全文获取类型
收费全文 | 4188篇 |
免费 | 53篇 |
国内免费 | 61篇 |
专业分类
测绘学 | 46篇 |
大气科学 | 333篇 |
地球物理 | 731篇 |
地质学 | 2088篇 |
海洋学 | 389篇 |
天文学 | 510篇 |
综合类 | 66篇 |
自然地理 | 139篇 |
出版年
2023年 | 18篇 |
2022年 | 52篇 |
2021年 | 71篇 |
2020年 | 92篇 |
2019年 | 103篇 |
2018年 | 233篇 |
2017年 | 228篇 |
2016年 | 265篇 |
2015年 | 118篇 |
2014年 | 253篇 |
2013年 | 333篇 |
2012年 | 326篇 |
2011年 | 325篇 |
2010年 | 349篇 |
2009年 | 285篇 |
2008年 | 266篇 |
2007年 | 293篇 |
2006年 | 227篇 |
2005年 | 114篇 |
2004年 | 43篇 |
2003年 | 46篇 |
2002年 | 40篇 |
2001年 | 33篇 |
2000年 | 32篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 25篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1958年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有4302条查询结果,搜索用时 15 毫秒
201.
202.
L’Her Alexandre Reinert Markus Prants Sergey Carton Xavier Morvan Mathieu 《Ocean Dynamics》2021,71(5):601-612
Ocean Dynamics - The Eastern Kamchatka Current (EKC) is the western boundary current of the North Pacific subpolar gyre. Southeast of the Kamchatka Peninsula lies a large anticyclonic eddy, the... 相似文献
203.
Hydrogeological information for the territories of the Republic of Estonia, Leningrad province, and northern Pskov province of the Russian Federation is generalized. A unified groundwater flow model was developed for the Lomonosov-Voronkovskii aquifer, including its Estonian part is developed. The methodological approaches for solving transboundary problems as applied to groundwater are determined. The results of studying transboundary hydrodynamic interaction in Lomonosov-Voronkovskii aquifer in the Russian-Estonian boundary area are given. The direction of undisturbed groundwater flow is determined, and changes caused by the exploitation of the aquifer are assessed. 相似文献
204.
Steven L. Morey Mark A. Bourassa Dmitry S. Dukhovskoy James J. O’Brien 《Ocean Dynamics》2006,56(5-6):594-606
A coupled ocean and boundary layer flux numerical modeling system is used to study the upper ocean response to surface heat
and momentum fluxes associated with a major hurricane, namely, Hurricane Dennis (July 2005) in the Gulf of Mexico. A suite
of experiments is run using this modeling system, constructed by coupling a Navy Coastal Ocean Model simulation of the Gulf
of Mexico to an atmospheric flux model. The modeling system is forced by wind fields produced from satellite scatterometer
and atmospheric model wind data, and by numerical weather prediction air temperature data. The experiments are initialized
from a data assimilative hindcast model run and then forced by surface fluxes with no assimilation for the time during which
Hurricane Dennis impacted the region. Four experiments are run to aid in the analysis: one is forced by heat and momentum
fluxes, one by only momentum fluxes, one by only heat fluxes, and one with no surface forcing. An equation describing the
change in the upper ocean hurricane heat potential due to the storm is developed. Analysis of the model results show that
surface heat fluxes are primarily responsible for widespread reduction (0.5°–1.5°C) of sea surface temperature over the inner
West Florida Shelf 100–300 km away from the storm center. Momentum fluxes are responsible for stronger surface cooling (2°C)
near the center of the storm. The upper ocean heat loss near the storm center of more than 200 MJ/m2 is primarily due to the vertical flux of thermal energy between the surface layer and deep ocean. Heat loss to the atmosphere
during the storm’s passage is approximately 100–150 MJ/m2. The upper ocean cooling is enhanced where the preexisting mixed layer is shallow, e.g., within a cyclonic circulation feature,
although the heat flux to the atmosphere in these locations is markedly reduced. 相似文献
205.
206.
207.
V. Mishin Z. Pu L. Sapronova A. Bazarzhapov Yu. Kuz’minykh X. Cao H. Zhang 《Geomagnetism and Aeronomy》2009,49(8):1193-1198
The maps of the field-aligned current (FAC) density distribution in the ionosphere obtained by the TIM-2 magnetogram inversion
technique are used to investigate the August 27, 2001 substorm. The open magnetic flux Ψ and intensity J of the substorm current wedge (SCW) have been determined with a step of 1–5 min. The substorm onsets are divided into two
types, PSR (plasma sheet reconnection) and TLR (tail lobe reconnection). The fast expansion tailward of the PSR region is
described as the transition from PSR to PSR+TLR. Assuming that the SCW FACs flow down into the ionosphere from the edges of
the disruption region of the cross-tail dawn-dusk current, several parameters of the disruption region have been estimated.
The disrupted magnetic field has been found to be ∼5% of the undisrupted one for PSR and ∼95% for PSR+TLR. The disturbance
power Q for PSR is an order of magnitude lower than that for PSR+TLR. The abrupt growth of Q during the transition from PSR to PSR+TLR is observed over the entire SCW area from its near-Earth part to the midtail and
distant tail. 相似文献
208.
The discreteness of the time series of the solar-related geophysical phenomena is justified. The balance of the formation and decomposition (neglecting diffusion) of fractal elements during the evolution of the equilibrium systems as applied to the heliophysical and geomagnetic phenomena is the original position in this case. The discreteness properties of the spatial-temporal characteristics of solar activity are simply justified based on a fractal analysis. The performed calculations in the solar wind medium in the near-Earth space make it possible to classify the fluxes depending on their fractal dimension. The possible mechanism by which high-speed solar wind streams are generated is also briefly discussed in the scope of the fractal paradigm. 相似文献
209.
Guojiang?WanEmail author Jing’an?Chen Siqin?Xu Fengchang?Wu P.?H.?Santschi 《中国科学D辑(英文版)》2005,48(4):484-496
The fundamental assumption of 210Pb sediment dating is the stable flux of 210Pbex, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively
constant, the 210Pbex activity in sediments will be exponentially reduced with sedimentation age. 210Pbex in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter
in lake water is suddenly increased, 210Pbex will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously
unfit for the fundamental assumption of 210Pb dating; on the other hand, the sudden enhancement of 210Pbex flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed
in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water
area of Lake Chenghai in June 1997. The vertical profile of 137Cs activity is characterized by a tree-peak pattern. This profile gave reliable ages, and also showed the stability of sediment
accumulation in the recent ten years. The vertical profile of 210Pbex activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mechanism of constraining the transfer of 210Pbex into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived
from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments,
i.e., “deposition-de-composition-accumulation”, the sedimentation fluxes (F(Corg)) of organic carbon (Corg) since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbex (F(210Pbex)) in different years display good synchronous relations with the sedimentation flux of organic carbon (F(Corg)), especially in the years of 1972–1974 and 1986–1989. The variation of F(Corg) led to the variation of F(210Pbex); the variation of F(210Pbex) reflects, to some extent, the historical variation of lake productivity. 相似文献
210.
Griliches’ knowledge production function has been increasingly adopted at the regional level where location-specific conditions drive the spatial differences in knowledge creation dynamics. However, the large majority of such studies rely on a traditional regression approach that assumes spatially homogenous marginal effects of knowledge input factors. This paper extends the authors’ previous work (Kang and Dall’erba in Int Reg Sci Rev, 2015. doi: 10.1177/0160017615572888) to investigate the spatial heterogeneity in the marginal effects by using nonparametric local modeling approaches such as geographically weighted regression (GWR) and mixed GWR with two distinct samples of the US Metropolitan Statistical Area (MSA) and non-MSA counties. The results indicate a high degree of spatial heterogeneity in the marginal effects of the knowledge input variables, more specifically for the local and distant spillovers of private knowledge measured across MSA counties. On the other hand, local academic knowledge spillovers are found to display spatially homogenous elasticities in both MSA and non-MSA counties. Our results highlight the strengths and weaknesses of each county’s innovation capacity and suggest policy implications for regional innovation strategies. 相似文献