全文获取类型
收费全文 | 2445篇 |
免费 | 438篇 |
国内免费 | 224篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 130篇 |
地球物理 | 790篇 |
地质学 | 681篇 |
海洋学 | 1225篇 |
天文学 | 43篇 |
综合类 | 62篇 |
自然地理 | 146篇 |
出版年
2024年 | 6篇 |
2023年 | 29篇 |
2022年 | 66篇 |
2021年 | 69篇 |
2020年 | 74篇 |
2019年 | 88篇 |
2018年 | 80篇 |
2017年 | 199篇 |
2016年 | 107篇 |
2015年 | 110篇 |
2014年 | 194篇 |
2013年 | 136篇 |
2012年 | 93篇 |
2011年 | 146篇 |
2010年 | 150篇 |
2009年 | 167篇 |
2008年 | 187篇 |
2007年 | 163篇 |
2006年 | 126篇 |
2005年 | 92篇 |
2004年 | 84篇 |
2003年 | 86篇 |
2002年 | 133篇 |
2001年 | 53篇 |
2000年 | 69篇 |
1999年 | 70篇 |
1998年 | 65篇 |
1997年 | 27篇 |
1996年 | 47篇 |
1995年 | 26篇 |
1994年 | 18篇 |
1993年 | 40篇 |
1992年 | 18篇 |
1991年 | 22篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1978年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有3107条查询结果,搜索用时 31 毫秒
1.
A growing body of evidence implies that the concept of 'treeless tundra' in eastern and northern Europe fails to explain the rapidity of Lateglacial and postglacial tree population dynamics of the region, yet the knowledge of the geographic locations and shifting of tree populations is fragmentary. Pollen, stomata and plant macrofossil stratigraphies from Lake Kurjanovas in the poorly studied eastern Baltic region provide improved knowledge of ranges of north‐eastern European trees during the Lateglacial and subsequent plant population responses to the abrupt climatic changes of the Lateglacial/Holocene transition. The results prove the Lateglacial presence of tree populations (Betula, Pinus and Picea) in the eastern Baltic region. Particularly relevant is the stomatal and plant macrofossil evidence showing the local presence of reproductive Picea populations during the Younger Dryas stadial at 12 900–11 700 cal. a BP, occurring along with Dryas octopetala and arctic herbs, indicating semi‐open vegetation. The spread of Pinus–Betula forest at ca. 14 400 cal. a BP, the rise of Picea at ca. 12 800 cal. a BP and the re‐establishment of Pinus–Betula forest at ca. 11 700 cal. a BP within a span of centuries further suggest strikingly rapid, climate‐driven ecosystem changes rather than gradual plant succession on a newly deglaciated land. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
Decoupling of stalagmite-derived Asian summer monsoon records from North Atlantic temperature change during marine oxygen isotope stage 5d 总被引:2,自引:0,他引:2
Houyun Zhou Jianxin Zhao Chuan-Chou Shen Yuexing Feng Huazheng Guan Chen-Feng You 《Quaternary Research》2008,70(2):315-321
The Asian monsoon is an important component of the global climate system. Seasonal variations in wind, rainfall, and temperature associated with the Asian monsoon systems affect a vast expanse of tropical and subtropical Asia. Speleothem-derived summer monsoon variation in East Asia was previously found to be closely associated with millennial-scale change in temperature in the North Atlantic region between 75 and 10 ka. New evidence recovered from East Asia, however, suggests that the teleconnection between summer monsoon in East Asia and temperature change in the North Atlantic region may have significantly reduced during 120 to ~ 110 ka, a period directly after the full last interglaciation and corresponding roughly to marine oxygen isotope stage 5d. This reduction may be due to the low ice volume in the North Hemisphere at that time, which makes the millennial-scale change in temperature in the North Atlantic region less effective in influencing the Asian summer monsoon. This is important for investigating the mechanisms controlling the Asian summer monsoon and the paleoclimatic teleconnection between East Asia and the North Atlantic region, and for predicting monsoon-associated precipitation in East Asia under a global-warming trend. 相似文献
3.
Chang-Guk Sun Sung-Ho Chun Tae-Gyun Ha Choong-Ki Chung Dong-Soo Kim 《Computers and Geotechnics》2008,35(3):436-449
An integrated GIS-based tool (GTIS) was constructed to estimate site effects related to the earthquake hazards in the Gyeongju area of Korea. To build the GTIS for the study area, intensive site investigations and geotechnical data collections were performed and a walk-over site survey was additionally carried out to acquire surface geo-knowledge data in accordance with the procedure developed to build the GTIS. For practical applications of the GTIS used to estimate the site effects associated with the amplification of ground motion, seismic microzoning maps of the characteristic site period and the mean shear wave velocity to a depth of 30 m were created and presented as a regional synthetic strategy addressing earthquake-induced hazards. Additionally, based on one-dimensional site response analyses, various seismic microzoning maps for short- and mid-period amplification potentials were created for the study area. Case studies of seismic microzonations in the Gyeongju area verified the usefulness of the GTIS for predicting seismic hazards in the region. 相似文献
4.
Curtis M. Oldenburg 《Environmental Geology》2008,54(8):1687-1694
A screening and ranking framework (SRF) has been developed to evaluate potential geologic carbon dioxide (CO2) storage sites on the basis of health, safety, and environmental (HSE) risk arising from CO2 leakage. The approach is based on the assumption that CO2 leakage risk is dependent on three basic characteristics of a geologic CO2 storage site: (1) the potential for primary containment by the target formation; (2) the potential for secondary containment
if the primary formation leaks; and (3) the potential for attenuation and dispersion of leaking CO2 if the primary formation leaks and secondary containment fails. The framework is implemented in a spreadsheet in which users
enter numerical scores representing expert opinions or published information along with estimates of uncertainty. Applications
to three sites in California demonstrate the approach. Refinements and extensions are possible through the use of more detailed
data or model results in place of property proxies. 相似文献
5.
Until recently the traditional spatial configuration of the European geography was based upon the core-periphery model. The
‘pentagon’, broadly defined as lying between London, Paris, Milan, Munich and Hamburg, was seen as the core area characterised
by having the highest concentration of economic development in the European Union (EU), with the remainder of the European
territory viewed as peripheral, albeit to varying degrees. In a number of cases such peripheral areas equated with clear regional
disparities. The elaboration of the European Spatial Development Perspective (ESDP) (CEC, European spatial development perspective, towards balanced and sustainable development in the territory of the
European Union, 1999) challenged this core-periphery model. European spatial planning policies, aimed at encouraging social
and economic, and with ever increasing importance, territorial cohesion, seek amongst other aspects to encourage the development
of a balanced and polycentric urban system. This paper adopts a network analysis approach to the analysis of air passenger
flows between some 28 principal European metropolitan urban regions. The evaluation of these flows contributes to an enhanced
comprehension of the spatial dynamics of the European metropolitan territory which goes beyond that deriving from the more
standard analyses of the individual components of the urban system. Several indicators are used, deriving from gravitational
modelling techniques, to analyse the complexity of the air passenger flows. A multidimensional scaling (MDS) technique is
introduced in order to interpret and visualise the resulting spatial configuration and positioning of the different metropolitan
centres within the conceptual European ‘space of air passenger flows’, thereby contrasting with the more traditional map-based
geographical image of Europe, based upon Cartesian coordinates.
相似文献
Malcolm C. BurnsEmail: |
6.
Nonlinear Analysis of Local Site Effects on Seismic Ground Response in the Bam Earthquake 总被引:1,自引:0,他引:1
M. H. T. Rayhani M. H. El Naggar S. H. Tabatabaei 《Geotechnical and Geological Engineering》2008,26(1):91-100
The influence of local geologic and soil conditions on the intensity of ground shaking is addressed in this study. The amplification
of the ground motion due to local site effects resulted in severe damage to dwellings in the Bam area during the 2003 Bam
Earthquake. A unique set of strong motion acceleration recordings was obtained at the Bam accelerograph station. Although
the highest peak ground acceleration recorded was the vertical component (nearly 1 g), the longitudinal component (fault-parallel
motion) clearly had the largest maximum velocity as well as maximum ground displacement. Subsurface geotechnical and geophysical
(down-hole) data in two different sites have been obtained and used to estimate the local site condition on earthquake ground
motion in the area. The ground response analyses have been conducted considering the nonlinear behavior of the soil deposits
using both equivalent linear and nonlinear approaches. The fully nonlinear method embodied in FLAC was used to evaluate the
nonlinear soil properties on earthquake wave propagation through the soil layer, and compare with the response from the equivalent
linear approach. It is shown that thick alluvium deposits amplified the ground motion and resulted in significant damage in
residential buildings in the earthquake stricken region. The comparison of results indicated similar response spectra of the
motions for both equivalent and nonlinear analyses, showing peaks in the period range of 0.3–1.5 s. However, the amplification
levels of nonlinear analysis were less than the equivalent linear method especially in long periods. The observed response
spectra are shown to be above the NEHRP building code design requirements, especially at high frequencies. 相似文献
7.
UV-B辐射对海洋微藻抗氧化系统的影响 总被引:4,自引:1,他引:4
研究了UV-B辐射对两种海洋微藻-小新月菱形藻(Ntzschia closterlum)和亚心形扁藻(Platymonas subcordiforming)的抗氧化系统的影响。结果表明:在本实验的辐射剂量范围内,随着UV-B辐射剂量的增强,两种藻的抗氧化防御系统的非酶性组分还原型谷胱甘肽(GSH)和类胡萝卜素(CAR)的含量随之下降;抗氧化防御系统的酶性组分超氧化歧化酶(SOD)和过氧化氢酶(CAT)的活性逐渐降低。加入外源性抗氧化剂GSH可减轻UV-B辐射对藻的伤害。分析表明海洋微藻的UV-B伤害是由于抗氧化防御系统遭到破坏而导致活性氧积累的结果。 相似文献
8.
1986年11月—1987年5月,在中国第三次南极考察和环球科学考察期间,收集了58个海洋气溶胶样品,采用中子活化法分析了Al,V,Mn,I,Br,Mg,Na,Cl等元素。应用因子分析、回归分析和富集因子分析对气溶胶中元素进行分类、定量评估和来源判别,讨论不同来源元素的特征,计算各主要来源的贡献分量。结果表明,海洋气溶胶中Al的99.99%是来自陆源地壳风化物,Na的99.2%。和Cl的99.99%是来自海水,V的91.4%。来自陆源污染物。因此,Al可作为海洋气溶胶中陆源地壳风化物的示踪元素,Na和Cl可作为海水源示踪元素,非地壳源的V则可选择为陆源污染物的示踪元素。 相似文献
9.
The expansion of offshore activities and the increasing need to meet international and national commitments to biodiversity conservation have led to an enhanced interest in marine spatial planning (MSP) as a tool for sea use management. Several European countries, on their own initiative or driven by European legislation and policy, have taken global leadership in implementing MSP. This article will discuss the Belgian experiences with MSP. It will give a short historical overview based on legal developments and review the implementation process of a ‘Master Plan’ as a spatial management policy for the Belgian Part of the North Sea. Additionally, this article will reflect on the research that has been done in Belgium to apply a land-use planning approach to the marine environment. The MSP process in Belgium shows that a spatial approach to sea use management is possible despite the lack of a legal zoning framework. However, it concludes that a legal basis for MSP, in addition to the current permit system, would provide a more strategic and integrated framework for ecosystem-based, sea use management. 相似文献
10.