全文获取类型
收费全文 | 371篇 |
免费 | 10篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 56篇 |
地球物理 | 75篇 |
地质学 | 138篇 |
海洋学 | 15篇 |
天文学 | 38篇 |
综合类 | 1篇 |
自然地理 | 29篇 |
出版年
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 13篇 |
2013年 | 17篇 |
2012年 | 30篇 |
2011年 | 19篇 |
2010年 | 12篇 |
2009年 | 17篇 |
2008年 | 19篇 |
2007年 | 21篇 |
2006年 | 9篇 |
2005年 | 27篇 |
2004年 | 22篇 |
2003年 | 16篇 |
2002年 | 11篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1970年 | 3篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 3篇 |
1965年 | 2篇 |
1950年 | 1篇 |
排序方式: 共有381条查询结果,搜索用时 31 毫秒
91.
This article addresses the importance and meanings of formal and informal social support relationships and neighbourhood ties for older adults ‘ageing in place’ in urban neighbourhoods in two different welfare state settings: Portland (Oregon, the United States) and Amsterdam (the Netherlands). The rising number of people growing old(er) in urban environments raises new demands and pressing challenges for urban development. The majority of older adults are and will be ageing in their homes and communities, as opposed to institutionalized care facilities and settings. At the same time, the provision of formal and public care is being increasingly challenged by government cutbacks. On top of this, the formerly strong welfare states in many European countries have weakened. In-depth interviews with 40 older adults and key informants in two neighbourhoods in each city provide the empirical basis for this study. In Portland, there are widespread local civic initiatives related to care provision for older adults. The city has a long tradition both of individual responsibility and community culture, which has emerged from and appears to compensate for the overall lack of state services and support. Amsterdam has a long tradition of state provision, but is experiencing a policy shift towards a stronger reliance on private market-led services, and an emphasis on family and community as providers of support. Although a few emerging local initiatives for elderly care in Amsterdam were identified, it is unclear whether this form of community support can compensate for decreasing state provision in Amsterdam. This study raises concerns about the future of care provision for older adults living in unsupportive urban neighbourhoods, without financial resources or nearby relatives. 相似文献
92.
93.
Estimation of satellite antenna phase center offsets for Galileo 总被引:2,自引:1,他引:1
P. Steigenberger M. Fritsche R. Dach R. Schmid O. Montenbruck M. Uhlemann L. Prange 《Journal of Geodesy》2016,90(8):773-785
94.
Abstract. The predator-prey interaction between two sea star species of the genus Astropecten known to be competitors was investigated at Costa Colostrai, Sardinia, Italy by means of SCUBA-Diving. It was estimated that predation of A. aranciacus would eliminate about 1 % of the prey population of A. bispinosus daily. Because densities of A. bispinosus were observed to be unaltered during the summer months, a considerable immigration of A. bispinosus into the area has to be postulated. A. bispinosus represents 40% of the dry organic matter consumed by A. aranciacus , and is one of the most important food items of this species.
A. aranciacus is not more efficient in preying upon A. bispinosus than in preying upon other food items; but efficiency is greater upon buried sea stars than upon walking ones.
Consequences for stability of the local ecosystem are discussed. 相似文献
A. aranciacus is not more efficient in preying upon A. bispinosus than in preying upon other food items; but efficiency is greater upon buried sea stars than upon walking ones.
Consequences for stability of the local ecosystem are discussed. 相似文献
95.
96.
Differential recruitment of introduced Pacific oysters and native mussels at the North Sea coast: coexistence possible? 总被引:5,自引:3,他引:5
Susanne Diederich 《Journal of Sea Research》2005,53(4):269-281
Pacific oysters (Crassostrea gigas Thunberg 1793) have been introduced into the Wadden Sea (North Sea), where they settle on native mussel beds (Mytilus edulis L.), which represent the only extensive insular hard substrata in this soft-sediment environment. As abundances of C. gigas rose, some mussel beds became increasingly overgrown with oysters, whereas others did not. Field experiments revealed that recruitment of C. gigas was higher in the lower intertidal than in the upper subtidal zone, that it was higher on conspecifics than on mussels, and that it was not affected by barnacle epigrowth except when settling on mussels. Mussel recruitment is known from inter- and subtidal zones. It occurred equally on oyster and mussel shells but showed a clear preference for barnacle epigrowth over clean shells. Assuming that settlement and recruitment are key processes for species abundances on the North Sea coast, it is predicted that the positive feedback in oyster settlement will lead to rapid reef formation of this invader at the expense of mussel beds. Mussels, however, may escape competitive exclusion by settling between or on the larger oysters especially when barnacles are abundant. Experimental patches with mussels were more often covered by fucoid algae (Fucus vesiculosus forma mytili Nienburg) than patches with oysters, and oyster recruitment was poor underneath such algal canopies. Thus, fucoids may provide the native mussels with a refuge from the invading oysters and the two bivalves may coexist, provided food is not limiting. 相似文献
97.
A model for a symbiotic system is presented which is not spherically symmetrical. The system consists of a cool, mass losing giant and a hot star. The stellar wind from the cool star is radiatively ionized by the hot companion, and the resulting nebular lines are emitted mainly close to the cool star. Due to the elliptical orbit, the line fluxes change with time because of the varying separation of the stars. The line profiles vary from symmetrical to asymmetrical, depending on the angle between the line of sight and the axis of symmetry. The calculated line profiles are compared with observed UV lines of the symbiotic star HBV 475.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables, Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986. 相似文献
98.
We employ numerical and analytical methods to investigate the effect of the presence of rigid porphyroblasts such as garnets on layer strengthening and the folding instability. We use a 50% fraction of non‐overlapping, circular‐shaped inclusions with a wide size distribution. These inclusions cause a fourfold effective viscosity increase and can significantly promote the folding instability. This is not only due to the increased viscosity but also due to the layer interface roughness generation driven by relative movement of inclusions. The increase in layer viscosity promotes strengthening of the whole system. However, with progressive fold development, the system undergoes an effective softening that may counteract the strengthening effect of the porphyroblast growth. 相似文献
99.
P. A. Durkee K. E. Nielsen P. J. Smith P. B. Russell B. Schmid J. M. Livingston B. N. Holben C. Tomasi V. Vitale D. Collins R. C. Flagan J. H. Seinfeld K. J. Noone E. Öström S. Gassó D. Hegg L. M. Russell T. S. Bates P. K. Quinn 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):484-497
Analysis of the aerosol properties during 3 recent international field campaigns (ACE‐1, TARFOX and ACE‐2) are described using satellite retrievals from NOAA AVHRR data. Validation of the satellite retrieval procedure is performed with airborne, shipboard, and land‐based sunphotometry during ACE‐2. The intercomparison between satellite and surface optical depths has a correlation coefficient of 0.93 for 630 nm wavelength and 0.92 for 860 nm wavelength. The standard error of estimate is 0.025 for 630 nm wavelength and 0.023 for 860 nm wavelength. Regional aerosol properties are examined in composite analysis of aerosol optical properties from the ACE‐1, TARFOX and ACE‐2 regions. ACE‐1 and ACE‐2 regions have strong modes in the distribution of optical depth around 0.1, but the ACE‐2 tails toward higher values yielding an average of 0.16 consistent with pollution and dust aerosol intrusions. The TARFOX region has a noticeable mode of 0.2, but has significant spread of aerosol optical depth values consistent with the varied continental aerosol constituents off the eastern North American Coast. 相似文献
100.
Markus Tum Franziska Strauss Ian McCallum Kurt Günther Erwin Schmid 《Carbon balance and management》2012,7(1):1-13