全文获取类型
收费全文 | 71413篇 |
免费 | 1429篇 |
国内免费 | 663篇 |
专业分类
测绘学 | 1728篇 |
大气科学 | 5061篇 |
地球物理 | 14322篇 |
地质学 | 25423篇 |
海洋学 | 6204篇 |
天文学 | 16370篇 |
综合类 | 208篇 |
自然地理 | 4189篇 |
出版年
2022年 | 398篇 |
2021年 | 707篇 |
2020年 | 791篇 |
2019年 | 831篇 |
2018年 | 1905篇 |
2017年 | 1779篇 |
2016年 | 2258篇 |
2015年 | 1332篇 |
2014年 | 2192篇 |
2013年 | 3803篇 |
2012年 | 2306篇 |
2011年 | 3143篇 |
2010年 | 2631篇 |
2009年 | 3543篇 |
2008年 | 3278篇 |
2007年 | 3073篇 |
2006年 | 2897篇 |
2005年 | 2374篇 |
2004年 | 2278篇 |
2003年 | 2128篇 |
2002年 | 1941篇 |
2001年 | 1809篇 |
2000年 | 1721篇 |
1999年 | 1382篇 |
1998年 | 1476篇 |
1997年 | 1393篇 |
1996年 | 1102篇 |
1995年 | 1147篇 |
1994年 | 963篇 |
1993年 | 874篇 |
1992年 | 858篇 |
1991年 | 764篇 |
1990年 | 856篇 |
1989年 | 720篇 |
1988年 | 653篇 |
1987年 | 817篇 |
1986年 | 663篇 |
1985年 | 856篇 |
1984年 | 923篇 |
1983年 | 863篇 |
1982年 | 831篇 |
1981年 | 708篇 |
1980年 | 665篇 |
1979年 | 606篇 |
1978年 | 603篇 |
1977年 | 553篇 |
1976年 | 541篇 |
1975年 | 499篇 |
1974年 | 507篇 |
1973年 | 468篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Surface circulation of the Levantine Basin: Comparison of model results with observations 总被引:1,自引:1,他引:1
The eastern Mediterranean (Levantine Basin) hydrography and circulation are investigated by comparing the results of a high-resolution primitive equation model with observations. After a 10-year integration, the model is able to reproduce the major water masses and the circulation patterns of the eastern Mediterranean. Comparisons with the POEM hydrographical observations show good agreement. The vertical distribution of the water masses matches that of the observations quite well in terms of monthly mean. The model surface circulation is in agreement with circulation schemes derived from recent observations. Some well-known mesoscale features of the upper thermocline circulation are also realistically reproduced. In agreement with satellite observations, the model shows that high-energy mesoscale eddies dominate the upper thermocline circulation in the southern and the central parts of the Levantine Basin. Most of the Atlantic Water follows the north African coast and forms a strong coastal jet near the Libyan coast rather than forming the Mid-Mediterranean Jet described by several authors. The sub-basin circulation shows a strong seasonal signal. A strong and stable current flows along the isobaths in winter, becoming weaker and with more meanders in summer. The mesoscale eddies throughout the whole basin are more energetic in summer than in winter. 相似文献
992.
We propose a method for the construction of dynamic-stochastic models of natural systems based on the assimilation of the data of observations in the prognostic equations of coupled processes. In these models, the method of adaptive balance of causes is used to deduce evolutionary equations of the analyzed processes and assimilate the data of observations in these equations. The deduced general equations are considered for an example of a marine ecosystem characterized by the development of four coupled processes. It is shown that the optimal prediction of these processes requires the solution of 11 systems of equations with simultaneous adaptation of prognostic estimates and the coefficients of the models to the data of observations. A numerical simulation experiment explaining the algorithm of the proposed method of modeling is considered. A conclusion is made that the application of this method in the geoinformation systems of monitoring of the environment is quite promising.__________Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 31–42, November–December, 2004. 相似文献
993.
A numerical model to compute wave field is developed. It is based on the Berkhoff diffraction-refraction equation, in which an energy dissipation term is added, to take into account the breaking and the bottom friction phenomena. The energy dissipation function, by breaking and by bottom friction, is introduced in the Berkhoff equation to obtain a new equation of propagation.The resolution is done with the hybrid finite element method, where lagrangians elements are used. 相似文献
994.
Ana P. Mucha M. Teresa S. D. Vasconcelos Adriano A. Bordalo 《Estuarine, Coastal and Shelf Science》2004,59(4):663
Vertical distribution (0–15 cm) of the macrobenthic community and its relationships to natural sediment characteristics and trace metal contents and bioavailability were studied at five locations in the lower Douro estuary, Portugal. An analysis of vertical metal distribution, for the interpretation of anthropogenic impact on the estuarine sediments, was also investigated. Sediment characterisation included organic matter, grain size, metals (Al, Fe, Cu, Pb, Cr, Ni, Cd, Zn and Mn), acid volatile sulphide (AVS) and simultaneously extracted metals (SEM). The macrobenthic community had low diversity (14 species), was dominated by small size opportunists and seemed to be controlled mainly by natural factors such as grain size distribution, Al and Fe contents and sediment depth. The vertically heterogeneous distribution of macrobenthic community appears to affect redox status of the sediments and consequently metal bioavailability. Despite anthropogenic contamination in terms of Zn, Cu, Pb, Cr and Ni having already been detected in the north bank, the analysis of vertical distribution was essential for the identification of current anthropogenic contamination in terms of Zn, Pb and Cd in the south bank. 相似文献
995.
N. D. Tsvetkova V. A. Yushkov A. N. Luk’yanov V. M. Dorokhov H. Nakane 《Izvestiya Atmospheric and Oceanic Physics》2007,43(5):592-598
The extremely cold winter of 2004/2005 was accompanied by an intensive formation of polar stratospheric clouds and a significant chemical destruction of ozone. The results of calculating chemical losses of ozone in the polar cyclone from the SAGE-III satellite data are given. Over the period January 1–March 25, 2005, at the isentropic levels 450–500 K, about 60% of ozone was destroyed. During that winter, the zone of formation of polar stratospheric clouds went down to levels with very low values of potential temperature (down to 350 K), thus resulting in a noticeable destruction of ozone at low altitudes. By March 25, 2005, the chemical losses of total ozone attained 116 ± 10 DU (128 ± 10 DU at the cyclone boundary), which is a recordbreaking value of the Arctic. 相似文献
996.
V. V. Efimov M. V. Shokurov D. A. Yarovaya 《Izvestiya Atmospheric and Oceanic Physics》2007,43(6):667-686
The paper describes results of numerical experiments on the simulation of a mesoscale quasi-tropical cyclone, a rare event for the Black Sea, with the MM5 regional atmospheric circulation model. General characteristics of the cyclone and its evolution and physical formation mechanisms are discussed. The balances of the momentum components have been estimated, and sensitivity experiments have been performed. It is shown that, according to its main physical properties and energy supply mechanisms, the cyclone can be related to quasi-tropical cyclones. 相似文献
997.
998.
Regional variation in maturation of sandeels in the North Sea 总被引:1,自引:0,他引:1
999.
1000.
Joana F.M.F. Cardoso Denis Langlet Jos F. Loff Ana R. Martins Johannes IJ. Witte Paulo T. Santos Henk W. van der Veer 《Journal of Sea Research》2007,57(4):303-315
The Pacific oyster Crassostrea gigas was introduced in Europe for commercial purposes in the mid 1960s. It was initially thought that low winter temperatures would restrain this species' reproduction and settlement; however, its present distribution in areas where no introduction has taken place suggests that natural invasion and expansion has occurred. Along the European coast, wild populations of Pacific oysters are already found from northern Germany to southern Portugal. Whether C. gigas will continue to further expand through northern waters will depend on its physiological performance. In this study, the performance of wild oyster populations has been studied in terms of growth and reproduction at three stations: La Rochelle (France; 46°N), Yerseke (Oosterschelde estuary, The Netherlands, 51°N), and Texel (Wadden Sea estuary, The Netherlands, 53°N). The French population had the lowest somatic-shell mass ratio and an increase in maximum shell length, somatic and gonadal mass was observed from France to the Netherlands. In addition, mean oocyte diameter decreased significantly from south to north. The combination of increasing gonadal mass and decreasing oocyte volume suggests an increasing reproductive output in terms of egg numbers from France to The Netherlands. Differences in temperature between locations will at least be partly responsible for the observed patterns; however, other environmental factors (such as food availability, predation pressure, sediment type and/or seston concentration) cannot be excluded. Since smaller eggs (oocytes) are thought to have a longer development time, the environmental conditions along the Dutch coast may result in increased larval dispersal and possibly in further population expansion. 相似文献