全文获取类型
收费全文 | 27927篇 |
免费 | 5221篇 |
国内免费 | 7974篇 |
专业分类
测绘学 | 4439篇 |
大气科学 | 4719篇 |
地球物理 | 6955篇 |
地质学 | 14774篇 |
海洋学 | 4019篇 |
天文学 | 259篇 |
综合类 | 2163篇 |
自然地理 | 3794篇 |
出版年
2024年 | 113篇 |
2023年 | 325篇 |
2022年 | 922篇 |
2021年 | 1091篇 |
2020年 | 1293篇 |
2019年 | 1560篇 |
2018年 | 1279篇 |
2017年 | 1458篇 |
2016年 | 1532篇 |
2015年 | 1712篇 |
2014年 | 1842篇 |
2013年 | 2020篇 |
2012年 | 1924篇 |
2011年 | 1997篇 |
2010年 | 1608篇 |
2009年 | 1825篇 |
2008年 | 1866篇 |
2007年 | 1998篇 |
2006年 | 1937篇 |
2005年 | 1646篇 |
2004年 | 1501篇 |
2003年 | 1259篇 |
2002年 | 1162篇 |
2001年 | 1008篇 |
2000年 | 921篇 |
1999年 | 838篇 |
1998年 | 765篇 |
1997年 | 677篇 |
1996年 | 574篇 |
1995年 | 518篇 |
1994年 | 485篇 |
1993年 | 390篇 |
1992年 | 268篇 |
1991年 | 209篇 |
1990年 | 141篇 |
1989年 | 111篇 |
1988年 | 110篇 |
1987年 | 76篇 |
1986年 | 33篇 |
1985年 | 33篇 |
1984年 | 22篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
261.
262.
1 .IntroductionEvery year ,Taiwanis subjectedtotwo or three typhoonintrusions in average which always causedisasters . Most of the disasters which occur around the coastal zone are due to seabed instability andcoastal structure destruction caused bytyphoo… 相似文献
263.
Estimation of Land Subsidence Based on Groundwater Flow Model 总被引:8,自引:0,他引:8
This article presents an approach for estimating land subsidence due to withdrawal of groundwater. The proposed method calculates the groundwater seepage in 3-D-condition and calculates the land subsidence one-dimensionally. The governing equation on groundwater seepage is based on the three-dimensional mass conservation law and the principle of effective stress. The land subsidence calculation method is derived based on the following assumptions: (1) displacements occur only in the vertical direction, and (2) in vertical direction the total stresses do not change. The governing equation is solved by numerical method, i.e., finite element method (FEM) in spatial discretization and finite difference method (FDM) in time series discretization. In FEM Galerkin method is adopted and in FDM, lumped matrix method is employed. The proposed method is calibrated via analyzing 1-D consolidation problem and the results are compared with those from Terzaghi's one-dimensional consolidation theory and oedometer test. The proposed method is employed to analyze the consolidation of a soft layer due to withdrawal of groundwater from an aquifer under it. Moreover, this method is also applied to a field case of land subsidence due to groundwater pumping in a gas production field in Japan. The analytical results are compared with the field observed data. The results show that this approach simulates the field case well. 相似文献
264.
Katsumi Matsumoto 《Journal of Oceanography》2006,62(6):887-902
Iron fertilization of nutrient-rich surface waters of the ocean is one possible way to help slow the rising levels of atmospheric
CO2 by sequestering it in the oceans via biological carbon export. Here, I use an ocean general circulation model to simulate
a patch of nutrient depletion in the subpolar northwest Pacific under various scenarios. Model results confirm that surface
fertilization is an inefficient way to sequester carbon from the atmosphere (Gnanadesikan et al., 2003), since only about 20% of the exported carbon comes initially from the atmosphere. Fertilization reduces future production
and thus CO2 uptake by utilizing nutrients that would otherwise be available later. Effectively, this can be considered as leakage when
compared to a control run. This “effective” leakage and the actual leakage of sequestered CO2 cause a significant, rapid decrease in carbon retention (only 30–45% retained after 10 years and less than 20% after 50 years).
This contrasts markedly with the almost 100% retention efficiency for the same duration using the same model, when carbon
is disposed directly into the northwest Pacific (Matsumoto and Mignone, 2005). As a consequence, the economic effectiveness
of patch fertilization is poor in two limiting cases of the future price path of carbon. Sequestered carbon in patch fertilization
is lost to the atmosphere at increasingly remote places as time passes, which would make monitoring exceedingly difficult.
If all organic carbon from one-time fertilization reached the ocean bottom and remineralized there, acidification would be
about −0.05 pH unit with O2 depletion about −20 μmol kg−1. These anomalies are probably too small to seriously threaten deep sea biota, but they are underestimated in the model because
of its large grid size. The results from this study offer little to advocate purposeful surface fertilization as a serious
means to address the anthropogenic carbon problem. 相似文献
265.
266.
Ice Sheet-Thermohaline Circulation Interactions in a Climate Model of Intermediate Complexity 总被引:3,自引:0,他引:3
A vertically integrated dynamic ice sheet model is coupled to the atmosphere-ocean-sea ice-land surface climate model recently
developed by Wang and Mysak (2000). The background lateral (east-west) ice sheet discharge rate used by Gallee et al. (1992) is reduced and the planetary emissivity is increased (to parameterize the cooling effect of a decrease of the atmospheric
CO2 concentration), in order to build up substantial ice sheets during a glacial period and hence set the stage for ice sheet-thermohaline
circulation (THC) interactions. The following iceberg calving scheme is then introduced: when the maximum model height of
the North American ice sheet reaches a critical value (2400 m), a prescribed lateral discharged rate is imposed on top of
the background discharge rate for a finite time. Per a small prescribed discharge rate, repeated small iceberg calving events
occur, which lead to millennial-scale climate cycles with small amplitudes. These are a crude representation of Dansgaard-Oeschger
oscillations. Over one such cycle, the zonally averaged January surface air temperature (SAT) drops about 1.5°C at 72.5°N.
However, a large prescribed lateral discharge rate leads to the shut down of the THC. In this case, the January SAT drops
about 5°C at 72.5°N, the sea ice extent advances equatorward from 57.5° to 47.5°N and the net ice accumulation rate at the
grid of maximum ice sheet height is reduced from 0.24 to 0.15 m/y. Since data strongly suggest that a collapsed THC was not
a steady state during the last glacial, we restore the THC by increasing the vertical diffusivity in the North Atlantic Ocean
for a finite time. The resulting climate cycles associated with conveyor-on and conveyor-off phases have much larger amplitudes;
furthermore, the strong iceberg calving events lead to a larger loss of ice sheet mass and hence the period of the oscillations
is longer (several thousand years).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
267.
268.
本文应用海洋围隔生态实验研究了浮游植物对石油烃污染物生物富集动力学过程 ,提出了“水相差法”测定海洋浮游植物体内石油烃浓度 ,以及包括石油烃挥发和生物生长等影响因素的石油烃生物富集动力学模型 ,并利用非线性拟合技术得到了海洋浮游植物对 0 #柴油 WAF中正构烷烃的生物富集动力学参数 kup,kel和 BCFPOC,结果与 Kováts色谱保留指数具有很好的相关性 ,与利用生物分析平衡法测定的文献数据基本一致。本模型及实验方法简便可靠 ,可在现场实验中广泛应用 ,得到的动力学参数应用于多介质环境模型和生态动力学模型 ,用以研究石油烃污染物中正构烷烃在海洋环境中的迁移变化规律 相似文献
269.
270.
A multidisciplinary study in the Gulf of Cadiz is revisited, using additional diagnostic modelling tools. The dissolved trace metal (Cu, Ni, Zn, Co) distributions in the Gulf of Cadiz are analysed using modelled tracer evolutions, field observations and the concept of tracer ages. This study shows that a significant part of the observed metal distributions can be explained by the metal inputs of three river systems (Guadiana, Rio Tinto and Odiel, Guadalquivir) discharging into the Gulf of Cadiz, while the remainder of the signal is most likely associated with the benthic metal remobilisation along the shelf of this coastal region. 相似文献