全文获取类型
收费全文 | 4095篇 |
免费 | 797篇 |
国内免费 | 1013篇 |
专业分类
测绘学 | 101篇 |
大气科学 | 1063篇 |
地球物理 | 1148篇 |
地质学 | 1396篇 |
海洋学 | 1019篇 |
天文学 | 189篇 |
综合类 | 243篇 |
自然地理 | 746篇 |
出版年
2024年 | 22篇 |
2023年 | 73篇 |
2022年 | 153篇 |
2021年 | 179篇 |
2020年 | 204篇 |
2019年 | 234篇 |
2018年 | 174篇 |
2017年 | 194篇 |
2016年 | 211篇 |
2015年 | 238篇 |
2014年 | 295篇 |
2013年 | 326篇 |
2012年 | 247篇 |
2011年 | 313篇 |
2010年 | 252篇 |
2009年 | 270篇 |
2008年 | 254篇 |
2007年 | 271篇 |
2006年 | 244篇 |
2005年 | 221篇 |
2004年 | 167篇 |
2003年 | 140篇 |
2002年 | 169篇 |
2001年 | 108篇 |
2000年 | 117篇 |
1999年 | 106篇 |
1998年 | 122篇 |
1997年 | 98篇 |
1996年 | 100篇 |
1995年 | 70篇 |
1994年 | 62篇 |
1993年 | 47篇 |
1992年 | 43篇 |
1991年 | 38篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1973年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有5905条查询结果,搜索用时 15 毫秒
31.
Seasonal DOC accumulation in the Black Sea: a regional explanation for a general mechanism 总被引:2,自引:0,他引:2
Gustave Cauwet Gaëlle Dliat Anton Krastev Galina Shtereva Sylvie Becquevort Christiane Lancelot Andr Momzikoff Alain Saliot Adriana Cociasu Lucia Popa 《Marine Chemistry》2002,79(3-4)
During three cruises in the Black Sea, organised in July 1995 and April–May 1997, biological and chemical parameters that can influence the carbon budget were measured in the water column on the NW shelf, particularly in the mixing zone with Danube River waters. We observed in early spring (end of April–May) conditions an important input of freshwater organisms that enhanced the microbial activity in the low salinity range. High bacterial activity regenerates nitrogen in the form of nitrates, but is also responsible for an important consumption of ammonium and phosphate, leading to a high N/P ratio and a strong deficit in phosphorus. The consequence is a limitation of phytoplankton development but also a production of carbohydrates that accumulate all along the salinity gradient. These mechanisms are responsible for a seasonal accumulation of dissolved organic carbon (DOC) that increases from 210 μM in winter to about 280 μM in summer. All this excess DOC disappears during winter, probably degraded by bacterial activity. The degradation of carbon-rich organic matter increases the phosphorus demand by bacteria bringing limitation to phytoplankton primary production. 相似文献
32.
33.
Xu Shikai Wang Hongchuan Hong Guangwen
Engineer Nanjing Hydraulic Research Institute Nanjing .
Professor Research Institute of Coastal Ocean Engineering Hohai University Nanjing 《中国海洋工程》1996,(4)
To solve problems concerning wave elements and wave propagation, an effective way is the wave energy balance equation, which is widely applied in oceanography and ocean dynamics for its simple computation. The present papaer advances wave energy balance equations considering lateral energy transmission and energy loss as the governing equation for the study of wave refraction-diffraction. For the mathematical model, numerical simulation is made by means of difference method, and the result is verified with two examples. 相似文献
34.
Following Bagnold's approach, a relationship between sediment transport and energy dissipation is developed. The major assumption made in the study is that the near bed velocity plays a dominant role in the process of sediment transport. A general relationship between energy dissipation and sediment transport is first proposed. Then the equations for total sediment transport are derived by introducing the appropriate expression of energy dissipation rate under different conditions, such as open channel flows, combination of wave and current, as well as longshore sediment transport. Within the flows investigated, the derived relationships are fairly consistent with the available data over a wide range of conditions. 相似文献
35.
Konstantin V. Lebedev Max Yaremchuk Humio Mitsudera Iwao Nakano Gang Yuan 《Journal of Oceanography》2003,59(6):751-763
A finite-difference quasigeostrophic (QG) model of an open ocean region has been employed to produce a dynamically constrained
synthesis of acoustic tomography and satellite altimetry data with in situ observations. The assimilation algorithm is based upon the 4D variational data interpolation scheme controlled by the model's
initial and boundary conditions. The data sets analyzed include direct and differential travel times measured at the array
of five acoustic transceivers deployed by JAMSTEC in the region of the Kuroshio Extension in 1997, Topex/Poseidon altimetry,
CTD soundings, and ADCP velocity profiles. The region monitored is located within the area 27.5°–36.5°N, 143°–155°. The results
of assimilation show that mesoscale variability can be effectively reconstructed by five transceivers measuring direct and
reciprocal travel times supported by relatively sparse in situ measurements. The misfits between model and data lie within the observational error bars for all the data types used in assimilation.
We have compared the results of assimilation with the statistical inversion of travel time data and analyzed energy balances
of the optimized model solution. Energy exchange between the depth-averaged and shear components of the observed currents
reveals a weak decay of the barotropic mode at the rate of 0.2 ± 0.7⋅10−5 cm2/s3 due to topographic interaction. Mean currents in the region are unstable with an estimate of the available potential energy
flux from the mean current to the eddies of 4.7 ± 2.3⋅10−5 cm2/s3. Kinetic energy transition has the same sign and is estimated as 2.8 ± 2.5⋅10−5 cm2/s3. Potential enstrophy is transferred to the mesoscale at a rate of 5.5 ± 2.7⋅10−18 s−3. These figures provide observational evidence of the properties of free geostrophic turbulence which were predicted by theory
and observed in numerical experiments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
36.
根据作者导得的AfKdV方程,理论上确定了先锋孤立子生成问题的理论平均波阻,能量劈分及能量劈分比。本文的能量劈分是确定先锋孤立子生成参数的理论基础。同时,本理论确定了现有理论中的自由未知参数问题,从而使先锋孤立子生成参数得到理论预报。 相似文献
37.
Abstract. A component analysis of the sugar and lipid fraction in foam layers around kelp beds on the South African west coast showed the following trends: In the residue of foam drainage of both 12 h and 120 h old foam the sugar fraction is represented by mannose (33–41 %), galactose (4–30%), fucose (3–29%) and glucose (19–26%). With the exception of fucose, the same components could be found in foam filtration. In the lipid fraction the main fatty acids are palmitic (23.3–27.3%), oleic (14.0–5.5%) and timnodonic acid (11.2–9.1%). Selacholeinic acid was only found in 12 h old foam while lignoceric acid could not be located in foam filtration. Against expectation mannitol was not identified in quantifiable amounts in foam samples although it is the dominant component of kelp mucilage, whose presence is of major importance for foam formation. Hypotheses explaining the lack of mannitol are forwarded. Component sugar and lipid content for 11 of foam was calculated and estimation of sugar and lipid content in an average foam patch (volume of 30001) is given. The importance of foam formation as a mechanism for binding and transfer of energy in the marine environment is emphasized. 相似文献
38.
39.
用不同浓度的丁香酚对体质量为 115~ 175 g的黄腊鲹( Trachinotus blochii)麻醉处理 15 min,每 1分钟测定容器内的氧饱和度 1次.实验结果表明,黄腊鲹的耗氧率明显地受到丁香酚的影响,在各处理组中以 10× 10- 6浓度组的耗氧率为最低( 0.33 mg/(g@ h)), 5× 10- 6浓度组次之( 0.42 mg/(g@ h)),而对照组则较高( 0.57 mg/(g@ h)).同时实验还表明经丁香酚麻醉处理的黄腊鲹鳃活动频率显著地比对照组低.此结果表明了在施用麻醉剂以后,鱼体的活动及对氧气的消耗有明显的下降,丁香酚可以作为活鱼运输过程中有效的麻醉剂. 相似文献
40.