全文获取类型
收费全文 | 79491篇 |
免费 | 894篇 |
国内免费 | 1235篇 |
专业分类
测绘学 | 2591篇 |
大气科学 | 5778篇 |
地球物理 | 14893篇 |
地质学 | 32074篇 |
海洋学 | 6026篇 |
天文学 | 14047篇 |
综合类 | 2229篇 |
自然地理 | 3982篇 |
出版年
2021年 | 404篇 |
2020年 | 407篇 |
2019年 | 458篇 |
2018年 | 7226篇 |
2017年 | 6464篇 |
2016年 | 4525篇 |
2015年 | 885篇 |
2014年 | 1086篇 |
2013年 | 2101篇 |
2012年 | 2761篇 |
2011年 | 5860篇 |
2010年 | 5177篇 |
2009年 | 5854篇 |
2008年 | 4775篇 |
2007年 | 5764篇 |
2006年 | 1683篇 |
2005年 | 1945篇 |
2004年 | 1941篇 |
2003年 | 1970篇 |
2002年 | 1614篇 |
2001年 | 1121篇 |
2000年 | 1064篇 |
1999年 | 826篇 |
1998年 | 839篇 |
1997年 | 836篇 |
1996年 | 674篇 |
1995年 | 661篇 |
1994年 | 621篇 |
1993年 | 574篇 |
1992年 | 530篇 |
1991年 | 500篇 |
1990年 | 512篇 |
1989年 | 500篇 |
1988年 | 480篇 |
1987年 | 560篇 |
1986年 | 495篇 |
1985年 | 616篇 |
1984年 | 656篇 |
1983年 | 598篇 |
1982年 | 533篇 |
1981年 | 603篇 |
1980年 | 498篇 |
1979年 | 461篇 |
1978年 | 438篇 |
1977年 | 440篇 |
1976年 | 392篇 |
1975年 | 384篇 |
1974年 | 377篇 |
1973年 | 390篇 |
1971年 | 225篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Hance D Smith 《Marine Policy》1995,19(6)
The environmental management of shipping requires systematic consideration of the geography of shipping routes, ship types and cargoes, and environments which can form the basis of a classificatory approach to Environmental Impact Assessment (EIA). Beyond this, effective environmental management depends in the first instance upon sound information management including monitoring of the environment, surveillance of shipping and information technology, followed by information assessment including, in particular, risk and environmental impact. The general management dimension includes co-ordination of technical management and organisational aspects related to shipping. It is suggested that effective environmental management of shipping may depend upon a regionalisation of the marine environment for EIA purposes akin to that found in the loadline rules, together with rationalisation of the increasing number of special areas in existence or proposed for this purpose. EIA will have to become an integral part of the overall management system in the shipping industry. 相似文献
902.
CTD data provided by the MGI-4204 and MARK-III probes are used to study the quasistationary subpolar front structure in the north-western Sea of Japan. In order to provide further insights into the intermittent scalar hydrophysical fields, the method of inhomogeneity identification using temperature pulsations calculated by the moving interval is suggested. The experimentally-derived inhomogeneity distribution is satisfactorily approximated by the exponential law.Translated by V. Puchkin. 相似文献
903.
An elongated sea bed depression (pit), 80 by 125 m and 10 m deep located on the Grand Banks of Newfoundland was identified on high resolution surficial geophysical survey lines and investigated using a manned submersible. The pit occurs at the termination of a long (greater than 3 km) iceberg scour, 1.5 m deep, and 80 m wide in 91 m of water. It is similar to other depressions in the region that indent the sea bed up to seven times deeper than the surrounding deepest iceberg furrows. The pit is interpreted to be the sea bed response to impact and loading by a rolling and grounding iceberg. The iceberg scour and pit appear to be of recent origin. 相似文献
904.
Reproductive variability in North Sea plaice, sole, and cod 总被引:4,自引:1,他引:4
Rijnsdorp A. D.; Daan N.; van Beek F. A.; Heessen H. J. L. 《ICES Journal of Marine Science》1991,47(3):352-375
905.
Sublethal effects of cadmium on reproduction can have detrimental consequences for the long-term survival, even of species with high LC50 values. The sea mussel, Mytilus edulis, is well-known for its use in biomonitoring work due to its relatively low sensitivity towards many toxicants, including cadmium.1 Because little is known on sublethal effects of this metal in invertebrates,2–6 we have studied these effects, with emphasis on reproduction, by exposing mussels to 100 ppb cadmium in sea water. This concentration significantly inhibits follicle development in both male and female gonads, but has subsequently a stimulating effect on the spawning frequency. Due to these opposite effects the consequences of cadmium stress for gamete production are expected to be small, as the average number of gametes released by spawning animals was not significantly changed. 相似文献
906.
John D. Wang 《Ocean Engineering》1987,14(3)
A 3-dimensional model methodology for predicting the upper ocean currents under the combined influence of Gulf Stream and hurricane is described. Predicted currents are highly dependent on the turbulence closure scheme and nonlinear interactions. New field data will be required to determine the appropriate formulation for turbulent momentum transfer. However, the model points out the importance of nonlinear terms in the equations of motions for preserving the jet-like structure of the Gulf Stream and for properly accounting for interaction between the Gulf Stream and a hurricane. A potentially worst case condition is obtained for the so-called resonant hurricane. 相似文献
907.
Sediment supply and pre-existing shoreline morphology are crucial factors in controlling coastal changes due to sea-level rise. Using examples from both southeast and northeast Ireland, it can be shown that sea-level change may trigger a sequence of events which leads to both static and dynamic shoreline equilibrium. Cliff erosion and longshore sediment movement in east Co. Wexford has led to injection of sediment onto the shelf, and the growth, under both wave and tide regimes, of linear offshore shoals. These shoals now control the pattern of shoreline erosion and provide a template for possible stepwise evolution of the coast under any future sea-level rise. In contrast, the nearby coast of south Co. Wexford comprises a series of coarse clastic barriers moving monotonously onshore, via overwash processes. Here the behavior of the barrier is conditioned by the antecedent morphology of both the beach face and stream outlet bedforms. Finally, the rock platform coast of Co. Antrim presents a far more resistant shoreline to incident marine processes, yet even here there is strong evidence of present process control over so-called ‘raised’ platforms and embayments. It is concluded that coastal sediment supply and dynamics, together with coastal morphology and its interaction with waves, present a far more complex variety of sea-level indicators than is normally acknowledged. 相似文献
908.
Accumulation of copper was studied between June 1979 and June 1980 in the oyster Ostrea edulis Linnaeus, cultivated in the Limski Kanal, on the Istria Peninsula (Yugoslavia).The copper distribution in different organs of oysters of the same age was compared with concentrations of copper existing in different physicochemical forms in ambient sea water, i.e., dissolved Cu in labile complexes determined at the natural pH of 8; ‘total’ dissolved Cu determined after acidification to pH 2; and Cu bound to suspended particles with a diameter above 0.45 μm. Copper concentrations in the water were determined by differential pulse anodic stripping voltammetry (DPASV) and in analyses of biotic material, graphite furnace atomic absorption spectrometry (GFAAS) was applied.Significant correlations have been found between copper complexed with dissolved organic ligands and its concentration in the soft part of the oyster. Copper contents increase gradually with the weight of the organs until enhanced gametogenetic activity of the oysters occurs. Thereafter the correlation factor between copper contents and the size of body parts varied significantly with the season. 相似文献
909.
The gadoid outburst in the North Sea 总被引:3,自引:3,他引:3
910.
D. Tolmazin 《Progress in Oceanography》1985,15(4):277-316
This article describes the hydrography of the Northwestern Shelf (NWS), of the Black Sea emphasizing the changes induced by water management in the Dniejer and Dniester river basins. The existing literature and previously unpublished data have been reviewed and synthesized to describe water property fields and transport mechanisms of the NWS and the Dnieper and Dniester estuaries before the early 1960s, or the so-called precontrol period, when the effect of artificial river flow control upon the coastal waters was insignificant.After the hydroenergy complexes and water withdrawal and disposal systems on rivers became fully operational in the early 1970s (the so-called postcontrol period), the annual river discharge from the Dnieper and Dniester had noticeably decreased and seasonal river flow patterns had been artificially modified. Instead of a powerful and short early spring flood, typical for the natural conditions in the Dnieper river, the hydrographs in the postcontrol period exhibit two smaller peaks of river discharge of much longer period. One of them (winter-early spring) is caused by intense hydroenergy generation and weir discharges through the cascade of storage reservoirs. Another is associated with spring flood, modified by intense water consumption and storage in this period. High average river discharge in late May—early June strengthened the summer pycnocline which inhibits vertical mixing in the estuaries and coastal waters. Owing to a slow summer circulation, the rate of natural purification of the entire coastal system has been reduced. This coupled with the increased nutrient, organic and pollutant transport, decreased the dissolved-oxygen concentration and led to anoxic events and mass mortalities of marine organisms in the previously productive regions. These effects have primarily plagued the benthic communities along the entire western coast of the NWS since 1973.Winter convective overturn in the Black Sea reaches its maximum depth at the southern boundary of the NWS. Thus, the NWS waters descend beneath the seasonal and main thermoclines in the open sea and are spread by the prevailing currents across the entire sea in the cold intermediate layer (CIL). By this dynamic mechanism the projected man-made modifications in the riverine-estuarine systems of the NWS will affect and change the large-scale thermohaline structure and marine life of the Black Sea. 相似文献