全文获取类型
收费全文 | 5935篇 |
免费 | 192篇 |
国内免费 | 89篇 |
专业分类
测绘学 | 169篇 |
大气科学 | 557篇 |
地球物理 | 1456篇 |
地质学 | 2026篇 |
海洋学 | 572篇 |
天文学 | 809篇 |
综合类 | 22篇 |
自然地理 | 605篇 |
出版年
2021年 | 61篇 |
2020年 | 70篇 |
2019年 | 89篇 |
2018年 | 125篇 |
2017年 | 117篇 |
2016年 | 159篇 |
2015年 | 149篇 |
2014年 | 205篇 |
2013年 | 326篇 |
2012年 | 248篇 |
2011年 | 272篇 |
2010年 | 195篇 |
2009年 | 308篇 |
2008年 | 291篇 |
2007年 | 267篇 |
2006年 | 224篇 |
2005年 | 195篇 |
2004年 | 198篇 |
2003年 | 192篇 |
2002年 | 184篇 |
2001年 | 135篇 |
2000年 | 143篇 |
1999年 | 116篇 |
1998年 | 109篇 |
1997年 | 92篇 |
1996年 | 86篇 |
1995年 | 87篇 |
1994年 | 78篇 |
1993年 | 65篇 |
1992年 | 65篇 |
1991年 | 72篇 |
1990年 | 68篇 |
1989年 | 59篇 |
1988年 | 58篇 |
1987年 | 67篇 |
1986年 | 43篇 |
1985年 | 74篇 |
1984年 | 94篇 |
1983年 | 80篇 |
1982年 | 66篇 |
1981年 | 76篇 |
1980年 | 63篇 |
1979年 | 57篇 |
1978年 | 39篇 |
1977年 | 55篇 |
1976年 | 63篇 |
1975年 | 46篇 |
1974年 | 56篇 |
1973年 | 49篇 |
1972年 | 25篇 |
排序方式: 共有6216条查询结果,搜索用时 15 毫秒
91.
Since the early 1970s the Australian economy has undergone major transformations common to other western industrialised countries. Jobs in manufacturing declined precipitately whilst the service economy grew, most significantly in producer services but also in lower skilled jobs. Tourism and services exports began to rival traditional agricultural and mining staples. Social outcomes, also typical of international trends, included rising unemployment and polarisation of incomes. Australia's changing global context, especially the nation's increasing orientation towards Asian growth economies, have underpinned restructuring. A political climate of economic rationalism has facilitated and accentuated restructuring. The economic shifts of the past quarter century have meant that everywhere the basis for economic growth has changed. Overlaying and reinforcing the re-definition of competitive advantage has been a shift in the pattern of agglomeration economies and diseconomies. New growth regions have emerged, others have had their prospects reinforced, and still others have had their outlook diminished in absolute or, more commonly, relative terms. The paper traces the regional outcomes of national economic restructuring and shifts in the balance of agglomeration economies and diseconomies over the period from 1971 to 1991. The focus is on the top end of the urban hierarchy, on specialised industrial cities where job loss from manufacturing has hit hard, amenity regions where international and domestic tourism have been major factors in growth, and non-metropolitan balances where growth has been uneven but generally low. Demographic, economic sectoral and welfare indicators are woven into a tableau of change expressed at national, intra-state and intrametropolitan scales. 相似文献
92.
93.
Tumbure Akinson Bretherton Mike R. Bishop Peter Hedley Mike J. 《Natural Resources Research》2020,29(3):1561-1570
Natural Resources Research - The physical and chemical characteristics of mined phosphate rock will vary temporally as the location and nature of the ore body changes and as the type of equipment... 相似文献
94.
Peter HUDSON 《《地质学报》英文版》2014,88(Z1):73-73
正Lakes Acraman,Gairdner,Harris and Everard are a cluster of large episodic salt lakes on Eyre Peninsula,South Australia.These lakes have a characteristic terrestrial invertebrate fauna including various spiders, 相似文献
95.
Combining in situ isotopic, trace element and textural analyses of quartz from four magmatic-hydrothermal ore deposits 总被引:2,自引:0,他引:2
Dominique Tanner Richard W. Henley John A. Mavrogenes Peter Holden 《Contributions to Mineralogy and Petrology》2013,166(4):1119-1142
This study couples in situ 16O, 17O and 18O isotope and in situ trace element analyses to investigate and characterize the geochemical and textural complexity of magmatic-hydrothermal quartz crystals. Euhedral quartz crystals contemporaneous with mineralization were obtained from four magmatic-hydrothermal ore deposits: El Indio Au–Ag–Cu deposit; Summitville Au–Ag–Cu deposit; North Parkes Cu–Au deposit and Kingsgate quartz-Mo–Bi–W deposit. The internal features of the crystals were imaged using cathodoluminescence and qualitative electron microprobe maps. Quantitative isotopic data were collected in situ using 157 nm laser ablation inductively coupled plasma mass spectrometry (for 40 trace elements in quartz) and sensitive high-resolution ion microprobe (for 3 isotopes in quartz). Imaging revealed fine oscillatory zoning, sector zoning, complex “macromosaic” textures and hidden xenocrystic cores. In situ oxygen isotope analyses revealed a δ18O range of up to 12.4 ± 0.3 ‰ in a single crystal—the largest isotopic range ever ascribed to oscillatory zonation in quartz. Some of these crystals contain a heavier δ18O signature than expected by existing models. While sector-zoned crystals exhibited strong trace element variations between faces, no evidence for anisotropic isotope fractionation was found. We found: (1) isotopic heterogeneity in hydrothermal quartz crystals is common and precludes provenance analysis (e.g., δD–δ18O) using bulk analytical techniques, (2) the trace element signature of quartz is not an effective pathfinder toward noble metal mineralization and (3) in three of the four samples, both textural and isotopic data indicate non-equilibrium deposition of quartz. 相似文献
96.
Paul Finegan Luis León Vintró Peter I. Mitchell Dominique Boust Aurélien Gouzy Peter J. Kershaw Julie A. Lucey 《Continental Shelf Research》2009,29(16):1995-2010
Recent studies have shown that accumulation of 99Tc in seabed sediments labelled by authorised radioactive liquid discharges into the NE Irish Sea from the Sellafield reprocessing complex is greater than previously thought. In this paper, new data on 99Tc concentration profiles in subtidal and intertidal sediments from the eastern and western Irish Sea are provided with a view to elucidating the processes responsible for the incorporation and retention of 99Tc in the seabed. The data show that substantial amounts of 99Tc have accumulated in the fine-grained subtidal sediments off the Cumbrian coast, particularly after increased releases from Sellafield following the commissioning of the Enhanced Actinide Removal Plant (EARP) in 1994. In all the cores taken in this area, 99Tc has been found to be present to depths in excess of 30 cm. Analysis of 137Cs and 241Am profiles, together with other supporting geochemical data, show a high degree of homogenisation of the sediments down to these depths as a result of physical and biological processes, and confirm that incorporation of 99Tc into the sediment compartment is actually the result of mixing and reworking, rather than active sediment accumulation. In contrast, active deposition of material transported from this mixed pool of sediment appears to be the dominant mechanism controlling 99Tc profiles in intertidal areas close to the Sellafield discharge outfall.Data obtained from the analysis of subtidal sediment cores from the western Irish Sea mud basin suggest that similar mixing processes to those occurring in the subtidal sediments of the eastern Irish Sea are also active in this area. Time-series data on 99Tc concentrations in surficial sediments from this basin, gathered in the period 1988–2004, inclusive, show a clear increase in concentrations, by a factor of ~2, between samples collected pre-EARP and post-EARP. The constancy of 99Tc concentrations in surface sediments throughout the 1980s and the early-1990s suggests that little redissolution and export of 99Tc occurred over this extended period. A similar observation applies to the post-EARP period, when concentrations remained relatively constant despite the reported steady decrease in 99Tc concentrations in the overlying waters.This apparent lack of remobilisation is consistent with data from sequential extraction analyses, which indicate that the bulk of the 99Tc is strongly bound to non-labile geochemical phases, with only a small proportion associated with exchangeable and acido-soluble phases. Further, these analyses show that 99Tc is not associated with oxygen-sensitive and highly-reactive acid-volatile sulphides (AVS) to any significant extent. 相似文献
97.
Peter B. Kelemen 《Journal of the Geological Society of India》2009,74(2):280-282
Discussion
Paleoproterozoic Boninite-Like Rocks in an Intracratonic Setting from Northern Bastar Craton, Central India by D.V. Subba Rao, V. Balaram, K. Naga Raju and D.N. Sridhar. Jour. Geol. Soc. India, v.72, 2008, pp.373–380 相似文献98.
Peter Jackson 《The Professional geographer》1982,34(4):440-440
99.
Fletcher Lyndsay López Fuentes Marcelo C. Mandrini Cristina H. Schmieder Brigitte Démoulin Pascal Mason Helen E. Young Peter R. Nitta Nariaki 《Solar physics》2001,203(2):255-287
We present multi-instrument observations of active region (AR) 8048, made between 3 June and 5 June 1997, as part of the SOHO
Joint Observing Program 33. This AR has a sigmoid-like global shape and undergoes transient brightenings in both soft X-rays
and transition region (TR) lines. We compute a magneto-hydrostatic model of the AR magnetic field, using as boundary condition
the photospheric observations of SOHO/MDI. The computed large-scale magnetic field lines show that the large-scale sigmoid
is formed by two sets of coronal loops. Shorter loops, associated with the core of the SXT emission, coincide with the loops
observed in the hotter CDS lines. These loops reveal a gradient of temperature, from 2 MK at the top to 1 MK at the ends.
The field lines most closely matching these hot loops extend along the quasi-separatrix layers (QSLs) of the computed coronal
field. The TR brightenings observed with SOHO/CDS can also be associated with the magnetic field topology, both QSL intersections
with the photosphere, and places where separatrices issuing from bald patches (sites where field lines coming from the corona
are tangent to the photosphere) intersect the photosphere. There are, furthermore, suggestions that the element abundances
measured in the TR may depend on the type of topological structure present. Typically, the TR brightenings associated with
QSLs have coronal abundances, while those associated with BP separatrices have abundances closer to photospheric values. We
suggest that this difference is due to the location and manner in which magnetic reconnection occurs in two different topological
structures.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013302317042 相似文献