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91.
Reproductive resilience of ice‐dependent Antarctic silverfish in a rapidly changing system along the Western Antarctic Peninsula 下载免费PDF全文
The Western Antarctic Peninsula (wAP) is globally one of the systems most heavily impacted by climate change, notably steep declines in sea ice extent. In forage species, reproductive resilience to change is particularly important because population fluctuations are rapidly communicated through the system via trophic interactions. The reproductive traits of the ice‐dependent forage species Antarctic silverfish (Pleuragramma antarctica) from different areas along the wAP and at the tip of the Antarctic Peninsula were investigated through macroscopic and histological analyses of gonads, with the aim to assess its reproductive potential and to test for spatial differences in fecundity and spawning season. Fish samples were collected in late summer off Charcot Island, in Marguerite Bay and off Joinville Island; no fish were caught in the central wAP. Samples from Charcot Island and Marguerite Bay consisted of adults in developing gonad stage, whereas those from Joinville consisted almost exclusively of juveniles. Mean GSI was relatively low (2–3%) and similar in both sexes, as specimens were still far from being actively reproducing. Developing females exhibited two discrete, though partially overlapping modes of oocytes of different size, with vitellogenic oocytes measuring 0.5–1.0 mm. Absolute and relative fecundity ranged between 3000 and 12,000 eggs per female and between 80 and 190 eggs·g?1, with a strong relationship between absolute fecundity and body size. These results were consistent with a single population at Charcot Island and Marguerite Bay and indicated substantial reproductive potential, which may mitigate population isolation and reductions in habitat availability but cannot ultimately offset catastrophic loss of spawning habitat linked to sea‐ice retreat. 相似文献
92.
93.
James T. Julian John A. Young John W. Jones Craig D. Snyder C. Wayne Wright 《Journal of Geographical Systems》2009,11(1):89-106
We examined whether spatially explicit information improved models that use LiDAR return signal intensity to discriminate
in-pond habitat from terrestrial habitat at 24 amphibian breeding ponds. The addition of Local Indicators of Spatial Association
(LISA) to LiDAR return intensity data significantly improved predictive models at all ponds, reduced residual error by as
much as 74%, and appeared to improve models by reducing classification errors associated with types of in-pond vegetation.
We conclude that LISA statistics can help maximize the information content that can be extracted from time resolved LiDAR
return data in models that predict the occurrence of small, seasonal ponds.
相似文献
94.
Joseph R. Bennett Brian F. Cumming Peter R. Leavitt Marian Chiu John P. Smol Julian Szeicz 《Quaternary Research》2001,55(3):332
Postglacial climatic conditions were inferred from cores taken from Big Lake in southern British Columbia. Low concentrations of nonarboreal pollen and pigments near the base of the core suggest that initial conditions were cool. Increases in both aquatic and terrestrial production suggest warmer and moister conditions until 8500 cal yr B.P. Hyposaline diatom assemblages, increases in nonarboreal pollen, and increased concentrations of pigments suggest the onset of arid conditions from 8500 to 7500 cal yr B.P. Slightly less arid conditions are inferred from 7500 until 6660 cal yr B.P. based on the diatoms, small increases and greater variability in biogenic silica and pigments, and higher percentages of arboreal pollen. At 6600 cal yr B.P., changes in diatoms, pigments, biogenic silica, and organic matter suggest that Big Lake became fresh, deep, and eutrophic until 3600 cal yr B.P., when water levels and nutrients decreased slightly. Our paleoclimatic inferences are similar to pollen-based studies until 6600 cal yr B.P. However, unlike these studies, our multiple lines of evidence from Big Lake imply large changes in effective moisture since 6000 cal yr B.P. 相似文献
95.
96.
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
97.
Robert C. Newton Julian R. Goldsmith Joseph V. Smith 《Contributions to Mineralogy and Petrology》1969,22(4):335-348
Aragonite, the dense form of CaCO3, grew hydrothermally at 100–300° C and dry at 300–400° C at very low pressures from calcite strained by grinding. Nearly complete inversion to aragonite occurred in some runs with Ca-Mg chloride solutions at 0–2.4 kb and 100–200° C on strained calcite having a (10¯14) reflection with a half-width of 0.48° 2 Cu K. A little aragonite grew dry at one atm. from the ground calcite at 300–400° C in a few hrs. Simultaneous shear during recrystallization of calcite in a rotating squeezer resulted in significant aragonite at 300–400° C several kb. below the stability field. No inversion occurred in any ground calcite when previously annealed in CO2 at 500° C for a few hrs. Thermochemical data show that at least 200 cal/mole of strain energy can be produced in calcite by mild deformation. This much stored energy would lower the pressure requirements of aragonite, relative to the strained calcite by more than 3 kb, and our observation that aragonite growth was faster than strain recovery of calcite indicates that aragonite can grow in nature at reduced pressures from strained calcite.Some experiments were also carried out on highly magnesian calcites with the thought that aragonite might also form at the expense of this metastable material. No aragonite was produced, but the possibility that this mechanism could be operative in nature cannot be discounted.The microtexture of aragonitic deformed marbles from NW Washington (prehnite-pumpellyite facies rocks, courtesy of J. A. Vance) as well as electron probe microanalysis of these rocks indicates that aragonite selectively replaced highly strained calcite. The calcite-aragonite transition is thus a questionable indicator of high-pressure in certain metamorphic rocks. 相似文献
98.
小波理论是研究多分辨率信号处理的理论,目前被公认为有前途的新理论。金字塔结构的影像处理、影像理解,现代GIS处理多比例尺的要求以及地形、场论中的逼近均需有关这一理论的支持。本文利用小波变换分解原始影像以实现影像的小波表示,并发展为任意方向的小波变换、逆变换,利用它检测航片中建筑物及其阴影的公共边缘。这种表示方式可为某些影像特征或识别目标提供较为经济的分辨率,该表示方式使影像中具有一定层次的结构更易于发现和利用。实验结果证明了此方法是有效的。 相似文献
99.
The stability field of the end-member scapolite meionite was determined in piston-cylinder apparatus. Meionite has very high thermal stability at high pressures, exceeding 1500° C at 20 kbar. Below 6 kbar and 1270 ° C scapolite breakdown is subsolidus, to an-orthite + gehlenite + wollastonite + CO2, with a slope of 20 bars/degree. An extrapolation of existing thermodynamic data for CO2 permits calculation of ΔG F o =-2384.5 kcal/mol for meionite at 1270 ° C, very close to the value for 3 anorthite + calcite. Above 1270 ° C, scapolite begins to melt to An+Geh+Liq+CO2, and as pressure increases the melting curve steepens, the Geh and An being progressively replaced by Liq+corundum with Al in 6-coordination. At pressures >25kbar dp/dt becomes negative, corundum is the only crystalline product, and CO2 bubbles disappear from the quenched glass, indicating a solubility of CO2 under these conditions of about 5 wt. percent in the liquid. The subsolidus breakdown of meionite at high pressures to grossularite + kyanite + quartz + calcite nearly coincides with the upper pressure limits of anorthite. Thus scapolite is essentially limited to crustal rocks. In view of its great thermal stability, meionite can play a role as a primary mineral in deep-seated basic or intermediate magmatic processes. It is also likely that CO2 coming from the earth's interior will be captured by reaction with plagioclase and clinopyroxene. Scapolite has been noted in basic granulite inclusions from basaltic pipes in three continents. It seems probable that scapolite acts as a major storage site for CO2 in the deep crust. 相似文献
100.
A Probabilistic Displacement-based Vulnerability Assessment Procedure for Earthquake Loss Estimation 总被引:8,自引:3,他引:5
Helen?Crowley Rui?PinhoEmail author Julian?J.?Bommer 《Bulletin of Earthquake Engineering》2004,2(2):173-219
Earthquake loss estimation studies require predictions to be made of the proportion of a building class falling within discrete damage bands from a specified earthquake demand. These predictions should be made using methods that incorporate both computational efficiency and accuracy such that studies on regional or national levels can be effectively carried out, even when the triggering of multiple earthquake scenarios, as opposed to the use of probabilistic hazard maps and uniform hazard spectra, is employed to realistically assess seismic demand and its consequences on the built environment. Earthquake actions should be represented by a parameter that shows good correlation to damage and that accounts for the relationship between the frequency content of the ground motion and the fundamental period of the building; hence recent proposals to use displacement response spectra. A rational method is proposed herein that defines the capacity of a building class by relating its deformation potential to its fundamental period of vibration at different limit states and comparing this with a displacement response spectrum. The uncertainty in the geometrical, material and limit state properties of a building class is considered and the first-order reliability method, FORM, is used to produce an approximate joint probability density function (JPDF) of displacement capacity and period. The JPDF of capacity may be used in conjunction with the lognormal cumulative distribution function of demand in the classical reliability formula to calculate the probability of failing a given limit state. Vulnerability curves may be produced which, although not directly used in the methodology, serve to illustrate the conceptual soundness of the method and make comparisons with other methods. 相似文献