首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   390篇
  免费   25篇
  国内免费   4篇
测绘学   16篇
大气科学   15篇
地球物理   135篇
地质学   126篇
海洋学   36篇
天文学   58篇
综合类   3篇
自然地理   30篇
  2024年   1篇
  2021年   11篇
  2020年   12篇
  2019年   9篇
  2018年   15篇
  2017年   15篇
  2016年   28篇
  2015年   16篇
  2014年   19篇
  2013年   23篇
  2012年   24篇
  2011年   26篇
  2010年   25篇
  2009年   27篇
  2008年   19篇
  2007年   15篇
  2006年   13篇
  2005年   22篇
  2004年   13篇
  2003年   12篇
  2002年   13篇
  2001年   7篇
  2000年   7篇
  1999年   4篇
  1998年   3篇
  1997年   3篇
  1996年   2篇
  1995年   4篇
  1994年   3篇
  1993年   1篇
  1991年   2篇
  1989年   1篇
  1988年   3篇
  1987年   2篇
  1986年   1篇
  1984年   8篇
  1983年   2篇
  1981年   3篇
  1980年   2篇
  1978年   1篇
  1975年   1篇
  1967年   1篇
排序方式: 共有419条查询结果,搜索用时 609 毫秒
91.
92.
93.
Small-scale fisheries and the communities they support are often given the protection of designated fishing zones from which non-artisanal vessels are excluded. This paper looks at one example of this approach, the trawl ban introduced in the Gulf of Castellammare (NW Sicily), focussing on the economic sustainability of the artisanal fishery currently operating within the protected area. The consequences of lifting the trawl ban and how far this would jeopardise the sustainability of the artisanal fishery are explored via an analysis of the financial viability of trammel net vessels under alternative assumptions concerning catch rates. The paper also investigates fishermen's attitudes towards the trawl ban and their predisposition either to remain in the fishery or to quit in the event of the ban being removed.  相似文献   
94.
95.
XMM-Newton is the direct precursor of the future ESA ATHENA mission. A study of its particle-induced background provides therefore significant insight for the ATHENA mission design. We make use of ~12 years of data, products from the third XMM-Newton catalog as well as FP7 EXTraS project to avoid celestial sources contamination and to disentangle the different components of the XMM-Newton particle-induced background. Within the ESA R&D AREMBES collaboration, we built new analysis pipelines to study the different components of this background: this covers time behavior as well as spectral and spatial characteristics.  相似文献   
96.
We investigate the inclusions hosted in peritectic garnet from metapelitic migmatites of the Kinzigite Formation (Ivrea Zone, NW Italy) to evaluate the starting composition of the anatectic melt and fluid regime during anatexis throughout the upper amphibolite facies, transition, and granulite facies zones. Inclusions have negative crystal shapes, sizes from 2 to 10 μm and are regularly distributed in the core of the garnet. Microstructural and micro‐Raman investigations indicate the presence of two types of inclusions: crystallized silicate melt inclusions (i.e., nanogranitoids, NI), and fluid inclusions (FI). Microstructural evidence suggests that FI and NI coexist in the same cluster and are primary (i.e., were trapped simultaneously during garnet growth). FI have similar compositions in the three zones and comprise variable proportions of CO2, CH4, and N2, commonly with siderite, pyrophyllite, and kaolinite, suggesting a COHN composition of the trapped fluid. The mineral assemblage in the NI contains K‐feldspar, plagioclase, quartz, biotite, muscovite, chlorite, graphite and, rarely, calcite. Polymorphs such as kumdykolite, cristobalite, tridymite, and less commonly kokchetavite, were also found. Rehomogenized NI from the different zones show that all the melts are leucogranitic but have slightly different compositions. In samples from the upper amphibolite facies, melts are less mafic (FeO + MgO = 2.0–3.4 wt%), contain 860–1700 ppm CO2 and reach the highest H2O contents (6.5–10 wt%). In the transition zone melts have intermediate H2O (4.8–8.5 wt%), CO2 (457–1534 ppm) and maficity (FeO + MgO = 2.3–3.9 wt%). In contrast, melts at granulite facies reach highest CaO, FeO + MgO (3.2–4.7 wt%), and CO2 (up to 2,400 ppm), with H2O contents comparable (5.4–8.3 wt%) to the other two zones. Our results represent the first clear evidence for carbonic fluid‐present melting in the Ivrea Zone. Anatexis of metapelites occurred through muscovite and biotite breakdown melting in the presence of a COH fluid, in a situation of fluid–melt immiscibility. The fluid is assumed to have been internally derived, produced initially by devolatilization of hydrous silicates in the graphitic protolith, then as a result of oxidation of carbon by consumption of Fe3+‐bearing biotite during melting. Variations in the compositions of the melts are interpreted to result from higher T of melting. The H2O contents of the melts throughout the three zones are higher than usually assumed for initial H2O contents of anatectic melts. The CO2 contents are highest at granulite facies, and show that carbon‐contents of crustal magmas are not negligible at high T. The activity of H2O of the fluid dissolved in granitic melts decreases with increasing metamorphic grade. Carbonic fluid‐present melting of the deep continental crust represents, together with hydrate‐breakdown melting reactions, an important process in the origin of crustal anatectic granitoids.  相似文献   
97.
We present an accurate characterization of the particle background behaviour on XMM-Newton based on the entire EPIC archive. This corresponds to the largest EPIC data set ever examined. Our results have been obtained thanks to the collaboration between the FP7 European program EXTraS and the ESA R&D ATHENA activity AREMBES. We used as a diagnostic an improved version of the diagnostic which compares the data collected in unexposed region of the detector with the region of the field of view in the EPIC-MOS. We will show that the in Field-of-View excess background is made up of two different components, one associated to flares produced by soft protons and the other one to a low-intensity background. Its origin needs to be further investigated.  相似文献   
98.
No-till (NT) is a conservation system that improves the hydrological regime of agricultural slopes by providing greater surface protection and benefits to the physical and hydrological properties of soils. However, the isolated use of NT is not enough to control runoff and its associated degradation processes. Therefore, this study aimed to evaluate the runoff of agricultural slopes under NT under different runoff control conditions by monitoring 63 rainfall events in two 2.4-ha zero-order catchments and 27 rainfall events in four 0.6-ha macroplots. The catchments are paired and similar in terms of the type of soil and relief, but different regarding the presence of terraces. The macroplots have different soil and crop management systems. By using monitoring techniques, the hyetographs and hydrographs revealed the influence of the different types of management on the catchments and macroplots and allowed rainfall characteristics, runoff volume, runoff coefficients, water infiltration, peak runoff, response times, and curve number to be analysed. The terraces positively affected the NT and controlled runoff and related variables, in addition to infiltration significantly increasing and runoff reducing in the terraced catchment. All the hydrological information assessed pointed to the positive effects provided by the presence of the terraces. The results in the macroplots showed that high amounts of phytomass and/or chiselling do not control runoff and its correlated variables in medium and high magnitude events. The study concludes by underlining the need for additional measures to control runoff (terraces), even in areas under NT and with high phytomass production. Additionally, the study emphasizes the importance of monitoring at the catchment scale to better understand the hydrological behaviour of agricultural areas and provide the necessary parameters to effectively control runoff.  相似文献   
99.
Our study aimed to identify possible relationships between the structure of the benthic macrofauna and the intense use of vehicles in Cassino Beach. Physical changes in the sediment were identified, with high compaction in the sector most affected by the vehicles, especially during the summer. The benthic macrofauna was significantly affected by vehicles, with lower densities observed in the most impacted sector, mainly in the summer, unlike the control sector, where higher densities were observed during the pre-summer and summer. We concluded that the vehicle traffic changes the physical environment of the beach and consequently affects the benthic community in the face of this disturbance. We conclude that the benthic macrofauna is highly impacted by vehicle traffic at Cassino Beach, mainly in the period with the highest traffic, and alternatives are needed for this impact, helping to recover this ecosystem.  相似文献   
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号