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1.
The presence and compositions of atmospheres on the terrestrial planets do not follow directly from condensation models which would have Earth accreting near 500°K. No single mechanism yet proposed adequately accounts for the abundances of noble gases and carbon and nitrogen in the atmospheres. We show that the composition of clathrates forming at low temperatures in cold regions of the nebula can be predicted. Addition of about 1 ppm clathrate material to the Earth can explain observed abundances of Ar, Kr, and Xe. Condensation and adsorption processes occuring at 400–500°K are necessary to explain the observed abundances of Ne, H2O, C, and N. Possible sources of clathrates could be cometary bodies formed in the outer solar system. 相似文献
2.
3.
BJRN K.ALSBERG 《地理学报(英文版)》1993,(3)
A general framework for manipulating spectra as functions in traditional multivariate methods such asPCA and PLS is described.The functional representation is very convenient for compression,ensuringsmoothness and continuity.There are two fundamentally different types of representations:(a)byfunctions and(b)by function coefficients.The use of coefficients is the most practical way of analysis. 相似文献
4.
Rob M. Ellam Brian G. J. Upton J. Godfrey Fitton 《Contributions to Mineralogy and Petrology》1998,133(1-2):51-59
The Myggbukta caldera complex and a swarm of basic dykes constitute the latest Tertiary magmatism in the Hold with Hope region,
East Greenland. The Sr and Nd isotope ratios of these rocks show coherent variations which extend to high 87Sr/86Sr and low 143Nd/144Nd values and require a contribution from continental lithosphere. Broad correlations with major element differentiation indices
suggest that the continental component was incorporated during magmatic differentiation thereby favouring a crustal contamination
process. Trace element concentrations are strongly correlated with isotopic compositions but display ranges for many incompatible
elements which extend beyond likely crustal contaminant compositions. This is readily modelled by AFC processes in which the
dominant cause of trace element enrichment is the concentration effect of fractional crystallisation rather than the composition
of the contaminant. The simplest such models still require unrealistically high degrees of fractional crystallisation to explain
the ten-fold enrichment of some trace elements. This can be overcome if the primary magmas entering the crust already had
highly variable trace element compositions. Such variability is readily achieved if melts from different parts of the melting
column escape without thorough homogenization. An AFC model which incorporates variability in parental magma composition is
then able to simulate the range of compositions observed at Hold with Hope. This carries the implication that the variations
observed are more readily attributed to changes in uncontaminated parental magma than to variations in the composition or
amount of contaminant.
Received: 5 March 1998 / Accepted: 16 June 1998 相似文献
5.
Andrew E. Godfrey 《Environmental Geology》1977,2(1):43-50
Physiography has been studied in the United States for more than 75 years, but only recently has it been applied to land use
planning. Advantages of a physiographic approach are that it 1) focuses on the problems at the proper scale and conserves
energy, effort, and time by selecting the critical parameters, 2) stresses geologic structure and process as factors which
should control land use, and 3) presents data in a form which the non-geologically trained planner can easily understand.
In 1928 Fenneman delineated and described the provinces and sections of the United States. This paper proposes a classification
of smaller physiographic units and presents two examples of how they can be used for planning purposes. Below the section,
the units used in this paper are the subsection, the land type, and the topographic element. Subsections delineate areas of
distinct geologic structure or process whereas land types delineate ranges in the intensity of those processes. Topographic
elements delineate units with distinct ranges of slopes or shapes of slopes, such as concave or convex. 相似文献
6.
豫西嵩县前范岭石英脉型钼矿床地质特征及辉钼矿Re-Os同位素年龄 总被引:14,自引:2,他引:12
位于熊耳山-外方山地区的前范岭钼矿是东秦岭地区新近发现的石英脉型钼矿床之一。赋矿围岩为古元古界熊耳群安山质火山岩类。矿体主要以含辉钼矿石英脉产出,矿石类型以石英脉型为主。金属矿物以辉钼矿和黄铁矿为主,脉石矿物以石英为主,其次为方解石、萤石等。围岩蚀变类型有硅化、钾长石化、青磐岩化等。对6件辉钼矿样品进行Re-Os同位素测年所获得的模式年龄为233.3±3.3~248.2±3.5Ma,等时线年龄为239±13Ma,表明矿床形成于中三叠世。矿床的成矿作用发生于华北与扬子两个板块碰撞对接的晚期阶段。区域上整体的挤压造成了局部的剪切和伸展环境,这种环境为控矿断裂的形成和成矿流体的运移提供了有利条件。嵩县境内现已发现的多处脉型钼矿床很可能形成于同一时期(三叠纪),它们构成了熊耳山与外方山之间的嵩县脉型钼矿田。 相似文献
7.
8.
Andrei M. Sobolev Edmund C. Sutton Dinah M. Cragg Peter D. Godfrey 《Astrophysics and Space Science》2005,295(1-2):189-196
In studies of the environment of massive young stellar objects, recent progress in both observations and theory allows a unified treatment of data for maser and quasi-thermal lines. Interferometric maser images provide information on the distribution and kinematics of masing gas on small spatial scales. Observations of multiple masing transitions provide constraints on the physical parameters.Interferometric data on quasi-thermal molecular lines permits an investigation of the overall distribution and kinematics of the molecular gas in the vicinity of young stellar objects, including those which are deeply embedded. Using multiple transitions of different molecules, one can obtain good constraints on the physical and chemical parameters. Combining these data enables the construction of unified models, which take into account spatial scales differing by orders of magnitude.Here, we present such a combined analysis of the environment around the ultracompact HII region in W3(OH). This includes the structure of the methanol masing region, physical structure of the near vicinity of W3(OH), detection of new masers in the large-scale shock front and embedded sources in the vicinity of the TW young stellar object. 相似文献
9.
收缩情境下城市用地结构时空格局演变及动力机制——以中国东北地区为例 总被引:3,自引:1,他引:2
构建城市用地结构时空格局演变分析框架,引入信息熵和偏移份额模型定量剖析2000—2017年中国东北地区城市用地结构时空格局演变特征,通过计量经济模型分阶段对比分析收缩情境下东北地区城市用地结构演变的动力机制。结果表明:东北地区城市用地总面积持续增长,用地结构信息熵整体呈现先上升、后下降的趋势。2011年以后,城市用地结构有序性、多样性不断提升,单一优势地类主导作用显著下降。公共设施用地、道路交通用地及绿地与广场用地为增长型地类,是东北地区城市用地规模扩张和结构演变的主要动因。用地结构竞争性偏移量具有显著的空间非均衡性,总体与辽中南和哈长两大城市群空间格局基本吻合,新增城市用地的集聚效应不断凸显。城市人口规模变迁、城市经济发展水平提升、产业结构升级与城市居住条件改善对城市用地结构演变具有显著的正向驱动作用。收缩情境下,各因素的拉动作用逐渐减弱,国家宏观政策的约束力不断增强,城市公共服务水平改善的强需求成为驱动用地结构演变的外在动力。 相似文献
10.
We report direct luminescence ages for the culture‐bearing sediments of the Kebaran site of Nahal Hadera V (NHV) in the coastal plain of Israel. Although the site contains, in addition to rich lithic deposits, plentiful mammalian bone, it has proved to be undatable using radiocarbon dating, in spite of the fact that the cultural context places the time of occupation well within the range of radiocarbon dating. In contrast, luminescence dating of the site sediments proved successful. Luminescence ages were determined using the single aliquot additive‐dose (SAA) method, applied to sand‐sized quartz extracts to determine past equivalent doses (De). Dose rates (R) were calculated using thick source alpha counting for the uranium (U) and thorium (Th) concentrations and x‐ray fluorescence analysis for the potassium (K20) concentration. Of the five samples collected at the site, four represent cultural and subcultural deposits and the fifth represents the geological substrate for the archaeological deposit, a quartz‐rich, carbonate‐cemented dune sand known as aeolianite or kurkar. The luminescence age of the kurkar is 42.7 ± 6.3 ka. Human occupation of the site occurred between 21.3 ka and 14.0 ka ago, during the Last Glacial Maximum. © 2003 Wiley Periodicals, Inc. 相似文献