全文获取类型
收费全文 | 1418篇 |
免费 | 81篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 51篇 |
大气科学 | 60篇 |
地球物理 | 444篇 |
地质学 | 537篇 |
海洋学 | 125篇 |
天文学 | 196篇 |
综合类 | 8篇 |
自然地理 | 92篇 |
出版年
2023年 | 6篇 |
2022年 | 17篇 |
2021年 | 32篇 |
2020年 | 39篇 |
2019年 | 35篇 |
2018年 | 62篇 |
2017年 | 70篇 |
2016年 | 93篇 |
2015年 | 67篇 |
2014年 | 78篇 |
2013年 | 84篇 |
2012年 | 77篇 |
2011年 | 104篇 |
2010年 | 64篇 |
2009年 | 91篇 |
2008年 | 89篇 |
2007年 | 39篇 |
2006年 | 42篇 |
2005年 | 32篇 |
2004年 | 32篇 |
2003年 | 33篇 |
2002年 | 27篇 |
2001年 | 19篇 |
2000年 | 22篇 |
1999年 | 25篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 16篇 |
1995年 | 17篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1952年 | 9篇 |
1951年 | 4篇 |
1950年 | 4篇 |
1948年 | 8篇 |
1939年 | 6篇 |
排序方式: 共有1513条查询结果,搜索用时 15 毫秒
951.
952.
Temporal and spatial variability in the Guadalquivir estuary: a challenge for real-time telemetry 总被引:1,自引:1,他引:0
Gabriel Navarro Francisco Javier Gutiérrez Manuel Díez-Minguito Miguel Angel Losada Javier Ruiz 《Ocean Dynamics》2011,61(6):753-765
Meteorological, hydrological, and hydrodynamic data for 3 years (2008–2010) have been used to document and explain the temporal
and spatial variability of the physical–biogeochemical interactions in the Guadalquivir River Estuary. A real-time, remote
monitoring network has been deployed along the course of the river between its mouth and Seville to study a broad range of
temporal scales (semidiurnal, diurnal, fortnightly, and seasonal). This network consists of eight hydrological monitoring
stations capable of measuring temperature, conductivity, dissolved oxygen, turbidity, and chlorophyll fluorescence at four
depths. In addition, six stations have been deployed to study hydrodynamics, obtaining 20-cell water column current profiles,
and there is a meteorological station at the river mouth providing data for understanding atmospheric interactions. Completing
this data-gathering network, there are several moorings (tide gauges, current/wave sensors, and a thermistor chain) deployed
in the estuary and river mouth. Various sources of physical forcing, such as wind, tide-associated currents, and river discharge,
are responsible for the particular temporal and spatial patterns of turbidity and salinity found in the estuary. These variables
force the distribution of biogeochemical variables, such as dissolved oxygen and chlorophyll fluorescence. In particular,
episodes of elevated turbidity (when suspended particle matter concentration >3,000 mg/l) have been detected by the network,
together with episodes of declining values of salinity and dissolved oxygen. All these patterns are related to river discharge
and tidal dynamics (spring/neap and high/low tide). 相似文献
953.
The survey of climatic drought trend in Iran 总被引:5,自引:3,他引:2
Hossein Bari Abarghouei Mohammad Amin Asadi Zarch Mohammad Taghi Dastorani Mohammad Reza Kousari Mehdi Safari Zarch 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(6):851-863
Drought is one of the most important natural hazards in Iran. Therefore, drought monitoring has become a point of concern
for most of the researchers. In the present study, the changes and trend of drought was surveyed, under the current global
climate changes, by non parametric Mann–Kendall statistical test for 42 synoptic stations at different places of Iran. Standardized
Precipitation Index (SPI) was calculated to recognize the drought condition at different time scales (3, 6, 9, 12, 18 and
24 months’ time series) for analyzing the drought trend in the recent 30 years. The obtained results have indicated a significant
negative trend of drought in many parts of Iran, especially the South-East, West and South-West regions of the country. According
to the results, although some parts of Iran such as North (around the Caspian Sea) and Northeast show no significant trend
but in other parts of country, the severity of drought has increased during the last 30 years. 相似文献
954.
Axel Horst Jürgen Mahlknecht Miguel Angel López-Zavala Bernhard Mayer 《Environmental Earth Sciences》2011,64(7):1931-1941
Chemical compositions and stable isotope ratios of water and sulphate were used to characterise sources and processes responsible
for elevated concentrations of sulphate and other constituents in groundwater from aquifers at Colima State along Mexico’s
Pacific Coast. The δ18O and δ2H values of the groundwater were similar to those of precipitation indicating a meteoric origin, and recharge processes are
relatively uniform in large parts of the study area with only slight local evaporation effects. δ34Ssulphate and δ18Osulphate analyses indicated that high sulphate concentrations of up to 1,480 mg/l are mainly due to dissolution of evaporites and
volcanic exhalations. Chloride is largely related to sources other than seawater. The Marabasco sub basin is affected by anthropogenic
contamination through manganese and iron ore mining activities. The obtained knowledge regarding sources and areas of contamination
will be essential for the development and design of a water quality monitoring program in the study area. 相似文献
955.
Mario?UchimiyaEmail author Hideki?Fukuda Shigeto?Nishino Takashi?Kikuchi Hiroshi?Ogawa Toshi?Nagata 《Journal of Oceanography》2011,67(5):589-599
This study examined possible environmental factors that affect prokaryote variables in surface waters (upper 100 m of water
column) in the Canada Basin, western Arctic Ocean. We collected data on prokaryote abundance and heterotrophic production
([3H]leucine incorporation) at eight stations deployed along a slope-to-offshore transect during September 2009. Prokaryote production
and growth tended to increase with increasing chlorophyll a (Chl. a) and temperature and with decreasing salinity. The combination of Chl. a, temperature, and salinity accounted for a large fraction (74%) of the variability in prokaryote production, with the highest
contribution made by Chl. a (r
2 = 0.56), followed by salinity (r
2 = 0.14) and temperature (r
2 = 0.03). Similarly, the variability in prokaryote growth rate was largely accounted for by the combination of the three environmental
variables (overall r
2 of 0.64), with Chl. a making the largest contribution to variability (r
2 = 0.33), followed by salinity (r
2 = 0.27) and temperature (r
2 = 0.05). These data are consistent with the notion that organic matter supply associated with freshwater inputs to surface
layers can result in enhanced prokaryote production and growth in the Canada Basin. Our results provide insights into the
regulation of the microbial loop in the Canada Basin where freshening has been proceeding rapidly due to increasing river
discharge and sea-ice melting. 相似文献
956.
Elisabet Beamud Josep Anton Muñoz Paul G. Fitzgerald Suzanne L. Baldwin Miguel Garcés Lluis Cabrera James R. Metcalf 《Basin Research》2011,23(3):309-331
The syntectonic continental conglomerates of the South‐Central Pyrenees record the late stages of thin‐skinned transport of the South‐Pyrenean Central Units and the onset of exhumation of the Pyrenean Axial Zone (AZ) in the core of the orogen. New magnetostratigraphic data of these syntectonic continental conglomerates have established their age as Late Lutetian to Late Oligocene. The data reveal that these materials were deposited during intense periods of tectonic activity of the Pyrenean chain and not during the cessation of the deformation as considered previously. The magnetostratigraphic ages have been combined with new detrital apatite fission track (AFT) thermochronology from AZ‐derived granite cobbles within the syntectonic conglomerates. Distribution of the granitic cobbles with different AFT ages and track lengths combined with their depositional ages reveal information on the timing and rate of episodes of exhumation in the orogen. Some AFT ages are considerably older than the AFT ages of the outcropping AZ granitic massifs, indicating erosion from higher crustal levels within the massifs than presently exposed or from completely eroded plutons. Inverse thermal modelling reveals two well‐defined periods of rapid cooling in the hinterland at ca. 50–40 and ca. 30–25 Ma, with another poorly defined cooling episode at ca. 70–60 Ma. The lowest stratigraphic samples experienced postburial annealing caused by the deposition of younger syntectonic sediments during progressive burial of the south Pyrenean thrust and fold belt. Moreover, samples from the deeper stratigraphic levels also reveal postorogenic cooling during the Late Miocene as a response to the excavation of the Ebro River towards the Mediterranean Sea. Our data strongly support previous ideas about the burial of the South Pyrenean fold and thrust belt by Late Palaeogene syntectonic conglomerates and their subsequent re‐excavation and are consistent with other thermochronological data and thermal modelling from the interior part of the orogen. 相似文献
957.
Juan Pablo Corella Ana Moreno Mario Morellón Valentí Rull Santiago Giralt María Teresa Rico Ana Pérez-Sanz Blas Lorenzo Valero-Garcés 《Journal of Paleolimnology》2011,46(3):351-367
Sedimentological, mineralogical and compositional analyses performed on short gravity cores and long Kullenberg cores from
meromictic Montcortès Lake (Pre-Pyrenean Range, NE Spain) reveal large depositional changes during the last 6,000 cal years.
The limnological characteristics of this karstic lake, including its meromictic nature, relatively high surface area/depth
ratio (surface area ~0.1 km2; z
max = 30 m), and steep margins, facilitated deposition and preservation of finely laminated facies, punctuated by clastic layers
corresponding to turbidite events. The robust age model is based on 17 AMS 14C dates. Slope instability caused large gravitational deposits during the middle Holocene, prior to 6 ka BP, and in the late
Holocene, prior to 1,600 and 1,000 cal yr BP). Relatively shallower lake conditions prevailed during the middle Holocene (6,000–3,500 cal years
BP). Afterwards, deeper environments dominated, with deposition of varves containing preserved calcite laminae. Increased
carbonate production and lower clastic input occurred during the Iberian-Roman Period, the Little Ice Age, and the twentieth
century. Although modulated by climate variability, changes in sediment delivery to the lake reflect modifications of agricultural
practices and population pressure in the watershed. Two episodes of higher clastic input to the lake have been identified:
1) 690–1460 AD, coinciding with an increase in farming activity in the area and the Medieval Climate Anomaly, and 2) 1770–1950 AD,
including the last phase of the Little Ice Age and the maximum human occupation in late nineteenth and early twentieth centuries. 相似文献
958.
Michael M. McGlue Aguinaldo Silva Fabrício A. Corradini Hiran Zani Mark A. Trees Geoffrey S. Ellis Mauro Parolin Peter W. Swarzenski Andrew S. Cohen Mario L. Assine 《Journal of Paleolimnology》2011,46(2):273-289
Sediment records from floodplain lakes have a large and commonly untapped potential for inferring wetland response to global
change. The Brazilian Pantanal is a vast, seasonally inundated savanna floodplain system controlled by the flood pulse of
the Upper Paraguay River. Little is known, however, about how floodplain lakes within the Pantanal act as sedimentary basins,
or what influence hydroclimatic variables exert on limnogeological processes. This knowledge gap was addressed through an
actualistic analysis of three large, shallow (<5 m) floodplain lakes in the western Pantanal: Lagoa Gaíva, Lagoa Mandioré
and Baia Vermelha. The lakes are dilute (CO3
2− > Si4+ > Ca2+), mildly alkaline, freshwater systems, the chemistries and morphometrics of which evolve with seasonal flooding. Lake sills
are bathymetric shoals marked by siliciclastic fans and marsh vegetation. Flows at the sills likely undergo seasonal reversals
with the changing stage of the Upper Paraguay River. Deposition in deeper waters, typically encountered in proximity to margin-coincident
topography, is dominated by reduced silty-clays with abundant siliceous microfossils and organic matter. Stable isotopes of
carbon and nitrogen, plus hydrogen index measured on bulk organic matter, suggest that contributions from algae (including
cyanobacteria) and other C3-vegetation dominate in these environments. The presence of lotic sponge spicules, together with patterns of terrigenous sand
deposition and geochemical indicators of productivity, points to the importance of the flood pulse for sediment and nutrient
delivery to the lakes. Flood-pulse plumes, waves and bioturbation likewise affect the continuity of sedimentation. Short-lived
radioisotopes indicate rates of 0.11–0.24 cm year−1 at sites of uninterrupted deposition. A conceptual facies model, developed from insights gained from modern seasonal processes,
can be used to predict limnogeological change when the lakes become isolated on the floodplain or during intervals associated
with a strengthened flood pulse. Amplification of the seasonal cycle over longer time scales suggests carbonate, sandy lowstand
fan and terrestrial organic matter deposition during arid periods, whereas deposition of lotic sponges, mixed aquatic organic
matter, and highstand deltas characterizes wet intervals. The results hold substantial value for interpreting paleolimnological
records from floodplain lakes linked to large tropical rivers with annual flooding cycles. 相似文献
959.
Valentí Rull Penélope González-Sampériz Juan Pablo Corella Mario Morellón Santiago Giralt 《Journal of Paleolimnology》2011,46(3):387-404
We report vegetation changes of the last millennium inferred from palynological analysis of a sediment core from Lake Montcortès,
situated at ~1,000 m elevation in the southern pre-Pyrenean flank. The record begins in the Middle Ages (~AD 800) and ends
around AD1920, with an average resolution of ~30 years. The reconstructed vegetation sequence is complex and shows the influence
of both climate and humans in shaping the landscape. Pre-feudal times were characterized by the presence of well-developed
conifer forests, which were intensely burned at the beginning of feudal times (AD 1000) and were replaced by cereal (rye)
and hemp cultivation, as well as meadows and pastures. In the thirteenth century, a relatively short period of warming, likely
corresponding to the Medieval Warm Period, was inferred from the presence of a low Mediterranean scrub community that is today
restricted to <800 m elevation. This community disappeared during Little Ice Age cooling in the fifteenth century, coinciding
with a decline in human activities around the lake. Forest recovery began around AD 1500, at the beginning of the Modern period,
coinciding with wetter climate. Forests, however, declined again during the seventeenth century, coinciding with maximum olive
and hemp cultivation. This situation was reversed in post-Modern times (nineteenth century), characterized by an intense agricultural
crisis and a significant decline in population that favored forest re-expansion. Correlations with nearby Estanya Lake, situated
about 350 m below, provide a regional picture of environmental change. Besides some climate forcing evident in both sequences,
human activities seem to have been the main drivers of landscape and vegetation change in the southern Pyrenean flank, in
agreement with conclusions from other studies in high-mountain environments. 相似文献
960.
A modification to the nonlinear Pastor–Zienkiewicz–Chan (PZC) constitutive model without any change in the number of model parameters is introduced in order to simulate stiffness degradation of dense sands at dynamic loading. The PZC model is based on generalized plasticity and was verified by good prediction of liquefaction and undrained behavior of saturated sand. The PZC is a robust model that can predict drained dynamic behavior of sands, especially stiffness increase in loose sand at reloading of dynamic loading. Yet, this model does not show stiffness degradation of dense sand at reloading. The modification is made through modifying the stress memory factor, H DM, which is multiplied by the plastic modulus, H L. This modification does not influence reloading behavior of loose sand. The modified PZC model is verified via results of drained cyclic tests. Two cyclic triaxial tests on loose and dense specimens, along with two cyclic plane strain tests on dense sand are utilized for validation. The model simulation shows that the modified PZC model is able to predict the stiffness degradation of dense sand at reloading well. 相似文献