全文获取类型
收费全文 | 56180篇 |
免费 | 1300篇 |
国内免费 | 1167篇 |
专业分类
测绘学 | 1279篇 |
大气科学 | 3890篇 |
地球物理 | 11302篇 |
地质学 | 21187篇 |
海洋学 | 5199篇 |
天文学 | 12413篇 |
综合类 | 275篇 |
自然地理 | 3102篇 |
出版年
2022年 | 512篇 |
2021年 | 817篇 |
2020年 | 793篇 |
2019年 | 866篇 |
2018年 | 1682篇 |
2017年 | 1565篇 |
2016年 | 1748篇 |
2015年 | 1020篇 |
2014年 | 1668篇 |
2013年 | 2938篇 |
2012年 | 2077篇 |
2011年 | 2671篇 |
2010年 | 2392篇 |
2009年 | 3013篇 |
2008年 | 2554篇 |
2007年 | 2740篇 |
2006年 | 2575篇 |
2005年 | 1690篇 |
2004年 | 1585篇 |
2003年 | 1481篇 |
2002年 | 1470篇 |
2001年 | 1270篇 |
2000年 | 1164篇 |
1999年 | 944篇 |
1998年 | 985篇 |
1997年 | 950篇 |
1996年 | 804篇 |
1995年 | 783篇 |
1994年 | 680篇 |
1993年 | 578篇 |
1992年 | 609篇 |
1991年 | 544篇 |
1990年 | 612篇 |
1989年 | 539篇 |
1988年 | 484篇 |
1987年 | 600篇 |
1986年 | 491篇 |
1985年 | 602篇 |
1984年 | 694篇 |
1983年 | 621篇 |
1982年 | 616篇 |
1981年 | 557篇 |
1980年 | 552篇 |
1979年 | 512篇 |
1978年 | 482篇 |
1977年 | 467篇 |
1976年 | 420篇 |
1975年 | 416篇 |
1974年 | 423篇 |
1973年 | 483篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
731.
732.
Estimation of the leeway drift of small craft 总被引:1,自引:0,他引:1
Small craft (<6·4 m) leeway is determined as a function of the wind speed in the range of 5–20 knots (3·6–10·3 m/sec). Leeway is calculated relative to the surface current by measurement of the separation distance of the small craft from a dyed patch of surface water at sea, using time-sequenced aerial photography. Leeway increases linearly with wind speed for small craft equipped with or without a sea anchor in the wind range studied. Leeway for small craft without sea anchor can be calculated from the equation UL = 0.07 UW + 0.04 where UW is the wind speed at 2 m elevation. Leeway for small craft drifted off the be calculated from the equation ULD = 0·05 UW − 0·12. The small craft drifted off the downwind direction in about 80% of the experiments. The drift angle is variable and difficult to predict. 相似文献
733.
The finite-elements technique is applied to study the effect of a basin’s geometry (bays, harbours) and location of the characteristics
of seiche oscillations in the basin and in the gulf proper. An increase of the length of the bay is shown to contribute to
the periods of natural oscillations and to cause their restructuring.
Translated by Vladimir A. Puchkin. 相似文献
734.
R.E. Rossi P.M. Belles P.A.A. Laura S. La Malfa L. Ercoli D. Pasqua 《Ocean Engineering》1996,23(3):271-276
A numerical solution is obtained for the title problem by means of the popular finite element method. An experimental investigation of the problem is also presented for plates of square planform. The agreement between theoretical and experimental values is very good in the case of the fundamental frequency, and reasonably good when the second and third normal modes of transverse vibration are considered. It is concluded that beneficial effects are obtained in the sense that one generates a lighter structural element with higher fundamental frequency of transverse vibration. Hence, dynamic stiffening is achieved. 相似文献
735.
Based on the MEGAPOLYGON data, it is shown that the large-scale elements of the thermohaline structure and the fields of currents in the baroclinic layer (down to 1200 m) are well coordinated. The circulation has a two-layer structure with a transitory layer at a depth of 1200 m. The topography of the isopycnic surface of the layer's core is formed under the influence of small-scale and mesoscale processes which realize the trans-frontal exchange.Translated by Mikhail M. Trufanov. 相似文献
736.
Experimental investigation of the combustive sound source 总被引:3,自引:0,他引:3
In this paper, we describe a unique low frequency underwater sound source called the combustive sound source (CSS). In this device, a combustible gas mixture is captured in a combustion chamber and ignited with a spark. The ensuing combustion produces expanding gases which in turn produce high intensity, low frequency acoustic pulses. With high-speed motion pictures of the CSS event, we relate the motion of the bubble to the acoustic waveform. We also compare the measured first bubble period in the CSS pressure signature with the predictions of the Rayleigh-Willis equation, including the dependence of the radiated acoustic waveform on the volume and depth of the bubble. Measurements of the first bubble period agree with Rayleigh-Willis theory in trend, but not in absolute value. In addition, we discuss the variation of the acoustic output with the fuel/oxygen mixture. Finally, several other factors that affect the acoustic output of CSS are discussed. These include the shape of the CSS combustion chamber, the type of oxidizer and fuel, and the ignition source 相似文献
737.
CTD data provided by the MGI-4204 and MARK-III probes are used to study the quasistationary subpolar front structure in the north-western Sea of Japan. In order to provide further insights into the intermittent scalar hydrophysical fields, the method of inhomogeneity identification using temperature pulsations calculated by the moving interval is suggested. The experimentally-derived inhomogeneity distribution is satisfactorily approximated by the exponential law.Translated by V. Puchkin. 相似文献
738.
A. A. Bezborodov S. L. Gokchen V. N. Eremeev I. T. Konuk A. K. Saidam E. M. Tirasin 《Physical Oceanography》1991,2(3):227-231
The hydrological and hydrochemical structures of the upper 300 m water column of the Black Sea in autumn 1988 have been studied. Regularities in the distribution of the physico-chemical characteristics in the zone of interaction between aerobic and anaerobic waters as well as the topography of the H2S zone boundary and its connection with a certain density gradient have been found.Translated by Mikhail M. Trufanov. 相似文献
739.
740.
Image processing techniques are discussed that correct distortions in GLORIA II side scan sonar imagery including water column
offset, slant-range distortion, multiple returns, aspect ratio, speckle noise, striping, and cross-track power drop-off. The
software operates within NASA's ELAS image processing system and is applied to the original 12-bit GLORIA II data. Procedures
are discussed for generating large scale mosaics and three-dimensional overlays with sea floor bathymetry. The results are
shown in four sonographs acquired off the southern coast of California. 相似文献