全文获取类型
收费全文 | 86016篇 |
免费 | 1197篇 |
国内免费 | 1354篇 |
专业分类
测绘学 | 2993篇 |
大气科学 | 6358篇 |
地球物理 | 16904篇 |
地质学 | 33781篇 |
海洋学 | 6415篇 |
天文学 | 15441篇 |
综合类 | 2276篇 |
自然地理 | 4399篇 |
出版年
2021年 | 401篇 |
2020年 | 465篇 |
2019年 | 556篇 |
2018年 | 7328篇 |
2017年 | 6544篇 |
2016年 | 4753篇 |
2015年 | 1094篇 |
2014年 | 1376篇 |
2013年 | 2455篇 |
2012年 | 3021篇 |
2011年 | 6026篇 |
2010年 | 5295篇 |
2009年 | 6097篇 |
2008年 | 5107篇 |
2007年 | 5929篇 |
2006年 | 2062篇 |
2005年 | 2106篇 |
2004年 | 2189篇 |
2003年 | 2105篇 |
2002年 | 1857篇 |
2001年 | 1295篇 |
2000年 | 1246篇 |
1999年 | 1035篇 |
1998年 | 1028篇 |
1997年 | 979篇 |
1996年 | 815篇 |
1995年 | 768篇 |
1994年 | 735篇 |
1993年 | 641篇 |
1992年 | 575篇 |
1991年 | 576篇 |
1990年 | 560篇 |
1989年 | 562篇 |
1988年 | 510篇 |
1987年 | 617篇 |
1986年 | 549篇 |
1985年 | 691篇 |
1984年 | 827篇 |
1983年 | 705篇 |
1982年 | 671篇 |
1981年 | 645篇 |
1980年 | 560篇 |
1979年 | 552篇 |
1978年 | 558篇 |
1977年 | 480篇 |
1976年 | 436篇 |
1975年 | 434篇 |
1974年 | 388篇 |
1973年 | 439篇 |
1972年 | 296篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
The analysis is performed on the basis of comparison of the hydrological characteristics of prestrait regions of the Sea of
Marmara. It is shown that, in summer, the Black-Sea waters are weakly mixed with the Mediterranean waters and the levels of
salinity in the prestrait regions differ by 0.6–0.9‰. In winter, the indicated difference increases and the level of salinity
near the entrance of Dardanelles reaches 29‰ and exceeds the level observed near the entrance of Bosporus by 5.5‰. In the
analyzed regions, we observe local temperature maxima and minima near the interface of two water masses. This is explained
by the presence of strong seasonal variations of temperature for the Black-Sea waters and their absence for the Mediterranean
waters. The physical mechanisms responsible for the seasonal variations of the intensity of transformations of the Black-Sea
waters are discussed.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 49–55, March–April, 2007. 相似文献
972.
The sandy quartzose parts of the Utsira Formation, the Middle Miocene to mid Pliocene Utsira Sand, extends north–south along the Viking Graben near the UK/Norwegian median line for more than 450 km and 75–130 km east–west. The Utsira Sand is located in basin-restricted seismic depocentres, east of and below prograding sandy units from the Shetland Platform area with Hutton Sands. The Utsira Sand reaches thicknesses up to ca. 300 m in the southern depocentre and 200 m in the two northern depocentres with sedimentation rates up to 2–4 cm/ka. Succeeding Plio–Pleistocene is divided into seismic units, including Base Upper Pliocene, Shale Drape, Prograding Complex and Pleistocene. The units mainly consist of clay, but locally minor sands occur, especially at toes of prograding clinoforms (bottom-set sands) and in the Pleistocene parts, and the total thickness covering the Utsira Sand is in most places more than 800 m, but thins towards the margins. 相似文献
973.
Pautet L. Tesei A. Guerrini P. Pouliquen E. 《Oceanic Engineering, IEEE Journal of》2005,30(4):912-920
Iterative Time Reversal (TR) procedures have been demonstrated to be successful in detecting scatterers even in a highly reverberant environment. The success of the method is attributable to a Time Reversal Mirror (TRM) consisting of an array of transceivers that allows one to reconstruct and reverse-propagate wavefronts of interest. This paper deals with the limiting case of a TRM reduced to a single transceiver, tested using a tank experiment with three scattering objects in free-field conditions. It is shown that it is possible to excite a resonance between the TR operator and the strongest mode of the target in the bandwidth of insonification. A simple free-field scattering model is used to study the mechanisms of convergence and to drive the physics-based analysis of data. 相似文献
974.
975.
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
976.
977.
Evaluating climate model simulations of tropical cloud 总被引:1,自引:0,他引:1
978.
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
979.
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
980.
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