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571.
572.
A multiple stable isotope record of Late Quaternary limnological changes and chironomid paleoecology from northeastern Iceland 总被引:1,自引:0,他引:1
We present results from multiple stable isotope analyses (δ18O of chironomid larval head capsules, chironomid adult thoraxes and other insect remains and δD, δ13C, δ15N of total organic matter—TOM) of a lake sediment core (04-SVID-03) taken from Stora Vidarvatn in northeastern Iceland to
reconstruct past environmental, limnological and δ18O of past lake water changes during the Holocene. Core 04-SVID-03 represents a ∼12,000 cal. yrs BP to present record. Large
magnitude changes in δ18O occurred during the Holocene at the site. Downcore shifts in δ18O of chironomids did not correlate with measurements of the δ13C and δ15N of chironomid head capsules, implying that the δ18O changes were not primarily driven by changes in chironomid diet during the Holocene. The δD of TOM provided a proxy of relative
lake-water δD changes at the site and also showed large magnitude changes during the record. This approach was supported by
analyses of a modern training set where δDTOM analyses were conducted using surface sediments from a suite of freshwater lakes over a large latitudinal gradient. The magnitude
of changes in both the δ18O and δD and the relatively negative δ18O values throughout much of the core suggest that the proxies represent more paleoenvironmental information than solely temperature.
Additional possible influences on lake-water isotopic composition are discussed, including changes in the seasonality of precipitation,
in the patterns of air masses supplying precipitation to Iceland and in the dominant mode of the North Atlantic Oscillation. 相似文献
573.
Aaron F. Diefendorf William P. Patterson Chris Holmden Henry T. Mullins 《Journal of Paleolimnology》2008,39(1):101-115
A 7.6-m lake sediment core from a marl lake, Lough Inchiquin, records variation in landscape evolution from 16,800 cal yrs
B.P. to 5,540 cal yrs B.P. We observe significant variations (up to 12‰) in δ
13Corg and δ
13Ccalcite values that are interpreted to reflect secular changes in lake water δ
13CDIC values that result from a regional landscape transition from barren limestone bedrock to a forested ecosystem. Lake water
δ
13CDIC values are therefore influenced by two isotopically distinct sources of carbon: terrestrial organic material (−27.1 to −31.2‰VPDB)
via oxidized soil organic matter and weathered limestone bedrock (+3.4‰VPDB). Isotope excursions in lacustrine sediment records
are forced not only by changes in productivity but also by changes in the terrestrial environment. This has profound implications
for the interpretation of paleoclimate records derived from lacustrine sediment and suggests that selection of appropriate
lakes can provide records of terrestrial change where other related records are not available. 相似文献
574.
Dissimilarity of Scalar Transport in the Convective Boundary Layer in Inhomogeneous Landscapes 总被引:1,自引:1,他引:0
A land-surface model (LSM) is coupled with a large-eddy simulation (LES) model to investigate the vegetation-atmosphere exchange
of heat, water vapour, and carbon dioxide (CO2) in heterogeneous landscapes. The dissimilarity of scalar transport in the lower convective boundary layer is quantified
in several ways: eddy diffusivity, spatial structure of the scalar fields, and spatial and temporal variations in the surface
fluxes of these scalars. The results show that eddy diffusivities differ among the three scalars, by up to 10–12%, in the
surface layer; the difference is partly attributed to the influence of top-down diffusion. The turbulence-organized structures
of CO2 bear more resemblance to those of water vapour than those of the potential temperature. The surface fluxes when coupled with
the flow aloft show large spatial variations even with perfectly homogeneous surface conditions and constant solar radiation
forcing across the horizontal simulation domain. In general, the surface sensible heat flux shows the greatest spatial and
temporal variations, and the CO2 flux the least. Furthermore, our results show that the one-dimensional land-surface model scheme underestimates the surface
heat flux by 3–8% and overestimates the water vapour and CO2 fluxes by 2–8% and 1–9%, respectively, as compared to the flux simulated with the coupled LES-LSM. 相似文献
575.
Spectra of CO<Subscript>2</Subscript> and Water Vapour in the Marine Atmospheric Surface Layer 总被引:1,自引:1,他引:0
Erik Sahlée Ann-Sofi Smedman Anna Rutgersson Ulf Högström 《Boundary-Layer Meteorology》2008,126(2):279-295
Spectra of CO2 and water vapour fluctuations from measurements made in the marine atmospheric surface layer have been analyzed. A normalization
of spectra based on Monin–Obukhov similarity theory, originally developed for wind speed and temperature, has been successfully
extended also to CO2 and humidity spectra. The normalized CO2 spectra were observed to have somewhat larger contributions from low frequencies compared to humidity spectra during unstable
stratification. However, overall, the CO2 and humidity spectra showed good agreement as did the cospectra of vertical velocity with water vapour and CO2 respectively. During stable stratification the spectra and cospectra displayed a well-defined spectral gap separating the
mesoscale and small-scale turbulent fluctuations. Two-dimensional turbulence was suggested as a possible source for the mesoscale
fluctuations, which in combination with wave activity in the vertical wind is likely to explain the increase in the cospectral
energy for the corresponding frequency range. Prior to the analysis the turbulence time series of the density measurements
were converted to time series of mixing ratios relative to dry air. Some differences were observed when the spectra based
on the original density measurements were compared to the spectra based on the mixing ratio time series. It is thus recommended
to always convert the density time series to mixing ratio before performing spectral analysis. 相似文献
576.
Fabien Gibert Irène Xuéref-Rémy Lilian Joly Martina Schmidt Juan Cuesta Kenneth J. Davis Michel Ramonet Pierre H. Flamant Bertrand Parvitte Virginie Zéninari 《Boundary-Layer Meteorology》2008,128(3):381-401
A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the mesoscale evolution of the
daily cycle of CO2 and related tracers in the atmospheric boundary layer (ABL) and its relation to ABL dynamics and nearby natural and anthropogenic
sources and sinks. A 2-μm heterodyne Doppler differential absorption lidar, which combines measurements of, (1) structure
of the atmosphere, (2) radial velocity, and (3) CO2 differential absorption was a particularly unique element of the observational array. We analyse the differences in the diurnal
cycle of CO, CO2, lidar reflectivity (a proxy for aerosol content) and H2O using the lidar, airborne measurements in the free troposphere and ground-based measurements made at two sites located few
kilometres apart. We demonstrate that vertical mixing dominates the early morning drawdown of CO and aerosol content trapped
in the former nocturnal layer but not the H2O and CO2 mixing ratio variations. Surface fluxes, vertical mixing and advection all contribute to the ABL CO2 mixing ratio decrease during the morning transition, with the relative importance depending on the rate and timing of ABL
rise. We also show evidence that when the ABL is stable, small-scale (0.1-km vertical and 1-km horizontal) gradients of CO2 and CO are large. The results illustrate the complexity of inferring surface fluxes of CO2 from atmospheric budgets in the stable boundary layer. 相似文献
577.
基于四川盆地震旦系灯影组16口井岩心和11条露头剖面的观察,结合128个碳氧同位素数据的系统分析,研究了震旦系灯影组储层特征、探讨了灯影组储层发育与桐湾期三幕构造运动的关系,预测了其优质储层分布区域。结果表明:1)四川盆地震旦系为典型的镶边碳酸盐岩台地沉积体系,围绕绵竹-长宁裂陷两侧发育大型的台缘丘滩体,岩石类型以泥粉晶白云岩、藻砂屑白云岩、层纹石白云岩、凝块石白云岩和雪花状白云岩为主;2)受桐湾期三幕构造运动和海平面频繁升降变化的影响,形成了灯二段和灯四段两套风化壳岩溶储层,储层以低孔低渗为特征,溶蚀孔洞发育,为裂缝-孔洞型储层;3)灯二段和灯四段两套储层横向上分布较稳定,纵向上互相叠置,大面积分布;优质储层主要分布在台地边缘相带,主要集中在高石梯、磨溪、荷包场、威远、资阳、蓬莱等地区。 相似文献
578.
This study performed a detailed geochemical analyses of the components, stable carbon isotopes of alkane gas and CO2, stable hydrogen isotopes of alkane gas and helium isotopes of reproducing gas from the largest tight gas field (Sulige) and shale gas (Fuling) field in China. The comparative study shows that tight gas from the Sulige gas field in the Ordos Basin is of coal-derived origin, which is characterized by a positive carbon and hydrogen isotopic distribution pattern (δ13C1 > δ13C2 > δ13C3 > δ13C4; δ2H1 > δ2H2 > δ2H3), i.e., the carbon and hydrogen isotopes increase with increasing carbon numbers. Carbon dioxide from this field are of biogenic origin and the helium is crust-derived. Shale gas from the Fuling shale gas field belongs to oil-derived gas which has complete carbon and hydrogen isotopic reversal of secondary alteration origin (δ13C1 < δ13C2 < δ13C3; δ2H1 < δ2H2 < δ2H3), i.e., the carbon and hydrogen isotopes decrease with increasing carbon numbers. Such complete isotopic reversal distribution pattern is due to the secondary alteration like oil or gas cracking, diffusion and so on under high temperature. In that case, positive carbon or hydrogen isotopic distribution pattern will change into complete isotopic reversal as the temperature increases. Carbon dioxide is of abiogenic origin resulting from the thermal metamorphism of carbonates and helium is crust-derived. 相似文献
579.
Sedimentary, isotopic and bulk geochemical proxies measured in sediment samples of five gravity cores collected in the distal part of the Ogooue turbidite system (around 4000 m-depth) were used to develop a conceptual model to describe the accumulation of terrigenous organic matter (OM) during the last 200,000 yrs BP in the eastern part of the Gulf of Guinea. This model takes into account the influence of the different depositional processes (turbiditic vs hemipelagic sedimentation), geomorphological features and sea-level variations.Total organic carbon (TOC) and the stable organic carbon isotopes of the OM (δ13C) variability follow the highstand/lowstand (interglacial/glacial) cyclicity with a very low accumulation rate of terrigenous OM during periods of high sea-level and higher accumulation rate during period of low sea-level. A sea-level of 80–120 m below present day seems to favor the transfer of terrigenous sediments to the deep offshore environment through the turbidite system and thanks to the connection of the canyons heads with the river system presently located at the shelf edge at −120 m water depth.In this system, terrigenous OM matter delivered by the river accumulate in the sediments via two main processes. Indeed, a part of the terrigenous OM settles in combination with the finest particles forming hemipelagites, while another part, formed of very well preserved land plant debris, is transported and deposited far offshore with turbidity currents. The proportion of terrigenous OM accumulated due to turbidity currents is important as it can represent more than 70% of the carbon accumulated during sea-level lowstand. Moreover, terrigenous OM seems to preferentially accumulate in the levees and the lobes of the system notably due to the higher frequency of organic-rich turbidites.This study demonstrates that gravity flows, influenced by the sea-level variations, can significantly affect the terrigenous OM budget of the deep offshore Atlantic margins and that channel-levee complexes as well as turbidite lobes can be regarded as good sink for terrestrial organic carbon. These processes should be taken into consideration in the context of source rocks exploration but also for the estimation of the general carbon accumulation in ocean sediment. 相似文献
580.
Lei Gao Qiuyue Zhou Xiangjuan Yu Kexiong Wu Ali H Mahfouz 《Marine Georesources & Geotechnology》2017,35(1):143-148
To study the effect and mechanism of carbon fiber reinforced clay, a series of unconfined compression tests for clay reinforced with carbon fiber have been performed under the conditions of controlled water content and dry density. The carbon fiber is mixed into soil with the quality percentage of 0.01, 0.02, 0.03, 0.05, 0.1, 0.15, 0.25, 0.35, and 0.5%, then a certain quality of water was added in the soil to achieve the optimum soil water content. Ten groups of samples were tested by the unconfined compression experiment. The results showed that the incorporation of carbon fiber elements can effectively improve the unconfined compressive strength and brittle failure mode of soil. The soil is strengthened at the beginning and then weakened with the increased incorporation of carbon fiber, the effect is especially significant when the mix percentage becomes 0.1%. The interaction at the interface between carbon fiber surface and soil matrix is analyzed by using scanning electron microscopy (SEM). It is found that the enhancement mechanisms of carbon fiber reinforced soil are one-dimensional reinforcement of a single carbon fiber thread and three-dimensional reinforcement caused by fiber network respectively. 相似文献