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301.
Assessment of Dissolution of Silicate Rock Reference Materials with Ammonium Bifluoride and Nitric Acid in a Microwave Oven 总被引:1,自引:0,他引:1
Thais T. Magaldi Margareth S. Navarro Jacinta Enzweiler 《Geostandards and Geoanalytical Research》2019,43(1):189-208
The complete dissolution of representative test portions of powdered rock samples for the determination of the mass fractions of trace elements by ICP‐MS relies either on aggressive and time‐consuming acid digestions or fusion/sintering with appropriate fluxes. Here, we evaluate a microwave oven dissolution method that employs a solution of NH4HF2 and HNO3. The entire procedure occurs in a closed vessel system and takes up to 4 h. In hundreds of digestions, the precipitation of fluorides was never observed. Replicate decomposition of 100 mg of twenty‐one international reference materials (RMs) of igneous rocks, and also one of a shale presented mostly satisfactory recoveries of forty‐one trace elements. Important exceptions were Zr and Hf in G‐2 and GSP‐2 (mean recoveries of ca. 70%), although for four other felsic rock RMs, the digestion was complete. For ultramafic rock RMs, we present Cr results that indicate quantitative dissolution of Cr‐bearing phases. We discuss the findings and conclude that advances in sample preparation of geological materials for instrumental analysis would benefit from a better understanding of how specific characteristics, such as composition and crystallinity of certain minerals, may affect their reactivity. 相似文献
302.
Peeter Nõges Lea Tuvikene Tiina Nõges Anu Kisand 《Aquatic Sciences - Research Across Boundaries》1999,61(2):168-182
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305.
Rubén?Fernández-Casal Sergio?Castillo-Páez Mario?Francisco-FernándezEmail authorView authors OrcID profile 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(3):675-684
In this work, a fully nonparametric geostatistical approach to estimate threshold exceeding probabilities is proposed. To estimate the large-scale variability (spatial trend) of the process, the nonparametric local linear regression estimator, with the bandwidth selected by a method that takes the spatial dependence into account, is used. A bias-corrected nonparametric estimator of the variogram, obtained from the nonparametric residuals, is proposed to estimate the small-scale variability. Finally, a bootstrap algorithm is designed to estimate the unconditional probabilities of exceeding a threshold value at any location. The behavior of this approach is evaluated through simulation and with an application to a real data set. 相似文献
306.
Joaquín?Martínez-MinayaEmail authorView authors OrcID profile Michela?Cameletti David?Conesa Maria?Grazia?Pennino 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(11):3227-3244
The use of complex statistical models has recently increased substantially in the context of species distribution behavior. This complexity has made the inferential and predictive processes challenging to perform. The Bayesian approach has become a good option to deal with these models due to the ease with which prior information can be incorporated along with the fact that it provides a more realistic and accurate estimation of uncertainty. In this paper, we first review the sources of information and different approaches (frequentist and Bayesian) to model the distribution of a species. We also discuss the Integrated Nested Laplace approximation as a tool with which to obtain marginal posterior distributions of the parameters involved in these models. We finally discuss some important statistical issues that arise when researchers use species data: the presence of a temporal effect (presenting different spatial and spatio-temporal structures), preferential sampling, spatial misalignment, non-stationarity, imperfect detection, and the excess of zeros. 相似文献
307.
Comparing ARIMA and computational intelligence methods to forecast daily hospital admissions due to circulatory and respiratory causes in Madrid 总被引:1,自引:0,他引:1
Ricardo?Navares Julio?Díaz Cristina?Linares José?L.?AznarteEmail author 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(10):2849-2859
Anticipating future workloads in a hospital may be of capital importance in order to distribute resources and improve patient attention. In this paper, we tackle the problem of predicting daily hospital admissions in Madrid due to circulatory and respiratory cases based on biometeorological indicators. A range of forecasting algorithms were proposed covering four model families: ensemble methods, boosting methods, artificial neural networks and ARIMA. Experiments show how the last two obtain better results in average, demonstrating that the problem can be properly solved with both approaches. Furthermore, a recently proposed technique known as stacked generalization was also used to dynamically combine the predictions from the four models, finally improving the performance with respect to the individual models. 相似文献
308.
Pablo?JuanEmail author Carlos?Díaz-Avalos Nancy?R.?Mejía-Domínguez Jorge?Mateu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(2):461-479
We modeled the spatial distribution of the most important Chagas disease vectors in Argentina, in order to obtain a predictive mapping method for the probability of presence of the vector species. We analyzed both the binary variable of presence-absence of Chagas disease and the vector species richness in Argentina, in combination with climatic and topographical covariates associated to the region of interest. We used several statistical techniques to produce distribution maps of presence–absence for the different insect species as well as species richness, using a hierarchical Bayesian framework within the context of multivariate geostatistical modeling. Our results show that the inclusion of covariates improves the quality of the fitted models, and that there is spatial interaction between neighboring cells/pixels, so mapping methods used in the past, which assumed spatial independence, are not adequate as they provide unreliable results. 相似文献
309.
Anderson H. Melo Peryclys R. O. Andrade Antonio J. C. Magalhães Daniel G. C. Fragoso Francisco P. Lima-Filho 《Basin Research》2020,32(5):1054-1080
Five 3rd-order depositional sequences are interpreted from the early Albian to late Campanian interval in the Potiguar Basin. An integrated analysis of seismic interpretations, well logs, cores and biostratigraphic data provides a stratigraphic framework composed by stratigraphic surfaces, systems tracts and sequences. Depositional Sequence 1 and 2 are, respectively, Albian and early to mid-Cenomanian aged and are composed by the falling stage, low stand, transgressive and high stand systems tracts. Depositional Sequence 3 is late Cenomanian to mid-Turonian aged and is composed by the transgressive and high stand systems tracts. Depositional sequences 4 and 5 are, respectively, late Turonian to mid-Santonian and late Santonian to mid-Campanian aged and are composed only by transgressive and high stand systems tracts. The lack of falling stage and low stand systems tracts in depositional sequences 3, 4 and 5, as well the increasing in transgressive and highstand systems tracts thickness as depositional sequences get younger, are reflection of an overall transgressive trend of a 2nd-order sequence. The interpretation proposed in this paper correlates onshore with offshore deposits within a seismic scale (3rd-order) sequence stratigraphy framework. This approach allows a better understanding of the Açu Formation, the primary oil-bearing formation of the Potiguar Basin. The Açu Formation is part of depositional sequences 1, 2 and 3 and is characterized by lateral and vertical variations of depositional systems instead of being associated to a specific depositional system. This sequence stratigraphy analysis can be used as a low-resolution framework for future high-resolution (4th-order scale) studies. 相似文献
310.
Yong Wai-Kuan Lim Phaik-Eem Vello Vejeysri Sim Kae-Shin Abdul Majid Nazia Mustafa Emienour Muzalina Nik Sulaiman Nik Meriam Liew Kan-Ern Chen Brenna Jia-Tian Phang Siew-Moi 《中国海洋湖沼学报》2019,37(1):186-198
Journal of Oceanology and Limnology - A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel... 相似文献