全文获取类型
收费全文 | 324篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 28篇 |
地球物理 | 125篇 |
地质学 | 88篇 |
海洋学 | 28篇 |
天文学 | 38篇 |
自然地理 | 19篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 18篇 |
2013年 | 18篇 |
2012年 | 12篇 |
2011年 | 22篇 |
2010年 | 24篇 |
2009年 | 30篇 |
2008年 | 14篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 21篇 |
2004年 | 4篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有339条查询结果,搜索用时 31 毫秒
151.
Lindsey Jones Clara Champalle Sabrina Chesterman Laura Cramer Todd A. Crane 《Climate Policy》2013,13(5):551-572
We carry out a structured review of the peer-reviewed literature to assess the factors that constrain and enable the uptake of long-term climate information in a wide range of sectoral investment and planning decisions. Common applications of long-term climate information are shown to relate to urban planning and infrastructure, as well as flood and coastal management. Analysis of the identified literature highlights five categories of constraints: disconnection between users and producers of climate information, limitations of climate information, financial and technical constraints, political economy and institutional constraints and finally psycho-social constraints. Five categories of enablers to the uptake of long-term climate information in decision-making are also identified: collaboration and bridge work, increased accessibility of climate information, improvement in the underlying science, institutional reform and windows of opportunity for building trust.Policy relevanceOur review suggests that stand-alone interventions aimed at promoting the uptake of climate information into decision-making are unlikely to succeed without genuine and sustained relationships between producers and users. We also highlight that not every decision requires consideration of long-term climate information for successful outcomes to be achieved. This is particularly the case in the context of developing countries, where the immediacy of development challenges means that decision makers often prioritize short-term interventions. Care should therefore be taken to ensure that information is targeted towards investments and planning decisions that are relevant to longer-term timescales. 相似文献
152.
153.
154.
Potential effects of organochlorine contaminant (OC) exposure on humoral immune function and health of free-ranging northern fur seals were investigated. Forty-two "neonates" were captured for blood sample collection and re-sampled as "pups" 29-51 days later. OCs were extracted from whole blood to identify polychlorinated biphenyl congeners and chlorinated pesticides by high performance liquid chromatography. Humoral immune function was assessed by antibody responses to vaccination and immunoglobulin concentrations. Additional health status indicators included leukocyte counts and haptoglobin concentrations. Mean OC concentrations were higher in neonates than at recapture. Neonates of young dams had higher mean OC concentrations than neonates of older dams. A higher proportion of old dam's pups developed a twofold or greater increase in antigen-specific antibodies compared to young dam's pups. Higher OC exposure and poor immune responses in first-born pups may indicate a higher risk of secondary morbidity and mortality than pups of multiparous dams. 相似文献
155.
Future shoreline changes on a sandy beach with a structure such as a jetty or groin can be estimated when wave time series is known (i.e. sequence of wave height, period, and direction). This paper presents an extension of an existing solution (Pelnard-Considere, 1956) for the linearized partial differential equation for shoreline change at an infinite jetty where waves are time varying and when the angle of the shoreline is small with respect to the waves breaking at the shoreline. The novel solution provided in this paper allows the previous constant wave condition solution to be extended to the case where wave properties (i.e. wave direction, wave height, and wave period) are time varying. Example usage of the method presented shows that shorelines may be of different final plan form shape for time varying wave conditions even though the sediment transport along adjacent beaches is not spatially varying (i.e. spatially constant) from time step to time step. Although this difference in shape may have been known previously using numerical models, it could not be proved analytically. Reversals of wave height, period, and direction time series are shown to provide different final shoreline shapes even though the time series consists of the same waves although in different ordered time. The solution provided will allow one line numerical shoreline models to be tested using an analytic solution. 相似文献
156.
Rob A. Holman K. Todd Holland Dave M. Lalejini Steven D. Spansel 《Ocean Dynamics》2011,61(11):1927-1935
We investigate the issues and methods for estimating nearshore bathymetry based on wave celerity measurements obtained using
time series imagery from small unmanned aircraft systems (SUAS). In contrast to time series imagery from fixed cameras or
from larger aircraft, SUAS data are usually short, gappy in time, and unsteady in aim in high frequency ways that are not
reflected by the filtered navigation metadata. These issues were first investigated using fixed camera proxy data that have
been intentionally degraded to mimic these problems. It has been found that records as short as 50 s or less can yield good
bathymetry results. Gaps in records associated with inadvertent look-away during unsteady flight would normally prevent use
of the required standard Fast Fourier Transform methods. However, we found that a full Fourier Transform could be implemented
on the remaining valid record segments and was effective if at least 50% of total record length remained intact. Errors in
image geo-navigation were stabilized based on fixed ground fiducials within a required land portion of the image. The elements
of a future method that could remove this requirement were then outlined. Two test SUAS data runs were analyzed and compared
to survey ground truth data. A 54-s data run at Eglin Air Force Base on the Gulf of Mexico yielded a good bathymetry product
that compared well with survey data (standard deviation of 0.51 m in depths ranging from 0 to 4 m). A shorter (30.5 s) record
from Silver Strand Beach (near Coronado) on the US west coast provided a good approximation of the surveyed bathymetry but
was excessively deep offshore and had larger errors (1.19 m for true depths ranging from 0 to 6 m), consistent with the short
record length. Seventy-three percent of the bathymetry estimates lay within 1 m of the truth for most of the nearshore. 相似文献
157.
Grace Xingxin Gao Liang Heng Achim Hornbostel Holmer Denks Michael Meurer Todd Walter Per Enge 《GPS Solutions》2013,17(4):561-573
The Galileo E5a/E5b signals and the Global Positioning System (GPS) L5 signal lie within the aeronautical radionavigation services (ARNS) band. They suffer interference from the services in this frequency band, in particular, pulsed signals from distance measuring equipment (DME) and tactical air navigation (TACAN) systems. To maintain system accuracy and integrity, interference mitigation is beneficial and necessary. We first present the real DME/TACAN environment at Stanford, CA as an example to illustrate the need for mitigating DME/TACAN interference. We then propose a time and frequency joint mitigation algorithm—Hybrid Blanking and its simplified version, frequency domain adaptive filtering (FDAF) for hardware implementation. Finally, a flight measurements campaign was performed over a European DME/TACAN hotspot near Frankfurt, Germany, to record a worst-case DME interference environment. Recorded data from the flight tests mixed with injected GNSS signals verify the effectiveness of the proposed mitigation algorithm. 相似文献
158.
Determining aquifer type, unconfined, semi‐confined, or confined, by drilling or performing pumping tests has inherent problems (i.e., cost and complex field issues) while sometimes yielding inconclusive results. An improved method to cost‐effectively determine aquifer type would be beneficial for hydraulic mapping of complex aquifer systems like fractured rock aquifers. Earth tides are known to influence water levels in wells penetrating confined aquifers or unconfined thick, low‐porosity aquifers. Water‐level fluctuations in wells tapping confined and unconfined aquifers are also influenced by changes in barometric pressure. Harmonic analyses of water‐level fluctuations of a thick (~1000 m) carbonate aquifer located in south‐central Oklahoma (Arbuckle‐Simpson aquifer) were utilized in nine wells to identify aquifer type by evaluating the influence of earth tides and barometric‐pressure variations using signal identification. On the basis of the results, portions of the aquifer responded hydraulically as each type of aquifer even though there was no significant variation in lithostratigraphy. The aquifer type was depth dependent with confined conditions becoming more prevalent with depth. The results demonstrate that harmonic analysis is an accurate and low‐cost method to determine aquifer type. 相似文献
159.
Rapid temporal variability of SO2 and SO in the Venus 85–100 km mesosphere (Sandor, B.J., Clancy, R.T., Moriarty-Schieven G.H. [2007]. Bull. Am. Astron. Soc. 39, 503; Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60) requires in situ sources and sinks for these molecules. While many loss mechanisms are recognized, no process for in situ production is known. Observational investigations to find, or constrain other potential sulfur reservoirs offer one method toward understanding the applicable photochemistry. Here, we report upper limits for gas-phase H2SO4 (sulfuric acid) abundances in Venus’ 85–100 km upper mesosphere, derived from 16 ground-based sub-mm spectroscopic observations in the period 2004–2008. Unlike the ubiquitous sulfuric acid solid/liquid aerosol, the gas phase would be photochemically active, potentially both source and sink for SO and SO2. H2SO4 is retrieved from sub-mm lines located in the same bandpass as the SO2 and SO lines described by Sandor et al. (Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60). H2SO4 upper limits reported here are thus simultaneous and spatially coincident with measurements of SO2 and SO, providing for analysis of the three sulfur species collectively. The average H2SO4 abundance over 16 observations is 1 ± 2 ppb (i.e. <3 ppb). Upper limits for individual observations range from 3 to 44 ppb, where quality of the observing weather is the dominant constraint on measurement precision. The sum of H2SO4, SO2 and SO varies widely. In one comparison, the sum [H2SO4 + SO2 + SO] measured on one date differs by 10-σ from the sum measured 2 months later. We conclude that upper mesospheric sulfur atoms are not conserved among the three molecules, that H2SO4 is not a significant sulfur reservoir for balancing the observed variations of [SO2 + SO], and is not relevant to the (still unknown) photochemistry responsible for observed behavior of SO2 and SO. Having ruled out H2SO4, we infer that elemental sulfur is the most probable candidate for the needed third reservoir. 相似文献
160.
A case of offshore convective initiation by interacting land breezes near Darwin, Australia is investigated using convection-permitting model simulations, radar-derived precipitation observations, thermodynamic profiles from radiosonde soundings and surface measurements. These analyses elucidate the convergence of two land breezes in the Van Diemen Gulf, one originating from the Tiwi Islands and the other from mainland Australia; the convergence is sufficient to initiate a line of convection that forms parallel to the mainland coast in the early morning. While differing in small-scale features, the modeled system shows reasonably good agreement with the observed precipitation accumulations. However, using simulations with different initialization times and examining a second case, it is shown that the representation of the land-breeze system and subsequent convective initiation is very sensitive to the upstream wind and thermodynamic conditions, making correct simulation of these processes challenging. 相似文献