全文获取类型
收费全文 | 384篇 |
免费 | 15篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 14篇 |
地球物理 | 108篇 |
地质学 | 110篇 |
海洋学 | 72篇 |
天文学 | 55篇 |
综合类 | 3篇 |
自然地理 | 34篇 |
出版年
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 10篇 |
2013年 | 15篇 |
2012年 | 14篇 |
2011年 | 17篇 |
2010年 | 23篇 |
2009年 | 24篇 |
2008年 | 25篇 |
2007年 | 21篇 |
2006年 | 19篇 |
2005年 | 16篇 |
2004年 | 9篇 |
2003年 | 9篇 |
2002年 | 17篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 13篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 10篇 |
1993年 | 2篇 |
1992年 | 7篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 7篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有405条查询结果,搜索用时 31 毫秒
51.
In the chemical evolution of the Galaxy, Type II supernovae (SNe II)have contributed to the early metal enrichment and later
Type Iasupernovae (SNe Ia) have contributed to the delayed enrichment of Fe.In principle, hypothetical pre-galactic population
III objects couldcause the earliest heavy element enrichment. Here we present our twonew findings. 1) The peculiar abundance
pattern among iron peakelements (Cr, Mn, Co, and Fe) in the very metal poor can be reproducedwith SN II nucleosynthesis yields
without invoking the contributionfrom Pop III objects. 2) The observed chemical evolution in the solarneighborhood is well
reproduced with the metallicity dependentoccurrence of SNe Ia, where SNe Ia do not occur if the iron abundanceof the progenitors
is as low as [Fe/H] ≲ -1. We make theprediction that the cosmic SN Ia rate drops at z ∼ 1-2 because ofthe low-iron abundance, which can be observed with the Next GenerationSpace Telescope.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
52.
53.
A series of studies was conducted on three buildings of steel reinforced concrete structures with RC shear walls damaged in the 1995 Hyogo-ken Nanbu earthquake. These buildings are located in an area where structural damage centred around. Two of these buildings suffered severe damage, while the third was not structurally damaged. Our studies deal with site inspections, including micro-tremor measurement of buildings, the evaluation of input motions, and the response analyses considering soil–structure interaction. The results of simulation analyses of the two severely damaged buildings correspond to their actual damage state. From the response analyses of the one slender building with no structural damage, it was concluded that uplifting is the main reason it did not suffer any structural damage. Through these studies, the importance of soil–structure interaction and effective input motion is fully understood. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
54.
Hassan Mohamed AbdelazimNegm Mahmoud Salah Kazuo Nadaoka Mohamed Zahran 《Arabian Journal of Geosciences》2017,10(2):42
Bathymetric information for shallow coastal/lake areas is essential for hydrological engineering applications such as sedimentary processes and coastal studies. Remotely sensed imagery is considered a time-effective, low-cost, and wide-coverage solution for bathymetric measurements. This study assesses the performance of three proposed empirical models for bathymetry calculations in three different areas: Alexandria port, Egypt, as an example of a low-turbidity deep water area with silt-sand bottom cover and a depth range of 10.5 m; the Lake Nubia entrance zone, Sudan, which is a highly turbid, unstable, clay bottom area with water depths to 6 m; and Shiraho, Ishigaki Island, Japan, a coral reef area with varied depths ranging up to 14 m. The proposed models are the ensemble regression tree-fitting algorithm using bagging (BAG), ensemble regression tree-fitting algorithm of least squares boosting (LSB), and support vector regression algorithm (SVR). Data from Landsat 8 and Spot 6 satellite images were used to assess the performance of the proposed models. The three models were used to obtain bathymetric maps using the reflectance of green, red, blue/red, and green/red band ratios. The results were compared with corresponding results yielded by two conventional empirical methods, the neural network (NN) and the Lyzenga generalised linear model (GLM). Compared with echosounder data, BAG, LSB, and SVR results demonstrate higher accuracy ranges from 0.04 to 0.35 m more than Lyzenga GLM. The BAG algorithm, producing the most accurate results, proved to be the preferable algorithm for bathymetry calculation. 相似文献
55.
An analysis of the radar backscattering from the ocean surface covered by oil spill is presented using a microwave scattering model and Monte-Carlo simulation. In the analysis, a one-dimensional rough sea surface is numerically generated with an ocean waveheight spectrum for a given wind velocity. A two-layered medium is then generated by adding a thin oil layer on the simulated rough sea surface. The electric fields backscattered from the sea surface with two-layered medium are computed with the method of moments (MoM), and the backscattering coefficients are statistically obtained with N independent samples for each oil-spilled surface using the Monte-Carlo technique for various conditions of surface roughness, oil-layer thickness, frequency, polarization and incidence angle. The numerical simulation results are compared with theoretical models for clean sea surfaces and SAR images of an oil-spilled sea surface caused by the Hebei (Hebei province, China) Spirit oil tanker in 2007. Further, conditions for better oil spill extraction are sought by the numerical simulation on the effects of wind speed and oil-layer thickness at different incidence angles on the backscattering coefficients. 相似文献
56.
Hidehiko Suzuki Kazuo Shiokawa Masaki Tsutsumi Takuji Nakamura Makoto Taguchi 《Polar Science》2008,2(1):1-8
Spectroscopic observations of OH airglow undertaken on May 2, 2006 at Uji, Japan reveal variations in intensity and rotational temperature related to the passage of an atmospheric gravity wave. The variations exhibit a period of approximately 1 h and magnitudes of 2–6% in intensity and 0.5–2% in rotational temperature. The vertical wavelength and intrinsic frequency of the atmospheric gravity wave were determined from the horizontal wavelength derived by an OH airglow imager, the background horizontal wind velocity obtained by the middle and upper atmosphere (MU) radar, and the dispersion relationship. The observed variations are consistent with the values calculated using the model of Liu, A.Z., Swenson, G.R. [2003. A modeling study of O2 and OH airglow perturbations induced by atmospheric gravity waves. J. Geophys. Res. 108 (No. D4), 4151. doi:10.1029/2002JD002474]. 相似文献
57.
This paper discusses the variability of surface currents around Sekisei Lagoon using a nested grid ocean circulation model.
We developed a triple-nested grid system that consists of a coarse-resolution (1/60° or ∼1.85 km) model off Taiwan, an intermediate-resolution
(1/300° or ∼370 m) model around the Yaeyama Islands, and a fine-resolution (1/900° or ∼123 m) model of Sekisei Lagoon. The
nested grid system was forced by wind and heat flux calculated from six-hourly atmospheric reanalysis data and integrated
over the period from May to July 2003. The coarse-resolution model was driven by lateral boundary conditions calculated from
daily ocean reanalysis data to include realistic variation of the Kuroshio and mesoscale eddies with spatial scales of ∼500–700 km
in the open ocean. The tidal forcing was included in the intermediate-resolution model by interpolating sea level data obtained
from a data-assimilative tidal model. The results were then used to drive the fine-resolution model to simulate the surface
water circulation around Sekisei lagoon. Model results show that (1) currents inside the lagoon are mainly driven by tide
and wind; (2) there exists a strong southwestward current along the bottom slope in the southeast portion of the lagoon; the
current is mainly driven by remote mesoscale eddies and at times intensified by the local wind; (3) the flow relaxation scheme
is effective in reducing biases along the open boundaries. The simulated currents were used to examine the retention and dispersion
of passive particles in the surface layer. Results show that the surface dispersion in the strong open ocean current region
is significantly higher than that inside the lagoon. 相似文献
58.
The 8th October 2005 Kashmir Earthquake of magnitude 7.6 triggered a huge landslide 3.5 km upstream of Hattian Bala town in
the state of Azad Jammu Kashmir of Pakistan. The debris mass blocked two tributaries of the Karli branch of the Jhelum River
and was breached on 9th February 2010. This debris dam provided us with a rare opportunity to keep careful and continuous
eyes on its post-earthquake behavior especially as it was a serious threat to people living along the lower reaches of both
the Karli and Jhelum Rivers. This paper describes post-formation behaviors of the debris mass, breaching-inflicted changes
of not only the debris mass but also both upstream and downstream reaches based upon laser-scanned images of landforms and
Differential Global Positioning System survey results. 相似文献
59.
The space–time prism demarcates all locations in space–time that a mobile object or person can occupy during an episode of
potential or unobserved movement. The prism is central to time geography as a measure of potential mobility and to mobile
object databases as a measure of location possibilities given sampling error. This paper develops an analytical approach to
assessing error propagation in space–time prisms and prism–prism intersections. We analyze the geometry of the prisms to derive
a core set of geometric problems involving the intersection of circles and ellipses. Analytical error propagation techniques
such as the Taylor linearization method based on the first-order partial derivatives are not available since explicit functions
describing the intersections and their derivatives are unwieldy. However, since we have implicit functions describing prism
geometry, we modify this approach using an implicit function theorem that provides the required first-order partials without
the explicit expressions. We describe the general method as well as details for the two spatial dimensions case and provide
example calculations. 相似文献
60.
By using the Euler-Lagrangian method, we examine water movements within the layer of minimum oxygen concentration and estimate local oxygen consumption rates for 15 regions of the global ocean. To do this, a number of labeled particles (which represent water parcels) are deployed at the center of a grid with 15 depth levels and tracked backward in time for 50 years in a three-dimensional velocity field. We assume that a particle picks up oxygen when it encounters the point of maximum oxygen concentration along the 50 years segment of its path. We introduce a contribution rate from waters distributed throughout the global ocean to the oxygen concentration of a local layer under consideration. Water parcels which are assumed to pick up oxygen within the oxygen minimum layer of an oceanic region under consideration make a very small contribution to the overall oxygen concentration of this layer. In addition, these parcels move out of the layer and water parcels from the upper layers take their place. The averaged Lagrangian local oxygen consumption rate is 0.033 ml/l/yr for the depth of the oxygen minimum layer, 0.20 ml/l/yr at 100 m depth (euphotic layer), 0.043 ml/l/yr for layers from 150 m to 800 m depth and 0.012 ml/l/yr for deep layers from 800 m to 3000 m. The present Lagrangian numerical experiment produces a maximum difference between observed and calculated concentrations of oxygen and, therefore, a maximum oxygen consumption rate. Although the present method has an ambiguity as to how oxygen is picked up, we nevertheless were able to identify regions in which the water parcels pick up oxygen of maximum concentration. We found that the South Equatorial Current (SEC) transports oxygen of higher concentration to the middle latitude regions of both the North Atlantic and the North Pacific across the equator. 相似文献