全文获取类型
| 收费全文 | 448篇 |
| 免费 | 47篇 |
| 国内免费 | 59篇 |
专业分类
| 测绘学 | 28篇 |
| 大气科学 | 52篇 |
| 地球物理 | 57篇 |
| 地质学 | 208篇 |
| 海洋学 | 49篇 |
| 天文学 | 2篇 |
| 综合类 | 31篇 |
| 自然地理 | 127篇 |
出版年
| 2023年 | 3篇 |
| 2022年 | 7篇 |
| 2021年 | 2篇 |
| 2020年 | 5篇 |
| 2019年 | 4篇 |
| 2018年 | 6篇 |
| 2017年 | 9篇 |
| 2016年 | 9篇 |
| 2015年 | 14篇 |
| 2014年 | 15篇 |
| 2013年 | 15篇 |
| 2012年 | 20篇 |
| 2011年 | 19篇 |
| 2010年 | 20篇 |
| 2009年 | 23篇 |
| 2008年 | 28篇 |
| 2007年 | 23篇 |
| 2006年 | 33篇 |
| 2005年 | 22篇 |
| 2004年 | 27篇 |
| 2003年 | 24篇 |
| 2002年 | 24篇 |
| 2001年 | 27篇 |
| 2000年 | 19篇 |
| 1999年 | 24篇 |
| 1998年 | 18篇 |
| 1997年 | 16篇 |
| 1996年 | 8篇 |
| 1995年 | 20篇 |
| 1994年 | 18篇 |
| 1993年 | 15篇 |
| 1992年 | 11篇 |
| 1991年 | 6篇 |
| 1990年 | 8篇 |
| 1989年 | 4篇 |
| 1987年 | 6篇 |
| 1984年 | 1篇 |
| 1983年 | 1篇 |
排序方式： 共有554条查询结果，搜索用时 15 毫秒
101.
通过对爆管法对环境影响的理论分析,并结合有关的试验进行模拟分析,探讨了爆管法施工产生的碎片对新铺管道的影响,对周围结构设施的影响,重点论述了爆管法施工引起的地表位移。 相似文献
102.
103.
近年来,我国在矿山环境保护方面陆续实施了一系列新的政策,颁布了若干新的法规。在总结我国矿山环境保护新进展的基础上,分析我国矿山环境保护立法方面存在的若干问题,并提出要在法律层面明确对矿山环境的保护、制定专门保护矿山环境的行政法规和完善矿山环境治理恢复保证金制度的建议。 相似文献
104.
Viewshed analysis remains one of the most popular GIS tools for assessing visibility, despite the recognition of several limitations when quantifying visibility from a human perspective. The visual significance of terrain is heavily influenced by the vertical dimension (i.e. slope, aspect and elevation) and distance from the observer, neither of which are adjusted for in standard viewshed analyses. Based on these limitations, this study aimed to develop a methodology which extends the standard viewshed to represent visible landscape as more realistically perceived by a human, called the ‘Vertical Visibility Index’ (VVI). This method was intended to overcome the primary limitations of the standard viewshed by calculating the vertical degrees of visibility between the eye-level of a human and the top and bottom point of each visible cell in a viewshed. Next, the validity of the VVI was assessed using two comparison methods: 1) the known proportion of vegetation visible as assessed through imagery for 10 locations; and 2) standard viewshed analysis for 50 viewpoints in an urban setting. While positive, significant correlations were observed between the VVI values and both comparators, the correlation was strongest between the VVI values and the image verified, known values (r = 0.863, p = 0.001). The validation results indicate that the VVI is a valid method which can be used as an improvement on standard viewshed analyses for the accurate representation of landscape visibility from a human perspective. 相似文献
105.
This study addresses the question why intergroup conflicts over scarce, renewable resources in peripheral areas of the global South escalate into violence. In order to do so, twenty cases of such conflicts, seven of which turned violent, are analyzed. The method of fuzzy-set qualitative comparative analysis is used in order to bridge the gap between quantitative and qualitative accounts in the field and to detect patterns of conjunctural causation. In theoretical terms, structural conditions (negative othering and high power differences between the conflict parties) and triggering conditions (external resource appropriation and recent political change) of a violent escalation of renewable resource conflicts are distinguished. The empirical results as well as various robustness checks and comparisons with individual cases suggest that the simultaneous presence of negative othering, low power differences and recent political change is a sufficient condition for the violent escalation of conflicts over scarce renewable resources. I conclude that research on socio-environmental conflicts should pay more attention to conjunctural causation, local power differences and qualitatively different forms of conflict and political change. 相似文献
106.
Sum probability analysis of 1275 radiometric ages from 608 archaeological sites across northern and central Australia demonstrates a changing archaeological signature that can be closely correlated with climate variability over the last 2 ka. Results reveal a marked increase in archaeological records across northern and central Australia over the last 2 ka, with notable declines in western and northern Australia between ca. AD 700 and 1000 and post‐AD 1500 – two periods broadly coeval with the Medieval Climatic Anomaly and the Little Ice Age as they have been documented in the Asia–Pacific region. Latitudinal and longitudinal analysis of the dataset suggests the increase in archaeological footprint was continent wide, while the declines were greatest from 9 to 20° S, 110 to 135° E and 143 to 150° E. The change in the archaeological data suggests that, combined with an increase in population over the late Holocene, a disruption or reorganisation of pre‐European resource systems occurred across Australia between ca. AD 700 and 1000 and post‐AD 1500. These archaeological responses can be broadly correlated with transitions of the El Niño–Southern Oscillation (ENSO) mean state on a multi‐decadal to centennial timescale. The latter involve a shift towards the La Niña‐like mean state with wetter conditions in the Australian region between AD 700 and 1150. A transition period in ENSO mean state occurred across Australia during AD 1150–1300, with persistent El Niño‐like and drier conditions to ca. AD 1500, and increasing ENSO variability post‐AD 1500 to the present. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
107.
108.
随枣北部地区发育大量燕山期花岗岩体,以新黄断裂为界,南西侧主要为二长花岗岩,北东侧为钾长花岗岩。主要造岩矿物为钾长石、斜长石、黑云母和石英。岩浆岩总体酸度较高,高铝、相对富钾,以准铝质到过铝质钙碱性岩为主,属高钾一钾玄质系列。根据岩石化学参数判别为造山晚期花岗岩,属构造转折时期的岩石组合;微量元素蛛网图识别为同碰撞花岗岩和碰撞后花岗岩;微量元素对判别为同碰撞花岗岩（syn-COLG）和火山弧花岗岩（VAG）;采用巴尔巴林构造环境识别为富钾钙碱性花岗岩类（KCG）;Maniar和Piccoli构造环境判别属造山环境下的花岗岩。通过综合评判,结合区域大地构造演化规律,其构造环境应属于后碰撞阶段,地球动力学环境应为构造体制转换期。 相似文献
109.
In recent years, the empirical literature linking environmental factors and human migration has grown rapidly and gained increasing visibility among scholars and the policy community. Still, this body of research uses a wide range of methodological approaches for assessing environment–migration relationships. Without comparable data and measures across a range of contexts, it is impossible to make generalizations that would facilitate the development of future migration scenarios. Demographic researchers have a large methodological toolkit for measuring migration as well as modeling its drivers. This toolkit includes population censuses, household surveys, survival analysis and multi-level modeling. This paper's purpose is to introduce climate change researchers to demographic data and methods and to review exemplary studies of the environmental dimensions of human migration. Our intention is to foster interdisciplinary understanding and scholarship, and to promote high quality research on environment and migration that will lead toward broader knowledge of this association. 相似文献
110.