全文获取类型
收费全文 | 324篇 |
免费 | 23篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 22篇 |
地球物理 | 81篇 |
地质学 | 146篇 |
海洋学 | 22篇 |
天文学 | 46篇 |
综合类 | 2篇 |
自然地理 | 26篇 |
出版年
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 3篇 |
2018年 | 11篇 |
2017年 | 18篇 |
2016年 | 24篇 |
2015年 | 18篇 |
2014年 | 33篇 |
2013年 | 35篇 |
2012年 | 19篇 |
2011年 | 22篇 |
2010年 | 21篇 |
2009年 | 18篇 |
2008年 | 11篇 |
2007年 | 3篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 5篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1968年 | 1篇 |
1962年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有351条查询结果,搜索用时 15 毫秒
1.
In an earlier paper Arp, Bi, Chu and Zhu investigated various quasar samples and recognized a periodicity of remarkable degree in them. Their conclusion was that the existence of such a periodicity is a counterevidence against the cosmological origin of quasar redshifts. Since this question is of great importance in a cosmological context, here we reanalyze some of the samples together with a galaxy sample of the pencil-beam survey of Broadhurstet al. Our result is that on the plane of cosmological parameters (0, 0) there is a non-negligible region where two quasar samples and the galaxy sample are simultaneously fairly periodic. Pure periodicity is still compatible with cosmological principles, at least on length scales much longer than the period length. So the regularities can fit into a cosmological context. 相似文献
2.
This paper presents a computer investigation extending to the case of parabolic orbits, an earlier investigation conducted by Barricelli and Metcalfe (1969) on lunar impacts by external low eccentricity satellites as a means to interpret the asymmetric distribution of lunar maria. Parabolic orbits can be approximated by two kinds of objects:
- High eccentricity external satellites may, near periapsis, approach the Moon with orbital velocity and other characteristics closely resembling those of a parabolic orbit.
- Asteroids and meteoroids approaching the Earth-Moon system with a low velocity may have moved in a nearly parabolic orbit when they reached the lunar distance from the Earth at the time when the impacts which carved the lunar maria took place.
3.
The paper deals with a selection of the climatological baseline, GCM validity and construction of the climate change scenarios for an impact assessment in the Czech territory. The period of 1961–1990 has been selected as the climatological baseline. The corresponding database includes more than 50 monthly mean temperature and precipitation series, and 16 time series of daily meteorological data that contain also the solar radiation data. The 1× CO2 outputs produced by four GCMs, provided by the CSMT (GISS, GFD30, GFD01, and CCCM), were compared with observed temperature and precipitation conditions in western and central Europe with a particular attention devoted to the Czech territory. The GCM ability to simulate annual cycles of temperature, precipitation and radiation was thoroughly examined. The GISS and CCCM were selected as a basis for constructing climate change scenarios as they simulated reasonably the observed patterns. According to the GISS variant, 2× CO2 climate assumes a higher winter and lower summer warming, and an increase in annual precipitation amounts. A dangerous combination of the summer temperature increase and declining precipitation amounts is a specific feature of the CCCM scenario. An incremental scenario for temperature and precipitation is based on the combination of prescribed changes in both annual means and annual courses. 相似文献
4.
Andean grasslands ecosystems are fragile environments with rigorous climatologic conditions and low and variable food for the grazing. The Apolobamba area is located in the Bolivian Andean Mountains. Its high grasslands provide a natural habitat for wild and domestic camelids such as vicuna(Vicugna vicugna) and alpaca(Lama pacos). The botanical diversity plays an essential role in maintaining vital ecosystem functions. The objectives of this research were to determine the seasonal changes in soil properties, to study the vegetation changes during the wet and dry seasons and the influence of soil properties and camelid densities on the vegetation in the Apolobamba grasslands. Four zones with different vicuna populations were selected to be studied. The following soil parameters were determined: total organic carbon, total nitrogen, available phosphorous, cation exchange capacity, exchangeable cations, pH and texture. The vegetation season changes were studied through botanical identification, above-ground biomass, plant cover and species richness. Results showed that some soil properties such as C/N ratio, CEC, silt and clay percentages kept stable against the seasonal changes. Generally, soil nutrients were relatively higher during the dry season in the surface and subsurface. The results did not point out the predominant vegetation growth during the wet season. The seasonal vegetation growth depended on each species. Thegood soil fertility corresponded to the highest plant cover. Soil fertility presented no influence on the above-ground biomass of the collected species. The negative influence of camelid grazing on soil properties could not be assessed. However, overgrazing could affect some plant species. Therefore, protection is needed in order to preserve the biodiversity in the Andean mountain grasslands. 相似文献
5.
GeoJournal - The purpose of this study was to investigate the opportunities which accrue from application of PPPs in development of down market urban housing in Kenya, hence attracting private... 相似文献
6.
The rich Quaternary fossil record from the Cantabrian region (NW Iberia) is virtually restricted to the Late Pleistocene, with Middle Pleistocene findings very rare. This work presents the study of two Middle Pleistocene palaeontological sites in the Cantabrian region: Llantrales quarry and Mestas de Con mine, both discovered and first described in the 1950s but never studied in detail thereafter. The material was here re‐analysed and re‐evaluated. Taxonomic attributions have been changed in most cases and, consequently, chronological assignments of the fossils have also been changed. This first detailed study of the assemblage from Llantrales quarry revealed the occurrence of the large‐sized deer Praemegaceros solilhacus, which has never been reported previously in North Iberia. Cervus cf. elaphus and Stephanorhinus cf. hundsheimensis were also identified. The age of these fossils was originally regarded as Pontian (late Miocene), but new palaeontological results indicate a much younger age, most likely from around 0.8 to 0.5 Ma. A taxonomic re‐evaluation of the fossils from Mestas de Con provided different results with respect to the 1950s works. The faunal association is composed of a large‐sized deer (probably corresponding to Praemegaceros), Cervus elaphus, Capreolus cf. capreolus, Bison sp. (small sized), Equus sp. (large sized), Stephanorhinus hemitoechus, Ursus sp. and Homotherim latidens. This faunal association was evaluated within a western European context and proves to be highly analogous to other contemporary assemblages there. The chronology was initially regarded as late Villafranchian (in a broader sense). New results, documenting the co‐occurrence of Stephanorhinus hemitoechus and Homotherium latidens, indicate a more precise and younger age, most likely between 0.6 and 0.4 Ma. These two fossil assemblages provide new and relevant information on the Middle Pleistocene faunas from a geographical region where this information, compared with other western European areas, is rare and poorly known. 相似文献
7.
J. J. Álvaro E. Vennin A. Muñoz B. Sánchez-Valverde J. L. Ojeda 《International Journal of Earth Sciences》2000,89(2):366-376
The stratigraphy of carbonate/shale couplets, cycles and cycle-stacking patterns in a Cambrian shallow water platform (Iberian
Chains, NE Spain) are related to sea-level changes driven by orbital forcing and by tectonic pulses. The interplay of both
effects can be discriminated in the Iberian fault-controlled platform, in which the tectonic activity can be analysed by accurate
and detailed biostratigraphic correlations based on trilobite zonation. The stratigraphic hierarchy of rhythmically interbedded
limestones and shales, in two coeval but structurally separated geodynamic settings, yields cycle ratios of 1.44 :1. This
ratio is supported by time thickness and spectral analysis, which is based on a graphic method of analysis: the Map of Grey
Lines. The cycle ratio seems to be evidence for orbital forcing by obliquity and precession cycles predicted for early Paleozoic
time. Carbonate/shale couplets, the smallest rhythmic units recognisable in the field, represent short-term, periodic fluctuations
in supply of terrigenous sediments and carbonate productivity of uncertain origin, which could be associated with one of several
harmonics of the former orbital cycles. The pulsating tectonic activity was approximated by using a quantitative analysis
of tectonically induced subsidence (Shaw method). Recurrence frequencies of tectonic pulses were estimated and dated by biostratigraphy.
As a result, tectonic disturbances in the Cambrian Iberian platform show an episodic periodicity comparable to that of orbital
eccentricity cycles, which could mask their recognition.
Received: 15 November 1999 / Accepted: 9 February 2000 相似文献
8.
Crustacean decapod assemblages associated with fragmented Posidonia oceanica meadows in the Alboran Sea (Western Mediterranean Sea): composition,temporal dynamics and influence of meadow structure 下载免费PDF全文
Ángel Mateo‐Ramírez Javier Urra Pablo Marina José L. Rueda José Enrique García Raso 《Marine Ecology》2016,37(2):344-358
The decapod assemblage associated with a Posidonia oceanica meadow located near its western limit of biogeographic distribution was studied over an annual cycle. Fauna samples were taken seasonally over a year (five replicates per season) in two sites located 7 km apart, using a non‐destructive sampling method (airlift sampler) for the seagrass. The dominant species of the assemblage, Pisidia longimana, Pilumnus hirtellus and Athanas nitescens, were associated with the protective rhizome stratum, which is mainly used as a nursery. The correlations between decapod assemblage structure and some phenological parameters of the seagrass shoots and wave height were negative or null, which reflects that species associated with the rhizome had a higher importance than those associated with the leaf stratum. The abundance and composition of the decapod assemblage as well as the ecological indexes displayed a seasonality trend with maximum values in summer‐autumn and minimum in winter‐spring, which were related to the seawater temperature and the recruitment periods of the dominant species. The spatial differences found in the structure and dynamics of the assemblages may be due to variations in the recruitment of the dominant species, probably as a result of the influence of local factors (e.g. temperature, currents) and the high dispersal ability of decapods, together with the patchy configuration and the surrounding habitats. The studied meadows are fragmented and are integrated within a mosaic of habitats (Cymodocea nodosa patches, algal meadows, rocky and sandy bottoms), which promotes the movement of individuals and species among them, maintaining a high species richness and evenness. 相似文献
9.
Diana Tingley Jóhann Ásmundsson Edward Borodzicz Alexis Conides Ben Drakeford Ingi Rúnar Eðvarðsson Dennis Holm Kostas Kapiris Sakari Kuikka Bogi Mortensen 《Marine Policy》2010
This paper presents the findings of risk identification and risk perception research conducted in relation to the fisheries systems of four distinct and diverse European countries: Faroes, Iceland, Greece and the UK. Risk research traditionally attempts to quantify the potential threat or consequences from a range of risk events or hazards. This research, however, adopted a social sciences perspective and so assumed that a risk event or hazard can mean different things to different people and that these perceptions are also context and culturally dependent. Risk perceptions were examined and risk registers developed in each country for a range of stakeholder groups. A ‘mental modelling’ approach was adopted in a series of qualitative interviews. Findings were examined in terms of a wide range of psychological, social and cultural risk theories. Differences in risk perceptions were noted between stakeholder groups and countries and contextual influences were examined such as the widely differing fisheries management systems used in each country. This research provides one of the first attempts to systematically evaluate risks and perceptions across a range of fisheries-systems. The findings support social science theories which argue that risk is a subjective, as opposed to objective, concept and that this subjectivity will therefore affect our attempts to assess and manage those hazards we think we can potentially influence or control. 相似文献
10.
JiřÍ Polcar Martin Topinka Graziella Pizzichini Eliana Palazzi Nicola Masetti RenÉ Hudec Věra HudcovÁ 《Astrophysics and Space Science》2005,296(1-4):485-488
We report on our statistical research of space–time correlated supernovae and CGRO-BATSE gamma-ray bursts (GRBs). There exists
a significantly higher abundance of core-collapse supernovae among the correlated supernovae, but the subset of all correlated
objects does not seem to be physically different from the whole set. 相似文献