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   568篇
  免费   33篇
  国内免费   5篇
测绘学   15篇
大气科学   93篇
地球物理   120篇
地质学   206篇
海洋学   33篇
天文学   84篇
综合类   14篇
自然地理   41篇
  2024年   2篇
  2023年   3篇
  2021年   8篇
  2020年   10篇
  2019年   12篇
  2018年   26篇
  2017年   14篇
  2016年   31篇
  2015年   22篇
  2014年   25篇
  2013年   44篇
  2012年   36篇
  2011年   36篇
  2010年   33篇
  2009年   39篇
  2008年   38篇
  2007年   27篇
  2006年   25篇
  2005年   32篇
  2004年   16篇
  2003年   18篇
  2002年   8篇
  2001年   13篇
  2000年   5篇
  1999年   5篇
  1998年   6篇
  1997年   3篇
  1996年   5篇
  1995年   2篇
  1994年   7篇
  1993年   2篇
  1992年   1篇
  1991年   6篇
  1990年   5篇
  1989年   6篇
  1988年   7篇
  1987年   2篇
  1986年   4篇
  1982年   3篇
  1981年   3篇
  1980年   2篇
  1979年   1篇
  1971年   1篇
  1970年   2篇
  1969年   2篇
  1968年   1篇
  1967年   3篇
  1966年   1篇
  1955年   1篇
  1954年   1篇
排序方式: 共有606条查询结果,搜索用时 15 毫秒
11.
Climate is a major determinant of energy demand. Changes in climate may alter energy demand as well as energy demand patterns. This study investigates the implications of climate change for energy demand under the hypothesis that impacts are scale dependent due to region-specific climatic variables, infrastructure, socioeconomic, and energy use profiles. In this analysis we explore regional energy demand responses to climate change by assessing temperature-sensitive energy demand in the Commonwealth of Massachusetts. The study employs a two-step estimation and modeling procedure. The first step evaluates the historic temperature sensitivity of residential and commercial demand for electricity and heating fuels, using a degree-day methodology. We find that when controlling for socioeconomic factors, degree-day variables have significant explanatory power in describing historic changes in residential and commercial energy demands. In the second step, we assess potential future energy demand responses to scenarios of climate change. Model results are based on alternative climate scenarios that were specifically derived for the region on the basis of local climatological data, coupled with regional information from available global climate models. We find notable changes with respect to overall energy consumption by, and energy mix of the residential and commercial sectors in the region. On the basis of our findings, we identify several methodological issues relevant to the development of climate change impact assessments of energy demand.  相似文献   
12.
Metabasites were sampled from rock series of the subducted margin of the Indian Plate, the so-called Higher Himalayan Crystalline, in the Upper Kaghan Valley, Pakistan. These vary from corona dolerites, cropping out around Saif-ul-Muluk in the south, to coesite–eclogite close to the suture zone against rocks of the Kohistan arc in the north. Bulk rock major- and trace- element chemistry reveals essentially a single protolith as the source for five different eclogite types, which differ in fabric, modal mineralogy as well as in mineral chemistry. The study of newly-collected samples reveals coesite (confirmed by in situ Raman spectroscopy) in both garnet and omphacite. All eclogites show growth of amphiboles during exhumation. Within some coesite-bearing eclogites the presence of glaucophane cores to barroisite is noted whereas in most samples porphyroblastic sodic–calcic amphiboles are rimmed by more aluminous calcic amphibole (pargasite, tschermakite, and edenite). Eclogite facies rutile is replaced by ilmenite which itself is commonly surrounded by titanite. In addition, some eclogite bodies show leucocratic segregations containing phengite, quartz, zoisite and/or kyanite. The important implication is that the complex exhumation path shows stages of initial cooling during decompression (formation of glaucophane) followed by reheating: a very similar situation to that reported for the coesite-bearing eclogite series of the Tso Morari massif, India, 450 km to the south-east.  相似文献   
13.
14.
15.
根据2003和2006年长江口及邻近海域表层沉积物样品的粒度组成和元素铬、铜、镍、铅、锌、铝、钙和锶的含量,分析了重金属元素含量的分布特征,探讨了含量的变化趋势及其对人类活动的响应。自2003年三峡工程一期蓄水完成到2006年6月,长江输沙量逐年减少,长江口海域沉积物中黏土的百分含量明显增加,但是沉积物分布的总体格局并没有发生明显的变化。重金属元素大多在泥质区沉积物中富集,高值区沿岸线呈带状分布,在最大浑浊带和口外羽状锋处达到峰值。在长江大量物质输入的背景下,研究区沉积物中重金属元素含量相对其他类似河口较低。河流的陆源颗粒输入、水动力条件、细颗粒物质的吸附以及絮凝作用是控制沉积物中重金属元素含量分布的主要因素,氧化还原条件也对重金属元素含量变化有一定的影响。人类活动(重大工程的建设和人为污染)对长江口外泥质区中重金属元素含量有重要影响,尤其对铅和锌的含量及其分布的影响显著。自2003年三峡工程一期蓄水以来,长江口海域表层沉积物中重金属元素沉积机制未有明显的变化,但是重金属元素含量有逐渐降低的趋势。  相似文献   
16.
17.
We investigate the effects of an isolated meso-\(\gamma \)-scale surface heterogeneity for roughness and albedo on the atmospheric boundary-layer (ABL) height, with a case study at a semi-arid forest surrounded by sparse shrubland (forest area: \(28~\text{ km }^2\), forest length in the main wind direction: 7 km). Doppler lidar and ceilometer measurements at this semi-arid forest show an increase in the ABL height over the forest compared with the shrubland on four out of eight days. The differences in the ABL height between shrubland and forest are explained for all days with a model that assumes a linear growth of the internal boundary layer of the forest through the convective ABL upwind of the forest followed by a square-root growth into the stable free atmosphere. For the environmental conditions that existed during our measurements, the increase in ABL height due to large sensible heat fluxes from the forest (\(600~\text {W~m}^{-2}\) in summer) is subdued by stable stratification in the free atmosphere above the ABL, or reduced by high wind speeds in the mixed layer.  相似文献   
18.
Numerical weather prediction models are increasingly employed for providing meteorological data for urban air quality applications. Model resolution, physiographic parameters and surface-layer parameterisations need to be adapted to the requirements of the urban boundary layer. The Lokalmodell of the German Weather Service was triple-nested down to a horizontal grid resolution of 1.1 km, urbanised physiographic parameters were implemented, and an additional anthropogenic heat source was introduced. Results of a sensitivity study for a spring dust episode in Helsinki show a clear urbanisation effect of these measures on temperature, humidity and the partitioning of surface fluxes, leading to an increased Bowen ratio and heat storage and an urban heat island effect.  相似文献   
19.
This review gives an overview of the use and development of reference materials of geochemical and environmental interest in the literature of the years 2004 and 2005. In these years the performance of existing methods has been improved and new geochemical applications using new techniques have been developed. Accordingly, there was an increasing need for new reference materials, especially for in situ microanalysis and for precise stable isotope measurements. In addition, there was a notable trend for further characterisation of existing reference materials, mainly for the platinum-group elements. This review focuses on five topics: reference materials for platinum-group elements, reference glasses for in situ microanalysis, zircon reference materials, isotopic reference materials, and the development and certification of reference materials.  相似文献   
20.
We apply and evaluate a recent machine learning method for the automatic classification of seismic waveforms. The method relies on Dynamic Bayesian Networks (DBN) and supervised learning to improve the detection capabilities at 3C seismic stations. A time-frequency decomposition provides the basis for the required signal characteristics we need in order to derive the features defining typical “signal” and “noise” patterns. Each pattern class is modeled by a DBN, specifying the interrelationships of the derived features in the time-frequency plane. Subsequently, the models are trained using previously labeled segments of seismic data. The DBN models can now be compared against in order to determine the likelihood of new incoming seismic waveform segments to be either signal or noise. As the noise characteristics of seismic stations varies smoothly in time (seasonal variation as well as anthropogenic influence), we accommodate in our approach for a continuous adaptation of the DBN model that is associated with the noise class. Given the difficulty for obtaining a golden standard for real data (ground truth) the proof of concept and evaluation is shown by conducting experiments based on 3C seismic data from the International Monitoring Stations, BOSA and LPAZ.  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