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921.
The paper focusses on seismic damage analysis of reinforced concrete (R/C) members, accounting for shear–flexure interaction
in the inelastic range. A finite element of the beam-column type recently proposed by the writers for the seismic analysis
of R/C structures is first briefly described. The analytical model consists of two distributed flexibility sub-elements which
interact throughout the analysis to simulate inelastic flexural and shear response. The finite element accounts for shear
strength degradation with inelastic curvature demand, as well as coupling between inelastic flexural and shear deformations
after flexural yielding. Based on this model, a seismic damage index is proposed taking into account both inelastic flexural
and shear deformations, as well as their interaction. The finite element and the seismic damage index are used to analyse
the response of R/C columns tested under cyclic loading and failing either in shear or in flexure. It is shown that the analytical
model and damage index can predict and describe well the hysteretic response of R/C columns with different types of failure. 相似文献
922.
The effectiveness of simulating surge inundation using the Eulerian–Lagrangian circulation (ELCIRC) model over multi-scale
unstructured grids was examined in this study. The large domain model grid encompasses the western North Atlantic Ocean, the
Gulf of Mexico, and the Caribbean Sea to appropriately account for remote and resonance effects during hurricane events and
simplify the specification of the open boundary condition. The U.S. East and Gulf Coasts were divided into 12 overlapping
basins with fine-resolution (up to 30 × 30 m) grids to model overland surge flooding. These overlapping basins have different
fine-resolution grids near the coastal region, but have an identical coarse-resolution grid in the offshore region within
the large model domain. Thus, the storm surge prediction can be conducted without reducing computation efficiency by executing
multiple model runs with local fine-resolution grids where potential hurricane landfalls may occur. The capability of the
multi-scale approach was examined by simulating storm surge caused by Hurricanes Andrew (1992) and Isabel (2003) along the
South Florida coast and in the Chesapeake Bay. Comparisons between simulated and observed results suggest that multi-scale
models proficiently simulated storm surges in the Biscayne Bay and the Chesapeake Bay during two hurricanes. A series of sensitivity
tests demonstrated that the simulation of surge flooding was improved when LiDAR topographic data and special bottom drag
coefficient values for mangrove forests were employed. The tests also showed that appropriate representation of linear hydrologic
features is important for computing surge inundation in an urban area. 相似文献
923.
Kamila Wawrzyniak 《Acta Geophysica》2010,58(1):49-82
The paper deals with the application of time-frequency methods, Continuous Wavelet Transform (CWT) and Matching Pursuit algorithm
(MP), to acoustic full waveform processing. The goal of the research is to present possible ways of application of these methods,
particularly for the precise identification of selected acoustic waves, waveform decomposition into separate waves, and determination
of zones of different elastic parameters in the geological profiles.
The simulations, developed methodology, and results of each method are discussed in detail. The Continuous Wavelet Transform
is used to improve qualitative interpretation. Time-depth-frequency plots for a given frequency are constructed to distinguish
the waves and identify gas-bearing zones. The Matching Pursuit has a better resolution in time-frequency space than CWT; thus,
it is used to extract individual waves from the whole acoustic waveform, i.e., decompose the signal. For the extracted waves,
the slowness is calculated. Results from MP methods are compared with their counterpart parameters obtained from the original
waveforms. Additionally, time-frequency decompositions are used for the determination of the frequency content of each wave
packet to get unique information about formation in situ. 相似文献
924.
925.
利用地基GPS观测资料反演的垂直电子总含量(VTEC),本文考察了2008年5月12日汶川M_s8.0地震期间的电离层变化.在考察过程中,以前10天的VTEC均值和伴随的2倍标准偏差作为参考来识别电离层异常.最终的考察分析结果表明:(1)VTEC的异常增加出现在5月3日和5月9日,而VTEC的异常减小出现在4月29日和5月6日;(2)所有这4天的电离层VTEC异常持续时间均超过了4 h,且异常自东向西漂移;(3)相对于电离层的非扰动状态,在5次电离层异常的峰值时刻,震中附近VTEC增加或减小超过30%的空间区域沿经、纬向分别超过了4000 km和1500 km.鉴于地震期间的日-地空间环境和电离层VTEC异常特征,我们认为,5月3日下午和5月9日的VTEC正异常可能是本次汶川地震的电离层前兆. 相似文献
926.
Carlos Sainz Ismael Fuente Luis Quindós Jose Luis Gutierrez Jose Luis Arteche Luis Santiago Quindós 《Acta Geophysica》2010,58(5):957-962
People working with ionising radiation are receiving radiation coming from artificial and natural sources. In Spain, as in
many other countries, there is a serious control by the national authorities, Spanish Nuclear Safety Council, of the dose
the workers receive from artificial sources. However, until the publication of the European Basic Safety Standards Directive,
96/29/EURATOM, the old criteria referring to the “above natural background” were widely used. This directive was incorporated
to the Spanish legislation in July 2001 (BOE 178); in its Title VII it recommends to evaluate the dose coming from natural
sources and take it into account for establishing the safety criteria. It is noteworthy to assess the natural doses received
at homes and the dose received by workers of radioactive installations subject to regulations, and to compare the two results.
The social and economical implications of the results derived can be important in the practical application of the recommendations
included in the above-mentioned BOE 178 Directive. 相似文献
927.
2004年8月3日近地TC-1卫星在磁尾XGSM~-12RE的等离子体片内,观测到了伴随着高速流的低于离子回旋频率的波,即超低频波(ULF,Ultra Low Frequency).该波垂直分量的振幅在高速流及其振荡减速期间大致相当;而平行分量振幅在高速流时明显大于其振荡减速时. 利用一个扰动双流模型对完全磁化离子横场漂移驱动的电磁不稳定性计算后,预测结果表明:(1)对于垂直分量来说,横场漂移速度与Alfvén速度的比值影响不稳定性增长率和激发波频率,随其比值增加,增长率变大,激发波频率从负值增加到正值.(2)对于平行分量来说,温度各向异性时等离子体热速度与Alfvén速度比值只影响不稳定性增长率和激发波频率,未改变不稳定性模类别;而温度各向同性时离子横场漂移速度与Alfvén速度比值既影响不稳定性模的种类及其分支,又影响激发波频率.进一步将卫星观测到的等离子体密度、温度、整体流速和磁场代入模型方程,进行数值计算与上述预测结果对比后发现:卫星观测中垂直分量的功率谱密度(PSD,Power Spectrum Density)增强时间和频段与理论模型中由β//、β⊥和v⊥/VA引起不稳定性激发的波一致;卫星观测中平行分量的功率谱密度增强时间与理论模型基本相符,但是前者的频率明显地低于后者.因此,除了需考虑平行磁场的离子整体流速对不稳定性激发波频率的可能影响,还需要统计上进一步核实伴随有高速流的ULF波与不稳定性的相关性. 相似文献
928.
Giuseppe D. Chirico Massimiliano Favalli Paolo Papale Enzo Boschi Maria Teresa Pareschi Arthur Mamou-Mani 《Bulletin of Volcanology》2009,71(4):375-387
Mt. Nyiragongo is one of the most dangerous volcanoes in the world for the risk associated with the propagation of lava flows.
In 2002 several vents opened along a huge system of fractures, pouring out lava which reached and destroyed a considerable
part of Goma, a town of about 500,000 inhabitants on the shore of Lake Kivu. In a companion paper (Favalli et al. in Bull
Volcanol, this issue, 2008) we employed numerical simulations of probable lava flow paths to evaluate the lava flow hazard on the flanks of the volcano,
including the neighbouring towns of Goma (DRC) and Gisenyi (Rwanda). In this paper we use numerical simulations to investigate
the possibility of significantly reducing the lava flow hazard in the city through the construction of protective barriers.
These barriers are added to the DEM of the area as additional morphological elements, and their effect is evaluated by repeating
numerical simulations with and without the presence of barriers. A parametric study on barrier location, size, shape and orientation
led to the identification of barriers which maximize protection while minimizing their impact. This study shows that the highest
hazard area corresponding to eastern Goma, which was largely destroyed by lava flows in 2002, cannot be effectively protected
from future lava flows towards Lake Kivu and should be abandoned. On the contrary, the rest of the town can be sheltered from
lava flows by means of two barriers that deviate or contain the lava within the East Goma sector. A proposal for the future
development of the town is formulated, whereby “new” Goma is completely safe from the arrival of lava flows originating from
vents outside its boundaries. The proposal minimizes the risk of further destruction in town due to future lava flows. 相似文献
929.
Seismic refraction survey and DC resistivity measurements were made across the margin of the Lake Ngami. The structure and
stratigraphy at the lake were determined. High resolution aeromagnetic data showed a prominent anomaly coinciding with the
Kunyere Fault. Estimated depths to magnetic sources are increasing towards the lake. Two velocity layers were mapped. The
top layer (500 m/s) is thin outside the lake and thicker inside the lake. The underlying layer (3125 m/s) has undeterminable
thickness. Resistivity sounding results inside the lake showed that the low velocity layer has four sub-units: dry hard clays;
diatomaceous earth; soft clays interlayered with silts; and wet whitish clays interlayered with silts. Normal faults were
mapped along the profile with a total displacement up to 50 m. The results of the study indicate that the formation of the
Lake Ngami basin was structurally controlled and probably initiated by the tectonics of the Okavango Rift Zone. 相似文献
930.
We present a new development in the asymmetric continuum theory with the shear oscillations (twist motions) and independent
spin; these motions (displacement velocities and spin) can be shifted in phase to describe the independent rebound processes.
Our approach provides an extension of the asymmetric continuum theory by including the microfragmentation processes with a
double transport which may appear in an advanced fracture process under very high load. The related nonlinear equations, leading
to soliton solutions, are derived. 相似文献