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   11125篇
  免费   1954篇
  国内免费   1290篇
测绘学   530篇
大气科学   458篇
地球物理   1200篇
地质学   6509篇
海洋学   1072篇
天文学   11篇
综合类   970篇
自然地理   3619篇
  2024年   15篇
  2023年   165篇
  2022年   387篇
  2021年   454篇
  2020年   393篇
  2019年   374篇
  2018年   339篇
  2017年   397篇
  2016年   395篇
  2015年   435篇
  2014年   514篇
  2013年   672篇
  2012年   727篇
  2011年   721篇
  2010年   603篇
  2009年   684篇
  2008年   666篇
  2007年   749篇
  2006年   691篇
  2005年   626篇
  2004年   584篇
  2003年   551篇
  2002年   515篇
  2001年   489篇
  2000年   485篇
  1999年   406篇
  1998年   320篇
  1997年   256篇
  1996年   173篇
  1995年   130篇
  1994年   98篇
  1993年   91篇
  1992年   76篇
  1991年   47篇
  1990年   36篇
  1989年   20篇
  1988年   21篇
  1987年   18篇
  1986年   10篇
  1985年   9篇
  1984年   9篇
  1983年   3篇
  1982年   7篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   2篇
  1954年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
陈娜  任安之  马伯  黎璟玉  向辉 《地理学报》2021,76(1):153-166
发达国家的经验表明,基于低影响开发的雨洪管理措施可以有效缓解城市雨洪灾害。聚焦中国海绵城市建设过程中新旧城区的关联性问题,提出“现状评估—低影响开发指标分解—建设效果模拟验证”的雨洪管控路径。以湖南省凤凰县为例,基于城市内涝模型,对新旧城区进行雨洪风险性评估与改造可行性评估,在现状评估基础上,构建低影响开发控制指标分解体系,实现低影响开发理念和技术从宏观控制策略到详细规划过程中的落实,最后通过内涝节点的滞水量计算验证雨洪管控效果。结果表明:凤凰县旧城区所面临的雨洪淹没风险高于新城区;旧城区现状年径流总量控制率明显低于新城区,且旧城区改造可行性较低。在新旧城区协调统筹的整体性视角下,构建“城区—街区—地块”的三级指标分解体系可以实现径流总量与峰值的消减,但在暴雨情境下,单独依靠低影响开发措施缓解内涝较为困难,基于滞水量完善灰色基础设施可以有效控制短时强降雨导致的雨洪灾害。  相似文献   
2.
海洋科学是一门依赖于观测的学科, 而卫星是海洋研究的重要观测平台之一, 海洋卫星数据在海洋科学研究中具有重要的意义。21世纪初以来, 我国陆续发射了多颗专门用于海洋观测的卫星, 初步拥有自主海洋卫星全球观测网络。本文针对国内外海洋卫星资源基本情况, 总结了我国海洋卫星数据应用发展现状, 特别是海洋卫星数据接收、处理、管理、应用等方面的情况, 并分析、探讨了我国海洋科学研究对卫星数据的需求, 以及我国海洋卫星数据科学应用存在的问题和发展策略。  相似文献   
3.
油气储层流动单元在高、中、低渗储层表征中已经得到普遍应用,但在特低渗储层研究中仍然很少涉及。以松辽盆地北部三肇凹陷升554断块下白垩统泉头组四段扶余油层特低渗储层为例,划分出E、G、P三种流动单元类型,从E类至P类流动单元,渗流能力逐渐减小。流动单元物性特征、空间分布特征均表明流动单元储层非均质性较强。分析了沉积相及开启型正断层对流动单元发育的控制作用。研究发现,在特低渗储层尺度内,流动单元自身的渗流能力对油藏开发的作用已经很小,而不同流动单元之间的渗流能力差异引起油藏开发效果的不同也已不明显,开发效果主要取决于砂体射开厚度、注水效果等开发因素以及断层渗流通道、泥岩渗流屏障、砂体厚度等地质因素。这与以往储层流动单元研究中普遍认为的"流动单元渗流能力越强,油藏注水开发效果越好"的观点是截然不同的。通过本文以期为特低渗油气储层流动单元研究提供一定借鉴,为特低渗油藏开发提供一定参考依据。  相似文献   
4.
The introduction of productive gardens on public building roofs is an active way to use urban idle space. It has ecological, economic, and social values and helps alleviate many urban problems caused by the rapid advancement of land urbanization. This paper takes the productive rooftop garden of an urban commercial complex as an example, and assesses its development status based on methods including ArcGIS, field research, and questionnaire interviews, combined with the overall aspects of the country and key case analysis. The results indicate several key aspects of the current status of such gardens in China. (1) As affected by natural and social factors, the current spatial distribution of productive rooftop gardens of commercial complexes in Chinese mainland is uneven, with 84.21% located in the southeast coast and the Sichuan region. (2) The operation and development of this type of productive landscape is in good shape. The number of rooftop gardens has continued to increase since 2013, and the scale is generally greater. Currently, the business model which combines nature education and parent-child amusement experience activities is the most stable. (3) Cases in good operating condition tend to have relatively related characteristics in layouts, traffic functions, landscape elements, and space design. (4) Questionnaire interviews show that citizens are highly willing to participate in rooftop productive landscapes, while operators still experience challenges in policies, funds, and planting knowledge in practice. This paper analyses the existing problems in the development status and strategy of the rooftop productive landscape. It proposes complementary optimization strategies to serve as a reference for the rooftop design of commercial complexes and the utilization of a significant amount of idle space on the roofs.  相似文献   
5.
A conceptual model with water samples from ten geothermal fields (?smil, Ilg?n (Çavu?cugöl), Tuzlukçu-Ak?ehir, Seydi?ehir and Kavakköy, Hüyük, Ere?li-Akhüyük, Kad?nhan?, Cihanbeyli, Karap?nar and Bey?ehir) in the province of Konya defined the geothermal system. Carbonates, quartzite and marbles of Paleozoic metamorphics are the reservoir rocks and the heating sources are igneous rock intrusions and geothermal gradient. The variable thermal water (CaMgHCO3, CaSO4, NaSO4, CaHCO3, CaNaHCO3, NaCl and CaNaClHCO3) had EC and temperature between 177.8 and 56,100 μS/cm and between 18.3 and 44 °C, respectively. Ca2+ in geothermal fluids are associated with marble and carbonate rocks and the high chloride shows direct connection with deep geothermal system, and prolonged contact with evaporite rocks. Sulphate originates from dissolution of and oxidation of sulphate and sulphur-bearing minerals. The high As, B, F and Mn concentration in some thermal water samples were determined as 85 μg/l, 148.56 mg/l, 3.01 mg/l and 208.13 mg/l, respectively. Reservoir temperatures computed by Na/K geothermometers were between 85.37–158.89 °C for Ak?ehir thermal waters and 58.78–90.45 °C for Ere?li thermal waters. The maximum reservoir temperature of other geothermal waters was 75 °C by the silica geothermometers.  相似文献   
6.
Is economic development compatible with mitigation? On the one hand, development should promote effective climate policy by enhancing states’ capacities for mitigation. On the other hand, economic growth creates more demand for production, thereby inhibiting emissions reduction. These arguments are often reconciled in the environmental Kuznets curve (EKC) thesis. According to this approach, development initially increases emissions in poor economies, but begins to lower emissions after a country has attained a certain level of development.

The aim of this article is to determine empirically whether the EKC hypothesis seems plausible in light of emissions trends over the birth and implementation of the Kyoto Protocol. Drawing on data from the World Bank World Development Indicators and World Resources Institute Climate Data Explorer, it conducts a large-N investigation of the emissions behaviour of 120 countries from 1990 to 2012. While several quantitative studies have found that economic factors influence emissions activity, this article goes beyond existing research by employing a more sophisticated – multilevel – research design to determine whether economic development: (a) continues to be a significant driver once country-level clustering is accounted for and (b) has different effects on different countries. The results of this article indicate that, even after we account for country-level clustering and hold constant the other main putative drivers of emissions activity, economic development tends to inhibit emissions reduction. They also provide strong evidence that emissions trends resemble the EKC, with development significantly constraining emissions reduction in the South and promoting it in the North.

POLICY RELEVANCE

This article contributes to the understanding of the (changing) role of economic development in shaping emissions activity. It demonstrates the need for a contextualized, country-specific approach for evaluating the effectiveness of economic development in promoting emissions reduction and uncovers new evidence in support of the EKC hypothesis.  相似文献   
7.
中国区域水资源系统韧性与效率的发展协调关系评价   总被引:1,自引:0,他引:1  
孙才志  孟程程 《地理科学》2020,40(12):2094-2104
在界定水资源系统韧性概念的基础上,综合应用赋权法、SBM-DEA模型及发展协调度模型对2000—2016年全国31个省区的区域水资源系统的效率、韧性以及两者之间的发展协调关系进行评价。结果如下:① 中国区域水资源系统效率整体上处于非有效区,在研究期间呈现出在波动中上升的趋势。② 中国区域水资源系统韧性的平均值为0.39,总体水平较低,研究期间整体上呈波动上升趋势。③ 中国区域水资源系统效率与韧性的发展度总体呈现平稳上升—较快上升—急剧下降—上升的趋势,呈倒“U”型发展;协调度在研究期间呈现波动中上升趋势,大部分省区的发展度较好,而协调度较弱。④ 2000—2016年,水资源效率与韧性的发展协调度一直维持着“东?中?西”阶梯式递减格局,失调省区的数量降低,初级协调、中级协调、良好协调省区的数量逐渐提升,整体向协调趋势发展;空间格局上呈现由2000年倒“E”型对称式分布格局向如今北部围绕天津、中部围绕上海、南部围绕广东的三级格局演变,格局分布与中国三大经济区基本吻合,可知中国水资源系统效率与韧性的发展协调水平与经济发展水平之间有明显的关系。  相似文献   
8.
综合运用石油自给率、流动比率等方法,以“一带一路”沿线国家为研究对象,对1995—2014年各国石油资源流动类型时空演变进行研究。结果表明:1)1995—2014年石油净补给型国家数量较为稳定,无产型或低产型国家的石油贸易倾向变化相对较小;基本自给型国家数量占比最大,1995年占比1/2,其余四个年份占比稳定在1/3;净支出型国家数量显著增加,至2014年其中有5个国家保持不变,表明这些国家的石油产量具有较大的优势。2)1995年和2014年汇地国家均为39个国家,其中有34个国家一直保持汇地职能,空间分布上呈东多西少,南多北少,东西分化以西亚、中亚、东欧为界;有14个国家一直保持源地职能,其空间分布格局与汇地相应,西多东少,南多北少,主要分布于西亚、东欧及中亚;交流地数量较少,呈分散分布,且分布地不稳定。3)从数量变化来看,研究期内汇地略有增加,源地略有减少,交流地略有增加;“一带一路”源地总出口量与汇地总进口量的比呈逐年降低趋势。  相似文献   
9.
川西坳陷东坡沙溪庙组气藏成藏演化模式   总被引:1,自引:0,他引:1  
川西坳陷东坡气藏主力产层为沙溪庙组,其圈闭类型以构造-岩性圈闭为主,多为致密砂岩储层,但断层发育,有效改善了储层物性,断砂匹配样式与构造演化对油气成藏过程有重要影响。基于前人已有的认识,通过沙溪庙组气藏成藏动力演化、气水分布特征及生烃期次分析,结合构造演化、成藏幕次等研究,认为沙溪庙组天然气成藏受构造古隆起、断砂配置、储层物性、构造演化影响,形成了“构造控向、断砂控运、储层控藏、演化控调”的成藏演化模式,同中存异,高庙子地区古构造的控制作用更为明显,而中江地区岩性控制作用占主导。沙溪庙组气藏间歇性充注具“燕山期三幕成藏,喜山期调整改造”的成藏特征,多期构造演化和较强的储层非均质性影响了含气饱和度,导致沙溪庙组气藏分布、气藏产能差异大。  相似文献   
10.
The Belt and Road initiative has a significant focus on infrastructure, trade, and economic development across a vast region, and it also provides significant opportunities for sustainable development. The combined pressure of climate variability, intensified use of resources, and the fragility of ecosystems make it very challenging, however, to achieve future sustainability. To develop the path in a sustainable way, it is important to have a comprehensive understanding of these issues across nations and evaluate them in a scientific and well-informed approach. In this context, the Digital Belt and Road (DBAR) program was initiated as an international venture to share expertise, knowledge, technologies, and data to demonstrate the role of Earth observation science and technology and big Earth data applications to support large-scale development. In this paper, we identify pressing challenges, present the research priorities and foci of the DBAR program, and propose solutions where big Earth data can make significant contributions. This paper calls for further joint actions and collaboration to build a digital silk road in support of sustainable development at national, regional and global levels.  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