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131.
Linda Stalker Prokopy Nathan Mullendore Kathryn Brasier Kristin Floress 《社会与自然资源》2014,27(11):1177-1191
While much has been written about the benefits of collaborative watershed management to address nonpoint source pollution and other water quality concerns in the United States, few scholars have addressed the catalytic nature of events that generate these collective action responses. Further, because equivalent catalyst events in different communities do not always lead to collective action, it is critical to understand the interaction between a community's baseline conditions and the catalyst events that lead to collective action. This article presents a conceptual framework that illustrates the relationship between baseline conditions and events that lead to collective action. In this article a theoretical typology of catalyst events is presented that includes both intentional and nonintentional types of events. Understanding these types of catalyst events can help water quality advocates create and/or seize opportunities to nurture a collective action. This article concludes with a call for future research into catalyst events. 相似文献
132.
Bai Peng Wang Jia Chu Philip Hawley Nathan Fujisaki-Manome Ayumi Kessler James Lofgren Brent M. Beletsky Dmitry Anderson Eric J. Li Yaru 《Ocean Dynamics》2020,70(7):991-1003
Ocean Dynamics - A partly coupled wave-ice model with the ability to resolve ice-induced attenuation on waves was developed using the Finite-Volume Community Ocean Model (FVCOM) framework and... 相似文献
133.
Tanzhuo Liu Gerardo Iturrino David Goldberg Eric Meissner Kerry Swain Clayton Furman Peter Fitzgerald Nathan Frisbee Joe Chlimoun John Van Hyfte Ron Beyer 《Geo-Marine Letters》2013,33(1):83-93
The basic functionality and performance of a new Schlumberger active wireline heave compensation system on the JOIDES Resolution was evaluated during the sea trial and a 3-year period of the IODP Phase II operations. A suite of software programs was developed to enable real-time monitoring of the dynamics of logging tools, and assess the efficiency of wireline heave compensation during downhole operations. The evaluation of the system effectiveness was performed under normal logging conditions as well as during stationary tests. Logging data were analyzed for their overall quality and repeatability, and to assess the reliability of high-resolution data such as formation microscanner (FMS) electrical images. This revealed that the system reduces 65–80 % of displacement or 88–98 % variance of downhole tool motion in stationary mode under heave conditions of ±0.2–1.5 m and water depths of 300–4,500 m in open holes. Under similar water/heave conditions, the compensator system reduces tool displacement by 50–60 %, or 75–84 % variance in downhole tool motion during normal logging operations. Such compensation efficiency (CE) is comparable to previous compensation systems, but using advanced and upgradeable technologies, and provides 50–85 % heave motion and heave variance attenuation. Moreover, logging down/up at low speeds (300–600 m/h) reduces the system’s CE values by 15–20 %, and logging down at higher speeds (1,000–1,200 m/h) eliminates CE values by 55–65 %. Considering the high quality of the logging data collected, it is concluded that the new system can provide an improved level of compensation over previous systems. Also, if practically feasible, future integration of downhole cable dynamics as an input feedback into the current system could further improve its compensation efficiency during logging operations. 相似文献
134.
In deltaic marshes, mineral sediment promotes positive elevation change and counters subsidence and sea level rise. In many
such marshes sediment deficits result in wetland loss. One new way to address sediment deficiency is to supply marshes with
sediments in a slurry that deposits the sediment in a thin layer over a large area. The long-term effects of this strategy
are poorly understood. In a rapidly submerging,Spartina alterniflora salt marsh, we tested how different amounts of sediment ameliorated the effects of sea level rise and subsidence over 7 yr
(1992–1998). Sediment slurry enrichment likely affected plants and soils by two mechanisms. It increased elevation and soil
bulk density, leading to increased plant vigor and soil condition. These effects were long lasting, such that by 1998 areas
receiving moderate amounts of sediment (5–12 cm relative elevation) had better plant vigor and soil condition compared to
areas not receiving sediment (55% cover versus 20%; bulk densities of 0.4–1.0 g cm−3 versus 0.2 g cm−3; 0 mM hydrogen sulfide versus > 1.0 mM). The sediment slurry also had high nutrient content, which resulted in a pulse of
growth, especially in areas receiving the most sediment (areas > 12 cm relative elevation initially had >90% cover and canopy
heights >1.6 m). This nutrient-induced growth spurt was short lived and faded after 3 yr, at which point the long lasting
effects of increased elevation probably became the dominant factor promoting plant vigor and soil condition. Moderate levels
of sediment generated the most beneficial and long lasting effects to the vegetation and soils. This degree of sediment slurry
addition countered the effects of subsidence and sea level rise, but not so much as to surpass the intertidal position to
whichS. alterniflora is best adapted. 相似文献
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140.
Stefano Campagnola Nathan J. Strange Ryan P. Russell 《Celestial Mechanics and Dynamical Astronomy》2010,108(2):165-186
The announced missions to the Saturn and Jupiter systems renewed the space community interest in simple design methods for
gravity assist tours at planetary moons. A key element in such trajectories are the V-Infinity Leveraging Transfers (VILT)
which link simple impulsive maneuvers with two consecutive gravity assists at the same moon. VILTs typically include a tangent
impulsive maneuver close to an apse location, yielding to a desired change in the excess velocity relative to the moon. In
this paper we study the VILT solution space and derive a linear approximation which greatly simplifies the computation of
the transfers, and is amenable to broad global searches. Using this approximation, Tisserand graphs, and heuristic optimization
procedure we introduce a fast design method for multiple-VILT tours. We use this method to design a trajectory from a highly
eccentric orbit around Saturn to a 200-km science orbit at Enceladus. The trajectory is then recomputed removing the linear
approximation, showing a Δv change of <4%. The trajectory is 2.7 years long and comprises 52 gravity assists at Titan, Rhea, Dione, Tethys, and Enceladus,
and several deterministic maneuvers. Total Δv is only 445 m/s, including the Enceladus orbit insertion, almost 10 times better then the 3.9 km/s of the Enceladus orbit
insertion from the Titan–Enceladus Hohmann transfer. The new method and demonstrated results enable a new class of missions
that tour and ultimately orbit small mass moons. Such missions were previously considered infeasible due to flight time and
Δv constraints. 相似文献