全文获取类型
收费全文 | 80297篇 |
免费 | 953篇 |
国内免费 | 1281篇 |
专业分类
测绘学 | 2855篇 |
大气科学 | 6004篇 |
地球物理 | 15538篇 |
地质学 | 31628篇 |
海洋学 | 5872篇 |
天文学 | 14673篇 |
综合类 | 2259篇 |
自然地理 | 3702篇 |
出版年
2021年 | 347篇 |
2020年 | 386篇 |
2019年 | 470篇 |
2018年 | 7241篇 |
2017年 | 6466篇 |
2016年 | 4629篇 |
2015年 | 957篇 |
2014年 | 1242篇 |
2013年 | 2095篇 |
2012年 | 2854篇 |
2011年 | 5865篇 |
2010年 | 5120篇 |
2009年 | 5905篇 |
2008年 | 4914篇 |
2007年 | 5774篇 |
2006年 | 1840篇 |
2005年 | 1962篇 |
2004年 | 1982篇 |
2003年 | 1949篇 |
2002年 | 1662篇 |
2001年 | 1168篇 |
2000年 | 1125篇 |
1999年 | 928篇 |
1998年 | 920篇 |
1997年 | 907篇 |
1996年 | 730篇 |
1995年 | 682篇 |
1994年 | 641篇 |
1993年 | 560篇 |
1992年 | 489篇 |
1991年 | 499篇 |
1990年 | 475篇 |
1989年 | 495篇 |
1988年 | 442篇 |
1987年 | 516篇 |
1986年 | 471篇 |
1985年 | 557篇 |
1984年 | 683篇 |
1983年 | 591篇 |
1982年 | 581篇 |
1981年 | 534篇 |
1980年 | 486篇 |
1979年 | 447篇 |
1978年 | 461篇 |
1977年 | 391篇 |
1976年 | 350篇 |
1975年 | 357篇 |
1974年 | 329篇 |
1973年 | 367篇 |
1972年 | 261篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
I. Brandariz P. Castro M. Montes F. Penedo M.E. Sastre de Vicente 《Marine Chemistry》2006,102(3-4):291-299
Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl2 or CaCl2), with binary mixtures of MgCl2 and CaCl2, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl2, while it is increased by the other electrolytes used in this work. 相似文献
932.
Hideo Kawai 《Journal of Oceanography》2005,61(2):235-246
At present, the barotropic buoyant stability parameter has been derived from a vertical virtual displacement of a water parcel. The barotropic inertial stability parameter in the eccentrically cyclogeostrophic, basic current field was derived in 2003 from a horizontal cross-stream virtual displacement of a parcel. By expressing acceleration of a parcel due to a virtual displacement, which is arbitrarily sloping within a vertical section across the basic current, in terms of natural coordinates, we derived the vertical component of baroclinic buoyant stability parameter B
2
2, the horizontal component of baroclinic inertial stability parameter I
2
2, the baroclinic joint stability parameter J
2, its buoyant component B
2 and its inertial component I
2. B
2 is far greater than I
2
2, and when neglecting relative vorticity except for vertical shear, a downward convex curve of J
2 plotted against the slope of a virtual displacement follows a trend of B
2 curve. If a parcel displaces along a horizontal surface or an isopycnal surface, however, B
2 vanishes, and J
2 becomes equal to I
2. Actual parcel is apt to displace not only along the bottom slope, but also along the sea surface and an isopycnal interfacial surface, which is approximately equivalent to an isentropic surface, preferred by lateral mixing and exchange of momentum. Such actual displacement makes B
2 vanishing, and grants I
2 an important role. The present analysis of I
2 examining effects due to curvature and horizontal and vertical shear vorticities are useful in deepening our understanding of baroclinic instability in actual oceanic streams. 相似文献
933.
Yosuke Fujii 《Journal of Oceanography》2005,61(1):167-181
I present the derivation of the Preconditioned Optimizing Utility for Large-dimensional analyses (POpULar), which is developed for adopting a non-diagonal background error covariance matrix in nonlinear variational analyses (i.e., analyses employing a non-quadratic cost function). POpULar is based on the idea of a linear preconditioned conjugate gradient method widely adopted in ocean data assimilation systems. POpULar uses the background error covariance matrix as a preconditioner without any decomposition of the matrix. This preconditioning accelerates the convergence. Moreover, the inverse of the matrix is not required. POpULar therefore allows us easily to handle the correlations among deviations of control variables (i.e., the variables which will be analyzed) from their background in nonlinear problems. In order to demonstrate the usefulness of POpULar, we illustrate two effects which are often neglected in studies of ocean data assimilation before. One is the effect of correlations among the deviations of control variables in an adjoint analysis. The other is the nonlinear effect of sea surface dynamic height calculation required when sea surface height observation is employed in a three-dimensional ocean analysis. As the results, these effects are not so small to neglect. 相似文献
934.
We present the results of numerical experiments aimed at the simulation of the circulation of waters and transport of impurities
in the Balaklava Bay for typical wind conditions established on the basis of the analysis of the data of in-situ measurements. The currents are computed by using the nonlinear σ-coordinate model. The specific features of the integral
circulation and three-dimensional structure of the current field are investigated. The statistical characteristics of currents
are estimated on the basis of the in-situ data on winds and model calculations. Possible scenarios of propagation of impurities from the coastal sources are analyzed
for various hydrodynamic conditions. It is shown that the localized eddy structures in the current fields (in combination
with the zones of intense vertical motion) can result in a complex character of the transport of substances in the bay and
lead to the formation of local regions of maximum concentrations of impurities on the boundary of the north and central parts
of the bay.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 43–58, July–August, 2005. 相似文献
935.
936.
Trends in biorobotic autonomous undersea vehicles 总被引:1,自引:0,他引:1
The emergence of biorobotic autonomous undersea vehicle (AUV) as a focus for discipline-integrated research in the context of underwater propulsion and maneuvering is considered within the confines of the Biorobotics Program in the Office of Naval Research. The significant advances in three disciplines, namely the biology-inspired high-lift unsteady hydrodynamics, artificial muscle technology and neuroscience-based control, are discussed in an effort to integrate them into viable products. The understanding of the mechanisms of delayed stall, molecular design of artificial muscles and the neural approaches to the actuation of control surfaces is reviewed in the context of devices based on the pectoral fins of fish, while remaining focused on their integrated implementation in biorobotic AUVs. A mechanistic understanding of the balance between cruising and maneuvering in swimming animals and undersea vehicles is given. All aquatic platforms, in both nature and engineering, except during short duration burst speeds that are observed in a few species, appear to lie within the condition where their natural period of oscillation equals the time taken by them to travel the distance of their own lengths. Progress in the development of small underwater experimental biorobotic vehicles is considered where the three aforementioned disciplines are integrated into one novel maneuvering device or propulsor. The potential in maneuvering and silencing is discussed. 相似文献
937.
D. Evans M.S. Stoker P.M. Shannon STRATAGEM Partners 《Marine and Petroleum Geology》2005,22(9-10):969
The EC-funded STRATAGEM project ran from 2000 to 2003 and was a study of the Neogene evolution of the glaciated northeast Atlantic margin from Lofoten to Porcupine, an area extending over nearly 20 degrees of latitude. An extensive seismic, borehole and sample database has been used, much of it supplied by the oil industry. The main products of STRATAGEM have been an integrated, unified stratigraphic framework in the form of an atlas documenting and illustrating the detailed stratigraphy of the entire margin, and a detailed evolution model for this margin. A brief summary of the background to, and organisation of, the project is presented, together with an outline of the main objectives, the physiographic setting of the area and the database. 相似文献
938.
Ivanov V. A. Kubryakov A. I. Lyubartseva S. P. Mikhailova É. N. Shapiro N. B. 《Physical Oceanography》2004,14(2):67-83
In the present work, we generalize the results of our investigations in the field of simulation of hydrophysical and ecological processes in coastal regions of various seas and some closed basins. The developed and applied mathematical models and the results of numerical experiments are briefly analyzed. 相似文献
939.
J. Acosta E. Uchupi A. Muñoz P. Herranz C. Palomo M. Ballesteros 《Marine Geophysical Researches》2003,24(1-2):41-57
Circular to elliptical mounds in the Canary Channel with reliefs of 75 to 375 m and diameters of 4 to 8 km partially surrounded by moats with reliefs of 25 to 75 m, were formed by piercement of the seafloor by Mesozoic evaporites. Several long gullies, < 1km wide, with abrupt terminations and pockmarks associated with these mounds were probably eroded by dense brine and hydrocarbon seeps. The salt brines that eroded the gullies were formed where salt diapirs intersect the seafloor, or in the subsurface by circulating ground water heated by igneous activity along the Canary Ridge. If the brines originated in the subsurface they reached the seafloor along faults. Displacement of the surficial sediments by sliding and creep is probably the result of the expulsion of hydrocarbons and/or vertical motion of the Mesozoic evaporites. Microtopographic features along or near the east flank of the Canary Ridge are the creation of uplift of the ridge, hydrothermal activity, mass wasting processes and turbidity currents. 相似文献
940.
A survey of imposex in Thais orbita (Neogastropoda) along the New South Wales (NSW) coast, Australia, found imposex was still widespread 10 years after a partial ban on tributyltin (TBT) based antifouling paints. Transplant experiments also revealed that imposex was induced in T. orbita over a period of 9 weeks in Sydney Harbour, NSW. A comparison of the imposex data with that collected shortly after the introduction of restrictions on TBT revealed a general decline in imposex frequency occurring at open coast sites, an exception being the site at South West Rocks. Sites located within harbour/bay areas did not display a decline in imposex frequency but a decline in the severity of imposex was apparent. The observed decrease in imposex values in T. orbita may reflect a general decrease of butyltin contamination within the coastal environment. However, the persistence of contamination "hotspots" within harbours and bays remains a concern. 相似文献