全文获取类型
收费全文 | 314篇 |
免费 | 18篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 31篇 |
地球物理 | 117篇 |
地质学 | 96篇 |
海洋学 | 14篇 |
天文学 | 36篇 |
综合类 | 1篇 |
自然地理 | 32篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 13篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 15篇 |
2013年 | 19篇 |
2012年 | 11篇 |
2011年 | 16篇 |
2010年 | 18篇 |
2009年 | 17篇 |
2008年 | 15篇 |
2007年 | 16篇 |
2006年 | 18篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1971年 | 3篇 |
排序方式: 共有336条查询结果,搜索用时 296 毫秒
251.
Scott D. Samson James P. Hibbard Greg L. Wortman 《Contributions to Mineralogy and Petrology》1995,121(2):171-184
Nd isotopic analyses of whole-rock samples from the older portion of the Carolina terrane, one of the largest terranes in
the Appalachian orogen, demonstrate that part of this terrane is composed of juvenile, mantle-derived crust. These data suggest
that the terrane may not have originally been built upon old, evolved basement material but rather may have been built upon
oceanic crust. A recent study by other workers demonstrates a more crustally evolved Nd isotopic signature for younger components
of the Carolina terrane. These data may indicate that the terrane interacted with evolved crust at a later time, possibly
by amalgamation with a more evolved crustal fragment before final accretion to Laurentia, rather than indicating a primary
old basement. A juvenile nature for the older portion of the terrane contrasts with models that suggest it is an evolved crustal
fragment that formed in a continental margin setting — a scenario proposed to explain the high proportion of felsic volcanic
rocks within the terrane. It is herein suggested that Carolina is a chemically evolved but isotopically juvenile crustal fragment,
because it remained in an oceanic setting for an unusually long time. In this regard the Carolina terrane is similar to some
of the large accreted terranes in the Canadian Cordillera, such as Wrangellia and Alexander. The presence of juvenile crust
in the Carolina terrane documents that at least part of the southern Appalachian orogen is not composed solely of reactivated
pre-existing continental crust. The importance of this part of the orogen in terms of the volume of juvenile Phanerozoic crustal
material in North America may be larger than previously thought. However, until additional major Appalachian terranes have
been isotopically characterized the volume of juvenile crust in the whole orogen remains unknown. The isotopic make-up of
a terrane can be an important aspect of terrane analysis as different terranes may have significantly different isotopic compositions,
while even widespread pieces of a single terrane should have very similar isotopic characteristics. The Nd isotopic data for
the Carolina terrane form the beginning of an isotope database for terranes in the southern Appalachians.
Received: 15 June 1994/Accepted: 31 January 1995 相似文献
252.
The rate of sandstone weathering in the semi-arid climate of the Hunter Valley, New South Wales, Australia has been estimated
from observations of gravestone weathering in the area. The gravestone data points to two distinct stages in the weathering
process. The first stage covering the first century of exposure is characterised by a relatively low recession rate of 0.5 mm/100 years.
This is followed by a second stage in which the rate of weathering increases sharply to ca 2.5 mm/100 years. The non-linear
nature of the weathering trends over time suggests that during the first century of exposure, structural changes took place
within the sandstone material, which lay the foundation for accelerated weathering after further exposure. Laboratory trials
were also conducted to identify the effectiveness of different weathering processes in the decay of sandstone in this region.
Of the four processes examined, only the freeze–thaw cycle produced a significant degree of mass loss and is therefore most
likely a strong contributor to the weathering of sandstone in this region. 相似文献
253.
Understanding the nature and relative importance of various drivers of change is crucial for sustainable management of natural resources and in prioritizing management efforts, allocating limited resources, and understanding cumulative effects. For this article, we employed structured an expert judgments approach to identify, characterize, and assess the relative importance of the key biophysical and socioeconomic drivers of change within the Volta River Basin, West Africa. Precipitation variability, water availability, land use change, drought events, and population growth were perceived as most important, while biodiversity loss, social conflicts, pest and disease occurrence, urbanization, and pollution were viewed as less critical. A majority of these drivers were characterized as “slow” acting processes as compared to rapidly changing drivers. Intra- and interexpert groups agreement were found to be significant and convergent, indicating the reliability of the results. The implications of these results for sustainable water resources management and agricultural production are discussed. 相似文献
254.
255.
256.
Hiroshi Murakami Kosei Sasaoka Kohtaro Hosoda Hajime Fukushima Mitsuhiro Toratani Robert Frouin B. Greg Mitchell Mati Kahru Pierre-Yves Deschamps Dennis Clark Stephanie Flora Motoaki Kishino Sei-Ichi Saitoh Ichio Asanuma Akihiko Tanaka Hiroaki Sasaki Katsumi Yokouchi Yoko Kiyomoto Hiroaki Saito Cécile Dupouy Absornsuda Siripong Satsuki Matsumura Joji Ishizaka 《Journal of Oceanography》2006,62(3):373-393
The Global Imager (GLI) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) made global observations from 2 April
2003 to 24 October 2003. In cooperation with several institutes and scientists, we obtained quality controlled match-ups between
GLI products and in-situ data, 116 for chlorophyll-a concentration (CHLA), 249 for normalized water-leaving radiance (nLw) at 443 nm, and 201 for
aerosol optical thickness at 865 nm (Tau_865) and Angstrom exponent between 520 and 865 nm (Angstrom). We evaluated the GLI
ocean color products and investigated the causes of errors using the match-ups. The median absolute percentage differences
(MedPD) between GLI and in-situ data were 14.1–35.7% for nLws at 380–565 nm, 52.5–74.8% nLws at 625–680 nm, 47.6% for Tau_865, 46.2% for Angstrom, and 46.6%
for CHLA, values that are comparable to the ocean-color products of other sensors. We found that some errors in GLI products
are correlated with observational conditions; nLw values were underestimated when nLw at 680 nm was high, CHLA was underestimated
in absorptive aerosol conditions, and Tau_865 was overestimated in sunglint regions. The error correlations indicate that
we need to improve the retrievals of the optical properties of absorptive aerosols and seawater and sea surface reflection
for further applications, including coastal monitoring and the combined use of products from multiple sensors. 相似文献
257.
Thermal conductivity is an important parameter to consider when designing clay-based barriers for use in deep geological repositories (DGR). In the DGR environment, the infiltration of local saline groundwater can potentially change the pore fluid chemistry of a barrier over its lifetime. This change in chemistry is known to alter the thermal properties of the barrier materials. In order to examine the impact of pore fluid salinity on thermal conductivity, experiments were conducted under both distilled water and saline pore fluid conditions. The material mixtures were prepared at two different dry densities using two different salt types. Furthermore, five different thermal conductivity prediction models were selected and evaluated on their performance with respect to the experimental outcomes. In general, these results indicated that an increase in the constituent pore fluid’s salt concentration leads to a decrease in the thermal conductivity of the material. Additionally, the thermal conductivity values of the materials prepared at a high dry density were greater than of those compacted at a low dry density. 相似文献
258.
Exploring the Solution Space of Semi-structured Geographical Problems Using Genetic Algorithms 总被引:1,自引:0,他引:1
Semi-structured geographical problems are often addressed by groups of decision-makers. Each group member is likely to have a specific set of objectives that they wish to address and a unique perspective on the way in which the problem should be solved. The solution to such problems often requires consensus building and compromise among decision-makers as they attempt to optimize their own criteria. The set of criteria adopted by a particular decision-maker constrains the set of solutions he/she will deem acceptable. Compromise among multiple decision-makers can occur at the intersection of these constrained solution sets. Knowledge about the criteria space, the solution space, and the relation between the two is often incomplete for semi-structured problems. New tools are needed to explore, analyze, and visualize the solution space of a problem with respect to multiple analytical models and criteria. In this research we explore the utility of genetic algorithms as an effective means to: (1) search the solution space of geographical problems; (2) visualize the spatial ramifications of alternative criteria spaces; and (3) identify compromise solutions. 相似文献
259.
260.
Steady convective exchange flows down slopes 总被引:2,自引:0,他引:2
Jeff J. Sturman Carolyn E. Oldham Greg N. Ivey 《Aquatic Sciences - Research Across Boundaries》1999,61(3):260-278