全文获取类型
收费全文 | 69877篇 |
免费 | 463篇 |
国内免费 | 1134篇 |
专业分类
测绘学 | 2358篇 |
大气科学 | 4307篇 |
地球物理 | 12859篇 |
地质学 | 29984篇 |
海洋学 | 5102篇 |
天文学 | 12141篇 |
综合类 | 2261篇 |
自然地理 | 2462篇 |
出版年
2022年 | 488篇 |
2021年 | 709篇 |
2020年 | 757篇 |
2019年 | 828篇 |
2018年 | 7446篇 |
2017年 | 6501篇 |
2016年 | 4770篇 |
2015年 | 882篇 |
2014年 | 1506篇 |
2013年 | 2062篇 |
2012年 | 2968篇 |
2011年 | 5598篇 |
2010年 | 4746篇 |
2009年 | 5245篇 |
2008年 | 4399篇 |
2007年 | 5370篇 |
2006年 | 1828篇 |
2005年 | 1307篇 |
2004年 | 1397篇 |
2003年 | 1419篇 |
2002年 | 1143篇 |
2001年 | 827篇 |
2000年 | 713篇 |
1999年 | 430篇 |
1998年 | 458篇 |
1997年 | 474篇 |
1996年 | 337篇 |
1995年 | 358篇 |
1994年 | 335篇 |
1993年 | 281篇 |
1992年 | 284篇 |
1991年 | 290篇 |
1990年 | 337篇 |
1989年 | 272篇 |
1988年 | 258篇 |
1987年 | 260篇 |
1986年 | 191篇 |
1985年 | 302篇 |
1984年 | 302篇 |
1983年 | 295篇 |
1982年 | 274篇 |
1981年 | 269篇 |
1980年 | 287篇 |
1979年 | 203篇 |
1978年 | 242篇 |
1977年 | 204篇 |
1976年 | 183篇 |
1975年 | 184篇 |
1974年 | 171篇 |
1973年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
251.
By using the NCEP/NCAR reanalysis data sets for 1951–2001, we study the characteristics of Pacific cyclones. It is shown that the northeast-southwest
direction is predominant in the displacements of cyclones in the North Pacific. We study the variability of the field of surface
atmospheric pressure in different phases of the Pacific decadal oscillation characterizing the temperature anomalies on the
surface of the ocean in the region bounded by 20 and 60°N. It is shown that the decadal variations of the North Atlantic Oscillation
supported by the large-scale anomalies of the Pacific decadal oscillation is the most important cause of natural decadal oscillations
in the European region. We study and evaluate the regional response to the Pacific decadal oscillation by using, as an example,
the analysis of variations of the discharge of European rivers.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 13–23, July–August, 2007. 相似文献
252.
Calcareous nannoplankton from sediment trap samples collected at six sites in the Atlantic Ocean from 23° S to 73° N (cruise 20 of R/V Vityaz’ and cruise 33 and 34 of R/V Akademik Mstislav Keldysh). Those samples were studied with a scanning electron microscope. In the coastal and open-sea regions of the North and South Atlantic and in the subarctic region of the Norwegian Sea, the conditions are significantly different. In the shelf area of the Benguela upwelling, 11 species were recognized; some of them were agglutinated by diatoms and tintinnides or covered the surface of pellets. The Broken Spur and TAG pelagic areas of the North Atlantic contained up to 43 coccolith species. They included holococcoliths, large pelagic, and delicate easily soluble species distributed over the entire water column. The presence of coccoliths in the high-latitude area of the Norwegian Sea is related to their supply with the warmer North Atlantic waters. These assemblages are distinguished by a low species diversity and an enhancement of the coccolith solubility with the depth increase. 相似文献
253.
We present a numerical model of the dynamics of Lake Donuzlav, which enables one to perform simultaneous numerical analyses
of the currents, sea level, waves, and sediment transport. The model is based on the hydrodynamic block and the spectral wave
model. For typical storm situations, we study the specific features of the integral circulation of waters and the three-dimensional
structure of currents, investigate the wind-induced wave fields, and evaluate the flows of sediments and deformations of the
bottom. The presence of intense eddy structures is revealed in the field of currents caused by the bottom topography. A significant
intensification of waves in the south part of the lake is established in the case of penetration of storm waves through the
strait. It is shown that the account of waves leads to qualitative changes in the structure of circulation in the lake and
to the formation of well-pronounced areas of wave-induced elevations and lowerings of the sea level.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 43–65, March–April, 2006. 相似文献
254.
255.
Lysosomal sequestration of polynuclear aromatic hydrocarbons (PNAHs), a major class of environmental contaminant, is a well-established phenomenon;1 considerably less is known about their pathological effects on lysosomes. Marine molluscs contain a number of lysosome-rich tissues and PNAHs are known to induce deleterious alterations in lysosomal structure and latency of lysosomal enzymes.2 The latter are presumed to involve destabilisation of the lysosomal membrane, resulting in increased permeability and reduced enzyme latency. If lysosomal injury involves derangement of membrane-lipid structure due to the interaction of PNAHs then it would be expected that membrane damage would be closely linked to the structural characteristics of the intruding molecule. Our results show that the effects of the isomeric PNAHs phenanthrene and anthracene on digestive cell lysosomal stability were markedly different in the marine mussel (Mytilus edulis) over the same range of tissue concentrations. Lysosomal membrane stability was determined using a cytochemical test for enzyme latency.3 相似文献
256.
The bacterial populations of mangrove swamps of Killai backwaters (11°21–11°29N, 79°46–79°50E, South India) were studied during August 1968 (Pre monsoon period) and December (post monsoon period). The presence of these groups such as agar digesters, algin digesters, cellulose digesters, sulphate reducers etc., bring about transformation of organic matter in the mangrove swamps. The presence of denitrifiers in mangrove swamps and in association with the molluscs may bring about the precipitation of calcium carbonate by removing the acid radicals such as sulphate and nitrite, increasing alkalinity. The luminiscent bacteria such asVibrio andAeromonas were also isolated in mangrove swamps of Killai backwaters. The iron bacteria likeLeptothrix sp. andGallionella sp. were also isolated from mangrove swamps of Killai backwaters. 相似文献
257.
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
258.
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
259.
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
260.
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