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   222篇
  免费   2篇
  国内免费   1篇
测绘学   3篇
大气科学   14篇
地球物理   50篇
地质学   97篇
海洋学   29篇
天文学   16篇
自然地理   16篇
  2020年   2篇
  2019年   3篇
  2018年   2篇
  2017年   4篇
  2016年   9篇
  2015年   6篇
  2014年   4篇
  2013年   13篇
  2011年   15篇
  2010年   7篇
  2009年   7篇
  2008年   4篇
  2007年   6篇
  2005年   5篇
  2004年   6篇
  2003年   9篇
  2002年   6篇
  2001年   3篇
  2000年   5篇
  1999年   3篇
  1998年   5篇
  1997年   3篇
  1996年   6篇
  1995年   4篇
  1994年   4篇
  1993年   2篇
  1992年   2篇
  1991年   2篇
  1989年   5篇
  1988年   3篇
  1987年   4篇
  1986年   1篇
  1985年   3篇
  1984年   6篇
  1983年   2篇
  1982年   3篇
  1981年   5篇
  1980年   6篇
  1979年   4篇
  1978年   9篇
  1977年   4篇
  1976年   3篇
  1974年   1篇
  1973年   2篇
  1971年   3篇
  1970年   3篇
  1969年   3篇
  1968年   1篇
  1964年   1篇
  1962年   1篇
排序方式: 共有225条查询结果,搜索用时 46 毫秒
91.
The risks to human populations in coastal areas are changing due to climate and socio-economic changes, and these trends are predicted to accelerate during the twenty-first century. To understand these changing risks, and the resulting choices and pathways to successful management and adaptation, broad-scale integrated assessment is essential. Due to their complexity the two risks of flooding and erosion are usually managed independently, yet frequently they are interconnected by longshore exchange of sediments and the resulting broad scale morphological system behaviour. In order to generate new insights into the effects of climate change and coastal management practises on coastal erosion and flood risk, we present an integrated assessment of 72 km of shoreline over the twenty-first century on the East Anglian coast of England which is a site of significant controversy about how to manage coastal flood and erosion risks over the twenty-first century. A coupled system of hydrodynamic, morphological, reliability and socio-economic models has been developed for the analysis, implemented under scenarios of coastal management, climate and socio-economic change. The study is unique in coastal management terms because of the large spatial scale and extended temporal scale over which the analysis is quantified. This study for the first time quantifies what has for some years been argued qualitatively: the role of sediments released from cliff erosion in protecting neighbouring low-lying land from flooding. The losses and benefits are expressed using the common currency of economic risk. The analysis demonstrates that over the twenty-first century, flood risk in the study area is expected to be an order of magnitude greater than erosion risk. Climate and socio-economic change and coastal management policy have a significant influence on flood risk. This study demonstrates that the choices concerning coastal management are profound, and there are clear tradeoffs between erosion and flood impacts.  相似文献   
92.
93.
94.
Southern right whales (Eubalaena australis) were widespread in New Zealand waters before commercial whaling in the nineteenth century caused drastic declines in their abundance and distribution. Following the cessation of whaling, the population has been recovering and is now slowly recolonising its former range. Estimates of population demographics, including reproductive output, are essential for predicting the trajectory of this population. We gathered photo-identification data on female southern right whales during annual field trips to the Auckland Islands, the principal calving area in New Zealand waters. Forty-five calving intervals were observed between 2006 and 2013 (mean interval?=?3.31 years, 95% CI?=?3.06–3.57). Incorporating the effects of possible missed calving events produced a plausible range of mean calving intervals from 3.17 to 3.31 years. Our results suggest that the calving interval of New Zealand southern right whales is similar to that found in populations elsewhere.  相似文献   
95.
Records of icebergs near New Zealand are noted, and their implications on the interpretation of ice‐rafted sediments are discussed.  相似文献   
96.
A simple theory for predicting the response to cyclic lateral loading of piles deeply driven in either soft clay or sand is presented and formulas given for calculating, among other things, deflection and internal bending moment along the pile. The theory assumes the soil resistance to deflection to be characterized by an initial elastic reaction up to a critical deflection level, followed by a yield reaction independent of further deflection. Soil parameters are estimated and the theory is shown to provide good correlation with existing field data.  相似文献   
97.
The alkalic pyroxenite nodule consists of megacrysts of diopside, apatite, perovskite and titanomagnetite in a groundmass consisting of diopside, apatite, titanomagnetite, nepheline, melilite, garnet and vishnevite crystals of various shapes, including previously undescribed skeletal and dendritic shapes, together with vesicles and residual glass. The residual glass is poor in SiO2 (38–40 wt%), and extraordinarily rich in Na2O (12.8–15 wt%), SO3 (1–1.5 wt%), and Cl (0.25–0.7 wt%), as a result of rapid, non-equilibrium crystallization of groundmass phases from a CO2-rich nephelinite melt.The Oldoinyo Lengai alkalic carbonatite lavas do not represent extreme products of the fractional crystallization of pyroxene, wollastonite, nepheline and alkali feldspar from the carbonated nephelinite melt. The most likely connection between the carbonatite and silicate magma types is one of liquid immiscibility, probably involving phonolite melt.  相似文献   
98.
99.
We present results from a Keck optical and near IR spectroscopic study of the giant emission line halos of the z>3 High Redshift Radio Galaxies (HiZRGs) 4C 41.17, 4C 60.07 and B2 0902+34. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s−1 and velocity shears consistent with rotation. The inner regions contain shocked, clumpy cocoons of gas closely associated with the radio lobes with disturbed kinematics and expansion velocities and/or velocity dispersions >1000 km s−1. We also find evidence for the ejection of chemically enriched material in 4C 41.17 up to a distance of ∼60 kpc along the radio-axis. We infer that these HiZRGs are undergoing a final jet-induced phase of star formation with the ejection of most of their interstellar medium before evolving to become “red and dead” Elliptical galaxies.  相似文献   
100.
Nonlinear processes describing the interaction of neutrinos with collective plasma oscillations and the excitation of plasma turbulence by a large neutrino flux is discussed. The excitation considered is the inverse processes of neutrino emission by plasma waves first considered by Tsytovich (V.N. Tsytovich, Soviet Fiz. Dokl. 9 (1965) 1114). The process is similar to a beam plasma instability considered as inverse Landau damping in which the usual electromagnetic interactions are important. In the neutrino beam relaxation the weak interaction can play a similar role. We emphasize here the possibility of another process namely the interaction of an intense neutrino flux with a strongly turbulent plasma. The turbulence can also be assumed to be due to the shock produced at the early stages of a type II supernova (SN) explosion. The scattering of the neutrinos in the turbulent plasma is shown to be sufficient for transferring momentum and energy from the neutrino flux to the plasma causing the shock to continue moving outward and eventually creating the blow-off of the mantle of the star producing type II SN.  相似文献   
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