全文获取类型
收费全文 | 296篇 |
免费 | 19篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 9篇 |
地球物理 | 114篇 |
地质学 | 99篇 |
海洋学 | 26篇 |
天文学 | 43篇 |
综合类 | 1篇 |
自然地理 | 16篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 26篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 12篇 |
2012年 | 18篇 |
2011年 | 15篇 |
2010年 | 17篇 |
2009年 | 15篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 10篇 |
2005年 | 5篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有319条查询结果,搜索用时 31 毫秒
71.
72.
To characterize atmospheric particulate matter equal or less than 2.5 μm in diameter (PM2.5) over the Tropical Atlantic Ocean, aerosol sampling was carried out in Puerto Rico during August and September, 2006. Aerosols were analyzed by ion chromatography for water-soluble inorganic and organic ions (including Na+, NH4 +, Mg2+, Ca2+, K+, Cl?, SO4 2?, NH4 +, F?, methanesulfonate (MSA), and oxalate), by inductive coupled plasma mass spectrometry (ICPMS) for trace elements (Al, Fe, Zn, Mn, Cu, Ni, V, Pb, Cr, Sb, Co, Sc, Cd), and by scanning electron microscopy for individual aerosol particle composition and morphology. The results show that the dominant cations in aerosols were Na+, (mean: 631 ng m?3), accounting for 63.8 % of the total cation and NH4 + (mean: 164 ng m?3), accounting for 13.8 % of the total cation measured in this study. The main inorganic anions were Cl? (576 ng m?3, 54.1 %) and SO4 2? (596 ng m?3, 38.0 %). The main organic anion was oxalate (18 ng m?3). Crustal enrichment factor calculations identified 62 % of the trace elements measured (Cu, Ni, V, Co, Al, Mn, Fe, Sc, and Cr) with crustal origin. Single particle analysis demonstrated that 40 % of the aerosol particles examined were Cl? rich particles as sodium chloride from seawater and 34 % of the total particles were Si-rich particles, mainly in the form of aluminosilicates from dust material. Based on the combination of air-mass trajectories, cluster analysis and principal component analysis, the major sources of these PM2.5 particles include marine, Saharan dust and biomass burning from West Africa; however, volcanic emissions from the Soufriere Hills in Montserrat had significant impact on aerosol composition in this region at the time of sample collection. 相似文献
73.
Maria Antonia Brovelli Marco Minghini Rafael Moreno-Sanchez Ricardo Oliveira 《International Journal of Digital Earth》2017,10(4):386-404
ABSTRACTThe development, integration, and distribution of the information and spatial data infrastructure (i.e. Digital Earth; DE) necessary to support the vision and goals of Future Earth (FE) will occur in a distributed fashion, in very diverse technological, institutional, socio-cultural, and economic contexts around the world. This complex context and ambitious goals require bringing to bear not only the best minds, but also the best science and technologies available. Free and Open Source Software for Geospatial Applications (FOSS4G) offers mature, capable and reliable software to contribute to the creation of this infrastructure. In this paper we point to a selected set of some of the most mature and reliable FOSS4G solutions that can be used to develop the functionality required as part of DE and FE. We provide examples of large-scale, sophisticated, mission-critical applications of each software to illustrate their power and capabilities in systems where they perform roles or functionality similar to the ones they could perform as part of DE and FE. We provide information and resources to assist the readers in carrying out their own assessments to select the best FOSS4G solutions for their particular contexts and system development needs. 相似文献
74.
Carlos Angel Pérez Labajos Beatriz Blanco Rojo Rafael Mazas Arranz 《Marine Policy》1996,20(6):463-474
In the last 20 years the Canary Islands fishing fleet has gone from the privileged position of enjoying abundant catches in the old “Canary Islands-Saharan” fishing grounds to the precarious situation in which it currently finds itself. This paper aims to determine what the future holds for The Canaries fishing sector. Hence, fishing rights and policies are analysed and the special aids received from the EC are compared with those applied in other similar ultraperipheric regions. The adoption of a more interventionist role by the Canary Islands administration may solve at least part of the problem faced by this sector. 相似文献
75.
Study of the growth of southern black and white monkfish stocks 总被引:1,自引:0,他引:1
76.
Rafael Cid María-Eugenia San Saturio 《Celestial Mechanics and Dynamical Astronomy》1987,42(1-4):263-277
In this article we study the conditions for obtaining canonical transformationsy=f(x) of the phase space, wherey(y
1,y
2,...,y
2n
) andx(x
1,x
2,...,x
2m
) in such a way that the number of variables is increased. In particular, this study is applied to the rotational motion in functions of the Eulerian parameters (q
0,q
1,q
2,q
3) and their conjugate momenta (Q
0,Q
1,Q
2,Q
3) or in functions of complex variables (z
1,z
2,z
3,z
4) and their conjugate momenta (Z
1,Z
2,Z
3,Z
4) defined by means of the previous variables. Finally, our article include some properties on the rotational motion of a rigid body moving about a fixed point. 相似文献
77.
Most road‐stream crossings over ephemeral channels are vulnerable to extreme hydrologic events. Ford stream crossings (FSCs) are usually dangerous for the road traffic during periods of high flow, in particular under flash flood conditions. The present paper analyzes the flood hazards on the Mediterranean coast in the Region of Murcia (south‐east Spain), affecting this type of road‐stream crossing over dry channels, according to hydraulic variables and bedload transport rates estimated for discharges at bankfull and flood‐prone stages. Under such conditions, the safety of people and vehicles was obtained using numerical models, developed by previous researchers; in particular, water levels and flow velocities across ford reaches were compared with different trend curves between water depths and corresponding critical velocities for children and adults, and for various prototype vehicles. Specifically, two approaches to assess this type of hazards were proposed: a specific Hydraulic Hazard Index and an algorithm for estimating the flood hazard from criteria of bed stability and bedload transport capacity (Flood Hazard at Fords, FHF). In addition, different exposure levels were established, using a Flood Vulnerability Index, based on the FHF, the road category, and the annual average daily traffic. The FHF model gave the best results with regard to the magnitude of the damage observed in recent flash floods for flow stages similar to those simulated. According to the danger thresholds established for this index, half‐bankfull flows represent here a high risk: 27.3% of FSCs for mini‐cars and 18.2% for large cars. At bankfull, the FHF exhibits very high values for mini‐cars (77.3% of FSCs) and for large passenger vehicles (50% of FSCs), while at the floodprone stage, extreme FHF values are reached for all kinds of vehicles at most of the ford crossings. 相似文献
78.
Leach Chloe Hague Ben S. Kennedy David M. Carvalho Rafael C. Ierodiaconou Daniel 《Natural Hazards》2021,109(1):499-521
Natural Hazards - Warnings issued by meteorological or oceanographic agencies are a common means of allowing people to prepare for likely impactful events. Quantifying the relationships between... 相似文献
79.
80.
Coma Structures in Comet 73P/Schwassmann-Wachmann 3, Components B and C,Between January and May 2006
Jean-Baptiste Vincent Hermann Böhnhardt Ivano Bertini Luisa-Maria Lara Michael Küppers Rafael Rodrigo 《Earth, Moon, and Planets》2010,106(1):27-35
The Jupiter family comet 73P/Schwassmann-Wachmann 3 has been widely observed since 1995 after a nucleus break-up event produced
at least five components labeled 73P-A to E. During the 2006 appearance, two of them (B and C) showed very strong coma activity.
Our R-filter imaging of 73P-B & C from 21 January to 25 May 2006 revealed the presence of fan-like structures in the comae
of both components and evidence for further fragmentation events in component B. As of early April 2006, component C showed
two jets emanating from the nucleus, with one continuously visible. Through a simulation of the orbital geometry we infer
that the rotation axis of 73P-C has an inclination of 20° to the orbital plane and a longitude of 45° at perihelion. The coma
activity of component B was highly variable, displaying signatures of at least 3 fragmentation events. The coma was characterized
by the continuous presence of a jet roughly in sunward direction, starting from the beginning of May. The first fragmentation
event of component B may have happened between April 16 and April 26, leading to the presence of at least 6 fragments detected
in images of May 2. The second one happened on or shortly before May 8, the third one between May 18 and 24. For the rotation
axis of 73P-B we infer an inclination of 5°–15° to the orbital plane and a longitude of 20°–30° at perihelion. 相似文献