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991.
作者把辽宁本溪田师傅盆地及凤城赛马—阳盆地的早中侏罗世植物群简称田师傅植物群。该植物群由34属77种植物组成。本文是在已确定的名单基础上,着重讨论植物群的性质.组合序列的划分,与同期植物群的比较及其所属地理区和气候带等。田师傅植物群属我国北方锥叶蕨—拟刺葵植物群范围,可划分出早、中、晚3期组合,它与北票、门头沟等植物群最为相似,同属西伯利亚区的中国北方省,反映出温热潮湿的温带或温带—亚热带气候。 相似文献
992.
A survey of the modern physical setting of Lake El’gygytgyn, northeastern Siberia, is presented here to facilitate interpretation
of a 250,000-year climate record derived from sediment cores from the lake bottom. The lake lies inside a meteorite impact
crater that is approximately 18 km in diameter, with a total watershed area of 293 km2, 110 km2 of which is lake surface. The only surface water entering the lake comes from the approximately 50 streams draining from
within the crater rim; a numbering system for these inlet streams is adopted to facilitate scientific discussion. We created
a digital elevation model for the watershed and used it to create hypsometries, channel networks, and drainage area statistics
for each of the inlet streams. Many of the streams enter shallow lagoons dammed by gravel berms at the lakeshore; these lagoons
may play a significant role in the thermal and biological dynamics of the lake due to their higher water temperatures (>6°C).
The lake itself is approximately 12 km wide and 175 m deep, with a volume of 14.1 km3. Water temperature within a column of water near the center of this oligotrophic, monomictic lake never exceeded 4°C over
a 2.5 year record, though the shallow shelves (<10 m) surrounding the lake can reach 5°C in summer. Though thermally stratified
in winter, the water appears completely mixed shortly after lake ice breakup in July. Mean annual air temperature measured
about 200 m from the lake was −10.3°C in 2002, and an unshielded rain gage there recorded 70 mm of rain in summer of 2002.
End of winter snow water equivalent on the lake was approximately 110 mm in May 2002. Analysis of NCEP reanalysis air temperatures
(1948–2002) reveals that the 8 warmest years and 10 warmest winters have occurred since 1989, with the number of days below
−30°C dropping from a pre-1989 mean of 35 to near 0 in recent years. The crater region is windy as well as cold, with hourly
wind speeds exceeding 13.4 m s−1 (30 mph) typically at least once each month and 17.8 m s−1 (40 mph) in winter months, with only a few calm days per month; wind may also play an important role in controlling the modern
shape of the lake. Numerous lines of evidence suggest that the physical hydrology and limnology of the lake has changed substantially
over the past 3.6 million years, and some of the implications of these changes on paleoclimate reconstructions are discussed.
This is the second in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and
its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献
993.
Jennifer M. Galloway R. Timothy Patterson Christine T. Doherty Helen M. Roe 《Journal of Paleolimnology》2007,38(4):569-588
Pollen and diatoms preserved in the radiocarbon dated sediments of Two Frog Lake in the Seymour-Belize Inlet Complex of the
central mainland coast of British Columbia document postglacial climate change. Two Frog Lake was isolated from the sea prior
to 11,040 ± 50 yr BP (13,030 cal. yr BP) when the climate was cool and dry, and open Pinus contorta woodlands covered the landscape. These woodlands were replaced by a mixed conifer forest ca. 10,200 yr BP (ca. 12,300 cal.
yr BP) when the climate became moister. A relatively dry and warm early Holocene climate allowed Pseudotsuga menziesii to migrate northward to this site where it grew with Picea, Tsuga heterophylla and Alnus. The climate became cooler and moister at ca. 8,000 yr BP (ca. 9,200 cal. yr BP), approximately 500–1,000 years prior to
sites located south of Two Frog Lake and on the Queen Charlotte Islands, but contemporary with sites on the northern mainland
coast of British Columbia and south coastal Alaska. Climate heterogeneity in central coastal British Columbia appears to have
occurred on a synoptic scale, suggesting that atmospheric dynamics linked to a variable Aleutian Low pressure system may have
had an important influence on early Holocene climate change in the Seymour-Belize Inlet Complex. The transition to cooler
and moister conditions facilitated the expansion of Cupressaceae and the establishment of a modern-type coastal temperate
rainforest dominated by Cupressaceae and T. heterophylla. This was associated with progressive lake acidification. Diatom changes independent of vegetation change during the late
Holocene are correlative with the mid-Neoglacial period, when cooler temperatures altered diatom communities. 相似文献
994.
John W. Nielsen-Gammon 《GeoJournal》2007,70(1):21-26
The movie An Inconvenient Truth is a powerful portrayal of global warming and its impacts. The main scientific argument presented in the movie is for the
most part consistent with the weight of scientific evidence, but with some of the main points needing updating, correction,
or qualification. The detailed argument relies almost entirely on past and current evidence and neglects almost all information
that can be gained from computer models, perhaps because such information would be difficult for a lay audience to grasp,
believe, or connect with emotionally. This places an undue weight on current events as signs of ongoing climate change: some
such events are apparently not related at all to climate change, while for other specific events the role of global warming
is difficult or impossible to establish. 相似文献
995.
Kuo-Chin Hsu Chung-Ho Wang Kuan-Chih Chen Chien-Tai Chen Kai-Wei Ma 《Hydrogeology Journal》2007,15(5):903-913
The Pingtung Plain is one of the most important groundwater-resource areas in southwestern Taiwan. The overexploitation of
groundwater in the last two decades has led to serious deterioration in the quantity and quality of groundwater resources
in this area. Furthermore, the manifestation of climate change tends to induce the instability of surface-water resources
and strengthen the importance of the groundwater resources. Southwestern Taiwan in particular shows decreasing tendencies
in both the annual amount of precipitation and annual precipitation days. To effectively manage the groundwater resources
of the Pingtung Plain, a numerical modeling approach is adopted to investigate the response of the groundwater system to climate
variability. A hydrogeological model is constructed based on the information from geology, hydrogeology, and geochemistry.
Applying the linear regression model of precipitation to the next two decades, the modeling result shows that the lowering
water level in the proximal fan raises an alarm regarding the decrease of available groundwater in the stress of climate change,
and the enlargement of the low-groundwater-level area on the coast signals the deterioration of water quantity and quality
in the future. Suitable strategies for water-resource management in response to hydrological impacts of future climatic change
are imperative.
Resumen La llanura Pingtung constituye uno de los recursos de aguas subterráneas más importantes en el Suroeste de Taiwan. La sobreexplotación de las aguas subterráneas en las dos últimas décadas ha dado lugar a un serio deterioro de la calidad y la cantidad de los recursos subterráneos en esta área. En particular el Suroeste de Taiwan muestra una tendencia decreciente en las cantidades de precipitación y en los días anuales de lluvia. Para gestionar de forma efectiva los recursos subterráneos en la Llanura Pingtung, se ha utilizado un modelo numérico aproximado para investigar la respuesta de las aguas subterráneas a la variabilidad climática. Un modelo hidrogeológico se construye a partir de la información geológica, hidrogeológica y geoquímica. Aplicando el modelo de regresión linear de la precipitación para las próximas dos décadas, el modelo resultante muestra que el descenso de los niveles de agua en el abanico proximal es alarmante, observándose el descenso del agua subterránea disponible en la presión del cambio climático, y el crecimiento del área de descensos de niveles de agua subterránea en la costa apunta a un deterioro de la cantidad y calidad del agua subterránea en el futuro. Se imponen pues, estrategias apropiadas para la gestión de los recursos hídricos en respuesta a los impactos hidrológicos del futuro cambio climático.
Résumé La plaine de Pingtung est l’une des plus importantes zones de ressource en eau souterraine du Sud-Ouest de Taiwan. La surexploitation de l’eau souterraine durant les deux dernières décennies a conduit à une sérieuse détérioration de la quantité et de la qualité des ressources en eau souterraine dans cette zone. De plus, la manifestation des changements climatiques tend à induire une instabilité des ressources en eau souterraine et renforce l’importance des ressources en eau souterraine. Le Sud-Ouest de Taiwan montre, en particulier, des précipitations annuelles et des nombres annuels de jour de pluie à la baisse. Pour gérer efficacement les ressources en eau souterraine de la Plaine de Pingtung, une approche par modélisation numérique est adoptée pour étudier la réponse du système hydrogéologique aux variabilités climatiques. La construction du modèle hydrogéologique est basée sur les informations géologiques, hydrogéologiques et géochimiques. En appliquant le modèle de régression linéaire aux précipitations pour les deux prochaines décades, le résultat de la modélisation montre que la baisse du niveau d’eau atteint un état alarmant au regard de la décroissance des eaux souterraines disponibles et la contrainte du changement climatique, tandis que l’extension de la zone de niveau bas des eaux souterraines à la cote indique une détérioration de la quantité et de la qualité de l’eau dans le futur. Des stratégies convenables pour la gestion des ressources en eau souterraine en réponse aux impacts hydrologiques de futurs changements climatiques sont impératifs.相似文献
996.
Roy W. Spencer 《GeoJournal》2007,70(1):11-14
Al Gore’s movie An Inconvenient Truth gives a variety of unusually biased interpretations of the state of climate science and global warming theory. These cover
a wide range of natural events and processes which could potentially be impacted by global warming, but which the movie misrepresents
as clear examples of the human influence on climate. A few examples include the mixing up of cause and effect in his graphical
portrayal of temperature and carbon dioxide variations over hundreds of thousands of years; the repeated depiction of ice
calving from glaciers as a sign of global warming; the implication that Hurricane Katrina was the fault of humans; and the
particularly extreme view that the Greenland ice sheet will melt, flooding coastal cities worldwide. Ultimately, all of these
are related to the widespread perception that scientists have uniquely tied global warming to anthropogenic greenhouse gas
emissions. The real inconvenient truth is that science has no idea how much of recent warming is natural versus the result
of human activities. 相似文献
997.
Stephen Vermette 《Natural Hazards》2007,42(1):91-103
The tropical storm database used in this study was obtained from the National Oceanic and Atmospheric Administration’s (NOAA)
Coastal Service Center, using the Historical Hurricane Tracks tool. Queries were used to determine the number of storms of
tropical origin that have impacted the State and each of its counties. A total of 76 storms of tropical origin passed over
New York State between 1851 and 2005. Of these storms, 14 were classified as hurricanes. The remaining hurricanes passed over
New York State as weaker or modified systems—27 tropical storms, 7 tropical depressions, and 28 extratropical storms (ET).
Long Island experiences a disproportionate number of hurricanes and tropical storms. The average frequency of hurricanes and
storms of tropical origin (all types) is one in every 11 years and one in every 2 years, respectively. September is the month
of greatest frequency for storms of tropical origin, although the storms of greatest intensity tend to arrive later in the
hurricane season and follow different poleward tracks. While El Nino Southern Oscillation (ENSO) cycles appear to show some
influence, the frequency and intensity of storms of tropical origin appear to follow a multidecadal cycle. Storm activity
was greatest in both the late 19th and 20th centuries. During periods of increased storm frequency and intensity storms reached
New York State at progressively later dates. While the number and timing of storms of tropical origin is likely to increase,
this increase appears to be attributed to a multidecadal cycle, as opposed to a trend in global warming. 相似文献
998.
Fine-grained lacustrine, riverine and ash-fall sediments of the Shooting Iron Formation, whose late Pliocene age is established by Blancan gastropods and vertebrates, yield a pollen flora that is essentially similar in composition to the modern pollen rain in the Jackson Hole area. The Pliocene assemblage suggests a climate like that of the Jackson valley and foothills today. These spectra also resemble a Pliocene pollen flora from Yellowstone Park dated at ∼ 2.02 Ma. However, the underlying Miocene Teewinot sediments differ by containing pollen of four exotic deciduous hardwoods (Tertiary relicts) that suggest a summer-moist climate, unlike that of today. The Shooting Iron sediments lie with an angular unconformity on and above the Miocene lake sediments of the Teewinot Formation. Both of these deposits probably preceded the main uplift of the Teton Range based on the absence of Precambrian clasts in the Tertiary valley deposits. Because the Pliocene floras were modern in aspect, a Plio-Pleistocene transition would be floristically imperceptible here. The sequence denotes a protracted period of relative stability of climate during Teewinot time, and a shift in vegetational state (summer-wet trees drop out) sometime between the latest Miocene and latest Pliocene. The Pliocene spectra suggest a dry, cooler climate toward the end of Shooting Iron time. 相似文献
999.
Suzette G. A. Flantua John H. van Boxel Henry Hooghiemstra John van Smaalen 《Climate Dynamics》2007,29(7-8):697-712
Climate changes affect the abundance, geographic extent, and floral composition of vegetation, which are reflected in the
pollen rain. Sediment cores taken from lakes and peat bogs can be analysed for their pollen content. The fossil pollen records
provide information on the temporal changes in climate and palaeo-environments. Although the complexity of the variables influencing
vegetation distribution requires a multi-dimensional approach, only a few research projects have used GIS to analyse pollen
data. This paper presents a new approach to palynological data analysis by combining GIS and spatial modelling. Eastern Colombia
was chosen as a study area owing to the migration of the forest–savanna boundary since the last glacial maximum, and the availability
of pollen records. Logistic regression has been used to identify the climatic variables that determine the distribution of
savanna and forest in eastern Colombia. These variables were used to create a predictive land-cover model, which was subsequently
implemented into a GIS to perform spatial analysis on the results. The palynological data from the study area were incorporated
into the GIS. Reconstructed maps of past vegetation distribution by interpolation showed a new approach of regional multi-site
data synthesis related to climatic parameters. The logistic regression model resulted in a map with 85.7% predictive accuracy,
which is considered useful for the reconstruction of future and past land-cover distributions. The suitability of palynological
GIS application depends on the number of pollen sites, the distribution of the pollen sites over the area of interest, and
the degree of overlap of the age ranges of the pollen records. 相似文献
1000.
Detection and extraction of quasi-oscillatory dynamical modes from instrumental records of geophysical data became a useful tool in analyzing variability of observed phenomena reflected in complex, multivariate geophysical signals. Using the extension of the Monte Carlo singular system analysis (MC SSA), based on evaluating and testing regularity of dynamics of the SSA modes against the colored noise null hypothesis, we demonstrate detection of oscillatory modes with period of about 96 months in the long-term records of aa index as well as in the records of surface air temperature from several mid-latitude European locations and in the North Atlantic Oscillation index. 相似文献