthquake prediction research. 相似文献
383.
We present a method for studying local stability of a solution to an inverse problem and evaluate the uncertainty in determining
true values of particular observables. The investigation is done under the assumption that only the Gaussian part of fluctuations
about the local minimum of the cost (likelihood) function is essential. Our approach is based on the spectral analysis of
the Hessian operator associated with the cost function at its extremal point, and we put forward an effective iterative algorithm
suitable for numerical implementation in the case of a computationally large problem.
Received: 16 May 2001 / Accepted: 22 October 2001 相似文献
384.
Jost Eikenberg Guido Vezzu Irene Zumsteg Sixto Bajo Max Ruethi Georg Wyssling 《Quaternary Science Reviews》2001,20(18):129
In order to determine the geochemical evolution of a freshwater limestone cave system located in central Switzerland (Hell Grottoes at Baar/Zug,) young postglacial tufaceous limestone and travertine precipitates were investigated using the 230Th/234U ingrowth system. Additional analyses of further radionuclides within the 238U decay chain, i.e. 226Ra and 210Pb, showed that the Th/U chronometer started with insignificant inherited 230Th over the entire formation period of the travertine setting (i.e. 230Th(0)=0). A contribution from detrital impurities with 230Th/234U in secular equilibrium could be precisely subtracted by applying isochron dating of cogenetic phases and recently formed travertine. The resulting precise 230Th/234U formation ages were found to be consistent with the geological stratigraphy and were furthermore used to demonstrate the applicability of the next geologically important chronometer in the 238U-decay series, based on decay of excess 226Ra normalized to the initial, i.e.226Raex/226Ra(0). This system is suitable for dating phases younger than 7000 yr when the correction of a detritus component increasingly limits the precision of the 230Th/234U chronometer. Analytical solutions of the coupled 234U/230Th/226Ra radionuclide system predicted that the 226Raex/226Ra(0) chronometer is independent of the actual 230Th activity build up from decay of 234U, if the systems starts with zero inherited 230Th(0). The data set confirmed this hypothesis and showed furthermore that the initially incorporated 226Ra excess must have remained almost uniform in all limestone over a period of at least 7000 yr, i.e. 4–5 half-lives of 226Ra. This is concluded because (i) the 226Raex/226Ra(0) ages agreed well with those derived from 230Th/234U, (ii) all data plot within uncertainty on the 226Raex/226Ra(0) decay curve and (iii) the atomic Ba/Ca ratio was found to be constant in the travertine material independent of the sample ages. Provided that such boundary conditions hold, 226Raex/226Ra(0) should be applicable to materials which are suitable for 230Th/234U dating in sedimentology and oceanography, i.e. travertine, corals, phosphorites, etc., and should strongly support 230Th/234U for samples that have been formed a few thousand years ago. 相似文献
385.
High resolution bathymetric and fine-scale parametric subbottom profiling along a line to the SW of Stavanger, Norway near the NE flank of the Norwegian Channel, show pockmarks clustered over neotectonic shallow fold structures in Quaternary sediments. Detailed profiles of the pockmarks indicate that they are collapsed gas seeps, rather than being collapse structures that followed doming and breaching with a more dramatic gas burst. The gentle folding and weak structures along the margin of a Mesozoic through Cenozoic sedimentary basin are probably due to differential uplift generating light compressional strain. 相似文献
386.
Supply in fisheries is traditionally known for its backward bending nature, owing to externalities in production. Such a supply regime, however, exist only for pure open access fisheries. Since most fisheries worldwide are neither pure open access, nor optimally managed, rather between the extremes, the traditional understanding of supply regimes in fisheries needs modification. This paper identifies through a case study of the East Baltic cod fishery supply regimes in fisheries, taking alternative fisheries management schemes and mesh size limitations into account. An age-structured Beverton–Holt based bio-economic supply model with mesh sizes is developed. It is found that in the presence of realistic management schemes, the supply curves are close to vertical in the relevant range. Also, the supply curve under open access with mesh size limitations is almost vertical in the relevant range, owing to constant recruitment. The implications are that the effects on supply following from e.g. trade liberalisation and reductions of subsidies are small in several and probably most fisheries worldwide. 相似文献
387.
388.
Max Richter 《International Journal of Earth Sciences》1927,18(2):155-160
Ohne Zusammenfassung 相似文献
389.
Max Storz 《International Journal of Earth Sciences》1914,5(2):88-94
Ohne Zusammenfassung 相似文献
390.
Max Richter 《International Journal of Earth Sciences》1936,27(1):91-96
Ohne Zusammenfassung 相似文献