全文获取类型
收费全文 | 47927篇 |
免费 | 12060篇 |
国内免费 | 8301篇 |
专业分类
测绘学 | 7148篇 |
大气科学 | 6065篇 |
地球物理 | 7674篇 |
地质学 | 24994篇 |
海洋学 | 5130篇 |
天文学 | 3450篇 |
综合类 | 3748篇 |
自然地理 | 10079篇 |
出版年
2025年 | 11篇 |
2024年 | 1110篇 |
2023年 | 1145篇 |
2022年 | 1977篇 |
2021年 | 2241篇 |
2020年 | 2125篇 |
2019年 | 2446篇 |
2018年 | 1761篇 |
2017年 | 2180篇 |
2016年 | 2199篇 |
2015年 | 2352篇 |
2014年 | 2836篇 |
2013年 | 2995篇 |
2012年 | 3205篇 |
2011年 | 3172篇 |
2010年 | 2683篇 |
2009年 | 3196篇 |
2008年 | 3130篇 |
2007年 | 3252篇 |
2006年 | 3137篇 |
2005年 | 2829篇 |
2004年 | 2483篇 |
2003年 | 2319篇 |
2002年 | 2051篇 |
2001年 | 1797篇 |
2000年 | 1722篇 |
1999年 | 1501篇 |
1998年 | 1326篇 |
1997年 | 978篇 |
1996年 | 777篇 |
1995年 | 660篇 |
1994年 | 614篇 |
1993年 | 516篇 |
1992年 | 371篇 |
1991年 | 304篇 |
1990年 | 220篇 |
1989年 | 177篇 |
1988年 | 141篇 |
1987年 | 91篇 |
1986年 | 55篇 |
1985年 | 40篇 |
1984年 | 29篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
161.
Climate change impacts increase pressure on challenges to sustainability and the developmental needs of cities. Conventional, “hard” adaptation measures are often associated with high costs, inflexibility and conflicting interests related to the dense urban fabric, and ecosystem-based adaptation (EbA) has emerged as a potentially cost-efficient, comprehensive, and multifunctional approach. This paper reviews and systematises research on urban EbA. We propose an analytical framework that draws on theory from ecosystem services, climate change adaptation and sustainability science. It conceptualises EbA in terms of five linked components: ecological structures, ecological functions, adaptation benefits, valuation, and ecosystem management practices.Our review identified 110 articles, reporting on 112 cities, and analysed them using both quantitative statistical and qualitative content analysis. We found that EbA research in an urban context is fragmented due to different disciplinary approaches and concepts. Most articles focus on heat or flooding, and the most studied ecological structures for reducing the risk of such hazards are green space, wetlands, trees and parks. EbA is usually evaluated in bio-geophysical terms and the use of economic or social valuations are rare. While most articles do not mention specific practices for managing ecological structures, those that do imply that urban EbA strategies are increasingly being integrated into institutional structures. Few articles considered issues of equity or stakeholder participation in EbA.We identified the following challenges for future EbA research. First, while the large amount of data generated by isolated case studies contributes to systems knowledge, there is a lack of systems perspectives that position EbA in relation to the wider socio-economic and bio-geophysical context. Second, normative and ethical aspects of EbA require more thought, such as who are the winners and losers, especially in relation to processes that put people at risk from climate-related hazards. Third, there is room for more forward-looking EbA research, including consideration of future scenarios, experimentation in the creation of new ecological structures and the role of EbA in transformative adaptation. 相似文献
162.
Abstract Uptake rates of ammonium (NH4 + ), nitrate (NO3 ? ), and urea by three subgroups of phytoplankton (< 200, < 20, < 2 μm) off Westland, were measured using 15 N tracer techniques in midwinter 1988, after a recent upwelling. For all size fractions at surface irradiance (I100), nitrogen (N) was taken up primarily as NO3 ?. This accounted for 67–85% of total N uptake (SρN), whereas at 40 and 7% of surface irradiance, the regenerated N (NH4 + ) and urea) made up 31–72% of SρN. Depth profile experiments for all three size components showed that uptake of NO3 ? was most light‐sensitive, followed by that of NH4 + and urea. The irradiance and nutrient availability plot indicated that light was substantially more important than the nutrient concentrations in controlling the assimilation of N by microplankton (20–200 μm). Nano‐ (2–20 μm) and picoplankton (< 2 μm) however, were not as sensitive to either light or nutrient concentrations. High winds and the resulting deep mixing, combined with offshore and alongshore advection in the midwinter, were suggested to be the major cause of the low biomass and N productivity. 相似文献
163.
164.
165.
某工程设计采用轻质砼小型空心砌块墙体,在施工过程中,从各个建筑细部上很下工夫,精益求精,使施工质量得到保证,本文介绍其施工技术与细部做法。 相似文献
166.
The present study investigates the combined wave field that is induced by the continuous interaction of plane waves with an array of truncated circular cylinders in front of a rigid wall. The long-term goal of the study is the investigation of possible increase in the efficiency of cylindrical Wave Energy Converters (WECs) by putting in the vicinity of the array a barrier to propagation, a wall, that could assist the reflection of the incoming waves. The main task is to develop a generic solution method that is free of conceptual simplifications employed, e.g. by the method of images and the assumption of “pure” wave reflection. To cope with the set task, the proposed method relies on the semi-analytical formulation of the velocity potentials, while the solution is sought by combined expressions that involve polar and elliptical harmonics. The wall is represented as an elliptical cylinder with zero semi-minor axis. This assumption has eventually a beneficial effect to the underlying formulation given that it simplifies significantly the expansions of the involved diffraction potentials. 相似文献
167.
澳门海洋空间资源利用研究——澳门的填海造地工程 总被引:4,自引:0,他引:4
澳门原系海中孤岛,由于利用了自然条件,进行填海造地工程,使孤岛相连,土地面积扩大,城市发展,交通改善,经济增长,成为利用海洋空间资源的典型地区。文章论述了澳门有利于填海工程实施的自然条件,海洋空间利用的发展过程,及填海造地工程的巨大作用和深远意义。 相似文献
168.
简要论述了攀枝花市三区自然地理、地形地貌、地层岩性、地质构造、地震及新构造运动、岩土体工程地质特征及分布的基础上,统计了攀枝花市三区地质灾害情况,分析了三区地质灾害类型及分布特征,提出了相应的防治原则与对策措施。 相似文献
169.
170.
For spatial analyses, raster land cover/use maps are converted into points, where each point holds attribute of its corresponding land cover/use. However, these are not identical in terms of areas or shapes; thus assigning a point to each isolated shape is not an adequate solution and for that gridding is suggested. Square, hexagon and triangle are among the basic land use gridding systems where each of them has its own advantages in such process. This research aims to compare the systems in providing accurate representations of the original land cover/use maps, assess the data loss while increasing resolution and suggest suitable gridding system. The research finds the errors in area and feature numbers as criteria for selected classes. Modules that find out errors in each scale considering each criterion and class alone are proposed. The modules suggest both the best system for each criterion alone and for combined criteria. 相似文献