全文获取类型
收费全文 | 94819篇 |
免费 | 1140篇 |
国内免费 | 1395篇 |
专业分类
测绘学 | 2921篇 |
大气科学 | 6198篇 |
地球物理 | 18330篇 |
地质学 | 36876篇 |
海洋学 | 7681篇 |
天文学 | 18413篇 |
综合类 | 2291篇 |
自然地理 | 4644篇 |
出版年
2022年 | 573篇 |
2021年 | 926篇 |
2020年 | 978篇 |
2019年 | 1111篇 |
2018年 | 6776篇 |
2017年 | 5887篇 |
2016年 | 4869篇 |
2015年 | 1346篇 |
2014年 | 2213篇 |
2013年 | 3769篇 |
2012年 | 3366篇 |
2011年 | 5696篇 |
2010年 | 4857篇 |
2009年 | 5767篇 |
2008年 | 4902篇 |
2007年 | 5546篇 |
2006年 | 3069篇 |
2005年 | 2235篇 |
2004年 | 2326篇 |
2003年 | 2271篇 |
2002年 | 2044篇 |
2001年 | 1738篇 |
2000年 | 1562篇 |
1999年 | 1162篇 |
1998年 | 1200篇 |
1997年 | 1220篇 |
1996年 | 954篇 |
1995年 | 959篇 |
1994年 | 905篇 |
1993年 | 808篇 |
1992年 | 775篇 |
1991年 | 760篇 |
1990年 | 798篇 |
1989年 | 740篇 |
1988年 | 704篇 |
1987年 | 780篇 |
1986年 | 657篇 |
1985年 | 871篇 |
1984年 | 926篇 |
1983年 | 848篇 |
1982年 | 768篇 |
1981年 | 810篇 |
1980年 | 718篇 |
1979年 | 624篇 |
1978年 | 651篇 |
1977年 | 609篇 |
1976年 | 547篇 |
1975年 | 533篇 |
1974年 | 528篇 |
1973年 | 563篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
991.
D. Cossa 《Marine environmental research》1988,26(4)
A worldwide literature survey of data on cadmium concentration in the soft tissue of the mussel, Mytilus spp., from 591 stations is presented. These stations are from 13 regions. Geometric means for the regions vary from 0·6 to 3·3 μg g−1 (dry weight) for the Barents Sea and the Northeastern Pacific coast, respectively.The averages of seven of these regions, for which reliable cadmium concentrations in seawater were available, were used to calculate a relationship between cadmium concentrations in seawater and mussel soft tissue. The relationship was highly significant: (Cd) mussel (μg g−1, dry weight) = 0·074 (Cd) water (ng litre−1) + 0·39 (P ≤ 0·0005).This model has been successfully applied in the context of the contamination of the Gironde estuary (France). It can also be used to define a water quality criterion for mussel maturing parks consistent with the quality criterion defined for shellfish for human consumption. 相似文献
992.
Chemical and isotopic analyses of pore waters from Jamaican reef sediment suggest the importance of microbial sulfate reduction as a major control upon the origin, distribution, and composition of submarine cements in this fringing reef setting. Fore-reef sediment pore waters exhibit active sulfate reduction and enrichment in 18O which is consistent with associated active magnesian calcite cementation, alkalinity consumption, and cement enrichment in 18O. Conversely, lack of widespread submarine cementation in the back-reef corresponds to the diminished resupply of sulfate coupled with input of CO2-charged meteoric water from a nearby unconfined aquifer into the more stagnant pore waters which lower pore-water magnesian calcite saturation states and preclude active submarine cementation. 相似文献
993.
A high-resolution seismic survey covering more than 2,000 km2 has revealed the processes responsible for the slope morphology and channel sedimentation across the forearc slope-basin
of the Kurile Arc–NE Japan Arc collision zone, offshore from Tokachi (Hokkaido, Japan). The dominant slope contours parallel
the trench but, in the middle and lower reaches of the southern slope, contours are convex-shaped with an offshore trend.
This sector of the slope is traversed diagonally by the Hiroo submarine channel. The offshore-trending convex contours and
the channel course have developed through the interplay of tectonic and sedimentary processes, including the development of
anticlines, anticline-induced lobe sedimentation and channel avulsion. In its upper reaches, the channel is restricted by
a topographic low associated with NNW–SSE-trending anticlines which developed within the upper and middle slope sectors during
late Miocene uplift. The uplift timing and trend of these anticlines indicate that they resulted from collision, the channel
sedimentology and slope morphology of the middle and lower slopes having been influenced by Pliocene uplift of NE–SW-trending
anticlines. The trends of these anticlines parallel those of the Kurile Trench. The Pliocene and early Pleistocene strata
of the middle and lower slopes consist of ponded lobe sediments deposited along the palaeo-Hiroo submarine channel on the
landward side of the anticlines. As a lobe pile accumulated, the channel thalweg shifted to the north of the stack, allowing
the channel to bypass the topographic high formed by the growing stack. Thick levee deposits built up along the channel course
during the late Pleistocene and Holocene. These levees, along with the Pliocene and early Pleistocene lobes, are reflected
in the present-day sigmoid-shaped, convex offshore-trending contours. Thus, the interplay of subduction- and collision-related
anticlines, tectonic-related channel ponding, and avulsion has contributed to the slope morphology of the southern Kurile
Trench. 相似文献
994.
Freezing as a method of sample preservation for the analysis of dissolved inorganic nutrients in seawater 总被引:1,自引:0,他引:1
John E. Dore Terrence Houlihan Dale V. Hebel Georgia Tien Luis Tupas David M. Karl 《Marine Chemistry》1996,53(3-4)
It is often desirable or necessary to store collected seawater samples prior to analysis for dissolved inorganic nutrients. It is therefore important to establish preservation and storage techniques that will ensure sample integrity and will not alter the precision or accuracy of analysis. We have performed a series of experiments on the storage of nutrient samples collected at the oligotrophic North Pacific benchmark Station ALOHA, using both standard autoanalyses and low-level techniques. Our results reveal that for oligotrophic oceanic waters, the immediate freezing of an unfiltered water sample in a clean polyethylene bottle is a suitable preservation method. This procedure is simple, it avoids potentially contaminating sample manipulations and chemical additions, and it adequately preserves the concentrations of nitrate + nitrite, soluble reactive phosphate, and soluble reactive silicate within a single water sample. 相似文献
995.
Theoretical and laboratory results indicate that bottom velocities within shoaling internal gravity waves intensify upslope approximately inversely proportional to the water depth. The elevated velocities (and bottom stresses) caused by shoaling and, possibly, breaking internal waves might explain the generation and maintenance of near-bottom nepheloid zones and attached turbid plumes that have been observed over certain continental shelves and slopes. This process is proposed as an explanation of zones of relatively low transmissibility that emanate from the upper continental slope near Newport submarine canyon off southern California. 相似文献
996.
997.
Brent L. Lewis Pamela D. Holt Steven W. Taylor Steven W. Wilhelm Charles G. Trick Alison Butler George W. Luther III 《Marine Chemistry》1995,50(1-4)
Thermodynamic stability constants have been estimated for the complexation of iron(III) with catecholate-type siderophores isolated from the marine bacterium Alteromonas luteoviolacea and from the marine cyanobacterium Synechococcus sp. PCC 7002. Stability constants were determined utilizing the “chelate scale” of Taylor et al. (1994). The scale is based upon a linear relationship between the reduction potentials and the pH-independent thermodynamic stability constants for known iron(III) complexes. Log K values for the alterobactin B ferric iron complex are 43.6 ± 1.5 at pH 8.2 and 37.6 ± 1.2 at pH 6, consistent with a shift from bis-catecholate to monosalicylate/monocatecholate iron coordination with decreasing pH. Synechococcus isolates PCC 7002 Nos. 1 and 3 formed iron(III) complexes with stability constants of approximately 38.1 ± 1.2 and 42.3 ± 1.5, respectively. The binding strengths of the iron(III) complexes examined in this study are quite high, suggesting that catecholate siderophores may play a role in the solubilization and biological uptake of iron in the marine environment. 相似文献
998.
Cluster analysis is discussed in the context of its application to map various test areas in the sea. By analysing the correspondence of the identified categories to areas with specific hydrological conditions, an attempt is made to relate the types of fine structure to diverse background conditions. With two test areas mapped, a conclusion is made as to the possible application of cluster analysis to this end.Translated by Vladimir A. Puchkin. 相似文献
999.
The paper is concerned with the evaluation of the drift current parameters derived through the use of an analytical model.
In this model, effective when stratification is stable and indifferent, the vertical turbulence coefficient profile is prescribed
by the power function, and hydrodynamic quantities are prescribed using the external parameters of the problem (wind stress,
the Coriolis parameter, and the dimensionless stratification parameter). Model data are compared with the observations of
the upper mixed layer in the vicinity of the oceanic Station C, conducted during one year. It is shown that, under the spring-summer-time
warming conditions, the model at issue is capable of adequately simulating the upper ocean layer dynamics.
Translated by Vladimir A. Puchkin. 相似文献
1000.
Growth rate of Raia clavata in the Northeast Irish Sea 总被引:1,自引:0,他引:1