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931.
S. G. Gaonkar B. V. Srirama S. R. Samaddar D. V. Punekar Sagina Ram Reena De J. R. Kayal 《Journal of Earth System Science》2003,112(3):401-412
The Geological Survey of India (GSI) established a twelve-station temporary microearthquake (MEQ) network to monitor the aftershocks
in the epicenter area of the Bhuj earthquake (M
w7.5) of 26th January 2001. The main shock occurred in the Kutch rift basin with the epicenter to the north of Bhachao village,
at an estimated depth of 25 km (IMD). About 3000 aftershocks (M
d ≥ 1.0), were recorded by the GSI network over a monitoring period of about two and half months from 29th January 2001 to
15th April 2001. About 800 aftershocks (M
d ≥ 2.0) are located in this study. The epicenters are clustered in an area 60 km × 30 km, between 23.3‡N and 23.6‡N and 70‡E
and 70.6‡E. The main shock epicenter is also located within this zone.
Two major aftershock trends are observed; one in the NE direction and other in the NW direction. Out of these two trends,
the NE trend was more pronounced with depth. The major NE-SW trend is parallel to the Anjar-Rapar lineament. The other trend
along NW-SE is parallel to the Bhachao lineament. The aftershocks at a shallower depth (<10km) are aligned only along the
NW-SE direction. The depth slice at 10 km to 20 km shows both the NE-SW trend and the NW-SE trend. At greater depth (20 km–38
km) the NE-SW trend becomes more predominant. This observation suggests that the major rupture of the main shock took place
at a depth level more than 20 km; it propagated along the NE-SW direction, and a conjugate rupture followed the NW-SE direction.
A N-S depth section of the aftershocks shows that some aftershocks are clustered at shallower depth ≤ 10 km, but intense activity
is observed at 15–38 km depth. There is almost an aseismic layer at 10–15 km depth. The activity is sparse below 38 km. The
estimated depth of the main shock at 25 km is consistent with the cluster of maximum number of the aftershocks at 20–38 km.
A NW-SE depth section of the aftershocks, perpendicular to the major NE-SW trend, indicates a SE dipping plane and a NE-SW
depth section across the NW-SE trend shows a SW dipping plane.
The epicentral map of the stronger aftershocksM ≥ 4.0 shows a prominent NE trend. Stronger aftershocks have followed the major rupture trend of the main shock. The depth
section of these stronger aftershocks reveals that it occurred in the depth range of 20 to 38 km, and corroborates with a
south dipping seismogenic plane. 相似文献
932.
A GIS-Based Multivariate Statistical Analysis for Shallow Landslide Susceptibility Mapping in La Pobla de Lillet Area (Eastern Pyrenees,Spain) 总被引:22,自引:0,他引:22
Santacana Núria Baeza Baeza Corominas Jordi De Paz Ana Marturiá Jordi 《Natural Hazards》2003,30(3):281-295
This paper presents a GIS-aided procedure for shallow landslide susceptibility mapping at a regional scale. Most of the input data for the susceptibility assessment have been captured automatically. A total of 13 parameters, related to the slope geometry, have been derived from the digital elevation model (DEM) while vegetation cover and thickness of superficial formations have been obtained from photointerpretation and field work. The susceptibility assessment is based on multivariate statistical techniques (discriminant analysis), which hasbeen tested in a pilot area in La Pobla de Lillet (Eastern Pyreenes, Spain). Theresults obtained using a random sample show that 82% of all the cells, and 90% of cells including slope failures, have been properly classified. A susceptibility map based on the discriminant function has given consistent results. The susceptibilityassessment is very sensitive to the parameters selected. Compared to thetraditional methods, the main advantage of the GIS-aided procedure is the rapidityprovided by the automatic capture of parameters. It also has the capability of coveringlarge areas, and the objectivity and reproducibility of the results. The main drawbackis that, at present, not all regions have DEM accurate enough to cope with small landslides. 相似文献
933.
Gold mineralization related to a sulphide-bearing quartz vein within Triassic phyllites has been identified in a former study of an abandoned Cu–Zn–Pb mine in southern Tuscany–northern Latium. The vein-hosted mineral assemblage includes pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, and tetrahedrite; the gold content reaches up to 20 ppm. The mineralization was related to fluids characterised by moderate temperatures and moderate salinities (5–15% NaCl equivalent) and represents the highest grade of Au in the ore deposits of southern Tuscany. The difference in the estimated values of Te of primary, L+V, pseudo-secondary L+V, secondary L+V fluids inclusions reflects different components present in the solutions.Based on these results one can conclude that euhedral quartz and pyrite deposition was related to fluids having variable salinity and chemical components.The origin of gold in Ponte San Pietro (PSP) deposit may be related to leaching of metapelites/phyllites derived from pelitic rocks containing some amount of sulphur-bearing organic matter; it is worthy noting that quartz–marcasite bearing lenses, interstratified in Triassic phyllites, contain significant amount of visible gold. The Co, Ni, Mn, as well as the δ34S data, suggest a different origin for the phyllite-hosted marcasite, the PSP quartz-vein hosted pyrite, and for gold occurrences. 相似文献
934.
935.
对埋深≤30m的土(溶)洞做了理论模型,并对其进行研究(高斯射线束法),再依据三维地震勘探方法,根据我院在工作中的实测成果,指出了土(溶)洞异常的解释理论要点和解释依据,说明了土(溶)洞在实际工作中的复杂多变性。 相似文献
936.
937.
938.
939.
基于GIS的地下水模拟可视化系统开发的初步探讨 总被引:7,自引:2,他引:7
系统开发的目的是克服GIS时空分析能力的不足,实现地下水模型与MAPGIS的耦合集成,在集成的基础上构建系统的可视化功能,在GIS平台上为地下水模拟的全过程提供一个统一高效的计算机环境。系统开发采用面向对象的软件开发方法,对各种地下水模型进行分解、抽象,建立基本的C++类类型,每个模型都是基本类及其派生类对象的聚集类。系统实现的技术途径是以MAPGIS的二次开发函数作为“后台”支持,以VC++作为编程工具,在充分利用MAPGIS的可视化功能的基础上,借助于OpenGL并应用科学可视化技术开发更能满足地下水模拟需要的可视化功能。 相似文献
940.
常规的反射数据处理都假定介质为均匀且各向同位。研究表明,各向异性的存在会严重影响处理和解释的结果。在已有知识的基础上,研究了二维均匀横向各向同性介质中的射线传播规律并描述了速度各向异性波场的特征。对于准P波,各向异性参数ε,δ的绝对值决定波前面的形状,而ε与δ之差决定射线密度;对于准SV波,σ则是主要的控制因素。 相似文献