全文获取类型
收费全文 | 19435篇 |
免费 | 4905篇 |
国内免费 | 3709篇 |
专业分类
测绘学 | 423篇 |
大气科学 | 1602篇 |
地球物理 | 12479篇 |
地质学 | 9031篇 |
海洋学 | 1233篇 |
天文学 | 26篇 |
综合类 | 1737篇 |
自然地理 | 1518篇 |
出版年
2024年 | 87篇 |
2023年 | 359篇 |
2022年 | 731篇 |
2021年 | 959篇 |
2020年 | 900篇 |
2019年 | 1157篇 |
2018年 | 959篇 |
2017年 | 884篇 |
2016年 | 859篇 |
2015年 | 1061篇 |
2014年 | 1354篇 |
2013年 | 1201篇 |
2012年 | 1261篇 |
2011年 | 1319篇 |
2010年 | 1171篇 |
2009年 | 1403篇 |
2008年 | 1158篇 |
2007年 | 1264篇 |
2006年 | 1183篇 |
2005年 | 1126篇 |
2004年 | 978篇 |
2003年 | 924篇 |
2002年 | 750篇 |
2001年 | 659篇 |
2000年 | 614篇 |
1999年 | 528篇 |
1998年 | 498篇 |
1997年 | 469篇 |
1996年 | 459篇 |
1995年 | 400篇 |
1994年 | 374篇 |
1993年 | 287篇 |
1992年 | 245篇 |
1991年 | 142篇 |
1990年 | 106篇 |
1989年 | 74篇 |
1988年 | 55篇 |
1987年 | 28篇 |
1986年 | 21篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1979年 | 16篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
21.
昆仑山口大地震与地形变异常的讨论 总被引:7,自引:5,他引:2
针对昆仑山口大地震,总结了多种地形变(大地测量)手段所显示的异常变化及其时空分布,结果显示:8.1级大震前存在空间尺度大,时间尺度的地形变前兆异常,简要介绍了相关的异常图像,给出了初步解释,并对未来震情的发展进行了探讨,认为近期内强震活动向华北迁移的可能性不大。 相似文献
22.
A method of structural damage identification using harmonic excitation force is presented. It considers the effects of both measurement and modelling errors in the baseline finite element model. Damage that accompanies changes in structural parameters can be estimated for a damaged structure from the change between measured vibration responses and ones calculated from the analytical model of the intact structure. In practice, modelling errors exist in the analytical model due to material and geometric uncertainties and a reduction in the degrees of freedom as well as measurement errors, making identification difficult. To surmount these problems, bootstrap hypothesis testing, which enables statistical judgment without information about these errors, was introduced. The method was validated by numerical simulation using a three‐dimensional frame structure and real vibration data for a three‐storey steel frame structure. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
23.
形变大地测量学的进展、问题与地震预报 总被引:12,自引:7,他引:5
简要概括了形变大地测量学的革命性进展,研讨了它的科学特色、功能和定义以及对地球科学和防灾减灾的推动。形变大地测量学有助于从根本上击破多年来制约地震预报的“瓶颈”,但也存在不少急待解决的问题。着重研讨了在21世纪前10年,形变大地测量学如何依托多年的学科积累并充分受益于人造卫星和数字化等新技术,开展创新性研究和试验以推进地震预报。为此,对当前的研究工作提出了12条科学技术途径。最后对学科名称提出了建议。 相似文献
24.
25.
I INTRODUCTIONWetland has very important effect on retainingwater and against drought, regUlating climate, controlling soil erosion and so on ac. Today men often attachimportance to economic effect of wetland reclamation,but neglect and destroy other functions and effectswhich result in blind wetland development, a lot ofwetland degeneration. The area of freshwater wetland inthe 1950s was 134 x 10'ha, but in the 1970s 70% hadchanged into farmland (MITSCH, 1993). The area ofwetland in d… 相似文献
26.
In recent years,scholars at home and abroad have method,and that vanous disasters would be analyzed assynthetically studied natural dlsaste‘theoretically and an Integral.SHI Peilun(1991)putforwad a scientificmethodologlcally,as well as its cases analys。s(CND,term—regional disaster system,which Indicates that1987; MA et al,1990; MARBLE,1990; NE et al,the situation of a disaster(calamity loss)results from1999; PATAK et al,1982; SHI,1991;VAN et al,h… 相似文献
27.
Kenai, located on the west coast of the Kenai Peninsula, Alaska, subsided during the great earthquake of AD 1964. Regional land subsidence is recorded within the estuarine stratigraphy as peat overlain by tidal silt and clay. Reconstructions using quantitative diatom transfer functions estimate co‐seismic subsidence (relative sea‐level rise) between 0.28±0.28 m and 0.70±0.28 m followed by rapid post‐seismic recovery. Stratigraphy records an earlier co‐seismic event as a second peat‐silt couplet, dated to ~1500–1400 cal. yr BP with 1.14±0.28 m subsidence. Two decimetre‐scale relative sea‐level rises are more likely the result of glacio‐isostatic responses to late Holocene and Little Ice Age glacier expansions rather than to co‐seismic subsidence during great earthquakes. Comparison with other sites around Cook Inlet, at Girdwood and Ocean View, helps in constructing regional patterns of land‐level change associated with three great earthquakes, AD 1964, ~950–850 cal. yr BP and ~1500–1400 cal. yr BP. Each earthquake has a different spatial pattern of co‐seismic subsidence which indicates that assessment of seismic hazard in southern Alaska requires an understanding of multiple great earthquakes, not only the most recent. All three earthquakes show a pre‐seismic phase of gradual land subsidence that marked the end of relative land uplift caused by inter‐seismic strain accumulation. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
28.
Current plate motions 总被引:57,自引:0,他引:57
29.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
30.
1StrongtideandastronomicalconditionsPartial solar eclipse occurred 4 times in 1964, 1982 and 2000 respectively. Time interval is about 3 Saros periods (one Saros period is 18 years and 10.33~11.33 days). Total lunar eclipse occurred 2 times in 1964 and 2000 respectively and 3 times in 1982. However, there was no lunar eclipse in 1966, 1984 and 2002. It seems that they had similar astro-nomical conditions and the best was in 1982. The studies about the effect of tide on the global climate… 相似文献