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181.
The Estuarine Quality Paradox, Environmental Homeostasis and the difficulty of detecting anthropogenic stress in naturally stressed areas 总被引:2,自引:0,他引:2
Estuaries have long been regarded as environmentally naturally stressed areas because of the high degree of variability in their physico-chemical characteristics, for example oxygen, temperature and salinity in the water column and bed sediment dynamics. However, their biota is well-adapted to cope with that stress and so the areas may be regarded as resilient because of that inherent variability; their ability to absorb stress without adverse effects is regarded here as Environmental Homeostasis. Hence these areas may only be regarded as stressful for marine or freshwater-adapted organisms and that for estuarine organisms this environmental stress is regarded as a subsidy whereby they successfully capitalise on the stressful conditions. In addition, using examples of the estuarine fauna and flora, this article indicates that the characteristics of natural stress in estuaries are similar to those for anthropogenic stress. An over-reliance on ecosystem structural features, such as diversity, in quality indicators therefore makes the detection of the anthropogenic stress more difficult. This difficulty is termed the Estuarine Quality Paradox. Because of these difficulties, the article argues that functional characteristics either as well as or rather than structural ones should be used in detecting environmental perturbations in estuaries. 相似文献
182.
David A. Wright Eileen M. Setzler-Hamilton John A. Magee Victor S. Kennedy Stephen P. McIninch 《Estuaries and Coasts》1996,19(3):619-628
We reared larval zebra mussels,Dreissena polymorpha, and quagga mussels,D. bugensis, through and beyond metamorphosis (settlement) at salinities of 0–8‰. Juvenile zebra mussels gradually acclimated to 8‰ and 10‰ have been reared at these salinities for over 8 mo. Tolerance to both higher temperatures and higher salinities increases with larval age in both species (though zebra mussel embryos and larvae have a greater degree of salinity tolerance than quagga mussel embryos and larvae). Thus, only 6% of 3-day-old zebra mussel veligers survived after exposure to 4‰ for 8 additional days, whereas there was 22% survival of veligers placed in 4‰ at day 13 and grown to settlement 11 d later. Zebra mussel pediveligers, acclimated to increasing salinity in 2‰ increments beginning at day 23, continued to survive and grow in 8‰ after 5-mo exposure, though the growth rates of these juveniles were significantly less than those of juveniles reared in lower salinities. Quagga mussels did not metamorphose and settle as quickly as zebra mussel pediveligers. No quagga mussel pediveligers had settled before exposure to artificial fresh water (AFW), 2‰ 4‰, 6‰, and 8‰ on day 30. Percent settlement of these quagga mussel juveniles (based on 100% survival at the start of experiments on day 30) was 90% in AFW, 67% at 2‰, 69% at 4‰, 46% at 6‰, and 0.1% at 8‰. 相似文献
183.
Regional to detailed geochemical mapping of the Kariisk ore district, eastern Trans-Baikal region, Russia 总被引:1,自引:0,他引:1
The Kariisk ore district is situated in a dome-ring complex formed during late Mesozoic tectono-magmatic activity. The district comprises magmatic to post-magmatic vein-type mineralizations, which developed during four stages characterized by different mineral parageneses: (1) quartz-pyrite-tourmaline; (2) quartz-actinolite-magnetite; (3) quartz-arsenopyrite; and (4) quartz-carbonate-poly metallic. Geochemical surveys at regional to detailed scales involved ca. 12 000 rock samples which were analyzed for 40 elements including Au and associated elements Bi, W, Ag, B, As, Mo, Cu, Pb, Sn, and Zn. The results are presented as geochemical maps illustrating the distribution of anomalous gold and multi-element associations. The geochemically anomalous area shows a finger-like pattern radiating from the core of the ring complex and has a concentric zoning of element associations outwards from the margin of the core: W-Mo, Bi-Ag-B, Au-As-Cu-Pb, and B-Ag-Zn. These features are interpreted to reflect that the mineralising process induced by heat from the granitoid magma in the core of the complex occurred in a number of separate pulses. 相似文献
184.
Efstratios Stylianidis Daniela Poli Martin Hofer Armin Gruen Victor Sanchez Martin 《International Journal of Digital Earth》2020,13(8):854-885
ABSTRACT A 3D forest monitoring system, called FORSAT (a satellite very high resolution image processing platform for forest assessment), was developed for the extraction of 3D geometric forest information from very high resolution (VHR) satellite imagery and the automatic 3D change detection. FORSAT is composed of two complementary tasks: (1) the geometric and radiometric processing of satellite optical imagery and digital surface model (DSM) reconstruction by using a precise and robust image matching approach specially designed for VHR satellite imagery, (2) 3D surface comparison for change detection. It allows the users to import DSMs, align them using an advanced 3D surface matching approach and calculate the 3D differences and volume changes (together with precision values) between epochs. FORSAT is a single source and flexible forest information solution, allowing expert and non-expert remote sensing users to monitor forests in three and four (time) dimensions. The geometric resolution and thematic content of VHR optical imagery are sufficient for many forest information needs such as deforestation, clear-cut and fire severity mapping. The capacity and benefits of FORSAT, as a forest information system contributing to the sustainable forest management, have been tested and validated in case studies located in Austria, Switzerland and Spain. 相似文献
185.
Summary It is proposed that liquid water be recovered from the atmosphere through a partial duplication of natural moist convection processes within an experimental piece of equipment in which certain of the actions could be protected and enhanced. No source of driving energy other than the automatic release of latent heat of condensing water vapor is envisioned. Various problems of a scientific and engineering nature that arise are enumerated and discussed in a preliminary fashion. 相似文献
186.
The impact of predation by juvenile marbled gobies,Pomatoschistus marmoratus, on the meiobenthic harpacticoid copepodCanuella perplexa was investigated at a subtidal station located in a shallow-water, brackish embayment of the Po River delta, northern Italy, in summer and fall 1978. In august, predation mainly centered on adults, with a very large number of prey for each predator; the energy supplied by the harpacticoid is high enough to sustain, almost entirely, the gobies’ daily energy requirement. The situation is different in September and October, when the adult copepod population declines dramatically and predation is shifted to less energy-providing copepodites and marbled gobies sensibly widen their prey spectrum.C. perplexa showed alterations of biological parameters, such as clutch size and average brood size, to cope with such a heavy predation pressure. 相似文献
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190.
Victor Fung Shuen Sit 《Geoforum》1981,12(1):93-97
This short article outlines the objectives, organization, research frame and content areas of a comparative urbanization project which will start in 1981. The project involves a total of nine national teams each of which is composed of three or more experts from the fields of urban geography, city and regional planning, demography, development economics and other related disciplines. One unique feature of the project is that each of the countries covered will be researched on by its own local researchers. And, the organizer tries to get at least one government official involved, in his personal capacity, as a team member, to get better insight and interpretation of official policies and objectives regarding urbanization. The responsible persons of the national teams and the time table of the project have also been included in this article. 相似文献