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441.
Burkhard A. Hense Gabriele F. Severin Gerd Pfister Gerhard Welzl Wolfgang Jaser Karl‐Werner Schramm 《洁净——土壤、空气、水》2005,33(1):27-37
Microcosm tests were conducted to investigate the effects of the estrogenic substances nonylphenol (NP) and 17α‐ethinylestradiol (EE) on aquatic ecosystems. Maximum concentrations of 9 to 120 μg L—1 NP resp. 49 to 724 ng L—1 EE were induced by controlled release. The controlled release method allows the establishment of a continuous concentration course. The microcosms proved to run robustly with abiotic conditions close to natural. They developed biocenosis with similar characteristics as in natural ecosystems and, considering their given level of complexity, they can be used to describe possible risks for the environment. Both tested chemicals unveiled the potential to affect the plankton communities in the tested concentration range. NP exposure caused a reduction of Cladocera and Copepoda abundances and disturbed the phytoplankton structure. A NOECcommunity of 30 μg L—1 was calculated. In the first EE study, a flood in the lake where the microcosm water was collected caused additional stress and thereby a high variability, both between the microcosms and in each microcosm over time. Probably therefore the only effect found was a reduction of Copepoda abundance. In a second EE study Cladocera and Copepoda abundances were reduced, from which the phytoplankton benefited. Although a final interpretation is difficult for results of microcosm tests, there are indications that the found effects of EE and perhaps also NP may be caused at least partially by endocrine disruptive activity. 相似文献
442.
The Kreuznach Sandstone belongs to the youngest Rotliegend sediments in the Bad Kreuznach area, northeastern Nahe Syncline. Because of its large-scale crossbedding — the thickness of sets of cross-strata can exceed — it has been interpreted as a typical aeolian dune sandstone, and has been placed to the Upper Rotliegend/ Zechstein boundary. To find out the origin of the Kreuznach Sandstone, it was examined by various sedimentological methods: petrography, granulometry, bedding and frame of crossbedding, sedimentary structures, facies associations, and quartz grain morphoscopy by scanning electron microscope. Although most of the results do not permit a clear decision between aeolian and fluvial origin, there are some arguments speaking well for fluvial sedimentation of the Kreuznach Sandstone. The very large-scale crossbedding — which is uncommon for river sands — is the sedimentological projection of the tectonic rise of the Kreuznach Rhyolitic Massif. Between the latter and the alluvial fans at the southern edge of the Hunsrück uplift the floods of an (ephemeral ?) stream coming from E/SE were narrowed. Thus water depth, stream velocity and concentration of sands grew rapidly so that megaripples, dunes and giant ripples could be built up. In the East before and in the West behind this narrow pass (as to stream direction) the stream spread out over a large plain, as a system of braided channels. Sand- and mudstones with laminated and small-scale ripple bedding were deposited there instead of the Kreuznach Sandstone. 相似文献
443.
Wildfires in the sub‐alpine belt of the Austrian Limestone Alps sometimes cause severe vegetation and soil destruction with increased danger of secondary natural hazards such as avalanches and debris flows. Some of the affected areas remain degraded to rocky slopes even decades after the fire, raising the question as to whether the ecosystems will ever be able to recover. The mean fire interval, the duration of recovery and the role of geomorphic processes for vegetation regeneration are so far unknown. These questions were tackled in a broad research approach including investigation of historical archives to determine the frequency of historical wildfires, mapping vegetation regeneration on 20 slopes of different post‐fire ages, and soil erosion measurements on two slopes. To date, > 450 historical wildfires have been located in the study area. The mean fire interval per square kilometre is c. 750 years, but can be as low as 200–500 years on south‐facing slopes. Vegetation regeneration takes an extremely long time under unfavourable conditions; the typical window of disturbance is between 50 and 500 years, which is far longer than in any other wildfire study known to us. Soil erosion constantly increases in the years after the fires and the elevated intensity can be maintained for decades. A two‐part vegetation regeneration model is proposed depending upon the degree of soil loss. In the case of moderate soil erosion, spreading grassland communities can slow down shrub re‐colonization. In contrast, after severe soil destruction the slopes may remain degraded for a century or longer, before rather rapid regeneration occurs. The reasons are not fully understood but are probably governed by geomorphic process intensity. The interdependence of vegetation regeneration and geomorphic processes is a paradigm of ecology–geomorphology interaction, and is a unique example of a very long‐lasting disturbance response caused by wildfire in a non‐resilient ecosystem. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
444.
Karl Krejci-Graf 《International Journal of Earth Sciences》1962,51(1):73-122
Zusammenfassung Die Bildung der Sockel der makaronesischen Inseln erfolgte durch vulkanotektonischen Zusammenschub geschichteter Vulkan-Gesteine (+ Sedimente auf Maio), die dabei steil aufgerichtet wurden und (auf den Inseln mit heute anstehendem Tertiär) bis in den Bereich abtragender Kräfte (der Brandung) gelangten. Die Hebung ging weiter. Bald lagerten sich randlich um die Inselkerne tertiäre Sedimente (Tuffite, Kalke) ab, die ihrerseits wieder gehoben wurden; und zwar en bloc, wo der Vulkanismus erloschen war; zerstückelt, wo er weiter dauerte. - Ursachen der Vertikalbewegungen sind vulkanische Intrusionen.Von den Canaren werden mehrere Hebungen und Senkungen angegeben, auf den portugiesischen Makaronesen sind nur Hebungen mit Sicherheit nachweisbar.Vertikalbewegungen des Festen und eustatische Bewegungen des Meeres-Spiegels interferieren; es ist daher nicht möglich, Strand-Linien nur nach ihrer Höhe über dem Meeres-Spiegel zu korrelieren.6: N. Jahrb. Min. Abh.96, 31–47. 1961. 相似文献
445.
446.
We have reanalyzed the data used by Bessel, von Struve, and Henderson in the 1830s to measure the first parallax distances to stars. We can generally reproduce their results, although we find that von Struve and Henderson have underestimated some of their measurement errors, leading to optimistic parallax uncertainties. We find that temperature corrections for Bessel's measured positions are larger than anticipated, explaining some systematics apparent in his data. It has long been a mystery as to why von Struve first announced a parallax for Vega of 0.″125 only to later revise it to double that value using more data. We resolve this mystery by finding that von Struve's early result used two dimensions of position data, which independently give significantly different parallaxes but, when combined, only fortuitously give the correct result. With later data, von Struve excluded the “problematic” dimension, leading to the larger parallax value. Allowing for likely temperature corrections and using his data from both dimensions reduce von Struve's parallax for Vega to a value consistent with the correct value. 相似文献
447.
Karl -Heinz Nitsch 《Contributions to Mineralogy and Petrology》1971,30(3):240-260
This investigation was undertaken to find the typical conditions for the formation of low-grade metamorphic rocks in which prehnite and/or pumpellyite (± actinolite, chlorite, epidote, and quartz) occur as characteristic minerals. In the p, t diagram the slope of the equilibrium curve prehnite + chlorite + H2O=pumpellyite + actinolite + quartz is negative; the slope of the equilibrium curve pumpellyite + chlorite + quartz=epidote + actinolite + H2O is positive. The point of intersection of the two equilibrium curves is an invariant point. The relative positions of the six equilibrium curves surrounding the invariant point were found by applying Schreinemakers's analysis.Experimental results show that the paragenesis prehnite-pumpellyite-chlorite-quartz is stable at 2 kb up to 345±20 °C, and at 7 Kb up to 260±20 °C. The paragenesis actinolitechlorite-pumpellyite-quartz occurs only at pressures greater than 2.5±1 kb. It is stable at 7 kb in the strongly pressure-dependent temperature range 260±20 °C to 370±20 °C. The paragenesis actinolite-chlorite-epidote-quartz, typical of the greenschist facies, may occur at pressures of 2–3 kb at temperatures of at least 350±20 °C. This temperature limit is only slightly changed with increasing pressure.
Herrn Prof. Dr. H. G. F. Winkler möchte ich an dieser Stelle für die kritische Durchsicht des Manuskriptes sowie manche wertvolle Diskussion danken. Ebenso gilt mein Dank Herrn Dr. B. Storre und Herrn Doz. Dr. P. Metz für anregende Diskussionen. Herr Dr. P. Süße besorgte die Übersetzung des Abstracts.
Außerdem sei den Angestellten der Mineralogischen Anstalten und des Mineralogisch-Petrologischen Instituts gedankt, die zu dieser Arbeit einen Beitrag geleistet haben. Die Deutsche Forschungsgemeinschaft förderte durch apparative Unterstützung wesentlich den experimentellen Teil der vorliegenden Publikation. 相似文献
Herrn Prof. Dr. H. G. F. Winkler möchte ich an dieser Stelle für die kritische Durchsicht des Manuskriptes sowie manche wertvolle Diskussion danken. Ebenso gilt mein Dank Herrn Dr. B. Storre und Herrn Doz. Dr. P. Metz für anregende Diskussionen. Herr Dr. P. Süße besorgte die Übersetzung des Abstracts.
Außerdem sei den Angestellten der Mineralogischen Anstalten und des Mineralogisch-Petrologischen Instituts gedankt, die zu dieser Arbeit einen Beitrag geleistet haben. Die Deutsche Forschungsgemeinschaft förderte durch apparative Unterstützung wesentlich den experimentellen Teil der vorliegenden Publikation. 相似文献
448.
Paleoparasitology has contributed to resolving the debate about the peopling of the Americas and determining the antiquity of human parasite infection. Hookworm (Ancylostomidae) and whipworm (Trichuris trichiura) and other exclusive human intestinal parasites have been recorded in pre-Columbian America. These parasite species originated in pre-hominids and have accompanied humans across continents when people went out of Africa. However, for those human populations that crossed the Bering Land Bridge from Siberia to Alaska, cold climate conditions hampered parasite transmission. Alternative migration routes have been proposed to explain the presence of these parasites in pre-Columbian populations in the Americas. Other parasites were established in the New World long before humans entered the American continents.One such malady is Chagas disease. Chagas disease, caused by Trypanosoma cruzi, offers an example of how animals and humans have interacted in the past. Classical theory points to the origin and dispersion of human T. cruzi infection among Andean populations, starting with sedentary habits and animal domestication 6000 years ago. However, recent PCR results in mummified bodies outside the Andean region have challenged this theory. Pre-Columbian Brazilian mummies were found positive for T. cruzi infection, raising an alternative hypothesis on the antiquity of Chagas disease in the Americas. Paleoparasitology is a new tool to study past events, shedding light on human and other animal behavior, migration routes, diet, and other aspects of host–parasite environment evolution. 相似文献
449.
450.
Roberto De Propris Warrick J. Couch Matthew Colless Gavin B. Dalton Chris Collins Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Nicholas Cross Kathryn Deeley Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Stephen Moody Peder Norberg John A. Peacock Will Percival Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,329(1):87-101
We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information is used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10 per cent, whereas the APM catalogue suffers only 5 per cent contamination. If we use the original catalogue centroids, the level of contamination rises to approximately 15 per cent for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at that may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive a space density of clusters of This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum. 相似文献