全文获取类型
收费全文 | 5821篇 |
免费 | 568篇 |
国内免费 | 164篇 |
专业分类
测绘学 | 248篇 |
大气科学 | 667篇 |
地球物理 | 2142篇 |
地质学 | 2332篇 |
海洋学 | 318篇 |
天文学 | 384篇 |
综合类 | 191篇 |
自然地理 | 271篇 |
出版年
2023年 | 5篇 |
2022年 | 18篇 |
2021年 | 29篇 |
2020年 | 24篇 |
2019年 | 23篇 |
2018年 | 463篇 |
2017年 | 405篇 |
2016年 | 294篇 |
2015年 | 185篇 |
2014年 | 150篇 |
2013年 | 146篇 |
2012年 | 677篇 |
2011年 | 455篇 |
2010年 | 143篇 |
2009年 | 170篇 |
2008年 | 156篇 |
2007年 | 127篇 |
2006年 | 148篇 |
2005年 | 850篇 |
2004年 | 884篇 |
2003年 | 665篇 |
2002年 | 184篇 |
2001年 | 79篇 |
2000年 | 54篇 |
1999年 | 23篇 |
1998年 | 17篇 |
1997年 | 29篇 |
1996年 | 20篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1965年 | 3篇 |
1955年 | 2篇 |
1954年 | 2篇 |
1951年 | 2篇 |
1948年 | 2篇 |
排序方式: 共有6553条查询结果,搜索用时 62 毫秒
991.
992.
Passive seismic techniques have revolutionarised seismology,leading for example to increased resolution in surface wave tomography,to the possibility to monitor changes in the propagation medium,and to many new processing strategies in seismic exploration.Here we review applications of the new techniques to a very particular dataset,namely data from the Apollo 17 lunar network.The special conditions of the lunar noise environment are investigated,illustrating the interplay between the properties of the noise and the ability to reconstruct Green's functions.With a dispersion analysis of reconstructed Rayleigh waves new information about the shallow shear velocity structure of the Moon are obtained.Passive image interferometry is used to study the effect of temperature changes in the subsurface on the seismic velocities providing direct observation of a dynamic process in the lunar environment.These applications highlight the potential of passive techniques for terrestrial and planetary seismology. 相似文献
993.
Bertrand?GuillierEmail author Jean-Luc?Chatelain Hugo?Perfettini El?Hadi?Oubaiche Christophe?Voisin Rabah?Bensalem Djamel?Machane Mustapha?Hellel 《Bulletin of Earthquake Engineering》2016,14(8):2213-2227
Building frequencies (fundamental and higher modes) are a critical parameter especially in the field of structural health monitoring mainly based on the stability of the structural dynamic parameters of individual building (frequencies, damping and modes shape). One of the most used methods to find out these parameters is based on the use on ambient vibration analysis. In this work, we study the fluctuations over a month period of the fundamental frequencies (transverse and longitudinal) of a 3.5-story RC-building made of 2 identical units connected by a structural joint. Time independent building frequencies is a strong assumption; as illustrated by our experiment showing that over an observation period of a month, building frequencies fluctuate of about 3.5 %. A clear correlation is found between the building frequency fluctuations and temperature variations, with a phase-shift interpreted as the characteristic time of heat diffusion within the walls. This allows: (1) determining the thermal diffusivity of the structure, (2) inferring its relative stiffness variations, and (3) showing that its Young modulus varies linearly with temperature. 相似文献
994.
Underground mining of coal seams in the Upper Silesian Coal Basin in Poland is accompanied by seismic activity of varying magnitude. The investigations which have been performed for several years distinguished high energy mine tremors connected directly with mining or coupled with geological structures, such as large faults. In mined seams, local fault zones occur. Faults in these zones are usually small, with throws comparable with coal seams thicknesses. Local fault zone may be responsible for the occurrence of high energy tremors as well as large faults, as presented in this article. An analysis of source mechanism of high energy tremors generated during longwall mining of the coal seam No. 510, with presence of a local fault zone, in one of the Polish hard coal mines in the Upper Silesian Coal Basin was performed. For this purpose, the seismic moment tensor inversion method was used. In most of foci, the process of shear predominated. Determined nodal plane parameters were correlated with parameters of faults forming the local fault zone. High energy tremors were generated mostly by dislocations on faults of the local fault zone. Weakening of roof rocks in the neighborhood of local fault zone takes an important role too, and was responsible for share of implosion in the focal mechanism. 相似文献
995.
Leszek Błaszkiewicz Wojciech Lewandowski Andrzej Krankowski Jarosław Kijak Olga Koralewska Bartosz P. Dąbrowski 《Acta Geophysica》2016,64(1):293-315
LOFAR (LOw Frequency ARray) is a new generation digitally controlled radio telescope consisting of phased array antenna stations with sensitivity, bandwidth, range of frequency, and digital processing power that makes it an excellent tool for observations of pulsars. This interferometric instrument is able to work in a single-station mode as well as in group-of-selected-stations mode. This article discusses the great opportunity for conducting unique and independent research of pulsar sources with the three LOFAR stations located in Poland and maintained by the POLFAR consortium. 相似文献
996.
Mai Thanh Tan Mai Thanh Ha Kurt J. Marfurt Nguyen Trung Hieu Nguyen Thi My Hanh 《Acta Geophysica》2016,64(6):2214-2231
The fractured granite basement is the primary oil and gas reservoir in the Cuu Long Basin, Vietnam. Due to the complexity of this nonlayered unconventional target, combined with complicated fault and fracture systems, the seismic data quality near and within the basement section is very low. For this reason, it is important to apply improved seismic data processing workflows, filtering and migration techniques, as wells as attribute processing methods to enhance the imaging quality.Our studies show that applying different types of filters, including the f-k, Radon transform and Tau-P, improves signal to noise ratio, removing multiples, revealing basement’s top and its related fractured and fault zones. In addition, the application of multi-arrival-solution migration algorithms, such as Kirchhoff Migration and Controlled Beam Migration, provides improved imaging for identifying basement top and faults and fractures within the basement. Furthermore, the application of seismic attributes such as curvature, apparent dip, or energy gradient, is important in locating faults and fractures, whereas mapping of intensity and orientation of such structures assists the delineation of “sweet spots” and assists the planning of exploration. 相似文献
997.
Mirosław Jastrzębski 《International Journal of Earth Sciences》2009,98(8):1901-1923
Structural, petrological and geochronological data from marbles and mica schists combined with those from highly disputable
gneisses and eclogites of the Orlica-Śnieżnik Dome (OSD), gave new insights into Variscan evolution of eastern borderland
of the West Sudetes. It is shown that the Variscan tectonometamorphic evolution of the OSD began with E–W oriented subhorizontal
shortening (D1 stage) related to the collision of the West Sudetes terranes and the Brunovistulian terrane. The shortening
led to generally upright folding, which resulted in formation of the steep N–S trending metamorphic planar fabric S1, thickening
of the lithosphere and burial of the Stronie Formation under greenschist facies conditions. As a consequence of subsequent,
near-coaxial gravity-controlled vertical shortening (D2), the S1 foliation was deformed in tight recumbent folds F2. The flattening
strain was associated with the progression to amphibolite-facies conditions (from ca. 510 upto ca. 620°C) and uplift from
depths corresponding to 9–10 kbar to depths corresponding to 7–8 kbar. On microscale, the flattening strain is documented
by rotation of the mineral fabric overgrown by syn-D2 prograde garnet porphyroblasts. The Sm–Nd Grt–WR isochron age, correlated with the D2 event yields 346.5 ± 4.4 Ma. Further
deformation and progressive metamorphism led to development of the subhorizontally disposed S2 axial plane schistosity, which
terminated at the metamorphic temperature peak. During retrogression but still under ductile conditions of deformation, the
S2 planes were reactivated during successive top-to-the-N shear movement of the OSD (D3 stage). Due to the mutual interaction
of the OSD with the adjacent terranes the shear deformations were localized within marginal parts of these units. Finally,
as a result of the NE–SW and the NW–SE oriented shortenings (D4 stage and D5 stage, respectively), both the structural surfaces
and metamorphic isograds were regionally folded with W(NW)-ward plunges. A synthesis of new and existing data shows an overall
similarity in sequence of Variscan deformations (D1–D2–D3) in the West Sudetes borderland to that observed in the eastern
flank of the Moldanubian domain. 相似文献
998.
Soil erosion and its response to the changes of precipitation and vegetation cover on the Loess Plateau 总被引:8,自引:2,他引:6
Soil erosion is a major threat to our terrestrial ecosystems and an important global environmental problem. The Loess Plateau in China is one of the regions that suffered more severe soil erosion and undergoing climate warming and drying in the past decades. The vegetation restoration named Grain-to-Green Program has now been operating for more than 10 years. It is necessary to assess the variation of soil erosion and the response of precipita- tion and vegetation restoration to soil erosion on the Loess Plateau. In the study, the Revised Universal Soil Loss Equation (RUSLE) was applied to evaluate annual soil loss caused by water erosion. The results showed as follows. The soil erosion on the Loess Plateau between 2000 and 2010 averaged for 15.2 t hm-2 a 1 and was characterized as light for the value less than 25 t hm-2 a-1. The severe soil erosion higher than 25 t hm-2 a-~ was mainly distributed in the gully and hilly regions in the central, southwestern, and some scattered areas of earth-rocky mountainous areas on the Loess Plateau. The soil erosion on the Loess Plateau showed a deceasing trend in recent decade and reduced more at rates more than 1 t hm 2 a 1 in the areas suffering severe soil loss. Benefited from the improved vegetation cover and ecological construction, the soil erosion on the Loess Plateau was significantly declined, es- pecially in the east of Yulin, most parts of Yah'an prefectures in Shaanxi Province, and the west of Luliang and Linfen prefectures in Shanxi Province in the hilly and gully regions. The variation of vegetation cover responding to soil erosion in these areas showed the relatively higher contribution than the precipitation. However, most areas in Qingyang and Dingxi pre- fectures in Gansu Province and Guyuan in Ningxia Hui Autonomous Region were predomi- nantly related to precipitation. 相似文献
999.
Eunjin Park Wansoo Ha Wookeen Chung Changsoo Shin Dong-Joo Min 《Pure and Applied Geophysics》2013,170(12):2075-2085
The wavefield in the Laplace domain has a very small amplitude except only near the source point. In order to deal with this characteristic, the logarithmic objective function has been used in many Laplace domain inversion studies. The Laplace-domain waveform inversion using the logarithmic objective function has fewer local minima than the time- or frequency domain inversion. Recently, the power objective function was suggested as an alternative to the logarithmic objective function in the Laplace domain. Since amplitudes of wavefields are very small generally, a power <1 amplifies the wavefields especially at large offset. Therefore, the power objective function can enhance the Laplace-domain inversion results. In previous studies about synthetic datasets, it is confirmed that the inversion using a power objective function shows a similar result when compared with the inversion using a logarithmic objective function. In this paper, we apply an inversion algorithm using a power objective function to field datasets. We perform the waveform inversion using the power objective function and compare the result obtained by the logarithmic objective function. The Gulf of Mexico dataset is used for the comparison. When we use a power objective function in the inversion algorithm, it is important to choose the appropriate exponent. By testing the various exponents, we can select the range of the exponent from 5 × 10?3 to 5 × 10?8 in the Gulf of Mexico dataset. The results obtained from the power objective function with appropriate exponent are very similar to the results of the logarithmic objective function. Even though we do not get better results than the conventional method, we can confirm the possibility of applying the power objective function for field data. In addition, the power objective function shows good results in spite of little difference in the amplitude of the wavefield. Based on these results, we can expect that the power objective function will produce good results from the data with a small amplitude difference. Also, it can partially be utilized at the sections where the amplitude difference is very small. 相似文献
1000.
砂土液化大变形本构模型的三维化及其数值实现 总被引:2,自引:0,他引:2
基于砂土液化大变形机理和适用于二维条件的边界面弹塑性本构模型,发展了符合三维应力空间中边界面和剪胀面上的应力映射规则,建立了三维应力空间中砂土液化大变形本构模型.针对模型特点采用半显式的Cutting Plane算法进行应力积分,并采用Pegasus求根算法根据映射规则计算边界面上的应力映射点,在OpenSees开源有限元平台上实现了三维模型的数值化.结合完全耦合的u-p格式有限元单元,对饱和砂土不排水循环扭剪试验进行了模拟,并进行了一个真三维倾斜地基的动力反应分析.计算结果表明模型和所采用的数值算法具有很好的模拟和分析三维条件下砂土液化后大变形的能力. 相似文献