全文获取类型
收费全文 | 5840篇 |
免费 | 188篇 |
国内免费 | 89篇 |
专业分类
测绘学 | 173篇 |
大气科学 | 546篇 |
地球物理 | 1468篇 |
地质学 | 1997篇 |
海洋学 | 552篇 |
天文学 | 759篇 |
综合类 | 22篇 |
自然地理 | 600篇 |
出版年
2021年 | 63篇 |
2020年 | 64篇 |
2019年 | 87篇 |
2018年 | 130篇 |
2017年 | 121篇 |
2016年 | 158篇 |
2015年 | 149篇 |
2014年 | 204篇 |
2013年 | 326篇 |
2012年 | 244篇 |
2011年 | 264篇 |
2010年 | 192篇 |
2009年 | 305篇 |
2008年 | 289篇 |
2007年 | 262篇 |
2006年 | 223篇 |
2005年 | 189篇 |
2004年 | 198篇 |
2003年 | 190篇 |
2002年 | 182篇 |
2001年 | 133篇 |
2000年 | 136篇 |
1999年 | 113篇 |
1998年 | 107篇 |
1997年 | 91篇 |
1996年 | 84篇 |
1995年 | 85篇 |
1994年 | 75篇 |
1993年 | 63篇 |
1992年 | 65篇 |
1991年 | 69篇 |
1990年 | 66篇 |
1989年 | 59篇 |
1988年 | 58篇 |
1987年 | 65篇 |
1986年 | 43篇 |
1985年 | 73篇 |
1984年 | 80篇 |
1983年 | 72篇 |
1982年 | 65篇 |
1981年 | 76篇 |
1980年 | 63篇 |
1979年 | 57篇 |
1978年 | 38篇 |
1977年 | 54篇 |
1976年 | 63篇 |
1975年 | 46篇 |
1974年 | 56篇 |
1973年 | 47篇 |
1972年 | 25篇 |
排序方式: 共有6117条查询结果,搜索用时 0 毫秒
91.
92.
Lina Li Jean Guenzennec Peter Nichols Pierre Henry Miki Yanagibayashi Chiaki Kato 《Journal of Oceanography》1999,55(5):635-642
Dense populations of bivalves, primarily Calyptogena sp., were observed at cold seeps of the Nankai Trough. Bacterial input to the sediment was estimated through determination of phospholipid ester-linked fatty acid (PLFA) and DNA profiles. Results indicated a bacterial biomass of 109 cells (g dry wt)-1 while individual fatty acid profiles revealed a predominance of monounsaturated fatty acids, mainly 18:1 isomers. The presence of these fatty acids can be interpreted to reflect a response to low temperature and a predominance of psychrophilic bacteria. DNA fragments encoding bacterial ribosomal RNA small-subunit sequences (16S rDNA) were amplified by the polymerase chain reaction method using DNA extracted directly from the sediment samples. From the sequencing results, at least 19 kinds of bacterial 16S rDNAs related to mostly the Proteobacteria and a few gram-positive bacteria were identified. These results suggest that the bacterial community in the Nankai Trough sediments consists of mainly bacteria belonging to the Proteobacteria , , and subdivisions. Bacteria belonging to the and subdivisions, which are known to include epibiont and sulfate reducing bacteria, respectively, were mostly detected in the sediment obtained from inside the area of the Calyptogena community, and the -Proteobacteria may function to supply reduced sulfur to bacterial endosymbionts of Calyptogena. 相似文献
93.
The use of a system of continuous culture of phytoplankton at constant population density, the ‘cage-culture’ turbidostat, as a monitor of the bioavailability of pollutant materials, is illustrated. In the case of proposed dredge spoils from two polluted areas, it is shown that bulk analyses for scheduled materials cannot be equated with bioavailability. Monitoring for the effect of the whole pollutant mixture on a properly chosen test population could obviate the necessity for chemical analyses for each component. 相似文献
94.
Tritium data were collected between 1985 and 1987 on several cruises of the German research icebreaker “Polarstern” to the Weddell Sea. Maximum tritium concentrations in the surface waters are of the order of 200 mTU. The minimum values observed in the Weddell Sea Deep Water at about 1000 m depth are about 15–40 mTU. The bottom waters show tritium concentrations of about 70–100 mTU in the central gyre, increasing to about 120 mTU in the northwestern corner of the Weddell Sea. The overflowing Ice Shelf Water observed on the continental slope west of the Filchner Depression has tritium concentrations close to those of the surface waters, indicating rapid renewal of this water mass. The data reflect the rapid renewal of the bottom waters in the northwestern corner of the Weddell Sea and the mixing of bottom water from this boundary current into the bottom waters of the central Weddell Gyre. 相似文献
95.
Identification of Danish North Sea trawl fisheries 总被引:1,自引:3,他引:1
96.
Regional variation in maturation of sandeels in the North Sea 总被引:1,自引:0,他引:1
97.
We collected surface water along the 142nd E meridian from Tasmania to Antarctica in December 1999. We measured temperature,
salinity and total chlorophyll a; additionally, we collected suspended particle size fractions and used fluorometric analysis to determine the quantity of
chlorophyll a in each of four cell size classes: picoplankton (<3 μm), two nanoplankton fractions (3–10 μm and 10–20 μm) and microplankton
(> 20 μm). Changes in temperature and salinity show that we crossed 6 water masses separated by 5 fronts. We found low abundance
(<0.2 mg m−3) of chlorophyll in all size classes, with the exception of higher values near the continent (0.2 to 0.4 mg m−3). Lowest chlorophyll values (<0.1 mg m−3) were found in the Polar Frontal Zone (51° to 54°S). Microplankton made up the largest portion of total chlorophyll throughout
most of the region. We conclude that biomass of all phytoplankton fractions, especially pico-and nanoplankton, was constrained
by limiting factors, most probably iron, throughout the region and that ecosystem dynamics within a zone are not circumpolar
but are regionalized within sectors. 相似文献
98.
We present a new system of equations designed to study global-scale dynamics in the stably-stratified portion of the solar
tachocline. This system is derived from the 3D equations of magnetohydrodynamics in a rotating spherical shell under the assumption
that the shell is thin and stably-stratified (subadiabatic). The resulting thin-shell model can be regarded as a magnetic
generalization of the hydrostatic primitive equations often used in meteorology. It is simpler in form than the more general anelastic or Boussinesq equations, making it more
amenable to analysis and interpretation and more computationally efficient. However, the thin-shell system is still three-dimensional
and as such represents an important extension to previous 2D and shallow-water approaches. In this paper we derive the governing
equations for our thin-shell model and discuss its underlying assumptions, its context relative to other models, and its application
to the solar tachocline. We also demonstrate that the dissipationless thin-shell system conserves energy, angular momentum
and magnetic helicity. 相似文献
99.
It is well known that the interaction of an interplanetary coronal mass ejection (ICME) with the solar wind leads to an equalisation
of the ICME and solar wind velocities at 1 AU. This can be understood in terms of an aerodynamic drag force per unit mass
of the form F
D/M=−(ρe
AC
D/M)(V
i−V
e)∣V
i−V
e∣, where A and M are the ICME cross-section and sum of the mass and virtual mass, V
i and V
e the speed of the ICME and solar wind, ρe the solar wind density, C
D a dimensionless drag coefficient, and the inverse deceleration length γ=ρe
A/M. The optimal radial parameterisation of γ and C
D beyond approximately 15 solar radii is calculated. Magnetohydrodynamic simulations show that for dense ICMEs, C
D varies slowly between the Sun and 1 AU, and is of order unity. When the ICME and solar wind densities are similar, C
D is larger (between 3 and 10), but remains approximately constant with radial distance. For tenuous ICMEs, the ICME and solar
wind velocities equalise rapidly due to the very effective drag force. For ICMEs denser that the ambient solar wind, both
approaches show that γ is approximately independent of radius, while for tenuous ICMEs, γ falls off linearly with distance.
When the ICME density is similar to or less than that in the solar wind, inclusion of virtual mass effects is essential. 相似文献