全文获取类型
收费全文 | 241篇 |
免费 | 7篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 33篇 |
地球物理 | 54篇 |
地质学 | 107篇 |
海洋学 | 12篇 |
天文学 | 19篇 |
自然地理 | 18篇 |
出版年
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 11篇 |
2012年 | 9篇 |
2011年 | 12篇 |
2010年 | 17篇 |
2009年 | 12篇 |
2008年 | 13篇 |
2007年 | 6篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 8篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1967年 | 2篇 |
1965年 | 1篇 |
1957年 | 1篇 |
1952年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有253条查询结果,搜索用时 328 毫秒
141.
Finite computer resources force compromises in the design of transient numerical experiments with coupled atmosphere-ocean general circulation models which, in the case of global warming simulations, normally preclude a full integration from the undisturbed pre-industrial state. The start of the integration at a later time from a climate state which, in contrast to the true climate, is initially in equilibrium then induces a cold start error. Using linear response theory a general expression for the cold start error is derived. The theory is applied to the Hamburg CO2 scenario simulations. An attempt to estimate the global-mean-temperature response function of the coupled model from the response of the model to a CO2 doubling was unsuccessful because of the non-linearity of the system. However, an alternative derivation, based on the transient simulation itself, yielded a cold start error which explained the initial retardation of the Hamburg global warming curve relative to the IPCC results obtained with a simple box-diffusion-upwelling model. In the case of the sea level the behaviour of the model is apparently more linear. The cold start error estimations based on a CO2 doubling experiment and on an experiment with gradually increasing CO2 (scenario A) are very similar and explain about two thirds of the coupled model retardation relative to the IPCC results. 相似文献
142.
Claudio Del Don Kurt W. Hanselmann Raffaele Peduzzi Reinhard Bachofen 《Aquatic Sciences - Research Across Boundaries》1994,56(1):1-15
To study nutrient fluxes within aquatic ecosystems, the synthesis of biomass and of various storage polymers has been analysed in samples from a meromictic alpine lake. Methods are described for the quantitative determination of whole cell biomass, glycogen, polyhydroxyalkanoates (PHA) and sulfur. Methods were adapted to conditions present in natural environments and tested with samples from blooms of Chromatiaceae and with corresponding laboratory cultures. Dried bacterioplankton-biomass has been analyzed for sulfur, glycogen and polyhydroxyalkanoates, and after complete oxidation for SO
4
2-
, NO
3
-
and HPO
4
2-
. The average elemental composition of biomass from phototrophic sulfur bacteria, depleted of sulfur and carbon storage compounds, was C380H580O153N67P3S2.5M, where M stands for the content of the remaining minor elements. C, H, O, N, P and S accounted for 86.7% of the total dry mass. Storage sulfur in natural populations was equivalent to 2.5% to 13.5% of the dry mass; its content varied by 80% within a diurnal cycle. Glycogen contents fluctuated by approximately 50%; they accounted for 7.5% to 15.2% of the dry cell mass. The total content of reserve materials per cell never exceeded 30% of the dry mass. PHA had not been found in appreciable amounts in cells harvested from the natural lake habitat. Under certain conditions in the laboratoryChromatium okenii could be induced, however, to produce polyhydroxyalkanoates. Sulfur, glycogen and PHA contents of 33, 26 and 11%, respectively, were achieved under laboratory-culture conditions. Cells with up to 60% of their dry mass consisting of reserve materials can be obtained under selected laboratory conditions. 相似文献
143.
Reinhard Aesse 《中国地球化学学报》1987,6(2):99-114
The early diagenetic evolution of pore-water chemistry is closely linked to mineralization reactions which consume significant
portions of the metabolites released by bacterial organic matter decomposition. These reactions are most intense in high-sedimentation
rate basins and include the precipitation of iron-sulfides and various carbonates leading to concretion growth. Early diagenetic
pyrite is typically framboidal attesting to its recrystallization from precursor mackinawite, greigite or amorphous FeS which
are the favored phases at high supersaturation levels during the initial sulfate reduction stages. The sulfur isotopic composition
of early diagnetic pyrite can be used to differentiate diffusion-controlled, open-system conditions with isotopically light
sulfide (δ
34S = − 35 to − 20‰) from closed system conditions, under which Raleigh distillation produces increasingly heaver sulfide (δ
34 S = − 35 to + 18‰). Alabandite (Mn-sulfide) is a rare authigenic sulfide in Mn-rich environments such as certain restricted,
semi-stagnant basins (Baltic Sea).
pH-buffering by hydrogen sulfide and hydrogen ion uptake by the reduction of manganese and iron oxides and hydroxides in the
nitrate and sulfate reduction zones raise the pH sufficiently to cause supersaturation of the porewaters with respect to Ca-,
Mg-, Fe- and Mn-carbonates and complex solid solutions of them. Fe-carbonates cannot form in the sulfate reduction zone in
the presence of dissolved sulfide which competes for the dissolved iron. Likewise, dolomite formation appears to be inhibited
or slowed down in the presence of substantial dissolved sulfate. The appearance of siderite and ankerite therefore signals
carbonate precipitation below the sulfate reduction zone. Supporting evidence for the early diagenetic origin of many carbonate
concertions is provided by their high carbonate contents (70 to 90% reflecting the porosity existing at the time of precipitation,
called “minus-cement porosity”), isotopic composition, clay fabrics, and preservation of original bedding features including
the shapes of fossils and fecal pellets. In these environments increasing carbon isotope ratios (δ
13 C = − 20 to + 15‰) indicate concretion growth below the sulfate reduction zone, i.e., in the methane generation zones. Continuing
concretion growth at greater burial depth explains pore water profiles with constantly low Ca and downward decreasing Mg concentrations.
Dissolved ammonia and phosphate profiles reguire adsorption and ion-exchange reactions as additional removal machanisms (besides
apatite precipitation) in order to explain their downward decrease after they have reached maximum concentrations below the
alkalinity maximum.
Classification of early diagnetic environments into oxic and anoxic and further subdivision of the latter into sulfidic and
non-sulfidic (with suboxic or post-oxic and methanic as further subcategories of the non-sulfidic environment) according to
Berner (1981) is preferred over the previous classification in terms of pH/Eh fields. The temperature range of the early diagenetic
stage extends from O to about 75°C, at which temperature thermocatalytic organic matter decomposition replaces the earlier
bacterially mediated reactions and causes a whole set of new diagenetic reactions (such as feldspar dissolution, smectite
to illite transformation) to start. 相似文献
144.
Reinhard Hesse 《中国地球化学学报》1986,5(4):297-319
Pore water studies enable (1) the detection of diagenetic reactions actively occurring in the sediment at the time of sampling,(2)
the distinction between principal modes of solute transport, i.e., between advection (convection) and diffusion, and (3) the
assessment of mineral-solution equilibria, Pore waters are, therefore, preferred diagnostic objects in the study of diagenesis,
particularly early diagenesis.
The single most important factor for pore-fluid evolution in modern offshore basins is sedimentation rate which is closely
correlated with organtic matter content of the sediment. Organic matter represents the most reactive sediment constituent
which, through bacterial decomposition, provides some of the main solutes involved in early diagenetic mineralization reactions.
On the basis of sedimentation rate and organic matter content, it is convenient to distinguish two end-members of basins (environments)
with respect to early diagenesis: I. Low to intermediate-sedimentation rate basins with convection or diffusion-controlled
pore-water profiles and II. high-sedimentation rate basins with reaction-controlled pore-water profiles.
The first group of basins or environments, which is the subject of this paper, is typically represented by pelagic sediments.
Three principally different trends of pore-water evolution occur: 1. convection-controlled profiles with no pronounced vertical
gradients for the dissolved species; 2. diffusion-controlled profiles with vertical gradients but linear correlations between
major ions, especially Ca and Mg, and 3. profiles with gradients but no linear correlation between the major ions. The later
are transitional to the trends seen in high-sedimentation rate basins. With respect to redox-potentials, the diagenetic environments
of low-sedimentation rate basins are generally oxic to suboxic. 相似文献
145.
Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implications 总被引:1,自引:0,他引:1
Jens Wendt Reinhard Dietrich Mathias Fritsche Anja Wendt Alexander Yuskevich rey Kokhanov Anton Senatorov Valery Lukin Kazuo Shibuya Koichiro Doi 《Geophysical Journal International》2006,166(3):991-998
In the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed.
The derived ice flow velocity for Vostok Station is 2.00 m a−1 ± 0.01 m a−1 . Along the flowline of Vostok Station an extension rate of about 10−5 a−1 (equivalent to 1 cm km−1 a−1 ) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a−1 along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years. 相似文献
The derived ice flow velocity for Vostok Station is 2.00 m a
146.
David Frank Ulf Büntgen Reinhard Bhm Maurizio Maugeri Jan Esper 《Quaternary Science Reviews》2007,26(25-28):3298-3310
Comparison of tree-ring-based warm-season temperature reconstructions and their instrumental target data reveals substantial divergence between (warmer) early instrumental measurements and (colder) proxy estimates. Here we detail this systematic misfit for the Northern Hemisphere before 1900 and the European Alps before 1850. Five hypotheses related to both proxy and target uncertainties are presented towards explaining this phenomenon. These include: (1) tree-ring detrending methods, (2) biological persistence in the proxy time-series, (3) uncertainties and instabilities in the growth response to given climatic parameters, (4) reduced instrumental station availability back in time, and (5) instrumental data homogeneity. We suggest that uncertainties in the choice of instrumental targets at the hemispheric scale, and instrumental data inhomogeneities at the Alpine and possibly also the hemispheric-scale are the most important factors in explaining this offset. Assessment of homogeneity at larger scales remains challenging. Attention is drawn to possible warm biases in early thermometer shelters and the relevance of proxy/target discrepancies for understanding and quantifying the amplitude of both recent anthropogenic and past natural forced climate fluctuations. 相似文献
147.
Transient simulation of the last glacial inception. Part I: glacial inception as a bifurcation in the climate system 总被引:2,自引:2,他引:0
Reinhard Calov Andrey Ganopolski Martin Claussen Vladimir Petoukhov Ralf Greve 《Climate Dynamics》2005,24(6):545-561
We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which
encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional
polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at the Eemiam interglacial, at 126 ky
BP (126,000 years before present). The model runs for 26 kyr with time-dependent orbital and CO2 forcings. The model simulates a rapid expansion of the area covered by inland ice in the Northern Hemisphere, predominantly
over Northern America, starting at about 117 kyr BP. During the next 7 kyr, the ice volume grows gradually in the model at
a rate which corresponds to a change in sea level of 10 m per millennium. We have shown that the simulated glacial inception
represents a bifurcation transition in the climate system from an interglacial to a glacial state caused by the strong snow-albedo
feedback. This transition occurs when summer insolation at high latitudes of the Northern Hemisphere drops below a threshold
value, which is only slightly lower than modern summer insolation. By performing long-term equilibrium runs, we find that
for the present-day orbital parameters at least two different equilibrium states of the climate system exist—the glacial and
the interglacial; however, for the low summer insolation corresponding to 115 kyr BP, we find only one, glacial, equilibrium
state, while for the high summer insolation corresponding to 126 kyr BP only an interglacial state exists in the model.
相似文献
Reinhard CalovEmail: |
148.
Little is known about the spatial and temporal distribution of blast fishing which hampers enforcement against this activity. We have demonstrated that a triangular array of hydrophones 1 m apart is capable of detecting blast events whilst effectively rejecting other sources of underwater noise such as snapping shrimp and nearby boat propellers. A total of 13 blasts were recorded in Sepangor bay, North of Kota Kinabalu, Sabah, Malaysia from 7th to 15th July 2002 at distances estimated to be up to 20 km, with a directional uncertainty of 0.2 degrees . With such precision, a network of similar hydrophone arrays has potential to locate individual blast events by triangulation to within 30 m at a range of 10 km. 相似文献
149.
150.
Dirk?Sachse Jens?Radke Reinhard?Gaupp Lorenz?Schwark Guido?Lüniger Gerd?GleixnerEmail author 《International Journal of Earth Sciences》2004,93(4):554-564
For the first time 18O and 13C values from carbonates and D values of individual n-alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the Central European Zechstein Basin (CEZB). A 12-m core covering the complete Ca2 interval and adjacent anhydrites (A1 and A2) was analyzed for 18O and 13C values of dolomitized carbonates and D values of individual n-alkanes. 18Ocarb values (+2 to +5 vs. VPDB) were strongly influenced by evaporation and temporal freshwater input into the lagoon. The 13Ccarb values (–1 to +4 vs. VPDB) were controlled mainly by changes in primary production. Both isotopic ratios show an inverse relationship throughout most of the core, contradicting diagenetic alteration, since 13Ccarb values are not altered significantly during dolomitization. Assuming a temperature range of 35–40 °C in the lagoon, 18Ocarb values of +2.5 to +8 (vs. VSMOW) for the lagoonal water can be reconstructed. The lagoon may have desiccated twice during the Ca2 interval, as indicated by very high 18Ocarb and low 13Ccarb values, coinciding with increasing amount of anhydrite in the analyzed sample. These events seem to reflect not just local but a regional intra-Ca2 cyclicity. Measured D values of the short-chain n-alkanes, namely n-C16 and n-C18 which are widely used as indicators for photosynthetic bacterial and algal input, reflect the isotopic composition of the lagoonal water. Assuming constant fractionation during incorporation of hydrogen into lipids of –160, an average D value of +70 (vs. VSMOW) can be reconstructed for the lagoonal water, accounting for very arid conditions. The long-chain n-alkanes n-C27, n-C28, n-C29 and n-C30, thought to be derived from the leaf waxes of terrestrial higher plants, were shown to be depleted in D relative to the short-chain alkanes, therefore indicating a different hydrogen source. Terrestrial plants in arid areas mainly use water supplied by precipitation. By using a smaller fractionation of –120 due to evaporation processes in the leaves, reconstructed values vary between –74 and –9 (vs. VSMOW). These values are not indicating extremely arid conditions, implying that the long-chain n-alkanes were transported trough wind and/or rivers into the lagoon at the Zechstein Sea coast. Dwater values, reconstructed using the n-C16 alkane and 18O water values, independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon. Altogether, our results indicate that hydrogen isotopic ratios of n-alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction. 相似文献