全文获取类型
收费全文 | 1255篇 |
免费 | 48篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 27篇 |
大气科学 | 104篇 |
地球物理 | 307篇 |
地质学 | 312篇 |
海洋学 | 112篇 |
天文学 | 325篇 |
自然地理 | 122篇 |
出版年
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 14篇 |
2018年 | 15篇 |
2017年 | 17篇 |
2016年 | 28篇 |
2015年 | 24篇 |
2014年 | 30篇 |
2013年 | 52篇 |
2012年 | 32篇 |
2011年 | 46篇 |
2010年 | 42篇 |
2009年 | 68篇 |
2008年 | 49篇 |
2007年 | 50篇 |
2006年 | 68篇 |
2005年 | 47篇 |
2004年 | 61篇 |
2003年 | 51篇 |
2002年 | 39篇 |
2001年 | 43篇 |
2000年 | 29篇 |
1999年 | 24篇 |
1998年 | 29篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 24篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 27篇 |
1984年 | 16篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 17篇 |
1975年 | 13篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1971年 | 8篇 |
1969年 | 4篇 |
排序方式: 共有1309条查询结果,搜索用时 390 毫秒
191.
Barry Hankin Trevor J. C. Page Nick A. Chappell Keith J. Beven Paul J. Smith Ann Kretzschmar Rob Lamb 《水文研究》2021,35(11):e14418
The Q-natural flood management project has co-developed with the Environment Agency 18 monitored micro-catchments (~1 km2) in Cumbria, UK installing calibrated flumes aimed at quantifying the potential shift in observed flows resulting from a range of nature-based-solutions installed by local organizations. The small-scale reduces the influence of variability characterizing larger catchments that would otherwise mask any such shifts, which we attempt to relate to a shift in model parameters. This paper demonstrates an approach to applying donor-parameter-shifts obtained from modelling two of the paired micro-catchments to a much larger scale, in order to understand the potential for improved distributed modelling of nature-based solutions in the form of additional tree-planting. The models include a rainfall-runoff model, Dynamic Topmodel, and a 2D hydrodynamic model, JFlow, permitting analysis of changes in hillslope processes and channel hydrodynamics resulting from a range of distributed measures designed to emulate natural hydrological processes that evaporate, store or infiltrate flows. We report on attempts to detect shift in hydrological response using one of the paired-micro-catchment moorland versus forestry sites in Lorton using Dynamic Topmodel. A donor-parameter-shift approach is used in a hypothetical experiment to represent new woodland in a much larger catchment, although testing all combinations of spatial planting strategies, responses to multiple-extremes, failure-modes and changes to synchronization becomes intractable to support good decision making. We argue that the problem can be re-framed to use donor-parameter-shifts at multi-local-scale catchments above communities known to be at risk, commensurate with most of the evidence of NbS impacts being effective at the small scale (ca. 10 km2). This might lead to more effective modelling to help catchment managers prioritize those communities-at-risk where there is more evidence that NbS might be effective. 相似文献
192.
Jones Keith Pascale Federica Wanigarathna Nadeeshani Morga Mariantonietta Sargin Sinan 《Bulletin of Earthquake Engineering》2021,19(10):4115-4143
Bulletin of Earthquake Engineering - As cities become larger and more densely populated the impacts of major earthquake events on city communities become more severe. Improving community resilience... 相似文献
193.
194.
Victor Fernandez Nascimento Nazli Yesiller Keith C Clarke Jean Pierre Henry Balbaud Ometto Pedro R. Andrade Anahi Chimini Sobral 《地理信息系统科学与遥感》2017,54(5):657-677
??The proper management of solid waste (SW) is a global environmental challenge. A major issue is the proper disposal of SW while balancing a wide range of criteria and working with different spatial data. In this study, we used geographic information system as a tool to perform multi-criteria decision analysis with an analytical hierarchy process to develop an environmental impact susceptibility model (EISM) for landfills. The model was applied to the state of California, USA and results are presented herein. In particular, the EISM considers factors such as geology, pedology, geomorphology, water resources, and climate as represented by 13 associated environmental indicators. The results of the EISM indicate that more than 75% of California’s territory is situated in areas with very low, low, and medium environmental impact susceptibility categories. However, in the remaining 25% of the state’s land, 61 landfills are located in the high and very high categories. These results are alarming because during the period from 2000 to 2015, these 61 landfills received approximately 308 million tons of SW, which corresponds to more than 57% of all SW disposed in California. The model results can be used toward mitigating the environmental impacts of these facilities. 相似文献
195.
The Al26 activity has been measured by gamma-ray coincidence spectrometry in a total of 30 stony meteorites (13 bronzite, 13 hypersthene, 1 carbonaceous and 1 enstatite chondrite, and 2 achondrites). The measured Al26 content has been compared with calculated values based on the method developed by Lavrukhina and Ustinova (1972a, 1972b), which takes account of the modulation of the galactic cosmic ray intensity along the meteorite orbit due to solar magnetic activity. The predictions have been modified empirically to allow for the difference in chemical composition between H- and L-chondrites. Comparison of the measured value with that predicted in the absence of solar modulation permits the estimation of the aphelion of the orbit of the meteorite. The great majority of the derived aphelia lie within the range 2.05–2.45 AU. While this result must be treated with considerable reserve owing to the uncertainties associated with the model, it is consistent with recent data from photometric observations of the asteroid belt. 相似文献
196.
Most meteoritic chondrules and inclusions appear to have been liquid droplets at one time, or at least to have been close to the melting point so that they are easily deformed. The simplest mode of formation of such objects would be to have the liquid phases of the chondrules in thermodynamic equilibrium with gas in the primitive solar nebula, as suggested some years ago by Wood, but unfortunately pressures in the primitive solar nebula are orders of magnitude too small at temperatures in the range of the liquid mineral phases. This difficulty has led to an abandonment of this basic idea, but we suggest that the idea should be reexamined in view of the presence of higher pressures at moderate temperatures, together with water vapor enrichments, in the protoplanetary atmosphere of Jupiter prior to the collapse stage, which was recently studied by Perri and Cameron. A number of advantages arise from the complexities of such a model, and we discuss these together with a number of constraints. 相似文献
197.
A.G.W. Cameron 《Icarus》1973,18(3):407-450
Particle accumulation processes are discussed for a variety of physical environments, ranging from the collapse phase of an interstellar cloud to the different parts of the models of the primitive solar nebula constructed by Cameron and Pine. Because of turbulence in the collapsing interstellar gas, it is concluded that interstellar grains accumulate into bodies with radii of a few tens of centimeters before the outer parts of the solar nebula are formed. These bodies can descend quite rapidly through the gas toward midplane of the nebula, and accumulation to planetary size can occur in a few thousand years. Substantial modifications of these processes take place in the outer convection zone of the solar nebula, but again it is concluded that bodies in that zone can grow to planetary size in a few thousand years.From the discussion of the interstellar collapse phase it is concluded that the angular momentum of the primitive solar nebula was predominantly of random turbulent origin, and that it is plausible that the primitive solar nebula should have possessed satellite nebulae in highly elliptical orbits. It is proposed that the comets were formed in these satellite nebulae.A number of other detailed conclusions are drawn from the analysis. It is shown to be plausible that an iron-rich planet should be formed in the inner part of the outer nebular convection zone. Discussions are given of the processes of planetary gas accretion, the formation of satellites, the T Tauri solar wind, and the dissipation of excess condensed material after the nebular gases have been removed by the T Tauri solar wind. It is shown that the present radial distances of the planets (but not Bode's Law) should be predicted reasonably well by a solar nebula model intermediate between the uniform and linear cases of Cameron and Pine. 相似文献
198.
199.
J. R. Barnes T. A. Lister R. W. Hilditch A. Collier Cameron 《Astronomische Nachrichten》2004,325(3):233-236
We present high resolution Doppler images of the short period (P = 0.362 d) contact binary AE Phe. Using least squares deconvolution, we make use of the information content of the several thousand lines in each échelle spectrum to obtain the necessary S/N and time resolution required to resolve individual starspot features. A single pair of rotationally broadened profiles (free of sidelobes due to blending) with a typical S/N of 3000 ‐ 4000 per spectrum is thus obtained. With 300 sec exposures we achieve a cadence of 350 sec which is equivalent to sampling the rotation phase every 4°. We derive images for four nights of data which reveal starspots at most latitudes on both components of the common envelope system. Individual starspots evolve significantly on very short timescales, of order one day; significantly faster than the week timescales found on active single stars and the Sun. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
200.
Clinopyroxene + liquid equilibria to 100 kbar and 2450 K 总被引:5,自引:1,他引:4
Keith Putirka 《Contributions to Mineralogy and Petrology》1999,135(2-3):151-163
One of the most active issues in igneous petrology is the investigation of mantle melting, and subsequent differentiation.
To evaluate alternative hypotheses for melting and differentiation it is essential to accurately predict clinopyroxene compositions
in natural systems. Expressions have thus been derived that describe clinopyroxene-melt equilibria, and allow equilibrium
clinopyroxene compositions to be calculated. These equations were constructed from least-squares regression analysis of experimental
clinopyroxene-liquid pairs. The calibration database included clinopyroxenes synthesized from both natural and synthetic basalt
compositions; experimental conditions ranged from 0 to 100 kbar and 1350 to 2450 K. Regression equations were based on thermodynamic
functions. Empirical expressions were also derived, since such models yield more precise estimates of clinopyroxene compositions,
and may be easily incorporated into existing liquid line-of-descent models. Such equations may be useful for calculation of
high pressure liquid fractionation, or for constraining P-T conditions for basalts produced by partial melting of a pyroxene-bearing source. Models of mantle melting often rely on expressions
involving simple element ratios. Partition coefficients (K
d
cpx/liq
) for the minor elements, Na and Ti, were thus also calibrated as a function of P, T and composition. K
Ti
cpx/liq
, while sensitive to composition was relatively insensitive to P and T. In contrast, K
Na
cpx/liq
increases substantially with increasing P, and exceeded 1 in some experiments. Since oceanic basalts show variations in Na/Ti ratios, the potential exists for partial
melting depths to be inferred from K
Na
cpx/liq
.
Received: 28 May 1997 / Accepted: 20 November 1998 相似文献