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991.
Results of an experimental programme on heterogeneous rock-like specimens of dental plaster confirm the pronounced role of
tensile microcracks on brittle failure. Microbuckling of very small rock-columns formed amid closely located tensile cracks
was observed as the key incident connecting stable phenomenon of tensile cracking to unstable phenomenon of shearing and subsequent
macroscopic failure. Using the classical beam and buckling theories and considering geometry of the problem a new failure
criterion is proposed. As a novel attempt, this new failure criterion relates the compressive strength of rock to three basic
microstructural properties, i.e. degree of crystal interlocking, average Young modulus and average tensile strength of rock
forming minerals. 相似文献
992.
Bernhard Krautzer Wilhelm Graiss Giovanni Peratoner Christian Partl Sonia Venerus Brigitte Klug 《Natural Hazards》2011,56(2):547-557
Control of erosion, and all of its after effects, from increased surface drainage and erosion to the formation of karst, is
one of the essential problems when undertaking recultivation following necessary interventions in the sub-alpine and alpine
vegetation stage (high zones). Average slope inclinations of 30–45% in the vicinity of ski runs, and far above in areas of
natural erosion and avalanche zones, make restoration processes with sufficient erosion protection the prerequisite for success.
Only a sufficient vegetation development of more than 70% ground cover stabilises the topsoil in the long term and reduces
soil erosion to an acceptable degree. From 1999 to 2002, an international EU project with the participation of research groups
and private firms from Austria, Italy and Germany was carried out under the direction of the Agricultural Research and Education
Centre Raumberg-Gumpenstein (AREC) on five different Alpine sites at altitudes from 1,245 to 2,350 m above sea level. The
aim of the work was the formulation of practice-relevant requirements for recultivation following intervention in high zones,
especially following constructional measures in the vicinity of ski runs and lifts, torrent- and avalanche barriers. In a
statistical comparison, the relationship between restoration techniques, seed mixtures of differing ecological value and vegetation
cover was observed. The influence of application technique on erosion processes after restoration was obvious for the first
two vegetation periods. Only with the additional use of mulch covers could increase surface drainage and noticeable soil loss
be avoided. At high altitudes, the choice of seed mixture, irrespective of whether rapid or slow growing and independent of
the extent of accompanying fertilisation, had no significance in the first two vegetation periods following sowing. In the
following growing seasons, however, higher cover values were obtained with site-specific seed mixtures at three of the five
experimental sites. While few species of the commercial seed mixture showed satisfactory persistency, most of the grasses
and in particular the alpine leguminosae of site-specific seed mixtures increased their share during the observation period.
In the long-term, sufficient protection against erosion is only guaranteed by the use of stable, enduring and ecologically
adapted species. 相似文献
993.
Stratigraphy of the Triassic?Jurassic Boundary Successions of the Southern Margin of the Junggar Basin, Northwestern China 总被引:1,自引:1,他引:1
SHA Jingeng Vivi VAJDA PAN Yanhong Linda LARSSON YAO Xiaogang ZHANG Xiaolin WANG Yaqiong CHENG Xiansheng JIANG Baoyu DENG Shenghui CHEN Siwei PENG Bo 《《地质学报》英文版》2011,85(2):421-436
The Triassic?Jurassic (Tr?J) boundary marks a major extinction event, which (~200 Ma) resulted in global extinctions of fauna and flora both in the marine and terrestrial realms. There prevail great challenges in determining the exact location of the terrestrial Tr?J boundary, because of endemism of taxa and the scarcity of fossils in terrestrial settings leading to difficulties in linking marine and terrestrial sedimentary successions. Investigation based on palynology and bivalves has been carried out over a 1113 m thick section, which is subdivided into 132 beds, along the Haojiagou valley on the southern margin of the Junggar Basin of the northern Xinjiang, northwestern China. The terrestrial Lower Jurassic is conformably resting on the Upper Triassic strata. The Upper Triassic covers the Huangshanjie Formation overlaid by the Haojiagou Formation, while the Lower Jurassic comprises the Badaowan Formation followed by the Sangonghe Formation. Fifty six pollen and spore taxa and one algal taxon were identified from the sediments. Based on the key-species and abundance of spores and pollen, three zones were erected: the Late Triassic (Rhaetian) Aratrisporites?Alisporites Assemblage, the Early Jurassic (Hettangian) Perinopollenites?Pinuspollenites Assemblage, and the Sinemurian Perinopollenites?Cycadopites Assemblage. The Tr?J boundary is placed between bed 44 and 45 coincident with the boundary between the Haojiagou and Badaowan formations. Beds with Ferganoconcha (?), Unio?Ferganoconcha and Waagenoperna?Yananoconcha bivalve assemblages are recognized. The Ferganoconcha (?) bed is limited to the upper Haojiagou Formation, Unio?Ferganoconcha and Waagenoperna?Yananoconcha assemblages are present in the middle and upper members of the Badaowan Formation. The sedimentary succession is interpreted as terrestrial with two mainly lake deposit intervals within Haojiagou and Badaowan formations, yielding fresh water algae and bivalves. However, the presence of brackish water algae Tasmanites and the marine?littoral facies bivalve Waagenoperna from the Badaowan Formation indicate that the Junggar Basin was influenced by sea water caused by transgressions from the northern Tethys, during the Sinemurian. 相似文献
994.
995.
Victor Pinto Xavier Font Miquel Salgot Jose Tapias Tomas Mañá 《Environmental Geology》2002,41(5):495-503
One of the most important environmental impacts resulting from opencast mining, and especially quarries, is the visual impact. Evaluation of this impact considers two aspects: first, the area occupied by the quarry as seen by an observer from a specific place, and, second, the chromatic contrast existing between landscape and exploitation. In this study we develop a methodology to assess the chromatic impact in an objective and comparable form. To assess this impact we developed a method based on image analysis that allows us to obtain from a picture or image its equivalent as a function of chromatic impact, according to the sensibility of the human eye to different wavelengths. The methodology was applied to the Martinenca limestone quarry (Alcanar, Tarragona) and to Cerro Kori Kollo mine, La Joya district (Bolivia). 相似文献
996.
Coastal plains are amongst the most densely populated areas in the world. Many coastal peatlands are drained to create arable land. This is not without consequences; physical compaction of peat and its degradation by oxidation lead to subsidence, and oxidation also leads to emissions of carbon dioxide (CO2). This study complements existing studies by quantifying total land subsidence and associated CO2 respiration over the past millennium in the Dutch coastal peatlands, to gain insight into the consequences of cultivating coastal peatlands over longer timescales. Results show that the peat volume loss was 19.8 km3, which lowered the Dutch coastal plain by 1.9 m on average, bringing most of it below sea level. At least 66 % of the volume reduction is the result of drainage, and 34 % was caused by the excavation and subsequent combustion of peat. The associated CO2 respiration is equivalent to a global atmospheric CO2 concentration increase of ~0.39 ppmv. Cultivation of coastal peatlands can turn a carbon sink into a carbon source. If the path taken by the Dutch would be followed worldwide, there will be double trouble: globally significant carbon emissions and increased flood risk in a globally important human habitat. The effects would be larger than the historic ones because most of the cumulative Dutch subsidence and peat loss was accomplished with much less efficient techniques than those available now. 相似文献
997.
At about 8:30 p.m. on 27 August 2014, a catastrophic rock avalanche suddenly occurred in Fuquan, Yunnan, southwestern China. This landslide and related impulse water waves destroyed two villages and killed 23 persons. The impulse waves occurred after initiation of the landslide, caused by the main part of the slide mass rapidly plunging into a water-filled quarry below the source area. The wave, comprising muddy water and rock debris, impacted the opposite slope of the quarry on the western side of the runout path and washed away three homes in Xinwan village. Part of the displaced material traveled a horizontal distance of about 40 m from its source and destroyed the village of Xiaoba. To provide information for potential landslide hazard zonation in this area, a combined landslide–wave simulation was undertaken. A dynamic landslide analysis (DAN-W) model is used to simulate the landslide propagation before entering the quarry, while Fluent (Ansys Inc., USA) is used to simulate the impulse wave generation and propagation. Output data from the DAN-W simulation are used as input parameters for wave modeling, and there is good agreement between the observed and simulated results of the landslide propagation. Notably, the locations affected by recordable waves according to the simulation correspond to those recorded by field investigation. 相似文献
998.
999.
A geochemical evaluation of Niger Delta organic matter was carried out using supercritical fluid extraction (SFE) sample preparation
procedure. Comparison of geochemical significance of gas chromatographic data of rock extracts of SFE with those of Soxhlet
extraction method from previous studies was made in order to establish the usefulness of SFE in geochemical exploration. The
assessment of geochemical character of the rock samples from the comparison and interpretation of other geochemical parameters
were used to give more insights into understanding the source rocks characteristics of onshore and shelf portions of the Niger
Delta Basin. The results of the gas chromatographic (GC) analysis of the rock extracts across the lithostratigraphic units
show that Pr/Ph, Pr/nC17, Pr/nC18, CPI and odd/even preference ranged from 0.07 to 12.39, 0.04 to 6.66, 0.05 to 13.80, 0.12 to 8.4 and 0.06 to 8.12, respectively.
The Rock-Eval pyrolysis data and geochemical ratios and parameters calculated from the GC data showed that most of the samples
are mature and have strong terrestrial provenance while a few samples have strong marine provenance. The few marine source
rocks are located in the deeper depth horizon. Pr/Ph and standard geochemical plots indicate that most of samples were derived
from organic matter deposited in less reducing conditions, i.e. more of oxidizing conditions while a few samples have predominantly
influence of reducing conditions. The results of trace metal analysis of older samples from Agbada Formation also indicate
marine and mixed organic matter input deposited in less reducing conditions. The results obtained in this study are comparable
with those obtained from previous studies when Soxhlet extraction method was used and also indicated the presence of more
than one petroleum systems in the Niger Delta. 相似文献
1000.
Changes in the abundance of selected planktic foraminiferal species and some sedimentological parameters at ODP site 728A
were examined to understand the fluctuations in the surface productivity and deep sea oxygenation in the NW Arabian Sea during
last ∼540 kyr. The increased relative abundances of high fertility taxa, i.e., Globigerinita glutinata and Globigerina bulloides mainly during interglacial intervals indicate intense upwelling. Strong SW summer monsoon probably increased the upwelling
in the western Arabian Sea during interglacial intervals and caused high surface productivities due to the lateral transport
of eutrophic waters. Most of the glacial periods (i.e., MIS 2, 4, 6, 8 and 12) are characterized by higher relative abundances
of Neogloboquadrina pachyderma and Neogloboquadrina dutertrei associated with Globigerinoides ruber. The more stratified condition and deep mixed layer due to increased NE winter monsoon are mainly responsible for the higher
relative abundances of N. pachyderma during glacial periods. Some of the glacial intervals (i.e., MIS 6 and 8) are also characterized by pteropod spikes reflecting
deepening of aragonite compensation depth (ACD) and relatively less intense oxygen minimum zone (OMZ) in this region due to
deep sea mixing and thermocline ventilation, and relatively less intense surface productivity during winter monsoon. The interglacial
periods are largely devoid of pteropod shells indicating more aragonite dissolution due to increased intensity of OMZ in the
northwestern Arabian Sea. 相似文献