全文获取类型
收费全文 | 3290篇 |
免费 | 108篇 |
国内免费 | 91篇 |
专业分类
测绘学 | 70篇 |
大气科学 | 409篇 |
地球物理 | 819篇 |
地质学 | 1013篇 |
海洋学 | 666篇 |
天文学 | 301篇 |
综合类 | 49篇 |
自然地理 | 162篇 |
出版年
2023年 | 12篇 |
2022年 | 22篇 |
2021年 | 45篇 |
2020年 | 48篇 |
2019年 | 63篇 |
2018年 | 135篇 |
2017年 | 126篇 |
2016年 | 141篇 |
2015年 | 90篇 |
2014年 | 176篇 |
2013年 | 223篇 |
2012年 | 143篇 |
2011年 | 208篇 |
2010年 | 193篇 |
2009年 | 193篇 |
2008年 | 165篇 |
2007年 | 179篇 |
2006年 | 148篇 |
2005年 | 126篇 |
2004年 | 107篇 |
2003年 | 96篇 |
2002年 | 98篇 |
2001年 | 77篇 |
2000年 | 79篇 |
1999年 | 56篇 |
1998年 | 45篇 |
1997年 | 41篇 |
1996年 | 25篇 |
1995年 | 37篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 15篇 |
1984年 | 28篇 |
1983年 | 31篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 25篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 16篇 |
1975年 | 15篇 |
1974年 | 10篇 |
1973年 | 7篇 |
排序方式: 共有3489条查询结果,搜索用时 31 毫秒
211.
212.
213.
Application of the weighted residual method to diffraction by 2-D canyons of arbitrary shape: I. Incident SH waves 总被引:1,自引:0,他引:1
A solution for the two-dimensional scattering and diffraction of plane SH waves by canyons of arbitrary shape in an elastic half space is presented. The wave field for arbitrary geometry in this paper is computed numerically by the method of weighted residues (moment method). The wave displacement field computed by the present residual method for the case of a semi-circular canyon was shown to agree analytically and numerically with that computed by the exact closed form series solution. The same observations about ground amplifications, their dependence on frequencies and orientations of the incident waves, can be stated here for canyons of arbitrary shape as previously made for circular canyons. 相似文献
214.
L. N. Germanovich R. L. Salganik A. V. Dyskin K. K. Lee 《Pure and Applied Geophysics》1994,143(1-3):117-149
215.
Dong Ok Lee 《The Professional geographer》1995,47(2):184-195
The locations of Korean firms in Los Angeles reflect spatial segmentation in markets and the provision of labor, in that the ethnic neighborhoods facilitate positive business environments for ethnic small firms. While Korean small businesses serve both community needs and broader local markets, firm locations are closely associated with the residential patterns of some ethnic populations. To address the specificity of firm locations, this paper examines Koreatown using historical sources and recent property development, identifies changes in the locational patterns of Korean firms between 1975 and 1986, and analyzes relationships between business density and density of ethnic populations for zip code areas. The findings of this study indicate that both the development of Koreatown and the presence of ethnic neighborhoods are important influences on the location of Korean businesses. 相似文献
216.
Conclusion A simple method of estimating fracture porosity and permeability based on empirical relations between fracture aperture andJRC andJCS can be developed. This shows very close correlation with existing data, using simple discontinuity models. There is quite a good correlation between fracture porosity and permeability and depth for larger initial apertures. 相似文献
217.
The response of multi-degree-of-freedom (MDOF) structures with sliding supports is studied. The problem of sliding structures is a discontinuous one in that different numbers of equations of motion with varying forcing functions are required for the sliding and non-sliding phases. The numerical difficulties involved in this regard in an incremental finite element analysis can be circumvented through the introduction of a fictitious spring for the sliding support. Such a treatment enables one to study the higher mode effects on MDOF sliding structures under the excitation of harmonic or earthquake motions. The dynamic characteristics of MDOF sliding structures will be highlighted in the analysis of a four-storey shear building with sliding support. 相似文献
218.
Empirical regression equations are presented for scaling Pseudo Relative Velocity Spectra, PSV(T), in terms of the Modified Mercalli Intensity M.M.I., local soil classification at the recording site (‘rock’, stiff or deep soil), and local geological condition (depth of sediments). It is shown that both the local soil classification and the local geological depth of sediments should be used simultaneously in the evaluation of site specific response spectra. 相似文献
219.
C.Y. Lee 《Computers and Geotechnics》1991,11(4):295-313
This paper presents a simple discrete layer approach for the settlement analysis of axially loaded piles and pile groups. The soil profile may be arbitrarily layered and underlain by either a stiff or rigid stratum. The pile-soil-pile interaction is determined using a modified form of Mindlin's solution for finite soil depth. Good agreement between the present approach and more rigorous finite element and boundary element approaches is observed for the analysis of piles and pile groups embedded in finite soil layers. Settlement predictions obtained from the present approach also agree reasonably well with measurements from a number of published pile tests. Although the emphasis of this paper is on linear elastic solutions, it can easily be extended to include non-linear response. 相似文献
220.
An assessment of developing eutrophic conditions in small temperate lagoons along the coast of Rhode Island suggests that in such shallow, macrophyte based systems the response to nutrient enrichment differs from that described for plankton based systems. The nitrogen loadings per unit area of the salt ponds are 240–770 mmol N per m2 per year. Instead of the high nutrient concentrations, increased phytoplankton biomass and turbidity, leading to eventual loss of benthic macrophytes described for such systems as the Chesapeake, Patuxent and Appalachicola Bay, nutrient enrichment of the Rhode Island lagoons has led to increased growth of marine macroalgae. The increased macroalgal growth appears to alter the benthic habitat and a shift from a grazing to detrital food chain appears to be impacting important shellfisheries. As more extensive areas of organic sediments develop, geochemical cycling changes, resulting in higher rates of nitrogen remineralization and accelerated eutrophication. The major sources of nitrogen inputs to the salt ponds have been identified and a series of management initiatives have been designed to limit inputs from present and potential development within the watersheds of the lagoons. 相似文献