全文获取类型
收费全文 | 58264篇 |
免费 | 699篇 |
国内免费 | 508篇 |
专业分类
测绘学 | 1375篇 |
大气科学 | 3298篇 |
地球物理 | 11214篇 |
地质学 | 21621篇 |
海洋学 | 5442篇 |
天文学 | 14083篇 |
综合类 | 139篇 |
自然地理 | 2299篇 |
出版年
2022年 | 536篇 |
2021年 | 834篇 |
2020年 | 896篇 |
2019年 | 1021篇 |
2018年 | 2099篇 |
2017年 | 1944篇 |
2016年 | 2171篇 |
2015年 | 967篇 |
2014年 | 1924篇 |
2013年 | 3109篇 |
2012年 | 2216篇 |
2011年 | 2717篇 |
2010年 | 2541篇 |
2009年 | 3013篇 |
2008年 | 2670篇 |
2007年 | 2859篇 |
2006年 | 2639篇 |
2005年 | 1628篇 |
2004年 | 1554篇 |
2003年 | 1478篇 |
2002年 | 1380篇 |
2001年 | 1294篇 |
2000年 | 1198篇 |
1999年 | 929篇 |
1998年 | 925篇 |
1997年 | 944篇 |
1996年 | 704篇 |
1995年 | 723篇 |
1994年 | 712篇 |
1993年 | 577篇 |
1992年 | 572篇 |
1991年 | 526篇 |
1990年 | 616篇 |
1989年 | 518篇 |
1988年 | 490篇 |
1987年 | 514篇 |
1986年 | 413篇 |
1985年 | 596篇 |
1984年 | 619篇 |
1983年 | 598篇 |
1982年 | 564篇 |
1981年 | 486篇 |
1980年 | 508篇 |
1979年 | 406篇 |
1978年 | 433篇 |
1977年 | 398篇 |
1976年 | 343篇 |
1975年 | 358篇 |
1974年 | 338篇 |
1973年 | 359篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
511.
Mindhola River estuary, which receives industrial waste containing high concentrations of fluoride, and Purna River estuary, which is free from fluoride contamination, have been investigated. While fluoride behaved conservatively in Purna River estuary, significant deviation from the theoretical dilution line (TDL) in the chlorinity range 0·5–8‰ was observed in Mindhola River estuary due to the externally added fluoride which largely remained in solution. The excess of fluroide over the theoretically calculated value was at a maximum around a chlorinity of 3‰. High natural fluoride content of the river waters resulted in F/Cl ratios exceeding 300 × 10−5 at low chlorinities. The ratio decreased rapidly with increasing chlorinity and the value near to that of seawater was observed at chlorinities above 14‰. 相似文献
512.
513.
A new algorithm for calculating the vertical velocity is suggested. Horizontal current velocity components are expressed through
level inclination and wind/temperature forcing. The acquired relations are given in the difference form, with the accuracy
being sufficiently high. The algorithm is tested using cases where a numerical solution is matched up with an exact one. The
derived data are subsequently analysed.
Translated by Vladimir A. Puchkin. 相似文献
514.
515.
On low-pass digital filters in oceanography 总被引:1,自引:0,他引:1
-Two types of filters are widely used to remove semidirunal and diurnal tidal signals and other high frequency noises in oceanography. The first type of filters uses moving average with weights in time domain, and can be easily operated. Some data will be lost at each end of the time series, especially for the low low-pass filters. The second type of filters uses the discrete Fourier transform filter (DFTF) which operates in the frequency domain, and there are no data loss at the ends for the forward transform. However, owing to the Gibbs phenomenon and the discrete sampling (Nyquist effect) , ringing appears in the inverse transformed data, which is especially serious at each end. Thus some data at the ends are also discarded. The present study tries to find out what causes the ringing and then to seek for methods to overcome the ringing. We have found that there are two kinds of ringings, one is the Gibbs phenomenon, as defined before. The other is the "Nyquist"ringing due to sampling Nyquist critical 相似文献
516.
The radioelement and heavy mineral distribution in river, beach and innershelf areas of the southern Kerala coast is related
to placer mineral concentration on the beaches at Chavara. Southern Kerala rivers—Neyyar, Karamana and Vamanapuram—transport
higher amounts of radioactive elements than the larger Kallada River due to higher radioactive minerals in the hinterland
rocks. Coastal configurations and the seasonal longshore current pattern seems to control along-shore distribution of minerals.
The proposed model for placer concentration suggests that the energy difference and seasonal current direction along this
coast is important. 相似文献
517.
At first-order of approximation a sea-state may be considered as an infinite sum of Airy components with angular frequencies ωi and wave-number vectors ki. A second-order analysis shows the co-existence of long waves appearing at the difference frequencies ωi—ωj with wave-number vectors ki—kj. In shallow water they become appreciable in amplitudes and may induce slow-drift motion of moored structures.For small values of ωi—ωj,ki—kj may take all kinds of directions for an angular-spread wave system. Then it may be questioned how the in-line and transverse second-order accelerations compare to those obtained for a mono-directional wave-system.This analysis is carried out here by relating the spectra of the second-order horizontal accelerations to the directional wave-spectrum. Numerical applications are first performed for deep water. They show that at low frequencies, even for very narrowly spread wave systems, the transverse component is larger than the in-line component. In shallow water both components are dratically reduced as compared to the mono-directional case. As a consequence one may question the validity of model-testings or numerical models which take no account of the directionality of the wave-system. 相似文献
518.
The influence of inhomogeneities of surface currents on the intensity of breaking wind waves is considered and a model for the relation between whitecap contrasts and the tensor of current gradients is developed. The imagery of typical patterns of ocean currents is discussed. The results of field observations supporting this model are given.Translated by Mikhail M. Trufanov. 相似文献
519.
Dorrik A. V. Stow James R. Cochran ODP Leg Shipboard Scientific Party 《Geo-Marine Letters》1989,9(1):1-10
Three deep holes, with a maximum penetration of 960 m below sea floor, were drilled into the distal Bengal Fan just south of the equator during ODP Leg 116. The entire section recovered is dominated by sandy silt and mud turbidites derived from the Ganges Delta and from the continental margin of the western Bay of Bengal, interbedded with thin pelagic clays and with biogenic turbidites probably from a local sea mount source. The effects of Hi-Malayan uplift, sea level fluctuations, local tectonics, and fan channel/lobe processes have closely interacted to produce the observed sedimentary record of the past 17 million years since the early Miocene.Coauthors include: James R. Cochran, Lamont-Doherty Geological Observatory (Co-chief scientist); Dorrik A. V. Stow, Nottingham University, England (Co-chief scientist); Christian A. Auroux, Texas A & M University, USA (ODP staff scientist); Kazou Amano, Ibaraki University, Japan; Peter S. Balson, British Geological Survey, Keyworth, Notts, England; Jacques Boulegue, Pierre & Marie Curie University, Paris, France; Garrett W. Brass, University of Miami, Florida, USA; Jeffrey Corrigan, University of Texas, Austin, USA; Stefan Gartner, Texas A & M University, USA; Stuart A. Hall, University of Houston, Texas, USA; Silvia Iaccarino, University of Parma, Italy; Toshio Ishizuka, University of Tokyo, Japan; trena Kacmarska, Mount Allison University, New Brunswick, Canada; Heidemarie Kassens, Kiel University, West Germany; Gregory Leger, Dalhousie University, Halifax, Nova Scotia, Canada; Franca Proto Decima, University of Padova, Italy; C. V. Raman, Andhra University, Visakhapatnam, India; William W. Sager, Texas A & M University, USA; Kozo Takahashi, Woods Hole Oceanographic Institution, USA; Thomas Thompson, 580 Euclid Ave, Boulder, Colo, USA; Jean-Jacques Tiercelin, University of Bretagne, Brest, France; Mark Townsend, University of Nottingham, England; Andreas Wetzel, Tubingen University, West Germany; N. P. Wijayananda, National Aquatatic Resource Agency, Colombo, Sri Lanka; and Colin Williams, Lamont-Doherty Geological Observatory. 相似文献
520.
V. Sundar 《Ocean Engineering》1989,16(2)
Ocean waves and forces induced by them on offshore structures are random in nature. Experience has shown that short term statistics of wave heights can be described by the Rayleigh distribution for narrow band spectra (Longuet-Higgins, 1952) and that the long term statistics or the evaluation of design wave is based on certain well known extreme value distribution such as mixed Frechet distribution (Thom, 1973a, b).This paper presents a new application of the double bounded probability density function to describe the ocean wave statistics. The prime importance is to estimate the most probable maximum wave height for offshore structural designs. 相似文献