全文获取类型
收费全文 | 106917篇 |
免费 | 2010篇 |
国内免费 | 951篇 |
专业分类
测绘学 | 2844篇 |
大气科学 | 8012篇 |
地球物理 | 21325篇 |
地质学 | 36976篇 |
海洋学 | 9527篇 |
天文学 | 24247篇 |
综合类 | 312篇 |
自然地理 | 6635篇 |
出版年
2021年 | 883篇 |
2020年 | 1045篇 |
2019年 | 1110篇 |
2018年 | 2284篇 |
2017年 | 2218篇 |
2016年 | 2927篇 |
2015年 | 1781篇 |
2014年 | 2872篇 |
2013年 | 5554篇 |
2012年 | 2995篇 |
2011年 | 4102篇 |
2010年 | 3613篇 |
2009年 | 4898篇 |
2008年 | 4335篇 |
2007年 | 4146篇 |
2006年 | 4071篇 |
2005年 | 3215篇 |
2004年 | 3338篇 |
2003年 | 3141篇 |
2002年 | 2981篇 |
2001年 | 2654篇 |
2000年 | 2583篇 |
1999年 | 2193篇 |
1998年 | 2222篇 |
1997年 | 2117篇 |
1996年 | 1891篇 |
1995年 | 1760篇 |
1994年 | 1584篇 |
1993年 | 1452篇 |
1992年 | 1391篇 |
1991年 | 1274篇 |
1990年 | 1467篇 |
1989年 | 1233篇 |
1988年 | 1160篇 |
1987年 | 1351篇 |
1986年 | 1194篇 |
1985年 | 1487篇 |
1984年 | 1704篇 |
1983年 | 1553篇 |
1982年 | 1455篇 |
1981年 | 1364篇 |
1980年 | 1212篇 |
1979年 | 1188篇 |
1978年 | 1235篇 |
1977年 | 1079篇 |
1976年 | 1034篇 |
1975年 | 986篇 |
1974年 | 944篇 |
1973年 | 982篇 |
1971年 | 608篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
421.
422.
J.F.A. Sleath 《Coastal Engineering》1985,9(2):159-170
Measurements of energy dissipation have been made with an oscillating tray apparatus similar to that of Bagnold (1946). Two different bed profiles were examined: one was sinusoidal and the other consisted of fins projecting perpendicularly fromthe plate in a regular two-dimensional pattern. The tests with the sinusoidal profile showed that significant variation in energy dissipation coefficient with Reynolds number occurs near the point at which vortex formation first starts to take place. It is suggested that Bagnold did not observe this effect because of the particular profile used in his tests. The tests with the finned beds showed that even when vortex formation is fully developed there is still some variation in energy dissipation coefficient with Reynolds number, at constant a/ks, at high Reynolds numbers. 相似文献
423.
Topographic features affect the scattering properties of planetary surfaces by casting shadows and altering the local incidence and emission angles. Measurements of this phenomenon were obtained on the Cornell goniometer for both high and low albedo surfaces. For the low albedo surface, the decrease in reflected radiation due to topography increases sharply with increasing phase angle, whereas for the high albedo sample the effects are approximately constant between phase angles of 30 and 70°. The observations are in good agreement with a theoretical model in the case of the dark surface. However, for the high albedo surface the model overestimates the effects by about a factor of 2, since it does not include the partial illumination of shadows by multiple scattering. For both high and low albedo surfaces, the effects of topography do not become significant until a phase angle of 30–40°. 相似文献
424.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
425.
426.
The first year of sodium nightglow observations from Natal (6°S, 35°W) are examined. Time variations appear to follow a pattern of their own, different from low latitude results. The major seasonal peak occurs in September-October and the average variation during the night decreases from dusk to dawn. Statistics on cloud coverage show that Natal has roughly only about 3 clear hours per night. The best observing period is April with an average of 5 clear hours per night. 相似文献
427.
428.
We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase
of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for
by the field growth theories. 相似文献
429.
N. S. Chauhan 《Astrophysics and Space Science》1985,112(1):185-192
The treatment followed by Coxet al. (1973) for the estimation of the effects of thermal imbalance on the pulsational stability of stars is applied to Roche and point source (Chandrika Prashad) model. The calculations suggest that the eigenvalues obtained for the above model are correct to 0(t
ff/ts). The expressions for stability coefficients and corresponding eigenfunctions for the stars in thermal imbalance for the above models have also been derived. 相似文献
430.
P.S. Rainbow 《Estuarine, Coastal and Shelf Science》1985,21(5):669-686
The crab Carcinus maenas (L.) and the barnacle Elminius modestus Darwin were exposed to a range of dissolved concentrations of Zn, Cu and Cd for 21 days in artificial seawater. Accumulation of Zn and Cu by crabs has been interpreted in terms of the presence of a regulation mechanism to maintain constant body concentrations (83·2 ± 19·4 μg Zn g?1 dry wt.; 39·8 ± 9·8 μg Cu g?1 dry wt.) under varying external dissolved metal levels, until a threshold dissolved metal concentration (c. 400 μg Zn l?1; c. 170 μg Cu l?1) beyond which net accumulation of metal begins. Cadium appears to be accumulated by C. maenas at all exposures with no evidence for regulation of body cadmium concentrations. Exposure of E. modestus to Zn, Cu or Cd caused net accumulation of the respective metal in the bodies of the barnacles, with no evidence for regulation of body metal concentrations. 相似文献