全文获取类型
收费全文 | 5676篇 |
免费 | 694篇 |
国内免费 | 604篇 |
专业分类
测绘学 | 64篇 |
大气科学 | 265篇 |
地球物理 | 1281篇 |
地质学 | 1320篇 |
海洋学 | 1687篇 |
天文学 | 1706篇 |
综合类 | 160篇 |
自然地理 | 491篇 |
出版年
2024年 | 11篇 |
2023年 | 47篇 |
2022年 | 114篇 |
2021年 | 136篇 |
2020年 | 135篇 |
2019年 | 168篇 |
2018年 | 142篇 |
2017年 | 257篇 |
2016年 | 172篇 |
2015年 | 178篇 |
2014年 | 277篇 |
2013年 | 230篇 |
2012年 | 152篇 |
2011年 | 269篇 |
2010年 | 241篇 |
2009年 | 427篇 |
2008年 | 438篇 |
2007年 | 445篇 |
2006年 | 431篇 |
2005年 | 317篇 |
2004年 | 281篇 |
2003年 | 304篇 |
2002年 | 295篇 |
2001年 | 197篇 |
2000年 | 250篇 |
1999年 | 242篇 |
1998年 | 225篇 |
1997年 | 98篇 |
1996年 | 90篇 |
1995年 | 91篇 |
1994年 | 60篇 |
1993年 | 64篇 |
1992年 | 31篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有6974条查询结果,搜索用时 15 毫秒
41.
C. Christiansen F. Gertz M. J. C. Laima L. C. Lund-Hansen T. Vang C. Jürgensen 《Environmental Geology》1997,29(1-2):66-77
The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of
P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000
tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m–2 yr–1) and 477 ton of P (on average 0.9 g m–2 yr–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension
frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than
net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic
matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of
organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive
sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate
from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity
(56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic
N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively.
Received: 10 July 1995 · Accepted: 19 January 1996 相似文献
42.
43.
44.
45.
We present a 2D general circulation model of Titan's atmosphere, coupling axisymmetric dynamics with haze microphysics, a simplified photochemistry and eddy mixing. We develop a parameterization of latitudinal eddy mixing by barotropic waves based on a shallow-water, longitude-latitude model. The parameterization acts locally and in real time both on passive tracers and momentum. The mixing coefficient varies exponentially with a measure of the barotropic instability of the mean zonal flow. The coupled GCM approximately reproduces the Voyager temperature measurements and the latitudinal contrasts in the distributions of HCN and C2H2, as well as the main features of the zonal wind retrieved from the 1989 stellar occultation. Wind velocities are consistent with the observed reversal time of the North-South albedo asymmetry of 5 terrestrial years. Model results support the hypothesis of a non-uniform distribution of infrared opacity as the cause of the Voyager temperature asymmetry. Transport by the mean meridional circulation, combined with polar vortex isolation may be at the origin of the latitudinal contrasts of trace species, with eddy mixing remaining restricted to low latitudes most of the Titan year. We interpret the contrasts as a signature of non-axisymmetric motions. 相似文献
46.
V. I. Ferronsky S. A. Denisik S. V. Ferronsky 《Celestial Mechanics and Dynamical Astronomy》1996,64(3):167-183
The physical meaning of the terms of the potential and kinetic energy expressions, expanded by means of the density variation function for a nonuniform self-gravitating sphere, is discussed. The terms of the expansions represent the energy and the moment of inertia of the uniform sphere, the energy and the moment of inertia of the nonuniformities interacting with the uniform sphere, and the energy of the nonuniformities interacting with each other. It follows from the physical meaning of the above components of the energy structure, and also from the observational fact of the expansion of the Universe that the phase transition, notably, fusion of particles and nuclei and condensation of liquid and solid phases of the expanded matter accompanied by release of energy, must be the physical cause of initial thermal and gravitational instability of the matter. The released kinetic energy being constrained by the general motion of the expansion, develops regional and local turbulent (cyclonic) motion of the matter, which should be the second physical effect responsible for the creation of celestial bodies and their rotation. 相似文献
47.
48.
49.
50.
Mass heterogeneities and convection in the earth's mantle inferred from gravity and core-mantle boundary irregularities 总被引:1,自引:0,他引:1
Mass heterogeneities in the earth's mantle are retrieved from the gravity data and the topography of the core-mantle boundary as well as the topography of the earth's surface. A mantle circulation induced by the heterogeneities is modelled by solving the Stokes problem for incompressible Newtonian fluid. The derived models of mantle motions correlate well with the plate tectonics and point at a close relation between the surface tectonic activity and the processes in the vicinity of the core-mantle boundary. 相似文献