全文获取类型
收费全文 | 916篇 |
免费 | 27篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 60篇 |
地球物理 | 274篇 |
地质学 | 315篇 |
海洋学 | 44篇 |
天文学 | 157篇 |
综合类 | 2篇 |
自然地理 | 83篇 |
出版年
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 17篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 33篇 |
2011年 | 41篇 |
2010年 | 22篇 |
2009年 | 26篇 |
2008年 | 28篇 |
2007年 | 27篇 |
2006年 | 37篇 |
2005年 | 40篇 |
2004年 | 34篇 |
2003年 | 30篇 |
2002年 | 29篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 22篇 |
1998年 | 16篇 |
1997年 | 21篇 |
1996年 | 8篇 |
1995年 | 22篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1975年 | 15篇 |
1973年 | 8篇 |
1971年 | 6篇 |
1970年 | 9篇 |
1968年 | 6篇 |
1954年 | 8篇 |
1951年 | 6篇 |
排序方式: 共有954条查询结果,搜索用时 15 毫秒
151.
Recent earthquakes, that stroked Italian regions in past decades (Umbria— Marche 1997; Molise 2002; L’Aquila 2009), pointed out the high vulnerability of reinforced concrete existing buildings causing severe damages in the structures and consequently life losses. This is mainly due to the fact that such structures were often built without reference to seismic actions or on the basis of old standard provisions. Nowadays in Italy, Public Authorities are requested to evaluate the seismic vulnerability of their building stock assessing the actual capacity of such structures, as a consequence of new hazard levels and seismic microzonation introduced by new standards. According to Eurocode 8 or Italian standard NTC 2008, the seismic analysis of existing reinforced concrete buildings can be performed by one of the established procedure (i.e. Linear Static Analysis LSA, Linear Dynamic Analysis LDA, Nonlinear Static Analysis NSA, Nonlinear Dynamic Analysis NDA), depending on the achieved knowledge level about the structural system and materials. In order to compare efficiency and differences of previously described approaches, a deep investigation was executed on a reinforced concrete existing building whose dynamic behaviour was evaluated by an experimental dynamic analysis. In such a way, updated models were obtained and adopted for seismic analysis performed by using linear and nonlinear approaches, taking into account the stiffness and strength contribution of masonry infill walls. It was so possible to get useful indications on the reliability and discrepancies of different modelling approaches as well as on the influence of masonry infills on the seismic response of existing r.c. buildings. 相似文献
152.
Elizabeth Cottrell Michael J. Walter David Walker 《Earth and Planetary Science Letters》2010,289(3-4):631-634
153.
Morphology,structure and kinematics of a rainfall controlled slow‐moving Andean landslide,Peru
下载免费PDF全文
![点击此处可从《地球表面变化过程与地形》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Swann Zerathe Pascal Lacroix Denis Jongmans Jersy Marino Edu Taipe Marc Wathelet Walter Pari Lionel Fidel Smoll Edmundo Norabuena Bertrand Guillier Lucile Tatard 《地球表面变化过程与地形》2016,41(11):1477-1493
The large slow‐moving landslide of Maca is located in the upper Colca valley (southern Peru), a region characterized by a well pronounced rainy period, and intense and recurrent sustained seismicity. The landslide, developed in deep lacustrine deposits, has recently accelerated, threatening the Maca village. This work aims at understanding the rupture mechanism and the causes of the recent landslide reactivation/acceleration. We present a multidisciplinary characterization of the Maca landslide that includes: (i) geological and morphological mapping in the field; (ii) remote sensing analysis using an historical aerial photograph of 1955 and the Pléiades satellite images (2013); (iii) global positioning system (GPS) including time‐series of surveys over 13 years, and continuous measurements over 14 months; (iv) a geophysical campaign with deep electrical resistivity tomography profiles acquired across the landslide mass. Our study shows that this 60 Mm3 landslide, which can be classified as a clay/silt compound landslide, moved by 15 m between 2001 and 2014 with a large inter‐annual velocity variation (up to a factor of 500) depending on the rainfall intensity. We suggest that these dramatic changes in velocity are the result of the combination of a threshold mechanism and the short intense rainy season in Peru. This study reveals three main driving factors acting at different timescales: (i) over several decades, the river course has significantly changed, causing the Maca landslide reactivation in the 1980s due to the erosion of its toe; (ii) at the year scale, a minimum amount of rainfall is required to trigger the motion and this amount controls the landslide velocity; (iii) transient changes in slide velocity may occur anytime due to earthquakes. This study particularly highlights the non‐linear behaviour of the motion with rainfall. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
154.
Recent anti-systemic social movements have illustrated the central role of cities in social movement mobilization. We not only highlight the characteristics of urban social relations that make cities fertile ground for mobilization, but also point to the disjunctures between the geographies and spatialities of social relations in the city, and the geographies and spatialities of many systemic processes. Struggles for a more just society must consider the broad geographies and spatialities of oppression, which we illustrate with a brief analysis of the Occupy movement. Finally, we introduce the next five articles in this special issue, all illustrating the importance of the geographies and spatialities of urban social struggle. 相似文献
155.
Remediation of subsurface contamination requires an understanding of the contaminant (history, source location, plume extent and concentration, etc.), and, knowledge of the spatial distribution of hydraulic conductivity (K) that governs groundwater flow and solute transport. Many methods exist for characterizing K heterogeneity, but most if not all methods require the collection of a large number of small‐scale data and its interpolation. In this study, we conduct a hydraulic tomography survey at a highly heterogeneous glaciofluvial deposit at the North Campus Research Site (NCRS) located at the University of Waterloo, Waterloo, Ontario, Canada to sequentially interpret four pumping tests using the steady‐state form of the Sequential Successive Linear Estimator (SSLE) ( Yeh and Liu 2000 ). The resulting three‐dimensional (3D) K distribution (or K‐tomogram) is compared against: ( 1 ) K distributions obtained through the inverse modeling of individual pumping tests using SSLE, and ( 2 ) effective hydraulic conductivity (Keff) estimates obtained by automatically calibrating a groundwater flow model while treating the medium to be homogeneous. Such a Keff is often used for designing remediation operations, and thus is used as the basis for comparison with the K‐tomogram. Our results clearly show that hydraulic tomography is superior to the inversions of single pumping tests or Keff estimates. This is particularly significant for contaminated sites where an accurate representation of the flow field is critical for simulating contaminant transport and injection of chemical and biological agents used for active remediation of contaminant source zones and plumes. 相似文献
156.
Walter Hans GRAF 《水文科学杂志》2013,58(1):59-68
SYNOPSIS It has always been a problem for the hydraulic engineer to obtain reasonable values for the roughness in a waterway. The writer feels that the idea put forward in this essay could help the parcticing engineer to obtain a roughness value without complicated procedure. 相似文献
157.
The Horní Slavkov–Krásno Sn–W ore district is hosted by strongly altered Variscan topaz–albite granite (Krudum granite body) on the northwestern margin of the Bohemian Massif. We studied the fluid inclusions on greisens, ore pockets, and ore veins from the Hub Stock, an apical expression of the Krudum granite. Fluid inclusions record almost continuously the post-magmatic cooling history of the granite body from ~500 to <50°C. Rarely observed highest-temperature (~500°C) highest-salinity (~30?wt.% NaCl eq.) fluid inclusions are probably the result of secondary boiling of fluids exsolved from the crystallizing magma during pressure release which followed hydraulic brecciation of the gneissic mantle above the granite cupola. The greisenization was related to near-critical low-salinity (0–7?wt.% NaCl eq.) aqueous fluids with low amount of CO2, CH4, and N2 (≤10?mol% in total) at temperatures of ~350–400°C and pressures of 300–530 bar. Crush-leach data display highly variable and negatively correlated I/Cl and Br/Cl values which are incompatible with both orthomagmatic and/or metamorphic origin of the fluid phase, but can be explained by infiltration of surficial and/or sedimentary fluids. Low fluid salinity indicates a substantial portion of meteoric waters in the fluid mixture that is in accordance with previous stable isotope data. The post-greisenization fluid activity associated with vein formation and argillitization is characterized by decreasing temperature (<350 to <50°C), decreasing pressure (down to ~50–100 bar), and mostly also decreasing salinity. 相似文献
158.
During the last two decades, there has been growing interest in the integration of existing ideas and data to produce new
synthetic models and hypotheses leading to discovery and advancement in estuarine and coastal science. This essay offers an
integrated definition of what is meant by synthesis research and discusses its importance for exploiting the rapid expansion
of information availability and for addressing increasingly complex environmental problems. Approaches and methods that have
been used in published synthetic coastal research are explored and a list of essential steps is developed to provide a foundation
for conducting synthetic research. Five categories of methods used widely in coastal synthesis studies are identified: (1)
comparative cross-system analysis, (2) analysis of time series data, (3) balance of cross-boundary fluxes, (4) system-specific
simulation modeling, and (5) general systems simulation modeling. In addition, diverse examples are used to illustrate how
these methods have been applied in previous studies. We discuss the urgent need for developing curricula for classroom and
experiential teaching of synthesis in coastal science to undergraduate and graduate students, and we consider the societal
importance of synthetic research to support coastal resource management and policy development. Finally, we briefly discuss
the crucial challenges for future growth and development of synthetic approaches to estuarine and coastal research. 相似文献
159.
Gustavo Naumann Walter M. Vargas Juan L. Minetti 《Theoretical and Applied Climatology》2011,105(3-4):341-355
The persistence and long-term memories in daily maximum and minimum temperature series during the instrumental period in southern South America were analysed. Here, we found a markedly seasonal pattern both for short- and long-term memories that can lead to enhanced predictability on intraseasonal timescales. In addition, well-defined spatial patterns of these properties were found in the region. Throughout the entire region, the strongest dependence was observed in autumn and early winter. In the Patagonia region only, the temperatures exhibited more memory during the spring. In general, these elements indicate that nonlinear interactions exist between the annual cycles of temperature and its anomalies. Knowledge of the spatiotemporal behaviour of these long-term memories can be used in the building of stochastic models that only use persistence. It is possible to propose two objective forecast models based on linear interactions associated with persistence and one that allows for the use of information from nonlinear interactions that are manifested in the form of forerunners. 相似文献
160.
Partial pressure of CO2 in equilibrium with sample water (pCO2) for the coastal water in the Chukchi Sea was continuously observed in summer, 2008. Average daily CO2 flux calculated from the pCO2 and gas transfer coefficients ranged from −0.144 to −0.0701 g C m−2 day−1 depending on which gas transfer coefficient was used. The pCO2 before the landfast ice sheets melted appeared to be highly biologically controlled based on the following information: (1) the diurnal pattern of pCO2 was strongly correlated with Photosynthetic Photon Flux Density (PPFD); (2) high chlorophyll density was observed during periods of peak uptake; and (3) the day-to-day variation in the pCO2 strongly correlated with the presence or absence of near-shore ice sheets. The lowest pCO2 of 35 ppm together with the highest PPFD of 1362 μmol E m−2 s−1 were observed in the afternoon on June 28 in the presence of sea ice. The very low pCO2 observed in late June was likely caused by high photosynthetic rates related to high phytoplankton densities typically observed from spring to early summer near the ice edge, and by water low in salinity and CO2 released by melting sea ice early in the season. 相似文献