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741.
L. E. Sjöberg 《Journal of Geodesy》2000,74(2):255-268
The topographic potential and the direct topographic effect on the geoid are presented as surface integrals, and the direct
gravity effect is derived as a rigorous surface integral on the unit sphere. By Taylor-expanding the integrals at sea level
with respect to topographic elevation (H) the power series of the effects is derived to arbitrary orders. This study is primarily limited to terms of order H
2. The limitations of the various effects in the frequently used planar approximations are demonstrated. In contrast, it is
shown that the spherical approximation to power H
2 leads to a combined topographic effect on the geoid (direct plus indirect effect) proportional to H˜2 (where terms of degrees 0 and 1 are missing) of the order of several metres, while the combined topographic effect on the
height anomaly vanishes, implying that current frequent efforts to determine the direct effect to this order are not needed.
The last result is in total agreement with Bjerhammar's method in physical geodesy. It is shown that the most frequently applied
remove–restore technique of topographic masses in the application of Stokes' formula suffers from significant errors both
in the terrain correction C (representing the sum of the direct topographic effect on gravity anomaly and the effect of continuing the anomaly to sea
level) and in the term t (mainly representing the indirect effect on the geoidal or quasi-geoidal height).
Received: 18 August 1998 / Accepted: 4 October 1999 相似文献
742.
Deconvolution with wavelets and vaguelettes 总被引:2,自引:0,他引:2
The use of wavelets for the solution of convolution equations is studied as a possible alternative to the well-established
Fast Fourier Transform (FFT) technique. Two possible solution strategies are investigated: (1) The use of wavelets for the
representation of both the given data and the unknown solution. This leads to an algorithm with good de-noising and data-compression
properties. In terms of computational efficiency this algorithm is inferior to FFT. (2) The use of wavelets for the representation
of the unknown solution and of so-called vaguelettes for the representations of the given data. This leads to an algorithm
which is even faster than FFT.
Received: 14 October 1998 / Accepted: 30 November 1999 相似文献
743.
平面Radon变换的反演公式 总被引:2,自引:0,他引:2
王金平 《CT理论与应用研究》2000,9(1):8-11
本文借助球面平均法和Hilbert空间算子理论,给出了平面上Radon变换的反演公式,此公式是具体的、构造性的,便于数值计算,或者进一步探讨重建图象的性质。 相似文献
744.
Bridges with deck supported on either sliding or elastomeric bearings are very common in mid‐seismicity regions. Their main seismic vulnerabilities are related to the pounding of the deck against abutments or between the different deck elements. A simplified model of the longitudinal behavior of those bridges will allow to characterize the reaction forces developed during pounding using the Pacific Earthquake Engineering Research Center framework formula. In order to ensure the general applicability of the results obtained, a large number of system parameter combinations will be considered. The heart of the formula is the identification of suitable intermediate variables. First, the pseudo acceleration spectral value for the fundamental period of the system (Sa(Ts)) will be used as an intensity measure (IM). This IM will result in a very large non‐explained variability of the engineering demand parameter. A portion of this variability will be proved to be related to the relative content of high‐frequency energy in the input motion. Two vector‐valued IMs including a second parameter taking this energy content into account will then be considered. For both of them, a suitable form for the conditional intensity dependence of the response will be obtained. The question of which one to choose will also be analyzed. Finally, additional issues related to the IM will be studied: its applicability to pulse‐type records, the validity of scaling records and the sufficiency of the IM. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
745.
746.
主震和余震--从大森公式到ETAS模型 总被引:5,自引:0,他引:5
介绍了从描述余震发生频次的大森公式到ETAS模型的发展过程;给出了ETAS模型的主要理论,主要内容包括条件强度函数、参数估计和模型选择;讨论了ETAS模型在地震活动性研究中的应用情况,尤其是在前兆平静和前震研究中的应用,并对该模型的优缺点进行了评价。 相似文献
747.
Specialized to the Lie series based perturbation method of Kirchgraber and Stiefel (1978) a new computer algebra package called
ANALYTOS has been developed for constructing analytical orbital theories either in noncanonical or canonical form. We present
results on the (extended) Main Problem of orbital theory of artificial earth satellites and related issues. The order of the
solutions achieved is generally one order higher than those known from literature. Moreover, the analytical orbits have been
checked succesfully against precise numerical ephemerides.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
748.
沙丘地植物固沙灌溉单元及其计算公式 总被引:3,自引:1,他引:2
确定轮灌区面积是沙丘地灌溉设计中最重要的问题。在塔克拉玛干沙漠腹地,通过计算沙丘地入渗率、测定入渗过程与深层损失率以及进行不同流量、不同灌溉面积的反复试验,提出了灌溉单元的定义及计算公式。灌溉单元是一定地区、一定土壤或母质、一定灌溉方式条件下,某一水流量的最大合理灌溉面积。它是确定轮灌区面积的基本单位。对于沟畦灌而言,灌溉单元是指单沟或单畦的最大合理灌溉面积;对于滴灌而言,灌溉单元是指单个支管所能控制的最大合理灌溉面积。 相似文献
749.
世界城市网络研究方法论 总被引:12,自引:4,他引:8
20 世纪70 年代以来,随着全球贸易自由化的进程、多国公司逐渐确立了其经济全球化主要组织载体的地位以及国家决策权向城市的分散,国家作为独立的经济单元的重要性下降,国际竞争日渐被具体化为以城市为核心的区域间的竞争;城市作为经济单元的重要性迅速上升,成为全球治理体系中的重要行动者。作为全球经济的组织节点,世界城市按其在全球生产过程中的作用与地位的不同而构成具有一定经济控制能力和社会经济联系的网络体系。世界城市网络研究立足于世界/全球城市和世界城市体系中的城市间关系研究,经由基础设施、企业组织和社会文化等多个研究途径,以定量化的分析方式揭示了世界城市间的关系并探讨了世界城市网络形成的多重动力机制,是学术界对当代交通和通讯技术变革、企业组织变革及全球治理方式变革等对世界城市发展所施加影响的积极回应。最后,本文从城际关系秩序、空间组织逻辑、关系型数据的生产和获取、空间尺度和城市经济类型对城市网络的影响等5个方面探讨了世界城市网络研究对中国相关领域研究的借鉴和启示。 相似文献
750.