全文获取类型
收费全文 | 45157篇 |
免费 | 575篇 |
国内免费 | 354篇 |
专业分类
测绘学 | 1182篇 |
大气科学 | 2994篇 |
地球物理 | 9009篇 |
地质学 | 15748篇 |
海洋学 | 3848篇 |
天文学 | 11004篇 |
综合类 | 111篇 |
自然地理 | 2190篇 |
出版年
2021年 | 427篇 |
2020年 | 468篇 |
2019年 | 468篇 |
2018年 | 1077篇 |
2017年 | 995篇 |
2016年 | 1222篇 |
2015年 | 674篇 |
2014年 | 1176篇 |
2013年 | 2262篇 |
2012年 | 1323篇 |
2011年 | 1772篇 |
2010年 | 1570篇 |
2009年 | 2216篇 |
2008年 | 1831篇 |
2007年 | 1837篇 |
2006年 | 1725篇 |
2005年 | 1287篇 |
2004年 | 1283篇 |
2003年 | 1196篇 |
2002年 | 1156篇 |
2001年 | 1042篇 |
2000年 | 985篇 |
1999年 | 863篇 |
1998年 | 875篇 |
1997年 | 843篇 |
1996年 | 713篇 |
1995年 | 716篇 |
1994年 | 640篇 |
1993年 | 554篇 |
1992年 | 515篇 |
1991年 | 525篇 |
1990年 | 603篇 |
1989年 | 513篇 |
1988年 | 476篇 |
1987年 | 604篇 |
1986年 | 502篇 |
1985年 | 634篇 |
1984年 | 715篇 |
1983年 | 678篇 |
1982年 | 591篇 |
1981年 | 622篇 |
1980年 | 518篇 |
1979年 | 492篇 |
1978年 | 489篇 |
1977年 | 442篇 |
1976年 | 430篇 |
1975年 | 431篇 |
1974年 | 409篇 |
1973年 | 449篇 |
1971年 | 276篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
701.
The illegal plundering of fishing stocks worldwide is masked behind a maze of corporate structures that makes discovery of the beneficiaries of such activity, difficult, if not impossible to identify. This paper outlines the problem of illegal fishing and then develops a multi-layered response to avert the veil of corporate entity being used as a means of preventing domestic States from answering the principal thematic question—who is the true beneficiary of this illegal behaviour, and who should be held responsible. 相似文献
702.
Assessment of a Sr isotope vital effect (87Sr/86Sr) in marine taxa from Lee Stocking Island, Bahamas
Data from Lee Stocking Island, Bahamas, confirms the hypothesis that there are no vital effects with the uptake of Sr isotopes
(87Sr/86Sr) at the present mass spectrometer resolution [±2×10-5 (2σ)]. Our data set contains analyses of 40 samples derived from 37 different calcareous taxa inhabiting a wide range of
carbonate subenvironments (i.e., reefal, intertidal, supratidal, mangrove). The mean value of our analyses was 0.709179 with
a standard deviation of 2.4×10-5 (2σ) which was very close to the long-term uncertainty of the strontium isotope methodology [±2.0×10-5 (2σ)] and to the widely reported 87Sr/86Sr value of seawater, which clusters around 0.709175.
Received: 14 October 1997 / Revision received: 20 March 1998 相似文献
703.
J. C. Balanyá J. Galindo-Zaldívar A. Jabaloy G. Leitchenkov A. Maldonado J. Rodríguez-Fernández O. Vinnikovskaya 《Geo-Marine Letters》1999,18(3):215-224
The structure of the South Powell Ridge (SPR), separating the Late Cenozoic ocean-floored Powell Basin and the Mesozoic Weddell
Sea domain, is revealed by multichannel seismic data. The SPR appears as a basement high, bounded northward by transtensional
faults and by normal and major reverse faults to the south. These margin features seem to be linked to the Powell Basin southern
strike-slip margin and to the Jane Arc paleotrench, respectively. We suggest the ridge evolved from the Antarctic Peninsula
passive margin to become the deformational front of the Scotia/Antarctica Plate boundary, later being welded to the Antarctic
Plate.
Received: 18 August 1997 / Revision received: 4 May 1998 相似文献
704.
Direct Measurements of Deep Currents in the Northern Japan Sea 总被引:5,自引:0,他引:5
Masaki Takematsu Zentaro Nagano Alexander G. Ostrovski Kuu Kim Yuri Volkov 《Journal of Oceanography》1999,55(2):207-216
Long-term current measurements by means of subsurface moorings were made for the first time at seven sites in the Japan Basin,
the northern part of the Japan Sea. The objective was to directly explore the velocity field in the highly homogeneous deep
water mass (the Japan Sea Proper Water) that occupies depths below 500 m. On each mooring three current meters were equipped
at an approximately equal distance below about 1000 m depth. Duration of the measurements was 1 to 3 years depending on specific
site. This paper describes the basic data set from the moored measurements. It is found that the deep water of the Japan Basin
is very energetic with eddies and vertically coherent currents of the order of 0.1 m/s. Surprisingly, the currents and eddies
exhibit strong seasonal dependence even in the deepest layers of the Basin. The observed new current features are discussed
in comparison with conventional deep circulation pictures derived from hydrographic data.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
705.
Santiago Hernández-León Lutz Postel Javier Arístegui May Gómez María Fernanda Montero Santiago Torres Carlos Almeida Eugen Kühner Ullrich Brenning Eberhard Hagen 《Journal of Oceanography》1999,55(4):471-482
Plankton biomass and indices of metabolism and growth [electron transport system (ETS), glutamate dehydrogenase (GDH) and aspartate transcarbamylase (ATC) activities] were studied over a 2,800 km east-west section of the tropical North Atlantic Ocean (21°N) in <200, 200–500 and >;500 µm size classes. On the large-scale, zooplankton (>;200 µm) enzymatic activities increased westward in the study section, where large cyanobacteria chains (Trichodesmium spp.) were observed. Parallel to it, an increase in medium calanoids (1–2 mm length) was observed towards the western part of the transect, whereas small calanoids (<1 mm) were dominant throughout the boundary area of the subtropical gyre. Microplankton ETS and mesoplankton ETS and ATC activities seemed to match the wave length of low frequency waves. Our results suggest that such waves are related to the observed enhancement of metabolic activity of micro- and mesoplankton. The large-scale and mesoscale variability observed give evidence of the inadequacy of assuming a steady-state picture of the euphotic zone of tropical and subtropical waters. 相似文献
706.
707.
708.
The Effect of Macrofauna on Porewater Profiles and Nutrient Fluxes in the Intertidal Zone of the Humber Estuary 总被引:3,自引:0,他引:3
R. J. G. Mortimer J. T. Davey M. D. Krom P. G. Watson P. E. Frickers R. J. Clifton 《Estuarine, Coastal and Shelf Science》1999,48(6):683
Macrofauna, nutrient fluxes, porewater chemistry and sediment characteristics were measured at six intertidal mudflat sites in the Humber Estuary, U.K., during the different seasons. Nereis diversicolor , Macoma balthica and Corophium volutator were found to be the dominant macrofauna. Salinity was the baseline control on macrofauna distribution but this was overprinted by periodic impoverishment due to sediment mobilization. High resolution gel probe porewater samplers provided direct evidence for the impact of burrows on porewater chemistry. The macrofauna modified nutrient fluxes during periods of mud flat stability. Nereis caused a decrease in silicate and phosphate effluxes but enhanced ammonia release and nitrate uptake. Macoma enhanced ammonia and nitrite release. The impact of Corophium was not possible to discern. The Humber is a large, highly dynamic macrotidal estuary in which sediment resuspension has a large impact on porewater profiles, nutrient fluxes and macrofaunal communities. Simple patterns and inter-relationships which are seen in small sheltered estuaries are not observed in the Humber. 相似文献
709.
Oceanology - For the first time, the species composition of heterotrophic nanoflagellates, their quantitative characteristics, and abundance and biomass of their main food objects—bacteria... 相似文献
710.
Kulikov G. V. Spector S. V. Rogozhin E. A. Lukashova R. N. Sysolin A. I. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(11):1715-1725
Izvestiya, Atmospheric and Oceanic Physics - The permanent analysis of the hydrogeodeformation (HGD) field is one promising direction in the field of predicting strong earthquakes. As a result of... 相似文献