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   1440篇
  免费   245篇
  国内免费   335篇
测绘学   102篇
大气科学   162篇
地球物理   332篇
地质学   897篇
海洋学   149篇
天文学   42篇
综合类   128篇
自然地理   208篇
  2024年   13篇
  2023年   32篇
  2022年   61篇
  2021年   83篇
  2020年   70篇
  2019年   69篇
  2018年   57篇
  2017年   50篇
  2016年   72篇
  2015年   64篇
  2014年   74篇
  2013年   92篇
  2012年   80篇
  2011年   62篇
  2010年   76篇
  2009年   108篇
  2008年   87篇
  2007年   92篇
  2006年   90篇
  2005年   61篇
  2004年   70篇
  2003年   62篇
  2002年   74篇
  2001年   70篇
  2000年   70篇
  1999年   61篇
  1998年   37篇
  1997年   23篇
  1996年   27篇
  1995年   26篇
  1994年   26篇
  1993年   12篇
  1992年   12篇
  1991年   11篇
  1990年   6篇
  1989年   11篇
  1988年   5篇
  1987年   3篇
  1986年   5篇
  1985年   6篇
  1984年   3篇
  1983年   2篇
  1982年   3篇
  1981年   1篇
  1976年   1篇
排序方式: 共有2020条查询结果,搜索用时 15 毫秒
171.
《Climate Policy》2013,13(1):57-66
Abstract

This article discusses possible implications of early Joint Implementation (JI) action. Some projects which would otherwise be non-additional during the first commitment period, can become additional by implementing them before 2008 through early JI. For example, several environmental investments that will be mandatory under the European Union (EU) Acquis Communautaire as of, e.g. 2008 or 2010 could be carried out earlier than that with early JI action. As such, candidate countries could partly finance the accession process through JI credits and their environmental standards would earlier be in line with the Acquis. The theoretical risk that projects would have to follow a slow track if JI parties are not eligible for the fast track is not large for JI hosts that are candidate for EU membership.  相似文献   
172.
173.
RELATIONBETWEENδ~(18)OINATMOSPHERICPRECIPITATIONANDTEMPERATUREANDPRECIPITATIONZhangXinping(章新平)(DepartmentofGeography,HunanNo?..  相似文献   
174.
以滇东北地区某拟建公路沿线的地质灾害为例 ,分析研究该地区地质灾害的影响因素、影响机制、分布规律以及对公路工程的影响。区内地质灾害的发育受地层岩性、岩体结构、地质构造、地震、水文条件、气候条件、人类活动等因素的控制和影响。地质灾害类型主要有崩滑塌、滑坡、泥石流、岩溶塌陷等 ,另外还存在软土、膨胀土及可液化的砂土等特殊岩土灾害。不同类型的灾害对公路工程的影响和破坏机制不同  相似文献   
175.
Spatial Autocorrelation and Localization of Urban Development   总被引:1,自引:0,他引:1  
A nonlinear analysis of urban evolution is made by using of spatial autocorrelation theory. A first-order nonlinear autoregression model based on Clark’s negative exponential model is proposed to show urban population density. The new method and model are applied to Hangzhou City, China, as an example. The average distance of population activities, the auto-correlation coefficient of urban population density, and the auto-regressive function values all show trends of gradual increase from 1964 to 2000, but there always is a sharp first-order cutoff in the partial auto- correlations. These results indicate that urban development is a process of localization. The discovery of urban locality is significant to improve the cellular-automata-based urban simulation of modeling spatial complexity.  相似文献   
176.
地理学的逻辑方法和基本法则   总被引:5,自引:0,他引:5  
从科学哲学和科学学的角度考察地理学思想史,可以发现:地理学之所以徘徊于科学性不强的“经验科学”的水平,关键在于其科学的理论化和系统化不够。本文对地理学的逻辑方法及其公理系统作了初步探讨,并尝试就此推演地理定理,估计地理学的未来发展趋势。  相似文献   
177.
本文扼要介绍了中国科学院东川泥石流观测研究站对外开放三年来,在泥石流观测试验研究和防灾减灾工作中的新进展,同时也简述了站设基金课题、国家基金课题和中外合作交流项目的进展情况,并对今后的观测研究工作提出了展望和建议。  相似文献   
178.
李勇 《天文学报》2001,42(2):215-224
利用对具有月龄特征的历谱规律的研究成果,以推定甲骨文的绝对年代,从而提供了建立商后期甲骨文年代序列的新方法,并给出了13版卜辞的例证,通过分析殷历月的结构,得出殷历中“二癸月”和“四癸月”的月首分别为首甲日和首癸日,初步归纳出殷历月法,月首为初三,月长等于逆望月周期,建立固定,且找到建立丑之例,置闰规律未知,已存在年终,年中置闰两种闰法。  相似文献   
179.
The authors examine the propositions that the private banking sector is capable of assuring that liquefied natural gas (LNG) projects are economically viable and that the insurance sector is capable of rating the relative risks of LNG projects to assure their operations are as safe as possible. If the markets could assure these outcomes, government regulation of LNG projects could be reduced. Reviews of public and private regulation of safety and economic viability suggest that the private sector cannot serve these functions adequately. Unless private financial and insurance enterprises are induced by government regulations to smooth their own operating cycles, private self-regulation of major new developments is unlikely to be effective. In the case of LNG, the red tape of governmental bureaucracy may have prevented the large-scale development of costly, potentially hazardous, white elephants, but for all the wrong reasons.  相似文献   
180.
Bridge seismic isolation strategy is based on the reduction of shear forces transmitted from the superstructure to the piers by two means: shifting natural period and earthquake input energy reduction by dissipation concentrated in protection devices. In this paper, a stochastic analysis of a simple isolated bridge model for different bridge and device parameters is conducted to assess the efficiency of this seismic protection strategy. To achieve this aim, a simple nonlinear softening constitutive law is adopted to model a wide range of isolation devices, characterized by only three essential mechanical parameters. As a consequence of the random nature of seismic motion, a probabilistic analysis is carried out and the time modulated Kanai-Tajimi stochastic process is adopted to represent the seismic action. The response covariance in the state space is obtained by solving the Lyapunov equation for a stochastic linearized system. After a sensitivity analysis, the failure probability referred to extreme displacement and the mean value of dissipated energy are assessed by using the introduced stochastic indices of seismic bridge protection efficiency. A parametric analysis for protective devices with different mechanical parameters is developed for a proper selection of parameters of isolation devices under different situations.  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