全文获取类型
收费全文 | 3914篇 |
免费 | 147篇 |
国内免费 | 38篇 |
专业分类
测绘学 | 103篇 |
大气科学 | 319篇 |
地球物理 | 928篇 |
地质学 | 1455篇 |
海洋学 | 342篇 |
天文学 | 533篇 |
综合类 | 16篇 |
自然地理 | 403篇 |
出版年
2022年 | 13篇 |
2021年 | 52篇 |
2020年 | 58篇 |
2019年 | 89篇 |
2018年 | 125篇 |
2017年 | 66篇 |
2016年 | 110篇 |
2015年 | 93篇 |
2014年 | 116篇 |
2013年 | 231篇 |
2012年 | 145篇 |
2011年 | 163篇 |
2010年 | 151篇 |
2009年 | 204篇 |
2008年 | 199篇 |
2007年 | 171篇 |
2006年 | 163篇 |
2005年 | 140篇 |
2004年 | 144篇 |
2003年 | 145篇 |
2002年 | 134篇 |
2001年 | 92篇 |
2000年 | 81篇 |
1999年 | 65篇 |
1998年 | 71篇 |
1997年 | 63篇 |
1996年 | 53篇 |
1995年 | 45篇 |
1994年 | 44篇 |
1993年 | 46篇 |
1992年 | 41篇 |
1991年 | 29篇 |
1990年 | 46篇 |
1989年 | 46篇 |
1988年 | 41篇 |
1987年 | 46篇 |
1986年 | 38篇 |
1985年 | 49篇 |
1984年 | 56篇 |
1983年 | 52篇 |
1982年 | 50篇 |
1981年 | 39篇 |
1980年 | 55篇 |
1979年 | 39篇 |
1978年 | 26篇 |
1977年 | 29篇 |
1976年 | 25篇 |
1975年 | 23篇 |
1974年 | 18篇 |
1973年 | 21篇 |
排序方式: 共有4099条查询结果,搜索用时 31 毫秒
51.
52.
53.
Daniel S. Scheirer Ken C. Macdonald Donald W. Forsyth Stephen P. Miller Dawn J. Wright Marie-Hélène Cormier Charles M. Weiland 《Marine Geophysical Researches》1996,18(1):1-12
Four large-scale bathymetric maps of the Southern East Pacific Rise and its flanks between 15° S and 19° S display many of the unique features of this superfast spreading environment including abundant seamounts (the Rano Rahi Field), axial discontinuities, discontinuity migration, and abyssal hill variation. Along with a summary of the regional geology, these maps will provide a valuable reference for other sea-going programs on-and off-axis in this area, including the Mantle ELectromagnetic and Tomography (MELT) experiment. 相似文献
54.
We study the reaction of a global ocean–sea ice model to an increase of fresh water input into the northern North Atlantic under different surface boundary conditions, ranging from simple restoring of surface salinity to the use of an energy balance model (EBM) for the atmosphere. The anomalous fresh water flux is distributed around Greenland, reflecting increased melting of the Greenland ice sheet and increasing fresh water export from the Arctic Ocean. Depending on the type of surface boundary condition, the large circulation reacts with a slow-down of overturning and gyre circulations. Restoring of the total or mean surface salinity prevents a large scale redistribution of the salinity field that is apparent under mixed boundary conditions and with the EBM. The control run under mixed boundary conditions exhibits large and unrealistic oscillations of the meridional overturning. Although the reaction to the fresh water flux anomaly is similar to the response with the EBM, mixed boundary conditions must thus be considered unreliable. With the EBM, the waters in the deep western boundary current initially become saltier and a new fresh water mass forms in the north-eastern North Atlantic in response to the fresh water flux anomaly around Greenland. After an accumulation period of several decades duration, this new North East Atlantic Intermediate Water spreads towards the western boundary and opens a new southward pathway at intermediate depths along the western boundary for the fresh waters of high northern latitudes. 相似文献
55.
56.
Walter H Pearson Stephen E Miller J.W Blaylock Bori L Olla 《Marine environmental research》1981,5(1):3-11
The ability of the blue crab, Callinectes sapidus, to detect petroleum hydrocarbons was measured with behavioural techniques. When presented with a water-soluble fraction of Prudhoe Bay crude oil, blue crabs abruptly changed antennular orientation, began rhythmic beating of the maxillipedal flagellae, and increased antennular flicking rate. The threshold concentration at which 50% of the crabs detected the water-soluble fraction was 2 × 10?6 mg/litre. The blue crab apparently can readily detect petroleum hydrocarbons at concentrations found in chronically polluted areas as well as oil spill situations. 相似文献
57.
58.
A code of practice for ocean mining has been developed by the International Marine Minerals Society. The code provides general guiding Principles for development of marine mineral resources and delineates Operating Guidelines for application, as appropriate, at specific mining sites. In total 11 operating guidelines are provided to serve as benchmarks for industry and targets for regulatory agencies and other stakeholders. They include the following commitments: •To sustainable development, •To environmentally responsible corporate ethics, •To the development of effective community partnership, •To implementation of environmental risk management, •To the integration of environmental management into all phases of development, •To the establishment of corporate environmental performance targets, •To timely environmental improvements and upgrading, •To responsible rehabilitation of operations sites and decommissioning of facilities, and •To accurate and timely, reporting and documentation, archiving, and performance review. 相似文献
59.
Martina A. Doblin Stephen B. Baines Lynda S. Cutter Gregory A. Cutter 《Estuarine, Coastal and Shelf Science》2006,67(4):681-694
As part of a study of estuarine selenium cycling, we measured the concentration, chemical form (speciation), and distribution of particulate selenium under various river flow conditions in the North San Francisco Bay (from the Golden Gate to the Sacramento and San Joaquin Rivers). We also conducted laboratory studies on the accumulation of selenium by phytoplankton, the critical first step in the transformation of dissolved to particulate selenium. Total particulate selenium concentration in the North SF Bay was relatively constant between high and low flow periods, ranging spatially from 0.05 to 0.35 nmol l−1 and comprising between 5 and 12% of the total water column selenium inventory. Mean concentrations were generally highest in the Carquinez Strait–Suisun Bay region (salinity 0–17) and lowest in Central Bay. However, selenium content of suspended particles varied with river flow, with higher content during low flow (9.76 ± 4.17 nmol g−1; mean ± sd; n = 67) compared to high flow (7.10 ± 4.24 nmol g−1; n = 39). Speciation analyses showed that most particulate selenium is organic selenide (45 ± 27%), with a smaller proportion (typically <30%) of adsorbed selenite + selenate and a varying proportion (35 ± 28%) of elemental selenium. Based on the amount of elemental selenium in the seston (total suspended material), we calculate that resuspension of estuarine sediments could contribute 29–100% of particulate selenium in the water column. While selenium content of SF Bay seston (>0.4 μm) is relatively unenriched compared to phytoplankton (13.6–155 nmol g−1 dry weight) on a mass basis, when normalized to carbon or nitrogen, seston contains a similar selenium concentration to SF Bay sediments or phytoplankton cultures. SF Bay seston is thus comprised of selenium-rich phytoplankton and phyto-detritus, but also inorganic clay mineral particles that effectively “dilute” total particulate selenium. Selenium concentrations in algal cultures (11 species) exposed to 90 nmol l−1 selenite show relatively large differences in selenium accumulation, with the diatoms, chlorophytes and cryptophytes generally having lower selenium cell content (3.8 ± 2.7 × 10−9 nmol selenium cell−1) compared to the dinoflagellates (193 ± 73 × 10−9 nmol selenium cell−1). Because phytoplankton are such a rich (but variable) source of selenium, their dynamics could have a profound effect on the particulate selenium inventory in the North SF Bay. 相似文献
60.
Valeria Mattiangeli Anthony W. Ryan Paul Galvin Jarle Mork & Thomas F. Cross 《Marine Ecology》2003,24(4):247-258
Abstract. Nine allozyme and two minisatellite loci were used to investigate potential genetic differentiation among three samples of Mediterranean poor cod, Trisopterus minutus capelanus, from the Gulf of Lion, the Tuscan Archipelago and the Aegean Sea. Both types of markers showed consistent results, with FST values of 0.0262 and 0.0296 (P < 0.0015, after Bonferroni correction for multiple tests) for allozymes and minisatellites, respectively. Allele frequency heterogeneity tests between pairs of samples showed a clear separation between the two western Mediterranean samples (Gulf of Lion, Tuscan Archipelago) and the eastern one (Aegean Sea). The results indicate that at least two reproductively isolated populations of poor cod occur in the Mediterranean. 相似文献