全文获取类型
收费全文 | 37956篇 |
免费 | 6957篇 |
国内免费 | 7774篇 |
专业分类
测绘学 | 2656篇 |
大气科学 | 7119篇 |
地球物理 | 10460篇 |
地质学 | 17458篇 |
海洋学 | 4573篇 |
天文学 | 2142篇 |
综合类 | 3653篇 |
自然地理 | 4626篇 |
出版年
2024年 | 115篇 |
2023年 | 435篇 |
2022年 | 1421篇 |
2021年 | 1683篇 |
2020年 | 1374篇 |
2019年 | 1789篇 |
2018年 | 2051篇 |
2017年 | 1973篇 |
2016年 | 2296篇 |
2015年 | 2030篇 |
2014年 | 2438篇 |
2013年 | 2486篇 |
2012年 | 2253篇 |
2011年 | 2370篇 |
2010年 | 2459篇 |
2009年 | 2248篇 |
2008年 | 2132篇 |
2007年 | 1984篇 |
2006年 | 1556篇 |
2005年 | 1456篇 |
2004年 | 1113篇 |
2003年 | 1119篇 |
2002年 | 1060篇 |
2001年 | 1084篇 |
2000年 | 1237篇 |
1999年 | 1543篇 |
1998年 | 1227篇 |
1997年 | 1158篇 |
1996年 | 1056篇 |
1995年 | 942篇 |
1994年 | 805篇 |
1993年 | 723篇 |
1992年 | 581篇 |
1991年 | 465篇 |
1990年 | 344篇 |
1989年 | 320篇 |
1988年 | 284篇 |
1987年 | 173篇 |
1986年 | 157篇 |
1985年 | 103篇 |
1984年 | 125篇 |
1983年 | 104篇 |
1982年 | 86篇 |
1981年 | 72篇 |
1980年 | 58篇 |
1979年 | 44篇 |
1978年 | 18篇 |
1977年 | 27篇 |
1975年 | 17篇 |
1958年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
992.
Geometric form of Haiyuan fault zone in the crustal interior and dynamics implications 总被引:1,自引:0,他引:1
The deep seismic reflection data on profile HY2 are reprocessed by the method of simultaneous inversion of velocity distribution
and interface position. By the travel-time inversion with the data of the diving wave Pg and fault plane reflection wave,
we determine the geometric form and velocity of Haiyuan fault zone interior and surrounding rock down to 10 km depth. The
measured data show that the amplitudes have strong attenuation in the range of stake number 37–39 km, suggesting the fault
zone has considerable width in the crustal interior. The results of this paper indicate that to the north of the fault zone
the crystalline basement interface upheaves gradually from southwest to northeast and becomes shallow gradually towards northeast,
and that to the south of the fault zone, within the basin between Xihua and Nanhua mountains, the folded basement becomes
shallow gradually towards southwest. The obliquity of the fault zone is about 70° above the 3 km depth, about 60° in the range
of the 3–10 km depths. From the results of this paper and other various citations, we believe that Haiyuan fault zone is in
steep state from the Earth’s surface to the depth of 10 km.
Foundation item: Joint Seismological Science Foundation of China (201001) and State Key Basic Research Development and Programming Project
(95-13-02-02).
Contribution No. RCEG200308, Exploration Geophysical Center, China Earthquake Administration. 相似文献
993.
During the 1999 Chi-Chi, Taiwan earthquake, many sand boiling phenomena were observed in central Taiwan, which caused severe ground settlement and structure damages. According to the installed accelerograms, the peak ground surface horizontal accelerations in the liquefaction-affected areas range from 774.42 to 121.3 gal. The writers carried out an extensive investigation of soil liquefaction in this earthquake. In this paper, we present results of the CPT exploration and post-earthquake liquefaction analysis. Two hundred and seventy five (275) cone penetration test data were collected from the liquefaction-affected areas, and 46 liquefaction case histories and 88 non-liquefaction case histories were derived that can be used to evaluate the accuracy of existing liquefaction evaluation models. In addition, the strength of the liquefied soils after earthquake and the implication of its liquefaction potential in the future event are discussed. 相似文献
994.
995.
Introduction Now, shallow seismic reflection wave technique has been used extensively in geological ex-plorations of bridge, dam, high building and so on. Since shallow seismic reflection wave tech-nique is often implemented in industrial zone or city with dense population, the background dis-turbance including industrial noise, life noise, etc is very serious. Furthermore, the disturbance of seismic source is also serious due to short array length and offset of the method. In general, shal-lo… 相似文献
996.
The magnetic susceptibility has been used as a quantitative or semi‐quantitative proxy for reconstructing the summer monsoon intensity in the Chinese Loess Plateau based on extensive studies on climatic or/and environmental mechanisms producing the magnetic susceptibility signatures. However, the precise nature of the link between past climates and the susceptibility signatures has remained uncertain primarily due to lack of our understanding in the ?nalizing and preserving processes of the signatures. This paper attempts to examine the reliability or acceptability of this summer monsoon proxy from non‐magnetic perspectives of soil‐forming processes. We chose nine sections along two transects: one across the western part of the Chinese Loess Plateau and another across the eastern part. Several conclusions can be drawn from our analytical data. First, clay translocation within the S1 palaeosol pro?les, as indicated by ?eld‐observed clay coatings on ped faces in Bt and Bk horizons and demonstrated by laboratory‐analysed clay contents, must have moved some of the magnetic minerals downward so that the susceptibility re?ects only the post‐translocation distribution of the magnetic‐susceptibility‐producing minerals. Second, the best‐developed palaeosol S1S3 at most of the sections studied is not expressed by the magnetic susceptibility because this palaeosol developed in underlying coarse loess (L2) and coarse textures tend to lower the susceptibility. Third, carbonate concentration is normally negatively correlated with the magnetic susceptibility or simply suppresses the magnetic susceptibility peak when the susceptibility enhancement exceeds the carbonate dilution effect. To conclude, extreme caution must be observed when using magnetic susceptibility signatures to retrieve high‐resolution records of the last interglacial palaeoclimate in the Chinese Loess Plateau. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
997.
In this study a procedure for determining the optimum size and location of viscoelastic dampers is proposed using the eigenvalue assignment technique. Natural frequencies and modal damping ratios, required to realize a given target response, are determined first by the convex model. Then the desired dynamic structural properties are realized by optimally distributing the damping and stiffness coefficients of viscoelastic dampers using non‐linear programming based on the gradient of eigenvalues. This optimization method provides information on the optimal location as well as the magnitude of the damper parameters. The proposed procedure is applied to the retrofit of a 10‐story shear frame, and to a three‐dimensional structure with an asymmetric plan. The analysis results confirm that the responses of model structures retrofitted by the proposed method correspond well with the given target response. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
998.
This study investigates an electric‐type active mass driver (AMD) system for structural vibration control. Composed primarily of an electric servomotor and a ball screw, the electrical AMD system is free from noise problems, oil leakage, and labor‐intensive maintenance that commonly are associated with hydraulic AMD systems. The desired stroke amplification of the mass and the power demand of the servomotor can be adjusted via the ball screw pitch, which in turn affects the effectiveness and efficiency of the system. Meanwhile, an instantaneous optimal direct output feedback control algorithm is adopted. Numerical simulation is performed using a five‐story steel frame as the object structure under the conditions of the 1940 El Centro earthquake. The AMD system proves to be effective and efficient within a certain range of the ball screw pitch. The reductions of the peak responses can reach as high as 70% if properly designed. Requiring only the velocity measurement of the top floor for on‐line feedback control, the proposed control algorithm is recommended for practical implementation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
999.
Seepage driving effect on deformations of San Fernando dams 总被引:2,自引:0,他引:2
In the process of flow deformation of an earth dam, the seepage force inside the dam plays a role as a driving force. The seepage force acts just like the gravitational force in terms of pushing soils away from their original locations after liquefaction is triggered. This paper draws attention to this seepage driving effect by presenting a set of fully coupled finite element analyses on the well-known San Fernando dams, with the objective of evaluating the impact of this seepage effect. The results indicate that while this effect is always there, its practical significance depends on a number of factors. In the case of the upper San Fernando dam, which experienced a significant, but restricted, downstream movement during the 1971 earthquake, the seepage driving effect was indeed significant. On the contrary, for the lower dam, which failed and slid into the upstream reservoir during the same earthquake, this seepage effect was relatively less pronounced. The detailed results of the analyses reveal the likely mechanisms of failure and deformation of the two dams and the likely cause behind the difference between their responses during the earthquake. 相似文献
1000.