全文获取类型
收费全文 | 1631篇 |
免费 | 42篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 53篇 |
大气科学 | 94篇 |
地球物理 | 345篇 |
地质学 | 581篇 |
海洋学 | 109篇 |
天文学 | 343篇 |
综合类 | 16篇 |
自然地理 | 153篇 |
出版年
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 23篇 |
2019年 | 22篇 |
2018年 | 31篇 |
2017年 | 23篇 |
2016年 | 31篇 |
2015年 | 25篇 |
2014年 | 37篇 |
2013年 | 72篇 |
2012年 | 49篇 |
2011年 | 68篇 |
2010年 | 87篇 |
2009年 | 91篇 |
2008年 | 78篇 |
2007年 | 63篇 |
2006年 | 58篇 |
2005年 | 57篇 |
2004年 | 50篇 |
2003年 | 63篇 |
2002年 | 53篇 |
2001年 | 27篇 |
2000年 | 39篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 21篇 |
1995年 | 23篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 23篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 34篇 |
1984年 | 32篇 |
1983年 | 27篇 |
1982年 | 22篇 |
1981年 | 36篇 |
1980年 | 24篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 19篇 |
1973年 | 16篇 |
1971年 | 8篇 |
排序方式: 共有1694条查询结果,搜索用时 296 毫秒
371.
The impact of perturbations to ocean-model parameters on climate and climate change in a coupled model 总被引:2,自引:1,他引:1
Assessments of the impacts of uncertainties in parameters on mean climate and climate change in complex climate models have, to date, largely focussed on perturbations to parameters in the atmosphere component of the model. Here we expand on a previously published study which found the global impacts of perturbed ocean parameters on the rate of transient climate change to be small compared to perturbed atmosphere parameters. By separating the climate-change-induced ocean vertical heat transport in each perturbed member into components associated with the resolved flow and each parameterisation scheme, we show that variations in global mean heat uptake in different perturbed versions are an order of magnitude smaller than the average heat uptake. The lack of impact of the perturbations is attributed to (1) the relatively small impact of the perturbation on the direct vertical heat transport associated with the perturbed process and (2) a compensation between those direct changes and indirect changes in heat transport from other processes. Interactions between processes and changes appear to combine in complex ways to limit ensemble spread and uncertainty in the rate of warming. We also investigate regional impacts of the perturbations that may be important for climate change predictions. We find variations across the ensemble that are significant when measured against natural variability. In terms of the experimental set-up used here (models without flux adjustments) we conclude that perturbed physics ensembles with ocean parameter perturbations are an important component of any probabilistic estimate of future climate change, despite the low spread in global mean quantities. Hence, careful consideration should be given to assessing uncertainty in ocean processes in future probabilistic assessments of regional climate change. 相似文献
372.
Over 70 new Nd isotope analyses are presented for the Manicouagan area of the Grenville Province to estimate the crustal age of target rocks involved in the 214 Ma Manicouagan Impact Structure, and to reconstruct the Precambrian geological evolution of this crustal segment. The rocks fall into two main groups: Samples from the Archean-aged Gagnon Terrane to the north and west of the impact give TDM ages averaging 2.70 Ga. Samples from the Manicouagan Imbricate Zone (MIZ) and other allochthonous lithotectonic domains to the south of the impact yield Paleoproterozoic TDM ages averaging 2.01 Ga for the MIZ and 1.86 Ga for the southern domains. These Paleoproterozoic terranes are correlated with Makkovik-age crust in Labrador that was heavily reworked by Labradorian magmatism that increased in intensity southwards. The target rocks involved in the impact event would have consisted almost entirely of the MIZ, which formed a layer several kilometres thick, overlying Archean crust at depth. 相似文献
373.
Michael J.S. Belton Peter Thomas Peter Schultz Lori Feaga Olivier Groussin Casey Lisse Jessica Sunshine W. Alan Delamere 《Icarus》2007,187(1):332-344
We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441-446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230-238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253-263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136-2160; 1999a. Astron. J. 118, 1101-1119; 1999b. Astrophys. J. 526, 465-470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255-1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220-229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670-1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193-204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or “layered pile” model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects. 相似文献
374.
A large gyromagnetic effect in greigite 总被引:1,自引:0,他引:1
375.
The UK broadband seismology network 总被引:1,自引:0,他引:1
Alan Douglas 《Astronomy& Geophysics》2001,42(2):2.19-2.22
Alan Douglas considers the origins and the future of one of Britain's most successful seismic networks.
Broadband seismology is a powerful tool for geophysical research. Over the past decades, most seismometers have recorded only part of the spectrum of frequencies of vibration from earthquakes. Broadband seismology brings far greater research rewards. The UK has been a pioneer in its use and has had a broadband network for around 30 years. During this time, Britain has developed the technology and made significant research advances in the fields of earthquake source mechanisms, deep-Earth structure, detection and location of distant earthquakes and explosions, and nuclear explosion detection. The network has also played a part in the development of the Data Centre of the Observatories and Research Facilities for European Seismology. But changes in funding mean that the future of this pioneering network is now uncertain. 相似文献
Broadband seismology is a powerful tool for geophysical research. Over the past decades, most seismometers have recorded only part of the spectrum of frequencies of vibration from earthquakes. Broadband seismology brings far greater research rewards. The UK has been a pioneer in its use and has had a broadband network for around 30 years. During this time, Britain has developed the technology and made significant research advances in the fields of earthquake source mechanisms, deep-Earth structure, detection and location of distant earthquakes and explosions, and nuclear explosion detection. The network has also played a part in the development of the Data Centre of the Observatories and Research Facilities for European Seismology. But changes in funding mean that the future of this pioneering network is now uncertain. 相似文献
376.
Editorial responsibility: J. Hoefs 相似文献
377.
Wilson C. H. Chan Julian R. Thompson Richard G. Taylor Alistair E. Nay Tenalem Ayenew Alan M. MacDonald 《水文科学杂志》2020,65(10):1720-1737
ABSTRACT Uncertainty in climate change impacts on river discharge in the Upper Awash Basin, Ethiopia, is assessed using five MIKE SHE hydrological models, six CMIP5 general circulation models (GCMs) and two representative concentration pathways (RCP) scenarios for the period 2071–2100. Hydrological models vary in their spatial distribution and process representations of unsaturated and saturated zones. Very good performance is achieved for 1975–1999 (NSE: 0.65–0.8; r: 0.79–0.93). GCM-related uncertainty dominates variability in projections of high and mean discharges (mean: –34% to +55% for RCP4.5, – 2% to +195% for RCP8.5). Although GCMs dominate uncertainty in projected low flows, inter-hydrological model uncertainty is considerable (RCP4.5: –60% to +228%, RCP8.5: –86% to +337%). Analysis of variance uncertainty attribution reveals that GCM-related uncertainty occupies, on average, 68% of total uncertainty for median and high flows and hydrological models no more than 1%. For low flows, hydrological model uncertainty occupies, on average, 18% of total uncertainty; GCM-related uncertainty remains substantial (average: 28%). 相似文献
378.
Arthur Clive Bishop Alan Robert Woolley 《Contributions to Mineralogy and Petrology》1973,39(4):309-326
The paper describes a suite of volcanic and intrusive rocks from Ua Pu, one of the Marquesas Islands, situated in the central Pacific Ocean. The rocks comprise alkali olivine basalts, hawaiites, mugearites, trachytes, and phonolites. Their petrographic characters are briefly described and 24 new chemical analyses presented. The rocks fall into a sodic and a potassic series, since some rocks are richer in K2O than Na2O, whilst the phonolites have exceptionally high total alkali contents.The differentiation of the series is discussed and special attention is paid to the phonolites in which icositetrahedral pseudomorphs occur. It is concluded that these pseudomorphs are probably after analcime rather than leucite. 相似文献
379.
380.
Confocal scanning light microscopy is a valuable new method for examining the nature and progress of stone weathering at a level of resolution between optical microscopy and scanning electron microscopy. Not only is it non-destructive, but it can also create three-dimensional images. 相似文献