全文获取类型
收费全文 | 368篇 |
免费 | 12篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 34篇 |
地球物理 | 106篇 |
地质学 | 107篇 |
海洋学 | 41篇 |
天文学 | 63篇 |
综合类 | 3篇 |
自然地理 | 28篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 6篇 |
2019年 | 3篇 |
2018年 | 18篇 |
2017年 | 10篇 |
2016年 | 16篇 |
2015年 | 18篇 |
2014年 | 12篇 |
2013年 | 20篇 |
2012年 | 22篇 |
2011年 | 18篇 |
2010年 | 17篇 |
2009年 | 31篇 |
2008年 | 18篇 |
2007年 | 31篇 |
2006年 | 16篇 |
2005年 | 22篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 7篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1960年 | 1篇 |
1944年 | 1篇 |
排序方式: 共有386条查询结果,搜索用时 234 毫秒
81.
Alejandro?D.?Canepuccia Maria?S.?Fanjul Eugenia?Fanjul Florencia?Botto Oscar?O.?Iribarne Consejo Nacional de Investigaciones Científicas y Técnicas Departamento de Biología Universidad Nacional de Mar del Plata Mar del Plata Argentina 《Estuaries and Coasts》2008,31(5):920-930
The role of positive and indirect interactions is often crucial in communities with intense abiotic stress such as salt marshes.
The burrowing crab, Neohelice (=Chasmagnathus) granulata, is the dominant benthic macroinvertebrate of southwest Atlantic marshes (southern Brazil to Northern Argentinean Patagonia),
having strong direct and indirect effects on marsh soil and, in consequence, on marsh vegetation and primary consumers. In
this work, we investigate if this crab indirectly modifies habitat use by the granivorous rodents, Akodon azarae and Oligoryzomys flavescens, by increasing nutrient availability and thus enhancing seed production by the marsh plant Spartina densiflora. The study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37°32′ S). Rodent frequencies in S. densiflora were positively correlated with crab densities throughout the low and middle marsh. Additionally, the highest quality of
S. densiflora and inflorescence density was recorded at the highest crab densities. Experimental manipulation of crab densities shows that
N. granulata indirectly enhances the performance of S. densiflora (e.g., decreased fiber content and C/N ratios) and increases density of seeds. Moreover, N. granulata also facilitates S. densiflora seed availability to rodents by concentrating them in sediment mound at their burrows entrances. Experimental rodent exclusions
showed that rodent species used S. densiflora seeds, a variable positively related to crab burrow density. Thus, our results show that N. granulata drives the granivorous rodent distribution and the intensity of seeds–rodent interaction trough facilitative and indirect
interactions in marsh community. 相似文献
82.
83.
High pressure, hot water shore cleaning after an oil spill will release high concentrations of petroleum hydrocarbons to ambient marine ecosystems. The immediate increase of hydrocarbons observed in blue mussels, Mytilus edulis, went from background concentrations of 40 μg/g to 657 μg/g and 533 μg/g at a distance of 3 and 8m respectively from the shore. After two weeks the accumulated oil had decreased by 20–45 %. In comparison natural surf and ice cleaning of shores will only produce a small increase in hydrocarbon concentrations. We recommend that high pressure, hot water cleaning is not used in areas where no special bird or wild life protection is needed. 相似文献
84.
85.
Cecilia Möller Eva Alfredsson-Olsson Birgitta Ericsson Kjell Overvåg 《Norsk geografisk tidsskrift. Norwegian journal of geography》2018,72(4):217-233
The purpose of the study was to analyse how cross-border commuting differed from intranational commuting in Sweden, and how cross-border mobilities affected spatial integration. The authors analysed patterns and spatial flows of cross-border commuting by comparing them with characteristics of intranational commuting. In the article, they explore the assumption that the border constitutes an ‘engine’ for work-related mobility, which affects processes of spatial integration in cross-border areas. The empirical material comprised data from surveys of commuting from the Swedish county of Värmland to Norway and commuting within Värmland. The findings showed that cross-border commuting shared common features with intranational commuting, including how the frequency of commuting was dependent on distance. The motives for commuting differed, and the reasons for working in Norway were economic rather than professional. In terms of spatial integration, cross-border commuting was mainly one-directional, from Sweden to Norway, while leisure mobility and migration tended to be in the opposite direction. The authors conclude that the border region is characterised by integration through specialisation, which involves a permanent state of ‘transient’ mobility. Thus, a win-win situation can be distinguished, in which the border serves as a resource and an ‘engine’ for cross-border integration, mobility and economic activities. 相似文献
86.
Sergio Rocchi Alfredo Mazzotti Michele Marroni Luca Pandolfi Paolo Costantini Bertozzi Giuseppe Davide di Biase Francesco Federici Papa Goumbo L 《地学学报》2007,19(4):232-239
The Atlantic margin offshore Senegal has been explored by seismic reflection and GRAV‐MAG surveys. High‐amplitude, laterally transgressive seismic reflectors are found to coincide with gravimetric and magnetic highs. Once seismic data are integrated with potential fields modelling, these reflectors can be safely interpreted as saucer‐shaped igneous sills, up to some hundreds of metres thick, some km wide. The occurrence of hydrothermal vent complexes and forced folds in the stratigraphic sequence above the sills constrain the intrusion age to the Miocene. Field observations and in‐situ magnetic susceptibility measurements of Oligocene–Miocene and Quaternary igneous rocks emplaced in coastal Senegal support this interpretation. 相似文献
87.
K. Bensch A. del Olmo J. Sulentic J. Perea P. Marziani 《Journal of Astrophysics and Astronomy》2015,36(4)
We present a preliminary analysis of X-ray data of quasars in the context of the 4D eigenvector 1 parameter space (Sulentic et al. 2000a, b). 4DE1 serves as a surrogate H-R diagram for representing empirical diversity among quasars and identifying the physical drivers of the diversity. The soft X-ray spectral index (Γsoft) was adopted as one of the key 4DE1 that correlates contrasting extremes in Type 1 properties. 4DE1 motivated the hypothesis of two quasar populations (A and B) divided by L/L EDD≈0.2. Pop. A is a largely radio-quiet population with FWHM H β<4000 km/s and often showing a soft X-ray excess. Pop. B is a mix of radio-quiet and a majority of RL quasars shows only a hard X-ray power-law SED. The X-ray separation was based upon earlier ROSAT and ASCA data but we now confirm this dichotomy with large samples of X-ray spectra obtained with XMM-Newton and SWIFT. One popular idea connects the soft excess in Pop. A quasars as a signature of thermal emission from a hot accretion disk in sources radiating close to the Eddington limit. 相似文献
88.
Jos Luis Orgeira Mariela del Carmen Alderete Yohana Gisell Jimnez Juan Cruz Gonzlez 《极地研究(英文版)》2015,(2)
The Scotia Sea is one of the most biologically rich regions of Antarctica, and it hosts a large community of upper trophic-level predators. Long-term at-sea monitoring provides valuable information on ... 相似文献
89.
Introductions of non-indigenous species (NIS) are mostly discussed through their impact on biodiversity. However, NIS can also act as ecosystem engineers, influencing the habitat itself, positively or negatively, directly or indirectly, which should be included when making risk assessments. Special concern should be given to changes in ecological services provided by the ecosystem. Physically, NIS may affect the substrate itself, or alter habitat architecture, indirectly influencing water movements, sediment accumulation, and light conditions. Chemical changes brought upon by NIS occur both on small and large scales, some having positive effects on ecosystem services, others can perturb epibionts. Furthermore, NIS may negatively affect natural resources, aquaculture or create fouling communities, all resulting in a negative impact on economics. However, if removed, already established NIS can be used as bioremediators, having a positive effect on different ecosystems. Using NIS for habitat management may be economically profitable, but could affect the habitat adversely. 相似文献
90.
Rodolfo H. Barbá Jesús Maíz Apellániz Enrique Pérez Mónica Rubio Alberto Bolatto Cecilia Fariña Guillermo Bosch Nolan R. Walborn 《Astrophysics and Space Science》2009,324(2-4):309-313
We present the first high-spatial-resolution near-infrared (NIR) imaging of NGC604, obtained with the NICMOS camera onboard the Hubble Space Telescope (HST). These NICMOS broad-band images reveal new NIR point sources, clusters, and diffuse structures. We find an excellent spatial correlation between the 8.4 GHz radio continuum and the 2.2 μm nebular emission. Moreover, massive young stellar object candidates appear aligned with these radio peaks, reinforcing the idea that those areas are star-forming regions. Three different scaled OB associations are recognized in the NICMOS images. The brightest NIR sources in our images have properties that suggest that they are red supergiant stars, of which one was previously known. This preliminary analysis of the NICMOS images shows the complexity of the stellar content of the NGC604 nebula. 相似文献