全文获取类型
收费全文 | 42572篇 |
免费 | 892篇 |
国内免费 | 326篇 |
专业分类
测绘学 | 894篇 |
大气科学 | 2832篇 |
地球物理 | 8627篇 |
地质学 | 15451篇 |
海洋学 | 3880篇 |
天文学 | 9327篇 |
综合类 | 107篇 |
自然地理 | 2672篇 |
出版年
2022年 | 284篇 |
2021年 | 474篇 |
2020年 | 539篇 |
2019年 | 632篇 |
2018年 | 1081篇 |
2017年 | 1112篇 |
2016年 | 1189篇 |
2015年 | 679篇 |
2014年 | 1155篇 |
2013年 | 2086篇 |
2012年 | 1315篇 |
2011年 | 1845篇 |
2010年 | 1586篇 |
2009年 | 2002篇 |
2008年 | 1841篇 |
2007年 | 1881篇 |
2006年 | 1733篇 |
2005年 | 1215篇 |
2004年 | 1198篇 |
2003年 | 1256篇 |
2002年 | 1121篇 |
2001年 | 943篇 |
2000年 | 873篇 |
1999年 | 779篇 |
1998年 | 777篇 |
1997年 | 770篇 |
1996年 | 645篇 |
1995年 | 621篇 |
1994年 | 544篇 |
1993年 | 493篇 |
1992年 | 450篇 |
1991年 | 460篇 |
1990年 | 472篇 |
1989年 | 422篇 |
1988年 | 403篇 |
1987年 | 437篇 |
1986年 | 458篇 |
1985年 | 555篇 |
1984年 | 589篇 |
1983年 | 584篇 |
1982年 | 540篇 |
1981年 | 507篇 |
1980年 | 471篇 |
1979年 | 440篇 |
1978年 | 417篇 |
1977年 | 406篇 |
1976年 | 373篇 |
1975年 | 374篇 |
1974年 | 368篇 |
1973年 | 397篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
341.
Adrian E. Scheidegger 《Pure and Applied Geophysics》1966,65(1):160-163
Summary Recently, a new theory of the subsidence of rock masses has been advanced byLitwiniszyn and coworkers, which is based on the notion that the individual rock particles perform random walks. It is shown in the present paper that the final equations of the random walk theory can be justified from general principles of statistical mechanics in which no specific theoretical model of particle behaviour has to be made. The theory appears to account appropriately for subsidence phenomena.The research reported in this paper was supported by the Petroleum Research Fund of the American Chemical Society. Acknowledgment is made to the donors of the Petroleum Research Fund administered by the American Chemical Society for support of this reseach. 相似文献
342.
Summary Using the results of spherical harmonic analyses of the geomagnetic field for some fourteen different epochs, includingGauss' first analysis for epoch 1835, and theErman-Petersen analysis for epoch 1829, the strength and axes of geomagnetic multipoles have been computed. In particular, a dipole from the three first order spherical harmonic coefficients, a quadrupole from five second order coefficients, and an octupole from seven third order coefficients. The axes of the quadrupole and octupole have moved quite rapidly when compared with movements of the dipole axis, and show a general movement westwards. Although the strength of the dipole has generally diminished, the strengths of the quadrupole and octupole have generally increased.On leave National University of La Plata, Argentina 相似文献
343.
344.
A sonic well log was obtained within the basement complex of the Walvis Ridge during Deep Sea Drilling Project Leg 74. The top of the basement complex is characterized by smooth acoustic reflectors. The rocks recovered within the basement complex consist of basalts with intercalated sediments. According to the log ~-50% of the upper 75 m of basement are igneous rocks and the other 50% sedimentary. Sonobuoy results indicate that the ratio of sediments to basalt increases with depth for an additional 225 m until a typical oceanic velocity structure is observed. Paleontological results suggest that the processes forming this upper 300 m of the basement complex was accomplished within a short time interval. 相似文献
345.
E.R. Jefferys 《Applied Ocean Research》1983,5(3):145-149
The solution to the problem of calculating the hydrodynamic forces on multiple floating bodies is summarised. The complex coefficients which characterise the forces at each frequency of oscillation are expensive to compute; interpolation of intermediate values and extrapolation to high frequencies appear difficult since the coefficients seem to vary arbitrarily with frequency. Interpolation and extrapolation schemes based on a novel representation of the coefficients are proposed and tested. The excellent numerical results indicate that the values of the coefficients at a few frequency points can characterise the hydrodynamics at all frequencies. These techniques can save economically significant amounts of computer time and permit investigations which would otherwise be prohibitively expensive. 相似文献
346.
Surface currents influenced by a wind-driven upwelling event in San Pedro Bay moved total suspended matter (TSM) confined
to the inner shelf on 19 April 1978 seaward, so that by 27 April surface TSM had increased over the outer shelf. Near-bottom
concentrations of TSM also increased across the shelf during this time. This is explained by sediment resuspended by large
surface waves being advected from the inner shelf seaward by the mean flow after this flow had turned from southeasterly to
southerly when upwelling ceased on 26 April. These complex shelf dynamics contribute to the off-shelf transport of mud to
the slope and deep basins. 相似文献
347.
A new and inexpensive pop-up ocean-bottom hydrophone recorder has been developed for use in seismic refraction experiments. It is capable of operating in water depths of up to 4000 m and in very rugged topography, and uses an acoustic command system built by the U.K. Institute of Oceanographic Sciences for recovery. The instrument is mounted in an inexpensive cylindrical pressure case based on commercially available extruded aluminium alloy tubing, and uses glass spheres and syntactic foam for buoyancy. Hydrophone and clock signals are frequency modulated and recorded on tape cassettes, with a recording duration of three hours allowing up to 18 programmed shot windows. The prototype has made seven free descents on the Mid-Atlantic ridge and in the Gulf of Oman, and successfully recorded shots under operational conditions for the first time in September 1979. The total component cost of the prototype was £2740 (1979 prices).(Department of Earth Sciences, University of Cambridge Contribution No. ES135). 相似文献
348.
The asteroid Patiria miniata was used to develop a static bioassay for various crude oil water-soluble fractions (WSF). The criterion used is the size of 48-h exposed embryos. The reasons for choosing this species and the growth criterion are discussed. Experiments show that the body length of 48-h exposed embryos is inversely proportional to hydrocarbon concentration of the WSF and the time of exposure. It is also shown that the toxicity of the WSF decreases with the age of the preparation and that the first 12 h following fertilisation are most sensitive to the effects of WSF. 相似文献
349.
350.
Single-channel seismic reflection profiles show evidence for areas of significant gas accumulation at the head of the Cape Fear Slide on the continental rise off North Carolina. Gas accumulation appears to occur beneath a gas hydrate seal in landward-dipping strata and in domed strata associated with diapirism. In addition, gas venting may have occurred near diapirs located at the head of the slide. 相似文献