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11.
M. F. Pereira C. Ribeiro F. Vilallonga M. Chichorro K. Drost J. B. Silva L. Albardeiro M. Hofmann U. Linnemann 《International Journal of Earth Sciences》2014,103(5):1453-1470
This study combines geochemical and geochronological data in order to decipher the provenance of Carboniferous turbidites from the South Portuguese Zone (SW Iberia). Major and trace elements of 25 samples of graywackes and mudstones from the Mértola (Visean), Mira (Serpukhovian), and Brejeira (Moscovian) Formations were analyzed, and 363 U-Pb ages were obtained on detrital zircons from five samples of graywackes from the Mira and Brejeira Formations using LA-ICPMS. The results indicate that turbiditic sedimentation during the Carboniferous was marked by variability in the sources, involving the denudation of different crustal blocks and a break in synorogenic volcanism. The Visean is characterized by the accumulation of immature turbidites (Mértola Formation and the base of the Mira Formation) inherited from a terrane with intermediate to mafic source rocks. These source rocks were probably formed in relation to Devonian magmatic arcs poorly influenced by sedimentary recycling, as indicated by the almost total absence of pre-Devonian zircons typical of the Gondwana and/or Laurussia basements. The presence of Carboniferous grains in Visean turbidites indicates that volcanism was active at this time. Later, Serpukhovian to Moscovian turbiditic sedimentation (Mira and Brejeira Formations) included sedimentary detritus derived from felsic mature source rocks situated far from active magmatism. The abundance of Precambrian and Paleozoic zircons reveals strong recycling of the Gondwana and/or Laurussia basements. A peri-Gondwanan provenance is indicated by zircon populations with Neoproterozoic (Cadomian-Avalonian and Pan-African zircon-forming events), Paleoproterozoic, and Archean ages. The presence of late Ordovician and Silurian detrital zircons in Brejeira turbidites, which have no correspondence in the Gondwana basement of SW Iberia, indicates Laurussia as their most probable source. 相似文献
12.
Mehwish Bibi Michael Wagreich Shahid Iqbal Susanne Gier Irfan U. Jan 《Geological Journal》2020,55(1):671-693
The Pleistocene represents the youngest period of repeated widespread glaciation and interglacial intervals of both hemispheres. The Pleistocene–Holocene siliciclastics of the Peshawar Basin preserve a significant terrestrial record of palaeoclimatic fluctuations during this glacial time interval in northwest Pakistan at latitudes of 33–35°N. The sedimentological evidences indicate that the lower part of the stratal package consists of floodplain clay cycles overlain by lacustrine-glaciofluvial rhythmites, that are followed by loess deposits and finally recent floodplain clays. The geochemical proxies demonstrate an overall cold-arid climate with very low intensity of chemical weathering, whereas the clay mineralogy and related indices suggest intensifying physical erosion. The chemical index of alteration (CIA) reflects comparatively slightly higher (but still very low) intensity of chemical weathering for the lowermost part of the succession and uppermost loess deposits. The illite-rich clay mineralogy of these two lithofacies associations also indicates the prevailing cold-arid palaeoclimate. The low CIA and smectite-rich clay mineralogy of the rhythmites, on the other hand, reflect deposition in poorly drained lakes. Multiple evidences for break-out floods and the presence of ice-rafted debris (IRD) within the rhythmites provide conclusive evidences for ice damming in the Peshawar Basin and drainage blockage due to the uplift of the Attock–Cherat Range. The floodplain clays indicate deposition in an interglacial semiarid–semihumid palaeoclimate preceding the Shanoz stage glaciation. The rhythmites correlate with the Shanoz, Yunz, and Borit Jheel glacial stages. The loess deposits indicate aeolian deposition in a cold, periglacial environment spanning over the late glacial maximum (LGM) interval. 相似文献
13.
The benthic food web of the deep Faroe–Shetland Channel (FSC) was modelled by using the linear inverse modelling methodology. The reconstruction of carbon pathways by inverse analysis was based on benthic oxygen uptake rates, biomass data and transfer of labile carbon through the food web as revealed by a pulse-chase experiment. Carbon deposition was estimated at 2.2 mmol C m−2 d−1. Approximately 69% of the deposited carbon was respired by the benthic community with bacteria being responsible for 70% of the total respiration. The major fraction of the labile detritus flux was recycled within the microbial loop leaving merely 2% of the deposited labile phytodetritus available for metazoan consumption. Bacteria assimilated carbon at high efficiency (0.55) but only 24% of bacterial production was grazed by metazoans; the remaining returned to the dissolved organic matter pool due to viral lysis. Refractory detritus was the basal food resource for nematodes covering ∼99% of their carbon requirements. On the contrary, macrofauna seemed to obtain the major part of their metabolic needs from bacteria (49% of macrofaunal consumption). Labile detritus transfer was well-constrained, based on the data from the pulse-chase experiment, but appeared to be of limited importance to the diet of the examined benthic organisms (<1% and 5% of carbon requirements of nematodes and macrofauna respectively). Predation on nematodes was generally low with the exception of sub-surface deposit-feeding polychaetes that obtained 35% of their energy requirements from nematode ingestion. Carnivorous polychaetes also covered 35% of their carbon demand through predation although the preferred prey, in this case, was other macrofaunal animals rather than nematodes. Bacteria and detritus contributed 53% and 12% to the total carbon ingestion of carnivorous polychaetes suggesting a high degree of omnivory among higher consumers in the FSC benthic food web. Overall, this study provided a unique insight into the functioning of a deep-sea benthic community and demonstrated how conventional data can be exploited further when combined with state-of-the-art modelling approaches. 相似文献
14.
15.
Mokievsky V. O. Udalov A. A. Chava A. I. Simakova U. V. Kokarev V. N. Neretina T. V. 《Doklady Earth Sciences》2020,493(2):645-648
Doklady Earth Sciences - The species composition and structure of bottom communities with a predominance of bivalve mollusks of the Portlandia genus, which are widespread on the shelf of the... 相似文献
16.
A.-M. Ertel A. Lupo N. Scheifhacken T. Bodnarchuk O. Manturova T. U. Berendonk T. Petzoldt 《Environmental Earth Sciences》2012,65(5):1459-1473
A pronounced pollution of surface water bodies in the Western Bug River Basin, Ukraine, has been caused by outdated or overloaded wastewater treatment plants, agriculture, industry and coal mining. These pressures have led to a generally poor state of both chemical and microbiological variables creating health risks of various kinds. The state of surface water quality for the Western Bug and five main tributaries was assessed by measuring physical, chemical and microbiological indicators during field campaigns in autumn 2009 and spring 2010. Longitudinal profiles were sampled to identify major sources of pollution and to reveal dominant processes of matter turnover. In addition, the occurrence of antibiotic resistant strains in isolates from stations along the Bug River was investigated. Results clearly underpin the negative impact of the Poltva River as a major source of pollution for the Bug River and further outline an elevated potential health risk from pathogenic bacteria originating from this source. Despite these devastating impacts, a high elimination potential of the Bug River with respect to primary organic loads as well as elimination of pathogenic bacteria was observed particularly at Dobrotvir Reservoir. Further downstream, pollution is kept high because of untreated waste effluents and phytoplankton mass developments due to high phosphorus concentrations. 相似文献
17.
Four fluorotensides which are used mainly industrially are investigated with respect to their removability from waters. Since, in general, fluorotensides are difficult to remove or not at all removable biochemically, the effects of chemical or physicochemical treatment processes are tested. As the results represented in pictures and tables show, different modes of behaviour can be recognized with respect to the respective purification effect for the investigated fluorotensides, partly among them. Flocculation with Al- and Fe-salts as well as chlorination and ozonization show only partial effects. But all the investigated fluorotensides can be adsorptively eliminated by means of powder or granular active charcoal and adsorbent resin Wofatit EA60. 相似文献
18.
19.
Helios-1 and 2 spacecraft allowed a detailed investigation of the radial dependence of the interplanetary magnetic field components between 0.3 and 1 AU. The behaviour of the radial component B
ris in a very good agreement with Parker's model (B
r r
-2) and the azimuthal component B
also shows a radial dependence which is close to theoretical predictions (B
r
-1). Experimental results for the normal component B
and for the field magnitude B are consistent with those from previous investigations. The relative amplitude of the directional fluctuations with periods less than 12 hr is essentially independent of heliocentric distance, while their power decreases approximately as r
–3 without any appreciable difference between higher and lower velocity regimes.Also at Laboratorio Plasma nello Spazio, CNR, Frascati. 相似文献
20.
U. S. Chaubey 《Astrophysics and Space Science》1980,67(1):129-135
The O−C curve of SW Cyg between 1880 and 1977 is presented and discussed. It is found that the orbital period undergoes a
systematic change, becoming greater with time. In addition, a periodic oscillation of amplitude 0
.
d
015 with period of 43.8 years is superimposed on this general trend. It is concluded that the increase in the period is due
to a transfer of mass from the secondary star to the primary and the periodic oscillation is due to the light time effect
of the third body of mass functionf(m)=0.006M
⊙. 相似文献