全文获取类型
| 收费全文 | 5812篇 |
| 免费 | 564篇 |
| 国内免费 | 158篇 |
专业分类
| 测绘学 | 250篇 |
| 大气科学 | 630篇 |
| 地球物理 | 2087篇 |
| 地质学 | 2322篇 |
| 海洋学 | 330篇 |
| 天文学 | 440篇 |
| 综合类 | 187篇 |
| 自然地理 | 288篇 |
出版年
| 2023年 | 4篇 |
| 2022年 | 8篇 |
| 2021年 | 21篇 |
| 2020年 | 15篇 |
| 2019年 | 26篇 |
| 2018年 | 453篇 |
| 2017年 | 401篇 |
| 2016年 | 280篇 |
| 2015年 | 172篇 |
| 2014年 | 142篇 |
| 2013年 | 149篇 |
| 2012年 | 673篇 |
| 2011年 | 459篇 |
| 2010年 | 149篇 |
| 2009年 | 161篇 |
| 2008年 | 153篇 |
| 2007年 | 139篇 |
| 2006年 | 156篇 |
| 2005年 | 853篇 |
| 2004年 | 888篇 |
| 2003年 | 668篇 |
| 2002年 | 192篇 |
| 2001年 | 83篇 |
| 2000年 | 56篇 |
| 1999年 | 29篇 |
| 1998年 | 15篇 |
| 1997年 | 25篇 |
| 1996年 | 20篇 |
| 1995年 | 8篇 |
| 1994年 | 6篇 |
| 1993年 | 9篇 |
| 1992年 | 5篇 |
| 1991年 | 10篇 |
| 1990年 | 11篇 |
| 1989年 | 6篇 |
| 1988年 | 3篇 |
| 1987年 | 5篇 |
| 1985年 | 4篇 |
| 1984年 | 3篇 |
| 1983年 | 3篇 |
| 1980年 | 5篇 |
| 1976年 | 3篇 |
| 1975年 | 6篇 |
| 1971年 | 3篇 |
| 1970年 | 4篇 |
| 1966年 | 3篇 |
| 1965年 | 3篇 |
| 1963年 | 6篇 |
| 1961年 | 4篇 |
| 1940年 | 2篇 |
排序方式： 共有6534条查询结果，搜索用时 699 毫秒
141.
142.
Artur?BenisekEmail authorView author&#;s OrcID profile Edgar?Dachs 《Contributions to Mineralogy and Petrology》2018,173(11):90
The internal energies and entropies of 21 well-known minerals were calculated using the density functional theory (DFT), viz. kyanite, sillimanite, andalusite, albite, microcline, forsterite, fayalite, diopside, jadeite, hedenbergite, pyrope, grossular, talc, pyrophyllite, phlogopite, annite, muscovite, brucite, portlandite, tremolite, and CaTiO3–perovskite. These thermodynamic quantities were then transformed into standard enthalpies of formation from the elements and standard entropies enabling a direct comparison with tabulated values. The deviations from reference enthalpy and entropy values are in the order of several kJ/mol and several J/mol/K, respectively, from which the former is more relevant. In the case of phase transitions, the DFT-computed thermodynamic data of involved phases turned out to be accurate and using them in phase diagram calculations yields reasonable results. This is shown for the Al2SiO5 polymorphs. The DFT-based phase boundaries are comparable to those derived from internally consistent thermodynamic data sets. They even suggest an improvement, because they agree with petrological observations concerning the coexistence of kyanite?+?quartz?+?corundum in high-grade metamorphic rocks, which are not reproduced correctly using internally consistent data sets. The DFT-derived thermodynamic data are also accurate enough for computing the P–T positions of reactions that are characterized by relatively large reaction enthalpies (>?100 kJ/mol), i.e., dehydration reactions. For reactions with small reaction enthalpies (a few kJ/mol), the DFT errors are too large. They, however, are still far better than enthalpy and entropy values obtained from estimation methods. 相似文献
143.
Yong Chen Jing Duan Junling An Huizhi Liu Ulrich G?rsdorf Franz H.Berger 《大气和海洋科学快报》2021,14(5):24-29
卫星估雨精度的不确定性受到当地降雨类型和像元内降雨非均匀性影响,而结合这两个关键因素开展半干旱草原卫星估雨的研究有限.2009年夏,我们在中国锡林郭勒半干旱草原用多部微雨雷达和雨量计构建了9 km卫星像元降雨观测网,观测了像元内降雨非均匀性(空间变异系数CV),并评估了卫星估雨精度.结果表明:(1)CV值受像元内平均降雨量,降雨类型,降雨云面积及移向等影响,如高Cv值的降雨过程大多为平均降雨量小,对流性降雨过程,降雨云边缘像元CV值较高;(2)TRMM 3B42V7卫星估雨产品适用性较好,CMORPH和PERSIANN次之,但TRMM 3B42V7易在半干旱草原湖泊处高估降雨. 相似文献
144.
Aude?ValadeEmail authorView author&#;s OrcID profile Sebastiaan?Luyssaert Patrick?Vallet Sylvestre?Njakou Djomo Ingride?Jesus Van Der Kellen Valentin?Bellassen 《Carbon balance and management》2018,13(1):26
Background
Concern about climate change has motivated France to reduce its reliance on fossil fuel by setting targets for increased biomass-based renewable energy production. This study quantifies the carbon costs and benefits for the French forestry sector in meeting these targets. A forest growth and harvest simulator was developed for French forests using recent forest inventory data, and the wood-use chain was reconstructed from national wood product statistics. We then projected wood production, bioenergy production, and carbon balance for three realistic intensification scenarios and a business-as-usual scenario. These intensification scenarios targeted either overstocked, harvest-delayed or currently actively managed stands.Results
All three intensification strategies produced 11.6–12.4 million tonnes of oil equivalent per year of wood-based energy by 2026, which corresponds to the target assigned to French wood-energy to meet the EU 2020 renewable energy target. Sustaining this level past 2026 will be challenging, let alone further increasing it. Although energy production targets can be reached, the management intensification required will degrade the near-term carbon balance of the forestry sector, compared to continuing present-day management. Even for the best-performing intensification strategy, i.e., reducing the harvest diameter of actively managed stands, the carbon benefits would only become apparent after 2040. The carbon balance of a strategy putting abandoned forests back into production would only break even by 2055; the carbon balance from increasing thinning in managed but untended stands would not break even within the studied time periods, i.e. 2015–2045 and 2046–2100. Owing to the temporal dynamics in the components of the carbon balance, i.e., the biomass stock in the forest, the carbon stock in wood products, and substitution benefits, the merit order of the examined strategies varies over time.Conclusions
No single solution was found to improve the carbon balance of the forestry sector by 2040 in a way that also met energy targets. We therefore searched for the intensification scenario that produces energy at the lowest carbon cost. Reducing rotation time of actively managed stands is slightly more efficient than targeting harvest-delayed stands, but in both cases, each unit of energy produced has a carbon cost that only turns into a benefit between 2060 and 2080.145.
146.
Evaluating coastal scenery using fuzzy logic: Application at selected sites in Western Black Sea coastal region of Turkey 总被引：1，自引：0，他引：1
Coastal areas of the world are under treat due to the conflicting requirements of functions such as habitation and/or recreation, which affect the strategic asset of coastal scenery itself. Coastal managers, together with planners, need coastal landscape inventories, where the quality of coastal scenery is a part of the inventory. In order to provide an evidence-based approach for sound coastal management decisions,
[Ergin et al., 2004] and [Ergin et al., 2006] developed a novel technique ‘coastal scenic evaluation’ (CSE), which addresses the evaluation of coastal scenery. The CSE technique utilizes fuzzy logic to derive values obtained from a checklist of 26 physical and human parameters. The methodology enables the calculation of an evaluation index (D), which categorizes the scenic values of coastal sites into five distinct classes. Using this technique, coastal scenic evaluations were carried out at 34 selected sites on the Western Black Sea coast of Turkey. Based on the calculated D values, a five-class differentiation was obtained for the selected sites, to provide baseline information for any envisaged subsequent management plans for these areas. 相似文献
147.
148.
GIS-based assessment of landslide susceptibility on the base of the Weights-of-Evidence model 总被引：4，自引：2，他引：2
The major scope of the study is the assessment of landslide susceptibility of Flysch areas including the Penninic Klippen in the Vienna Forest (Lower Austria) by means of Geographical Information System (GIS)-based modelling. A statistical/probabilistic method, referred to as Weights-of-Evidence (WofE), is applied in a GIS environment in order to derive quantitative spatial information on the predisposition to landslides. While previous research in this area concentrated on local geomorphological, pedological and slope stability analyses, the present study is carried out at a regional level. The results of the modelling emphasise the relevance of clay shale zones within the Flysch formations for the occurrence of landslides. Moreover, the distribution of mass movements is closely connected to the fault system and nappe boundaries. An increased frequency of landslides is observed in the proximity to drainage lines, which can change to torrential conditions after heavy rainfall. Furthermore, landslide susceptibility is enhanced on N-W facing slopes, which are exposed to the prevailing direction of wind and rainfall. Both of the latter geofactors indirectly show the major importance of the hydrological conditions, in particular, of precipitation and surface runoff, for the occurrence of mass movements in the study area. Model performance was checked with an independent validation set of landslides, which are not used in the model. An area of 15% of the susceptibility map, classified as highly susceptible, “predicted” 40% of the landslides. 相似文献
149.
Mechanical properties of rocks change under the influence of, temperature. Stress at the onset of yielding, ultimate strength, dilatancy, strain hardening and softening, and the confining pressure at brittle-ductile transition are all reduced by the increasing temperature. This study presents a framework of constitutive modeling of thermo-brittle-plastic behavior of rocks which encompasses these changes. The constitutive law is based on a thermo-plasticity theory first proposed for metals byPrager (1958). Two phenomenological mechanisms have been identified as central for the modeling: temperature dependence of the yield locus (thermal softening), and temperature dependence of the strain-hardening function (thermally enhanced ductility). Material parameters for two rocks, Carrara marble and Westerly granite, were determined on the basis of additional hypotheses. These parameters are used in numerical simulations of triaxial tests at different temperatures. The obtained stress-strain curves compare well to the experimental results. The changes with temperature in the stress at the onset of yielding are more accurately reproduced that the evolution of hardening or softening. Suggestions for possible improvements and future research directions are indicated. 相似文献
150.
Lacustrine deposits of the Malanzán Formation record sedimentation in a small and narrow mountain paleovalley. Lake Malanzán was one of several water bodies formed in the Paganzo Basin during the Late Carboniferous deglaciation. Five sedimentary facies have been recognized. Facies A (Dropstones-bearing laminated mudstones) records deposition from suspension fall-out and probably underflow currents coupled with ice-rafting processes in a basin lake setting. Facies B (Ripple cross-laminated sandstones and siltstones) was deposited from low density turbidity currents in a lobe fringe environment. Facies C (Massive or graded sandstones) is thought to represent sedimentation from high and low density turbidity currents in sand lobes. Facies D (Folded sandstones and siltstones) was formed from slumping in proximal lobe environments. Facies E (Wave-rippled sandstones) records wave reworking of sands supplied by turbidity currents above wave base level.The Lake Malanzán succession is formed by stacked turbidite sand lobe deposits. These lobes were probably formed in proximal lacustrine settings, most likely relatively high gradient slopes. Paleocurrents indicate a dominant direction from cratonic areas to the WSW. Although the overall sequence shows a regressive trend from basin fine-grained deposits to deltaic and braided fluvial facies, individual lobe packages lack of definite vertical trends in bed thickness and grain size. This fact suggests aggradation from multiple-point sources, rather than progradation from single-point sources. Sedimentologic and paleoecologic evidence indicate high depositional rate and sediment supply. Deposition within the lake was largely dominated by event sedimentation. Low diversity trace fossil assemblages of opportunistic invertebrates indicate recolonization of event beds under stressed conditions.Three stages of lake evolutionary history have been distinguished. The vertical replacement of braided fluvial deposits by basinal facies indicates high subsidence and a lacustrine transgressive episode. This flooding event was probably linked to a notable base level rise during postglacial times. The second evolutionary stage was typified by the formation of sand turbidite lobes from downslope mass-movements. Lake history culminates with the progradation of deltaic and braided fluvial systems 相似文献