全文获取类型
收费全文 | 746篇 |
免费 | 26篇 |
国内免费 | 35篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 39篇 |
地球物理 | 186篇 |
地质学 | 309篇 |
海洋学 | 65篇 |
天文学 | 62篇 |
综合类 | 3篇 |
自然地理 | 124篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 20篇 |
2015年 | 11篇 |
2014年 | 42篇 |
2013年 | 48篇 |
2012年 | 19篇 |
2011年 | 47篇 |
2010年 | 28篇 |
2009年 | 39篇 |
2008年 | 44篇 |
2007年 | 29篇 |
2006年 | 20篇 |
2005年 | 30篇 |
2004年 | 21篇 |
2003年 | 30篇 |
2002年 | 21篇 |
2001年 | 17篇 |
2000年 | 13篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 19篇 |
1995年 | 12篇 |
1994年 | 20篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有807条查询结果,搜索用时 390 毫秒
311.
Keith Richards Mike Batty Kevin Edwards Allan Findlay Giles Foody Lynne Frostick Kelvyn Jones Roger Lee David Livingstone Terry Marsden Judith Petts Chris Philo David Simon Susan Smith David Thomas 《Area》2009,41(3):231-243
We present a summary of the kinds of outputs submitted to the Geography and Environmental Studies sub-panel (H-32) for the 2008 Research Assessment Exercise (RAE), and examine the relationships between the peer assessment of research quality that the RAE process has typified, and alternative modes of assessment based on bibliometrics. This comparison is effected using (in aggregate form) some of the results from the RAE, together with citation data gathered after completion of the RAE assessment, specifically for the purpose of this paper. We conclude that, if it continues to be necessary and desirable to assess, in some measure and however imprecisely, research quality, then peer assessment cannot be replaced by bibliometrics. Bibliometrics permit measurement of something that may be linked to quality but is essentially a different phenomenon – a measure of 'impact', for example. 相似文献
312.
Mineralogical and geochemical variations in ten rock surface crusts are described from a large rock shelter known as Carpenter's Gap 1 in the southern Kimberley, formed at the junction between a sandstone floor and an overlying limestone roof. The finely laminated crusts, containing quartz, clays, oxalate and phosphate minerals, and sulfate salts (bassanite, gypsum, epsomite), formed over quartz‐rich sandstones. Mineralogical analyses of crusts, determined by X‐ray diffraction, and major element geochemical trends, in the form of element maps of cross sections, show a complex distribution of hemi‐, mono‐, and dihydrated sulfate and oxalate minerals vertically and laterally within the shelter. These mineralogical changes have occurred under fluctuating moisture and temperature regimes, which follow a general drying trend spatially with distance from the back wall and temporally over a period of about 20,000 years. Documenting these mineralogical changes is a first step in understanding the nature of microclimatic controls on the formation of rock surface coatings in shelters and their implications for palaeoenvironmental reconstructions and for dating engravings covered by these crusts. © 2001 John Wiley & Sons, Inc. 相似文献
313.
Qingfu Xiao E. Gregory McPherson Susan L. Ustin Mark E. Grismer James R. Simpson 《水文研究》2000,14(4):763-784
A rainfall interception measuring system was developed and tested for open‐grown trees. The system includes direct measurements of gross precipitation, throughfall and stemflow, as well as continuous collection of micrometeorological data. The data were sampled every second and collected at 30‐s time steps using pressure transducers monitoring water depth in collection containers coupled to Campbell CR10 dataloggers. The system was tested on a 9‐year‐old broadleaf deciduous tree (pear, Pyrus calleryana ‘Bradford’) and an 8‐year‐old broadleaf evergreen tree (cork oak, Quercus suber) representing trees having divergent canopy distributions of foliage and stems. Partitioning of gross precipitation into throughfall, stemflow and canopy interception is presented for these two mature open‐grown trees during the 1996–1998 rainy seasons. Interception losses accounted for about 15% of gross precipitation for the pear tree and 27% for the oak tree. The fraction of gross precipitation reaching the ground included 8% by stemflow and 77% by throughfall for the pear tree, as compared with 15% and 58%, respectively, for the oak tree. The analysis of temporal patterns in interception indicates that it was greatest at the beginning of each rainfall event. Rainfall frequency is more significant than rainfall rate and duration in determining interception losses. Both stemflow and throughfall varied with rainfall intensity and wind speed. Increasing precipitation rates and wind speed increased stemflow but reduced throughfall. Analysis of rainfall interception processes at different time‐scales indicates that canopy interception varied from 100% at the beginning of the rain event to about 3% at the maximum rain intensity for the oak tree. These values reflected the canopy surface water storage changes during the rain event. The winter domain precipitation at our study site in the Central Valley of California limited our opportunities to collect interception data during non‐winter seasons. This precipitation pattern makes the results more specific to the Mediterranean climate region. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
314.
315.
The assessment of vitellogenin as a biomarker of exposure to estrogenic compounds in two Australian perciformes 总被引:1,自引:0,他引:1
Vitellogenin (Vtg) is a yolk protein precursor that has been identified as a sensitive biomarker for exposure to estrogenic compounds. We evaluated specific monoclonal and polyclonal antibodies for reactivity with plasma Vtg from two Australian Perciformes, the tropical barramundi (Lates calcarifer) and the temperate black bream (Acanthopagrus butcheri). Blood plasma from 17beta-estradiol exposed (E2) male barramundi (20 mg kg(-1)) and male black bream (2.5-5.0 mg kg(-1)) were sent to Biosense Laboratories (Norway) for cross-reactivity testing using their extensive anti-Vtg antibody selection. Indirect ELISA results determined barramundi plasma displayed the highest binding affinities to ND-3G2 (monoclonal-Mab) and PO-1 (polyclonal-Pab). Black bream was most cross-reactive with ND-1C8 (Mab) and PO-2 (Pab). Next, plasma was assessed for Vtg induction in E2-dosed (5 mg kg(-1)), hatchery-reared barramundi and black bream versus a non-injected control group. Vtg production was assessed by Western blot and indirect ELISA using ND-3G2 and ND-1C8 Mabs, respectively. A prominent band was identified in the range of 100-200 kDa for all female black bream and for all E2-treated barramundi and black bream males, which was confirmed as Vtg by Western blot. Indirect ELISA results for barramundi demonstrated highly significant differences in E2-dosed fish as compared to control fish (Student t, P<0.001). E2 male black bream were significantly different than control males (Student t, P<0.001) and control and E2 females displayed highly significant differences (Student t, P<0.001). These results indicate that exposure to 17beta-estradiol induces significant Vtg production in males of the two Australian Perciformes, with potential use as a biomarker for exposure to estrogenic compounds. 相似文献
316.
Michael R. Landry Susan L. Brown Yoshimi M. Rii Karen E. Selph Robert R. Bidigare Eun Jin Yang Melinda P. Simmons 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1348
As part of E-Flux III cruise studies in March 2005, we investigated phytoplankton community dynamics in a cyclonic cold-core eddy (Cyclone Opal) in the lee of the Hawaiian Islands. Experimental incubations were conducted under in situ temperature and light conditions on a drift array using a two-treatment dilution technique. Taxon-specific estimates of growth, grazing and production rates were obtained from analyses of incubation results based on phytoplankton pigments, flow cytometry and microscopy. Cyclone Opal was sampled at a biologically and physically mature state, with an 80–100 m doming of isopycnal surfaces in its central region and a deep biomass maximum of large diatoms. Depth-profile experimentation defined three main zones. The upper (mixed) zone (0–40 m), showed little compositional or biomass response to eddy nutrient enrichment, but growth, grazing and production rates were significantly enhanced in this layer relative to the ambient community outside of the eddy. Prochlorococcus spp. dominated the upper mixed layer, accounting for 50–60% of its estimated primary production both inside and outside of Opal. In contrast, the deep zone of 70–90 m showed little evidence of growth rate enhancement and was principally defined by a 100-fold increase of large (>20-μm) diatoms and a shift from Prochlorococcus to diatom dominance (80%) of production. The intermediate layer of 50–60 m marked the transition between the upper and lower extremes but also contained an elevated biomass of physiologically unhealthy diatoms with significantly depressed growth rates and proportionately greater grazing losses relative to diatoms above or below. Microzooplankton grazers consumed 58%, 65% and 55%, respectively, of the production of diatoms, Prochlorococcus and the total phytoplankton community in Cyclone Opal. The substantial grazing impact on diatoms suggests that efficient recycling was the major primary fate of diatom organic production, consistent with the low export fluxes and selective export of biogenic silica, as empty diatom frustules, in Cyclone Opal. 相似文献
317.
Nancy Soontiens Susan E. Allen Doug Latornell Kate Le Souëf Idalia Machuca Jean-Philippe Paquin 《大气与海洋》2016,54(1):1-21
The Strait of Georgia is a large, semi-enclosed body of water between Vancouver Island and the mainland of British Columbia connected to the Pacific Ocean via Juan de Fuca Strait at the south and Johnstone Strait at the north. During the winter months, coastal communities along the Strait of Georgia are at risk of flooding caused by storm surges, a natural hazard that can occur when a strong storm coincides with high tide. This investigation produces storm surge hindcasts using a three-dimensional numerical ocean model for the Strait of Georgia and the surrounding bodies of water (Juan de Fuca Strait, Puget Sound, and Johnstone Strait) collectively known as the Salish Sea. The numerical model employs the Nucleus for European Modelling of the Ocean architecture in a regional configuration. The model is evaluated through comparisons of tidal elevation harmonics and storm surge with observations. Important forcing factors contributing to storm surges are assessed. It is shown that surges entering the domain from the Pacific Ocean make the most significant contribution to surge amplitude within the Strait of Georgia. Comparisons between simulations and high-resolution and low-resolution atmospheric forcing further emphasize that remote forcing is the dominant factor in surge amplitudes in this region. In addition, local wind patterns caused a slight increase in surge amplitude on the mainland side of the Strait of Georgia compared with Vancouver Island coastal areas during a major wind storm on 15 December 2006. Generally, surge amplitudes are found to be greater within the Strait of Georgia than in Juan de Fuca Strait. 相似文献
318.
A new, physically-based snow hydrology has been implemented into the NCAR CCM1. The snow albedo is based on snow depth, solar zenith angle, snow cover pollutants, cloudiness, and a new parameter, the snow grain size. Snow grain size in turn depends on temperature and snow age. An improved expression is used for fractional snow cover which relates it to surface roughness and to snow depth. Each component of the new snow hydrology was implemented separately and then combined to make a new control run integrated for ten seasonal cycles. With the new snow hydrology, springtime snow melt occurs more rapidly, leading to a more reasonable late spring and summer distribution of snow cover. Little impact is seen on winter snow cover, since the new hydrology affects snow melt directly, but snowfall only indirectly, if at all. The influence of the variable grain size appears more important when snow packs are relatively deep while variable fractional snow cover becomes increasingly important as the snow pack thins. Variable surface roughness affects the snow cover fraction directly, but shows little effect on the seasonal cycle of the snow line. As an applicaion of the new snow hydrology, we have rerun simulations involving Antarctic and Northern Hemisphere glaciation; these simulations were previously made with CCM1 and the old snow hydrology. Relatively little difference is seen for Antarctica, but a profound difference occurs for the Northern Hemisphere. In particular, ice sheets computed using net snow accumulations from the GCM are more numerous and larger in extent with the new snow hydrology. The new snow hydrology leads to a better simulation of the seasonal cycle of snow cover, however, our primary goal in implementing it into the GCM is to improve the predictive capabilities of the model. Since the snow hydrology is based on fundamental physical processes, and has well-defined parameters, it should enable model simulations of climatic change in which we have increased confidence.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil 相似文献
319.
Je-Hun Jang Ryan Mathur Laura J. Liermann Shane Ruebush Susan L. Brantley 《Chemical Geology》2008,250(1-4):40-48
We measured the Fe isotope fractionation during the reactions of Fe(II) with goethite in the presence and absence of a strong Fe(III) chelator (desferrioxamine mesylate, DFAM). All experiments were completed in an O2-free glove box. The concentrations of aqueous Fe(II) ([Fe(II)aq]) decreased below the initial total dissolved Fe concentrations ([Fe(II)total], 2.15 mM) due to fast adsorption within 0.2 day. The concentration of adsorbed Fe(II) ([Fe(II)ads]) was determined as the difference between [Fe(II)aq] and the concentration of extracted Fe(II) in 0.5 M HCl ([Fe(II)extr]) (i.e., [Fe(II)ads] = [Fe(II)extr] − [Fe(II)aq]). [Fe(II)ads] also decreased with time in experiments with and without DFAM, documenting that fast adsorption was accompanied by a second, slower reaction. Interestingly, [Fe(II)extr] was always smaller than [Fe(II)total], indicating that some Fe(II) was sequestered into a pool that is not HCl-extractable. The difference was attributed to Fe(II) incorporated into goethite structure (i.e., [Fe(II)inc] = [Fe(II)total] −[Fe(II)extr]). More Fe(II) was incorporated in the presence of DFAM than in its absence at all time steps. Regardless of the presence of DFAM, both aqueous and extracted Fe(II) (δ56/54Fe(II)aq and δ56/54Fe(II)extr) became isotopically lighter than or similar to goethite (− 0.27‰) at day 7, implying that the isotope exchange occurred between bulk goethite and aqueous Fe. Consistently, the mass balance indicated that the incorporated Fe is isotopically heavier than extracted Fe. These observations suggested that (i) co-adsorption of Fe(II) with DFAM resulted in more pervasive electron transfer, (ii) the electron transfer from heavy Fe(II) in the adsorbed Fe(II) to light Fe(III) in goethite results in the fixation of heavy adsorbed Fe(III) on the surface and accumulation of Fe(II) within the goethite, and (iii) desorption of the reduced, light Fe from goethite does not necessarily occur at the same surface sites where adsorption occurred. 相似文献
320.
Nickel sulphide fire assay for the collection of the platinum group elements and gold from chromitites using reduced bead size 总被引:1,自引:0,他引:1
Summary Fire assay is a classical method for the separation of the platinum group elements and gold (PGE + Au). In nickel sulphide fire assay nickel and sulphur are used for the preconcentration of PGE + Au. In the past the authors have successfully reduced the weight of the collectors used without affecting the recovery of the elements from silicate material and eliminated the reagent blank problem. In this work the authors have applied the small bead size to chromitites. Chromitites can be difficult to fuse, and the authors have applied their modified technique to improve the dissolution of chromitites. This paper describes the application of the reduced bead size to the preconcentration of the PGE + Au from chromitites, by using only 0.5 g of nickel compared to the 10 g used by other fire assay workers.
Nickelsulfid Fire assay zur Anreicherung von Platingruppenelementen und Gold aus Chromititen
Zusammenfassung Fire assay ist die klassische Methode um Platingruppenelemente und Gold (PGE + Au) vor der Analyse anzureichern und von der Matrix abzutrennen. Zum Sammeln der PGE und Au wird Nickelsulfid verwendet. Durch Verwendung möglichst kleiner Mengen konnte das Problem eventueller Verunreinigung der verwendeten Reagenzien ausgeschaltet werden. In der vorliegenden Arbeit wird diese Methode bei Chromititen angewendet, wobei hier ein modifiziertes Verfahren zum Lösen dieser Gesteine verwen det wird. Es werden 0.5 g Nickel zum Abtrennen der PGE und Au von Chromititen verwendet, was einer 20-fachen Mengenreduktion des Kollektormaterials gegenüber herkömmlichen Methoden entspricht.相似文献