全文获取类型
收费全文 | 974篇 |
免费 | 20篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 25篇 |
大气科学 | 36篇 |
地球物理 | 231篇 |
地质学 | 436篇 |
海洋学 | 70篇 |
天文学 | 106篇 |
综合类 | 7篇 |
自然地理 | 84篇 |
出版年
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 21篇 |
2017年 | 16篇 |
2016年 | 24篇 |
2015年 | 12篇 |
2014年 | 23篇 |
2013年 | 47篇 |
2012年 | 35篇 |
2011年 | 37篇 |
2010年 | 44篇 |
2009年 | 59篇 |
2008年 | 50篇 |
2007年 | 40篇 |
2006年 | 42篇 |
2005年 | 52篇 |
2004年 | 43篇 |
2003年 | 50篇 |
2002年 | 25篇 |
2001年 | 22篇 |
2000年 | 21篇 |
1999年 | 12篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 20篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 4篇 |
1970年 | 5篇 |
1969年 | 5篇 |
排序方式: 共有995条查询结果,搜索用时 0 毫秒
951.
This paper presents an example of the application of error monitoring techniques to the results of a pseudodynamic test performed at variable testing speeds. For the faster testing speeds, the control errors increased and the test reliability was lost in terms of accuracy and stability, as observed by the evolution of the monitoring parameters. The applied monitoring methods were the spatial model identification of frequency and damping distortions and the error energy, which have been proposed in previous publications. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
952.
Connie Chapman Ian J. Walker Patrick A. Hesp Bernard O. Bauer Robin G. D. Davidson‐Arnott Jeff Ollerhead 《地球表面变化过程与地形》2013,38(14):1735-1747
Reynolds shear stress (RS = –u′ w′) and sand transport patterns over a vegetated foredune are explored using three‐dimensional velocity data from ultrasonic anemometers (at 0 · 2 and 1 · 2 m) and sand transport intensity from laser particle counters (at 0 · 014 m). A mid‐latitude cyclone on 3–4 May 2010 generated storm‐force winds (exceeding 20 m s–1) that shifted from offshore to obliquely alongshore. Quadrant analysis was used to characterize the spatial variation of RS quadrant components (Q1 through Q4) and their relative contributions were parameterized using the flow exuberance relation, EXFL = (Q1 + Q3)/(Q2 + Q4). The magnitudes of RS and sand transport varied somewhat independently over the dune as controlled by topographic forcing effects on flow dynamics. A ‘flow exuberance effect’ was evident such that Q2 (ejection‐like) and Q4 (sweep‐like) quadrants (that contribute positively to RS) dominated on the beach, dune toe, and lower stoss, whereas Q1 and Q3 (that contribute negatively to RS) dominated near the crest. This exuberance effect was not expressed, however, in sand transport patterns. Instead, Q1 and Q4, with above‐average streamwise velocity fluctuations (+u′), were most frequently associated with sand transport. Q4 activity corresponded with most sand transport at the beach, toe, and stoss locations (52, 60, 100%). At the crest, 25 to 86% of transport was associated with Q1 while Q4 corresponded with most of the remaining transport (13 to 59%). Thus, the relationship between sand transport and RS is not as straightforward as in traditional equations that relate flux to stress in increasing fashion. Generally, RS was poorly associated with sand transport partly because Q1 and Q4 contributions offset each other in RS calculations. Thus, large amounts of transport can occur with small RS. Turbulent kinetic energy or Reynolds normal stresses (u′2, w′2) may provide stronger associations with sand transport over dunes, although challenges exist on how to normalize and compare these quantities. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
953.
954.
A continuous Soil Conservation Service (SCS) curve number (CN) method that considers time‐varied SCS CN values was developed based on the original SCS CN method with a revised soil moisture accounting approach to estimate run‐off depth for long‐term discontinuous storm events. The method was applied to spatially distributed long‐term hydrologic simulation of rainfall‐run‐off flow with an underlying assumption for its spatial variability using a geographic information systems‐based spatially distributed Clark's unit hydrograph method (Distributed‐Clark; hybrid hydrologic model), which is a simple few parameter run‐off routing method for input of spatiotemporally varied run‐off depth, incorporating conditional unit hydrograph adoption for different run‐off precipitation depth‐based direct run‐off flow convolution. Case studies of spatially distributed long‐term (total of 6 years) hydrologic simulation for four river basins using daily NEXRAD quantitative precipitation estimations demonstrate overall performances of Nash–Sutcliffe efficiency (ENS) 0.62, coefficient of determination (R2) 0.64, and percent bias 0.33% in direct run‐off and ENS 0.71, R2 0.72, and percent bias 0.15% in total streamflow for model result comparison against observed streamflow. These results show better fit (improvement in ENS of 42.0% and R2 of 33.3% for total streamflow) than the same model using spatially averaged gauged rainfall. Incorporation of logic for conditional initial abstraction in a continuous SCS CN method, which can accommodate initial run‐off loss amounts based on previous rainfall, slightly enhances model simulation performance; both ENS and R2 increased by 1.4% for total streamflow in a 4‐year calibration period. A continuous SCS CN method‐based hybrid hydrologic model presented in this study is, therefore, potentially significant to improved implementation of long‐term hydrologic applications for spatially distributed rainfall‐run‐off generation and routing, as a relatively simple hydrologic modelling approach for the use of more reliable gridded types of quantitative precipitation estimations. 相似文献
955.
Angelo Ferro Salvatore Gambino Stefano Panepinto Giuseppe Falzone Giuseppe Laudani Bernard Ducarme 《Acta Geophysica》2011,59(3):618-632
In 2007–2008, we installed on Mt. Etna two deep tilt stations using high resolution, self-leveling instruments. These installations
are a result of accurate instrument tests, site selection, drilling and sensor positioning that has allowed detecting variations
related to the principal diurnal and semidiurnal tides for first time on Mt. Etna using tilt data. 相似文献
956.
A Compilation of Silicon and Thirty One Trace Elements Measured in the Natural River Water Reference Material SLRS-4 (NRC-CNRC) 总被引:1,自引:0,他引:1
Delphine Yeghicheyan Jean Carignan Michel Valladon Martine Bouhnik Le Coz Florence Le Cornec Maryse Castrec-Rouelle Michel Robert Luc Aquilina Emmanuel Aubry Carine Churlaud Aline Dia Samuel Deberdt Bernard Dupré Rémi Freydier Gérard Gruau Odile Hénin Anne-Marie de Kersabiec Joël Macé Luc Marin Nicole Morin Patrice Petitjean Elodie Serrat 《Geostandards and Geoanalytical Research》2001,25(2-3):465-474
The natural river water certified reference material SLRS-4 (NRC-CNRC, National Research Council-Conseil National de Recherches Canada) has been routinely analysed for major and trace elements by six French laboratories. Most measurements were made using inductively coupled plasma-mass spectrometry. For silicon and thirty one trace elements (rare earth elements, Ag, B, Br, Cs, Ga, Ge, Li, P, Pd, Rb, Se, Th, Ti, Tl, W, Y and Zr), no certified values are assigned by NRC-CNRC. We propose some compilation values and related uncertainties according to the results obtained by the different laboratories. 相似文献
957.
Darrell Anthony Herbert William B. Perry Bernard J. Cosby James W. Fourqurean 《Estuaries and Coasts》2011,34(5):973-992
Historic changes in water-use management in the Florida Everglades have caused the quantity of freshwater inflow to Florida
Bay to decline by approximately 60% while altering its timing and spatial distribution. Two consequences have been (1) increased
salinity throughout the bay, including occurrences of hypersalinity, coupled with a decrease in salinity variability, and
(2) change in benthic habitat structure. Restoration goals have been proposed to return the salinity climates (salinity and
its variability) of Florida Bay to more estuarine conditions through changes in upstream water management, thereby returning
seagrass species cover to a more historic state. To assess the potential for meeting those goals, we used two modeling approaches
and long-term monitoring data. First, we applied the hydrological mass balance model FATHOM to predict salinity climate changes
in sub-basins throughout the bay in response to a broad range of freshwater inflow from the Everglades. Second, because seagrass
species exhibit different sensitivities to salinity climates, we used the FATHOM-modeled salinity climates as input to a statistical
discriminant function model that associates eight seagrass community types with water quality variables including salinity,
salinity variability, total organic carbon, total phosphorus, nitrate, and ammonium, as well as sediment depth and light reaching
the benthos. Salinity climates in the western sub-basins bordering the Gulf of Mexico were insensitive to even the largest
(5-fold) modeled increases in freshwater inflow. However, the north, northeastern, and eastern sub-basins were highly sensitive
to freshwater inflow and responded to comparatively small increases with decreased salinity and increased salinity variability.
The discriminant function model predicted increased occurrences of Halodule wrightii communities and decreased occurrences of Thalassia testudinum communities in response to the more estuarine salinity climates. The shift in community composition represents a return to
the historically observed state and suggests that restoration goals for Florida Bay can be achieved through restoration of
freshwater inflow from the Everglades. 相似文献
958.
Jennifer M. McKinley Patricia Warke Christopher. D. Lloyd Alastair H. Ruffell Bernard J. Smith 《地球表面变化过程与地形》2006,31(8):950-969
Geostatistical techniques for spatial prediction and spatial simulation have been used in an innovative application to the study of weathering of natural building stone. The study investigates the differences in the spatial variation of permeability characteristics between fine‐ and coarse‐grained Stanton Moor building sandstone. Non‐destructive permeability measurements, using an unsteady‐state Portable Probe Permeameter, were made on three adjacent faces of two cubic blocks representative of fine‐ to medium‐grained and medium‐ to coarse‐grained Stanton Moor Sandstone. The findings provide greater understanding in the investigation of the durability characteristics of the Stanton Moor Sandstone and show that the spatial distribution and variability of permeability is more important in predicting the overall strength and weathering properties than mean permeability and absolute minimum and maximum values. The results suggest that both primary textural characteristics (such as grain size) and extent of cementation appear to be important factors in determining the overall durability properties of Stanton Moor Sandstone as a building stone. Geostatistical analysis has been shown to be an important tool in the characterization of spatial variation for the investigation of weathering of building stones. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
959.
Bernard Henry Mohamed E. M. Derder Mohamed Amenna Said Maouche Boualem Bayou 《Studia Geophysica et Geodaetica》2017,61(2):185-198
The reliability of an Apparent Polar Wander Path (APWP) obviously depends on the paleomagnetic poles used to determine it. The APWP of Africa and South America are fairly well defined for the 330–260 Ma interval. However, this study pointed out a moderate shift between these two curves, and an incoherency of the South American data, contrary to the African ones, which are homogeneous. A number of South American pole positions were re-evaluated in an effort to better constrain the APWP for the entire continent. Most of discarded poles correspond to sites at the area of the junction of Cordillera with the stable craton. That could have structural implications for the evolution of the western margin of the Gondwana. A new criterion for the evaluation of paleomagnetic poles reliability for APWP is presented. Based on comparison of data from different continents and labeled “coherence” criterion, it is independent from Van der Voo’s ones. 相似文献
960.
Dynamics of a large tropical lake: Lake Maracaibo 总被引:1,自引:0,他引:1