全文获取类型
收费全文 | 1654篇 |
免费 | 601篇 |
国内免费 | 1206篇 |
专业分类
测绘学 | 69篇 |
大气科学 | 179篇 |
地球物理 | 759篇 |
地质学 | 1890篇 |
海洋学 | 309篇 |
天文学 | 92篇 |
综合类 | 92篇 |
自然地理 | 71篇 |
出版年
2013年 | 8篇 |
2012年 | 3篇 |
2011年 | 184篇 |
2010年 | 99篇 |
2009年 | 165篇 |
2008年 | 43篇 |
2007年 | 117篇 |
2006年 | 223篇 |
2005年 | 264篇 |
2004年 | 507篇 |
2003年 | 295篇 |
2002年 | 236篇 |
2001年 | 177篇 |
2000年 | 115篇 |
1999年 | 112篇 |
1998年 | 128篇 |
1997年 | 133篇 |
1996年 | 94篇 |
1995年 | 82篇 |
1994年 | 71篇 |
1993年 | 120篇 |
1992年 | 79篇 |
1991年 | 47篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1966年 | 6篇 |
1965年 | 16篇 |
1960年 | 2篇 |
1959年 | 2篇 |
1955年 | 4篇 |
1954年 | 3篇 |
1952年 | 2篇 |
1949年 | 5篇 |
1948年 | 2篇 |
1937年 | 2篇 |
1933年 | 7篇 |
1924年 | 2篇 |
1923年 | 2篇 |
排序方式: 共有3461条查询结果,搜索用时 15 毫秒
971.
972.
层状介质弹性参数反演问题研究综述 总被引:9,自引:3,他引:6
地震波动方程反问题的研究具有重要的理论意义和实践意义。由于高维波动方程反演问题理论研究的困难和巨大的计算量,层次介质弹性参数研究在数学界和地球物理学引起了广泛的关注。经过前人近三十年的努力,一维声波方程的单参数反演理论已趋成熟,并已逐步实用化。基于矢量波动方程的多参数反演,非脉冲响应对应的反问题是层状介质弹性参数反演需要进一步深入研究的问题。 相似文献
973.
Wang Weidong Bai Kezhuang Zu Donglin Bao Shanglian Jerome Z. Liang )The Biomedical engineering research office Chinese PLA General Hospital Beijing )Beijing document service Beijing )The 《CT理论与应用研究》1998,7(4):44-49
许多共振成像(MRI)的应用,要求人体组织磁化强度的空间分布Fourier变换的幅度和相位的精确分离,及利用正交双通道采集时间和空间高分辨图象序列。在传统的基于Fourier变换的成象方法中,图象序列从一帧空间编码独立地重建得到,因此给定空间分辨率的情况下,每帧空间编码的数量限制了图象序列的时间分辨力;又常通过牺牲空间分辨率来提高图象序列的空间分辨录。由于传统Fourier变换的核函数是线性相位,若变换MRI技术必须很好地满足主磁场均匀性和梯度场线性的条件,因此传统Fourier变换成象方法对临床应用中常出现MR信号相位失真极为敏感。本文提出:利用主磁场中组织的磁化强度不变,能很好消除图象的相位失真。 相似文献
974.
FriedrichAckermann 《地球空间信息科学学报》1998,(1)
A geo-reference is a global or regional geographical or geodetic coor-dinate system to which sensors or spatial object data are related.Hence,geo-ref-erencing is close to the well known photogrammetric concept of exterior or abso-lute orientation,the common execution of which is indirect,via the use of groundcontrol point.GPS and INS technologies have changed the situation,permittingdirect measurement of position and attitude parameters and making exterior orien-tation feasible without ground control at all,in principle.The analysis of accuracyand reliability performance discloses,however,that especially INS does not yetmeet the high demands of photogrammetry.Moreover,control of systematic er-rors,the problem of datum transformation,and reliability conditions make theuse of some ground control points still mandatory,at least for any high perfor-mance geo-referencing. 相似文献
975.
NING JinshengLI JianchengCHAO DingboNING Jinsheng Academician Professor School of Geo-science Surveying Engineering WTUSM Wuhan China 《地球空间信息科学学报》1998,(1)
This paper presents a method for the computation of the Stokes for-mula using the Fast Hartley Transform(FHT)techniques.The algorithm is mostsuitable for the computation of real sequence transform,while the Fast FourierTransform(FFT)techniques are more suitable for the computaton of complex se-quence transform.A method of spherical coordinate transformation is presented inthis paper.By this method the errors,which are due to the approximate term inthe convolution of Stokes formula,can be effectively eliminated.Some numericaltests are given.By a comparison with both FFT techniques and numerical integra-tion method,the results show that the resulting values of geoidal undulations byFHT techniques are almost the same as by FFT techniques,and the computation-al speed of FHT techniques is about two times faster than that of FFT techniques. 相似文献
976.
CHEN Yongqi TANG HongwaiCHEN Yongqi Professor School of Geo-science Surveying Engineering WTUSM Wuhan China 《地球空间信息科学学报》1998,(1)
A monitoring scheme must be so designed that several possible mod-els can be efficiently separated in the stage of analysis of deformation measure-ments.Based on the concept of separability developed by Chen and Chrzanowski,a methodology for the design of monitoring schemes has been developed by the au-thors.In the method a computer simulation technique is employed,into whichsome rules have been elaborated allowing minimal human intervention.In this pa-per the criterion is first presented and the design technique using the step one up-dating procedure is discussed.Finally,design of a simulated monitoring networkis made as a demonstrating example. 相似文献
977.
GlobalOceanicClimateAnomaliesin1980′sFuCongbin(符淙斌)andXieLi(谢力)InstituteofAtmosphericPhysics,ChineseAcademyofSciences,Beijing... 相似文献
978.
王英鉴 《Acta Meteorologica Sinica》1998,(4)
The SME satellite data of solar UV radiation and mesospheric ozone during solar flare in 1982are analyzed.The results show that the Ha line index used in the solar flare classification is not aproper parameter for studying the effects of solar activity on the photochemical process in themiddle atmosphere. 相似文献
979.
Zhou Huilan Liu Zhen and Gao YuanGraduate School University of Sciences Technology of China Beijing China 《中国地震研究》1998,(1)
By using the SLC(Single-Link Cluster)method,this study worked in three respects:(a)set up three-dimensional(3-D)SLC software that can deal with a large catalogue of earthquakes and analyze the characteristics of earthquakes' clustering and scattering in time-space:(b)defined several parameters to describe the distinguishing feature for the SLC frame and developed a technique to calculate the 3-D SLC frames and these parameters with gradual time-sliding,and inspected their variations with time,especially before large events; and(c)by using these means,treated the earthquake catalogue in the top area of the Kunlun-Altun-Arc as well as some valuable results that had been obtained. 相似文献
980.
Fault Geometry and Departure of Precursors From the Epicenter 总被引:3,自引:0,他引:3
Different tectonic elements may play different roles and their deformation styles and types of anomalies are also different in the process of deformation.Such differences may be the cause of the phenomena of the departure from the region with obvious anomalies from the coming epicenter,which are called "departure of precursors from epicenter." From some new experimental and numerical modeling results,five types of deformation elements are identified according to their roles in the process of deformation in a region.They are the brake(or locked),slip,yield,sensitive,and valve elements.Spatial distribution of different elements,especially sensitive and slip elements,are discussed by taking the bend fault,extension,compression,and complex en-echelon faults as examples.These elements with different roles may overlap each other in some cases or be separated in other cases.It is obvious that for different fault geometry,the spatial layout of these elements is different and thus the position and style of possi 相似文献