全文获取类型
收费全文 | 29307篇 |
免费 | 17312篇 |
国内免费 | 42254篇 |
专业分类
测绘学 | 2402篇 |
大气科学 | 20725篇 |
地球物理 | 11564篇 |
地质学 | 32275篇 |
海洋学 | 15538篇 |
天文学 | 671篇 |
综合类 | 3948篇 |
自然地理 | 1750篇 |
出版年
2024年 | 119篇 |
2023年 | 203篇 |
2022年 | 278篇 |
2021年 | 527篇 |
2020年 | 1766篇 |
2019年 | 5213篇 |
2018年 | 5422篇 |
2017年 | 5152篇 |
2016年 | 5180篇 |
2015年 | 4569篇 |
2014年 | 3998篇 |
2013年 | 4551篇 |
2012年 | 4289篇 |
2011年 | 4057篇 |
2010年 | 4021篇 |
2009年 | 3353篇 |
2008年 | 2659篇 |
2007年 | 2684篇 |
2006年 | 2334篇 |
2005年 | 2261篇 |
2004年 | 2633篇 |
2003年 | 2382篇 |
2002年 | 2111篇 |
2001年 | 1893篇 |
2000年 | 1519篇 |
1999年 | 1532篇 |
1998年 | 1647篇 |
1997年 | 1718篇 |
1996年 | 1331篇 |
1995年 | 1298篇 |
1994年 | 1161篇 |
1993年 | 1131篇 |
1992年 | 955篇 |
1991年 | 721篇 |
1990年 | 691篇 |
1989年 | 575篇 |
1988年 | 488篇 |
1987年 | 382篇 |
1986年 | 306篇 |
1985年 | 244篇 |
1984年 | 274篇 |
1983年 | 161篇 |
1982年 | 201篇 |
1981年 | 143篇 |
1980年 | 107篇 |
1979年 | 108篇 |
1978年 | 46篇 |
1977年 | 43篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
961.
It has been well studied that the γ-function explicit method can be effective in providing favorable numerical dissipation for linear elastic systems. However, its performance for nonlinear systems is unclear due to a lack of analytical evaluation techniques. Thus, a novel technique is proposed herein to evaluate its efficiency for application to nonlinear systems by introducing two parameters to describe the stiffness change. As a result, the numerical properties and error propagation characteristics of the γ-function explicit method for the pseudodynamic testing of a nonlinear system are analytically assessed. It is found that the upper stability limit decreases as the step degree of nonlinearity increases; and it increases as the current degree of nonlinearity increases. It is also shown that this integration method provides favorable numerical dissipation not only for linear elastic systems but also for nonlinear systems. Furthermore, error propagation analysis reveals that the numerical dissipation can effectively suppress the severe error propagation of high frequency modes while the low frequency responses are almost unaffected for both linear elastic and nonlinear systems. 相似文献
962.
格尔木井水温异常特征及其与地震关系分析 总被引:1,自引:1,他引:1
简要介绍了格尔木井水温动态观测的环境与条件,在研究正常动态特征和影响因素的基础上,对水温异常的映震关系进行了分析,并成功地进行了一次短临地震趋势预测。探讨了水温异常的形成原因。 相似文献
963.
Introduction The Great North China, located at longitude 106E to 124E and latitude 31N to 42N, in-cludes three secondary active tectonic blocks, Ordos, Yanshan and North China plain (Figure 1). The geological tectonics of these three secondary blocks is much different from each other. As a stable block with high rigidity, the Ordos block is mostly surrounded by down-faulted basins with an inactive interior since Cenozoic, although the fault zones along its boundary are strongly active wi… 相似文献
964.
Introduction East Kunlun active fault is one of the largest sinistral slip fault zones in northern Tibetan Pla-teau. The fault tails primarily after the ancient eastern Kunlun suture zone, which was reactivatedby the northward subduction of the Indian plate beneath the Eurasian plate. The western end of thefault starts near the western flank of the Buxedaban peak in Qinghai Province. The fault then ex-tends eastwards through the Kusai Lake, Xidatan, Dongdatan, Alag Lake, Tuosuo Lak… 相似文献
965.
Introduction The observation records of strong ground motion previously, on the one hand, supplied basicdata both to research on earthquake engineering and to constitute the criterion of aseismatic de-signing of all project structures; on the other hand, it provided important information for the re-search on the process of epicenter burst in seismology. With the development of research on strongground motion observation, especially the development of the new generation accelerograph,which… 相似文献
966.
Introduction In recent years, with the development of earthquake observation technology, increasing ofobservation stations and improvement of observation instruments which are digitalized and con-nected by network, a great deal of data is recorded, to some extend, which brings difficulty for usto manage and store them. It leads to traditional methods, which use the file system to managemass data, could not satisfy our requirement, and it is necessary to find a new method in place oftradit… 相似文献
967.
Introduction The acceleration response spectrum and peak ground acceleration are the necessary and im-portant parameters in earthquake-resistant design at present. They are still active research field. With the increase of digital high accurate strong motion observation data, especially the earth-quakes of Loma Prieta (M=7.0) in 1989; Landers (M=7.3) in 1992; Big Bear (M=6.4) in 1994 and Northridge (M=6.7) in 1994 in USA; Kozani (M=6.6) earthquake and afteshocks in 1995 in Greece; Dinar… 相似文献
968.
ZHANG Renhua LI Zhaoliang SUN Xiaomin ZHU Zhilin & WANG Weimin Institute of Geographical Sciences Natural Resources Research Chinese Academy of Sciences Beijing China LSIIT 《中国科学D辑(英文版)》2005,(1)
This paper proposes a basic equation of thermal radiation interaction between surface objects on the basis of the principle of heat balance in the interface. The solution of this equation takes account of the contribution of sensible heat flux and latent heat flux more completely, compared with traditional solution for surface cooling and heating processes. By the aid of the experimental data conducted in the Xiaotangshan experimental site, Beijing, both the non-applicability of Kirchoff's law and the measurability of surface emissivity in a non-isothermal system have been highlighted. Two methods called ventilation and time-delay compensations have been proposed to reduce the error induced by change of surface temperatures of non-isothermal objects during the measurement of emissivity. Based on the solution of the basic equation, this paper has analyzed and pointed out the misunderstanding in comprehension and application of Kirchoff's law published in literature. 相似文献
969.
HE Yongfeng & CHEN Xiaofei . Department of Geophysics School of Earth & Space Sciences Peking University Beijing China . North-West Institute of Nuclear Technology Xi’an China 《中国科学D辑(英文版)》2005,48(12):2118-2122
Since the sign up of CTBT (Comprehensive Test Ban Treaty), the nuclear monitoring and distinguishing has gained great attention by the treaty countries. Seismology is one of the primary technical means available for monitoring compliance to a CTBT. However, there does not exist a single criterion, so far, that can effectively distinguish explorations from earthquakes. It has been known that source time function (abbreviated to STF) of an underground nuclear explosion contains important p… 相似文献
970.