全文获取类型
收费全文 | 211篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 17篇 |
地球物理 | 43篇 |
地质学 | 93篇 |
海洋学 | 8篇 |
天文学 | 39篇 |
综合类 | 1篇 |
自然地理 | 19篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 12篇 |
2012年 | 11篇 |
2011年 | 15篇 |
2010年 | 6篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 11篇 |
2006年 | 10篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1992年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
51.
This paper is devoted to the formulation of the direct differentiation method and adjoint state method in quasi‐static linear poroelasticity. We derive the strong and weak formulation of both methods and discuss their solutions using the finite element method. The techniques are illustrated and tested on two numerical examples for the case of isotropic and homogeneous material. The presented formulations can be extended to more complex behaviour in poromechanics. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
52.
Andrei V. IVANOV Glenn J. MACPHERSON Michael E. ZOLENSKY Nataliya N. KONONKOVA Lyudmila F. MIGDISOVA 《Meteoritics & planetary science》1996,31(5):621-626
Abstract— Metal nodules are one of the major textural components of Kaidun sample #01.3.06 EH3-4. In terms of structure, the nodules are of three types: (1) globular, (2) zoned with a massive core and globular mantle, and (3) nodules with no internal structure. The size and composition of the globules in the nodules and grains of metal of the matrix are almost identical: no greater than 20 μm and Ni, 5.95; Si, 3.33 wt%. The nodules contain small (usually <5 μm) inclusions of SiO2; albitic glass; enstatite; roedderite; and a mixture of SiO2 and Na2S2. This is the first reported occurrence of a simple sulfide of an alkaline metal in nature. The formation of the inclusions appears to be related to condensation of material onto the surfaces of metal grains. The nodules appear to have formed by aggregation of separate grains (globules) of metal, with conservation of condensates on the grain surfaces as inclusions. The inclusions probably condensed over a significant temperature range from 1400 to 600 K. The aggregation of metal grains and formation of the nodules probably occurred simultaneously with condensation. 相似文献
53.
A region's elderly population has two sources of growth: net migration and the net aging-in-place of its resident population. This paper outlines a method for identifying the projected relative contribution of these two sources of elderly population growth over time, and illustrates it with data for the states of Arizona, California, Florida, Illinois, and New York. The sources of elderly population growth differ between regions and over time. 相似文献
54.
Derek T. Robinson Andrei M. Balulescu 《International journal of geographical information science》2018,32(6):1061-1086
Data and estimates on the spatial distribution of consumer spending form the foundation of retail location analysis and location-allocation spatial interaction models. The presented research presents and compares four methods to estimate consumer spending that combine different levels of detail in household spending data across multiple levels of household aggregation (i.e. census units). Results demonstrate that these methods, which use publicly available census data, can capture a substantial amount of reported sales. Furthermore, comparison of the best method with the de facto industry standard for business data in Canada shows a strong correlation (R2 > 0.85) across space and is within 10% of aggregate industry-derived spending estimate. Analysis of the spending data across space finds that the majority of spending occurs in census metropolitan areas with high spending clusters that offer unique opportunities for retail location. We interrogate the socio-demographic characteristics of the population in these high spending clusters and find that only a few variables are required to explain a large proportion of the variance in consumer spending. The overarching outcome of the presented research is that small-to-medium businesses, planners, and municipalities do not need expensive proprietary data to estimate and predict consumer spending and market demand. 相似文献
55.
A. S. Ivleva V. N. Podkovyrov V. B. Ershova O. A. Anfinson A. K. Khudoley P. V. Fedorov A. V. Maslov D. Yu. Zdobin 《Doklady Earth Sciences》2016,468(2):593-597
Here we present the results of U–Pb LA–ICP–MS dating of detrital zircons from the Ediacaran–Early Cambrian deposits of the eastern part of the Baltic monoclise (Leningrad Region). The obtained age spectra of the detrital zircons suggest that, in the Ediacaran–Early Cambrian, the main clastic material source to the northwest of the Russian Platform was the Baltic Shield. Then in the Early Cambrian along with the Baltic Shield provenance, a clastic source from the Timanian margin of Baltica (northeast in modern coordinates) contributed to the deposits. The obtained data either somewhat set limits of the Timanian orogen formation as older than the previously suggested Middle Cambrian (about 510 Ma), based on the “absence of a Proto–Uralian–Timanian provenance signal” in the Sablino Formation rocks in the south Ladoga, or suggest another rearrangement of detritus transportation paths at the end of Stage 3 (Atdabanian). 相似文献
56.
The effect of respiratory conditions and priming compound on dechlorination patterns of heptachlorodibenzo-p-dioxins (HpCDD) was investigated using estuarine sediment-eluted cultures in the presence and absence of 20 mM sulfate, and 0.2 microM 2-bromodibenzo-p-dioxin (2-BrDD) as a priming compound. Electron balance calculations based on fatty acid turnover, hydrogen production, and electron acceptor depletion/methane formation indicated that whereas fermentative processes dominated in sulfate-free incubations, sulfate-reduction was predominant in the sulfate-amended incubations. The dechlorination of 1,2,3,4,6,7,8-HpCDD exhibited the following trends: (i) the relative yields of product formation did not exceed 30% and the presence of 2-BrDD increased the yield by up to 10%; (ii) sulfidogenic conditions resulted in a lower 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) formation, and the presence of 2-BrDD decreased the formation of 2,3,7,8-TCDD by additional 4-5-fold; (iii) the presence of 2-BrDD effected a predominance in lateral (2,3,7,8 positions) over peri (1,4,6,9 positions)-dechlorination. Denaturing gradient gel electrophoresis (DGGE) banding patterns indicated significant shifts of microbial community structure in response to terminal electron accepting processes as well as to the presence of the priming compound. The latter resulted in a similar community structure independent of dioxin spike, indicating that subsets of populations in the sediment are capable of exploiting the new niche provided by the priming compound. 相似文献
57.
Innovative applications of capillary zone electrophoresis (CZE) to the determination of inorganic ions in environmental aquatic samples of high salinity and, particularly, in seawater are reviewed. Emphasis is placed on advanced approaches utilized for securing separation performance from being degraded by the presence of matrix salts and for simultaneous separation of ions different in natural abundance. Also covered are methodologies of present or possible use to evolve the method's practical utility to trace-level ions. Surveyed procedures are tabulated for the purpose of facilitating the method selection or further development. In addition, brief background information on basic methodological principles of CZE in inorganic ion analysis is given for a better orientation of those intending or just beginning to put CZE to work. Finally, possible future research trends and developments of CZE in the area are briefly discussed. 相似文献
58.
Svetlana V. Pakhomova Per O.J. Hall Mikhail Yu. Kononets Alexander G. Rozanov Anders Tengberg Andrei V. Vershinin 《Marine Chemistry》2007
Fluxes of dissolved forms of iron and manganese across the sediment–water interface were studied in situ in the Gulf of Finland and the Vistula Lagoon (Baltic Sea), and in the Golubaya Bay (Black Sea) from 2001 to 2005. Fluxes were measured using chamber incubations, and sediment cores were collected and sliced to assess the porewater and solid phase metal distribution at different depths. Measured and calculated benthic fluxes of manganese and iron were directed out of sediment for all sites and were found to vary between 70–4450 and 5–1000 µmole m− 2 day− 1 for manganese and iron, respectively. The behavior of the studied metals at various redox conditions in the near-bottom water and in the sediment was the main focus in this study. Our results show the importance of bottom water redox conditions for iron fluxes. We measured no fluxes at oxic conditions, intermediate fluxes at anoxic conditions (up to 200 μmole m− 2 day− 1) and high fluxes at suboxic conditions (up to 1000 μmole m− 2 day− 1). Total dissolved iron fluxes were generally dominated by iron(II). Contribution of iron(III) to the total iron flux did not exceed 20%. Obtained fluxes of manganese at all studied regions showed a linear correlation (r2 = 0.97) to its concentration in the porewater of the top sediment layer (0–5 mm) and did not depend on dissolved oxygen concentrations of bottom water. Organically complexed iron and manganese were in most cases not involved in the benthic exchange processes. 相似文献
59.
Gennady G. Boeskorov Peter A. Lazarev Andrei V. Sher Sergei P. Davydov Nadezhda T. Bakulina Marina V. Shchelchkova Jonas Binladen Eske Willerslev Bernard Buigues Alexey N. Tikhonov 《Quaternary Science Reviews》2011,30(17-18):2262-2272
A nearly complete frozen mummy of a woolly rhinoceros (Coelodonta antiquitatis Blum., 1799) was discovered in a gold mine on the lower reaches of the Kolyma River, north–eastern Siberia. This is the first find of the whole body of woolly rhino in permafrost. A large part of the mummified body was preserved, including the left part of the body, covered by skin, including skin of the head and ear, fore and hind legs. The skull with 2 horns and the lower jaw were also preserved. Most of the internal organs were lost, except the intestines, stomach, and their contents. A rib fragment from this individual was dated by AMS-radiocarbon method to 39,140 ± 390 years BP (OxA-18755). Spore and pollen analyses of the stomach contents indicate that grasses and sagebrushes formed the main part of the diet of C. antiquitatis in this region of Arctic Siberia. 相似文献
60.
Andrei Lobanov 《Astrophysics and Space Science》2007,311(1-3):263-267
Compact relativistic jets in active galactic nuclei offer an effective tool for investigating the physics of nuclear regions
in galaxies. The emission properties, dynamics, and evolution of jets in AGN are closely connected to the characteristics
of the central supermassive black hole, accretion disk and broad-line region in active galaxies. Recent results from studies
of the nuclear regions in several active galaxies with prominent outflows are reviewed in this contribution. 相似文献