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排序方式: 共有753条查询结果,搜索用时 15 毫秒
1.
Xuechao Wu Qingzhen Hao B Marković Slobodan Yu Fu Namira Yang Song Zhengtang Guo 《地球科学进展》2020,35(4):363-377
Danube loess, located at the westernmost part of the widespread Eurasian loess belt, is one of the most well-preserved aeolian dust deposits in Europe with the basal age dating back over 1 Ma. Owing to its unique location and formation processes, Danube loess plays an important role in understanding the linkage of climate changes in different climate regimes over Eurasian continent and paleoclimatic changes in middle-high northern latitudes. Major research advances of the Danube loess, including compositions, provenance, chronology, stratigraphy and paleoenvironment changes were systematically reviewed and the focuses of future research were suggested. To better understand loess provenance, the compositions of sediments in all the potential source areas should be investigated, and methodological study of provenance indicators and application of multi-proxies approaches need to be carried out. Chronologically and stratigraphically, feldspar luminescence dating and tephrochronology methods should be widely used, and the establishment of a uniform stratigraphic framework and correlation scheme should be constrained by precise chronology. In terms of the paleoenvironment, it is necessary to conduct high-resolution multi-proxies reconstruction of paleoenviroment for the entire loess-paleosol sequence, extending from the last interglacial period (130 ka to present) to interval of last 1 Ma. The future progress in Danube loess is crucial to improving the study of continental paleoclimate comparison and paleoclimate dynamics over the Eurasian loess region. 相似文献
2.
Throughout history, dry-stone masonry structures have been strengthened with different types of metal connectors in order to increase their resistance which enabled their survival, especially in the seismically active area. One such example is the ancient Protiron monument placed in the Peristyle square of the Diocletian's Palace in Split, Croatia. The Protiron was built at the turn of the 3rd century as a stone masonry structure with dowels embedded between its base, columns, capitals and broad gable. The stone blocks in the broad gable were connected by metal clamps during restoration at the beginning of the 20th century. In order to study the seismic performance of the strengthened stone masonry structures, an experimental investigation of seismic behaviour of a physical model of the Protiron was performed on the shaking table. The model was designed as a true replica model in a length scale of 1:4 and exposed to representative earthquake with increasing intensities up to collapse. The tests provided a clear insight into system behaviour, damage mechanism and failure under intensive seismic load, especially into the efficiency of connecting elements, which had a special role in increasing seismic resistance and protection of the structure from collapse. Additionally, this experiment provided valuable data for verification and calibration of numerical models for strengthened stone masonry structures. 相似文献
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A New Genus and Species of Damsel-Dragonfly (Odonata: Isophlebioidea: Campterophlebiidae) in the Middle Jurassic of Inner Mongolia, China 总被引:1,自引:0,他引:1
The campterophlebiid new genus and species Ctenogampsophlebia reni is described from the Middle Jurassic of Inner Mongolia, China. It shows close similarities with the Lower to Middle Jurassic genera Gampsophlebia, and Petrophlebia, with closed and short subdiscoidal cells, confirming the attribution of these two other genera to the Campterophlebiidae. 相似文献
6.
Stanislav Frančišković-Bilinski Mladen Juračić Darko Tibljaš 《Environmental Earth Sciences》2011,64(7):1755-1761
Surface sediments (fraction <63 μm) from the source to the mouth of the Rječina, short (18.3 km) karst allogenic river in
Croatia, which is an important source of drinking water, were studied to investigate their mineral (by XRD) and chemical (by
ICP-MS) composition to check possible anthropogenic influence at the lower course due to paper industry and mills, and in
the prodelta area from untreated municipal sewage and the large harbor of Rijeka town. In all analyzed sediment samples and
in the sandstone source, rock quartz is a major mineral, while feldspar and mica group minerals are less abundant. Chlorite
is a minor or trace mineral in all samples. Calcite and dolomite are abundant in the river prodelta, reflecting changes in
bedrock lithology from flysch to carbonates. In river sediments, Fe is the most abundantly analyzed element, while Ca is the
most abundant in prodelta sediments. Concentrations of Al, Mn, Ni, Cr, Co, La and Nd decrease downstream, while Mg, S, Na,
B, Pb, Zn, As, Sn, U, Mo, Hg and Ag have relatively higher concentration in prodelta sediments. The results are compared with
sediments of other rivers in the area: Raša, Rižana and Dragonja, as well as with those of the Rosandra Creek (Italy). Sediments
in the Raša River showed similar behavior as those in the Rječina, as the highest concentration of metals was found in the
restricted upper part of the estuary, characterized by rapid deposition of clay particles and terrestrial sedimentary organic
matter. The comparison also showed that the most contaminated were the sediments from the Rižana, followed by those from the
Rječina and Rosandra Creek, which had similar results. Among the studied elements, As was present in all sediment samples
at concentrations >6 ppm that might have the lowest toxic effects. At the lower Rječina and in prodelta sediments, Pb was
also present at slightly elevated concentrations (>31 ppm) that could cause such effects. Concentrations of Zn in the prodelta
correspond to those occurring in moderately polluted sediments (90–200 ppm). In the prodelta sediments, Hg is slightly below
toxicity threshold (1 ppm), while Ag is present at toxicity threshold (0.5 ppm) or close to it. Rječina River could act as
a good illustrative example for behavior of toxic metals in allogenic karstic rivers, in which accumulation of anthropogenically
introduced pollutants usually occurs in their estuaries, as a result of transport and deposition of fine particles. 相似文献
7.
Dubravka Relić Dragana Đorđević Aleksandar Popović 《Environmental Earth Sciences》2011,63(6):1303-1317
We used elemental carbon, nitrogen, hydrogen and sulfur as well as ratios of hydrogen and nitrogen with total organic carbon
for investigation of source and conditions of organic matter in alluvial Danube sediments. We also determined the pseudo total
concentrations of metals presented as a sum of extracted concentration after five sequential extraction steps. The pseudo
total metal concentrations were found to be (mg kg−1) for Mn, 666; Fe, 25,852; Mg, 16,193; K, 2,063; Ni, 32.4; Zn, 72.2; Pb, 15.0; Cu, 26.0 and for Cr, 15.9. Correlation analysis
and two multivariate analysis methods (principal component and cluster analysis) were helpful in determining the associations
between the pseudo total extracted fractions of metals and with elemental carbon, hydrogen, nitrogen, sulfur, total inorganic
and organic carbon. These correlations will help us to identify substrates of trace metals in different oxic/anoxic conditions.
The correlation results of the trace metals and Fe, K, Mg and Mn suggest their adsorption, mainly onto Fe and Mn (hydro)oxides
and K alumosilicates, whereas correlations of metals with sulfur indicate that they were precipitated as Fe-sulfides. 相似文献
8.
Comparison of quantitative petrographic, stable isotope and cathodoluminescence data for fingerprinting Czech marbles 总被引:1,自引:1,他引:0
Various marbles from both historic quarries and historical artefacts of the Czech Republic were examined in order to make determinations of their provenance. The methodology used was based upon a combination of petrographic image analysis (PIA) of thin sections, stable isotope geochemistry of carbonates, and cathodoluminescence. Multivariate statistical methods (i.e. cluster analysis and discriminant analysis) confirmed the geoscientific relevance of the marble’s different characteristics with a high degree of consistency as well as the enhanced significance of stable C and O isotopes in correlation with the petrographic data. The qualitative cathodoluminescence data provided a useful additional tool to help recognise the fingerprinting of marbles with similar petrographic and/or geochemical characteristics. 相似文献
9.
John Davenport Daria Ezgeta-Balić Melita Peharda Sanda Skejić Živana Ninčević-Gladan Slavica Matijević 《Estuarine, Coastal and Shelf Science》2011
The endangered fan shell Pinna nobilis is a large bivalve mollusc (<120 cm shell length) endemic to the Mediterranean that lives one-third buried in soft substrata, generally in shallow coastal waters. We hypothesised that P. nobilis of different sizes would ingest different food sources, because small fan shells will inhale material from closer to the substratum than do large fan shells. We studied stomach contents and faeces of 18 fan shells, 6 small (mean 23.0 cm length), 6 medium-sized (mean 41.5 cm length) and 6 large (mean 62.7 cm length) living in a small area of a low-energy coastal detritic bottom characterised by mud, sand and macroalgae at Mali Ston Bay, Croatia. We found that all P. nobilis ingested copious quantities of undetermined detritus (probably at least 95% of ingested material), phytoplankton, micro and mesozooplankton and pollen grains. Large P. nobilis stomach contents showed a preponderance of water column calanoid copepods, while small fan shells had higher numbers of bivalve larvae. All fan shells took in high numbers of harpacticoid copepods that are benthonic, feeding on microbial communities of detritus and benthic vegetation. There was also a significant selection of phytoplankton species, some apparently occurring between inhalation and ingestion. The stomach contents of small P. nobilis had a higher organic matter content than either medium-sized or large fan shells; this indicated that small fan shells ingested detritus of higher organic content than did larger P. nobilis. As the faeces of all P. nobilis had similar organic matter content, this also indicates higher assimilation efficiencies in small fan shells. The demonstration of differential dietary selectivity by different sized animals has implications for future trophic studies of this endangered species. This study also provides the first demonstration of predation on zooplankton by P. nobilis. 相似文献
10.