全文获取类型
收费全文 | 2112篇 |
免费 | 251篇 |
国内免费 | 290篇 |
专业分类
测绘学 | 581篇 |
大气科学 | 199篇 |
地球物理 | 585篇 |
地质学 | 593篇 |
海洋学 | 284篇 |
天文学 | 92篇 |
综合类 | 128篇 |
自然地理 | 191篇 |
出版年
2024年 | 9篇 |
2023年 | 21篇 |
2022年 | 48篇 |
2021年 | 71篇 |
2020年 | 64篇 |
2019年 | 95篇 |
2018年 | 70篇 |
2017年 | 86篇 |
2016年 | 98篇 |
2015年 | 108篇 |
2014年 | 122篇 |
2013年 | 142篇 |
2012年 | 119篇 |
2011年 | 89篇 |
2010年 | 83篇 |
2009年 | 111篇 |
2008年 | 122篇 |
2007年 | 156篇 |
2006年 | 117篇 |
2005年 | 96篇 |
2004年 | 107篇 |
2003年 | 96篇 |
2002年 | 65篇 |
2001年 | 59篇 |
2000年 | 71篇 |
1999年 | 61篇 |
1998年 | 54篇 |
1997年 | 53篇 |
1996年 | 45篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 33篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有2653条查询结果,搜索用时 15 毫秒
31.
The evaluation of seismic site response in the urban area of Catania was tackled by selecting test areas having peculiar lithological
and structural features, potentially favourable to large local amplifications of ground motion. The two selected areas are
located in the historical downtown and in the northern part of Catania where the presence of a fault is evident. Site response
was evaluated using spectral ratio technique taking the horizontal- to-vertical component ratio of ambient noise. Inferences
from microtremor measurements are compared with results from synthetic accelerograms and response spectra computed at all
drillings available for this area. Such method is particularly suitable in urban areas where the nature of the outcropping
geological units is masked by city growth and anthropic intervention on the surface geology. The microtremor H/V spectral
ratios evaluated at soft sites located within the downtown profile tend to be smaller than that usually reported in the literature
for such soils. A tendency for amplifications to peaks near 2 Hz is observed only in some sites located on recent alluvial
deposits. Evidences for amplifications of site effects (frequency range 4–8 Hz) were observed in the sampling sites located
on the fault, with a rapid decrease of spectral amplitude just a few tenths of metres away from the discontinuity. Numerical
simulations evidenced the importance of geolithological features at depth levels even greater than 20–30 m. Besides this,
the results strongly confirm the importance of the subsurface geological conditions, in the estimate of seismic hazard at
urban scale. 相似文献
32.
Assessing the Vibrational Frequencies of the Cathedral of Cologne (Germany) by Means of Ambient Seismic Noise Analysis 总被引:1,自引:0,他引:1
Andreas Fäcke Stefano Parolai Sandra M. Richwalski Lothar Stempniewski 《Natural Hazards》2006,38(1-2):229-236
Ambient seismic noise measurements were conducted inside the Cathedral of Cologne (Germany) for assessing its frequencies
of vibration and for checking whether these occur in the range where soil amplification is expected. If this is the case,
damages may increase in case of an earthquake due to an increased structural response of the building. Analysis of the ratio
between the horizontal and vertical components of the spectra recorded at stations located inside the building as well as
the ratio between the corresponding components of the spectra recorded simultaneously inside the building and at a reference
station placed in the basement of the cathedral indicated several modes of vibration. Facilitated by these results an assessment
of the seismic vulnerability was attempted for a 2D ground motion scenario using the finite element method. 相似文献
33.
The area of Serravalle, sited in the northern part of the town of Vittorio Veneto (TV), NE Italy, has been the target of a
seismic microzonation campaign. 10 seismic stations have been deployed for a 7 months period to record in continuous mode.
Three stations were installed on bedrock outcrops and seven on sedimentary sites with variable cover thickness. Spectral analyses
have been performed on the collected data-set using the Generalized Inversion Technique (GIT, e.g. Andrews, 1986). In particular,
spectral ratios have been calculated for each station relatively to the average of the three reference, bedrock sites. The
spectral ratios provide quantitative estimates of the seismic motion amplifications which occur in each of the monitored sites.
Two sites show high values of amplification, 5 times larger than signal amplitude at the reference sites, in correspondence
of well discernible peak frequencies of 5 Hz. Results for the other stations show smaller amounts of site amplification spreading
over a broad range of frequencies. Sites where the highest amplifications were recorded all lie on the left bank of the Meschio
River and in areas farther away from its outlet into the plain correlating with the presence of thick layers of Quaternary
deposits. 相似文献
34.
Spherical Slepian functions and the polar gap in geodesy 总被引:4,自引:0,他引:4
The estimation of potential fields such as the gravitational or magnetic potential at the surface of a spherical planet from noisy observations taken at an altitude over an incomplete portion of the globe is a classic example of an ill-posed inverse problem. We show that this potential-field estimation problem has deep-seated connections to Slepian's spatiospectral localization problem which seeks bandlimited spherical functions whose energy is optimally concentrated in some closed portion of the unit sphere. This allows us to formulate an alternative solution to the traditional damped least-squares spherical harmonic approach in geodesy, whereby the source field is now expanded in a truncated Slepian function basis set. We discuss the relative performance of both methods with regard to standard statistical measures such as bias, variance and mean squared error, and pay special attention to the algorithmic efficiency of computing the Slepian functions on the region complementary to the axisymmetric polar gap characteristic of satellite surveys. The ease, speed, and accuracy of our method make the use of spherical Slepian functions in earth and planetary geodesy practical. 相似文献
35.
Tingting Yao Craig Calvert Tom Jones Glen Bishop Yuan Ma Lincoln Foreman 《Mathematical Geology》2006,38(1):51-62
Spectral simulation has gained application in building geologic models due to the advantage of better honoring the spatial continuity of petrophysical properties, such as reservoir porosity and shale volume. Distinct from sequential simulation methods, spectral simulation is a global algorithm in the sense that a global density spectrum is calculated once and the inverse Fourier transform is performed on the Fourier coefficient also only once to generate a simulation realization. The generated realizations honor the spatial continuity structure globally over the whole field instead of only within a search neighborhood, as with sequential simulation algorithms. However, the disadvantage of global spectral simulation is that it traditionally cannot account for the local information such as the local continuity trends, which are often observed in reservoirs and hence are important to be accounted for in geologic models. This disadvantage has limited wider application of spectral simulation in building geologic models. In this paper, we present ways of conditioning geologic models to the relevant local information. To account for the local continuity trends, we first scale different frequency components of the original model with local-amplitude spectrum ratios that are specific to the local trend. The sum of these scaled frequency components renders a new model that displays the desired local continuity trend. The implementation details of this new method are discussed and examples are provided to illustrate the algorithm. 相似文献
36.
SUN Xiao-jie LI Chao-lin WANG Li-bin REN Ri-chun LI Hai-yan ZHUANG Yi-ming LIU Ying-xin SUN Ke .Daqing Petroleum Institute Daqing Heilongjiang China .Coalfield Geological Geophysical Exploration Company of Jilin Province Changchun China .Coal Field Geology Bureun of Jilin Province Changchun China 《吉林大学学报(地球科学版)》2006,(Z2)
已知勘查区深度范围前提下,最大炮检X和道间距ΔX,不可以太大也不可以太小,施工前能够计算出它的允许值范围。 相似文献
37.
38.
Masao Komazawa Hitoshi Morikawa Kajuro Nakamura Junpei Akamatsu Keiichi Nishimura Sumio Sawada Ayfer Erken Akin Onalp 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):829-836
The 1999 Kocaeli earthquake brought serious damage to downtown of Adapazari. To study why strong motions were generated at the town, a bedrock structure was investigated on the basis of Bouguer gravity anomaly, and SPAC and H/V analyses of microseisms. It was revealed that, the basin consists of three narrow depressions of bedrock with very steep edges, extending in E–W or NE–SW directions along the North Anatolia faults, and the depth to bedrock reaches 1000 m or more. Downtown of Adapazari is located 1–2 km apart from the basin-edge. It is considered that, the specific configuration of bedrock amplifies ground motions at the downtown area by focusing of seismic waves and/or interference between incident S-waves and surface-waves secondarily generated at the basin-edge. Studying 3D bedrock structure is an urgent issue for microzoning an urban area in a sedimentary basin. 相似文献
39.
40.
In continent Lg is usually one of the predominant phases recorded by short-period or broad-band seismometers. A ray-theoretical approach shows that Lg wave is the superposition of higher-mode surface waves propagating in the continental crust[1—4]. The g… 相似文献