全文获取类型
收费全文 | 17591篇 |
免费 | 2385篇 |
国内免费 | 3952篇 |
专业分类
测绘学 | 5172篇 |
大气科学 | 2468篇 |
地球物理 | 3608篇 |
地质学 | 6467篇 |
海洋学 | 1758篇 |
天文学 | 1248篇 |
综合类 | 1587篇 |
自然地理 | 1620篇 |
出版年
2024年 | 82篇 |
2023年 | 217篇 |
2022年 | 600篇 |
2021年 | 711篇 |
2020年 | 806篇 |
2019年 | 966篇 |
2018年 | 737篇 |
2017年 | 927篇 |
2016年 | 953篇 |
2015年 | 968篇 |
2014年 | 1145篇 |
2013年 | 1363篇 |
2012年 | 1250篇 |
2011年 | 1208篇 |
2010年 | 952篇 |
2009年 | 1148篇 |
2008年 | 1150篇 |
2007年 | 1273篇 |
2006年 | 1230篇 |
2005年 | 1009篇 |
2004年 | 913篇 |
2003年 | 711篇 |
2002年 | 591篇 |
2001年 | 504篇 |
2000年 | 400篇 |
1999年 | 372篇 |
1998年 | 307篇 |
1997年 | 231篇 |
1996年 | 223篇 |
1995年 | 193篇 |
1994年 | 175篇 |
1993年 | 148篇 |
1992年 | 104篇 |
1991年 | 80篇 |
1990年 | 58篇 |
1989年 | 46篇 |
1988年 | 37篇 |
1987年 | 20篇 |
1986年 | 23篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1977年 | 12篇 |
1976年 | 4篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 7篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
123.
A New Methodology for Incorporating Tide Gauge Data in Sea Surface Topography Models 总被引:1,自引:0,他引:1
As part of the Vertical Offshore Reference Frames (VORF) project sponsored by the U. K. Hydrographic Office, a new model for Sea Surface Topography (SST) around the British Isles has been developed. For offshore areas (greater than 30 km from the coast), this model is largely derived from satellite altimetry. However, its accuracy and level of detail have been enhanced in coastal areas by the inclusion of not only the 60 PSMSL tide gauges with long-term records around the coasts of the United Kingdom and Ireland but also some 385 gauges established at different epochs and for different observation spans by the U. K. Admiralty. All tide gauge data were brought into a common reference frame by a combination of datum models and direct GPS observations, but a more significant challenge was to bring all short-term sea level observations to an unbiased value at a common epoch. This was achieved through developing a spatial-temporal correlation model for the variations in mean sea level around the British Isles, which in turn meant that gauges with long-term observation spans could be used as control points to improve the accuracy of Admiralty gauges. It is demonstrated that the latter can contribute point observations of mean sea level (MSL) with a precision of 0.078 m. A combination of least squares collocation and interpolation was developed to merge the coastal point and offshore gridded data sets, with particular algorithms having to be developed for different configurations of coastal topology. The resulting model of sea surface topography is shown to present a smooth transition from inshore coastal areas to offshore zones. Further benefits of the techniques developed include an enhanced methodology for detecting datum discontinuities at permanent tide gauges. 相似文献
124.
125.
In this study, the dynamic stresses within the seabed induced by non-linear progressive waves were explored through a series of hydraulic model tests on a movable bed within a wave flume. By comparing Stokes’ 2nd-order wave theory with the theory of wave-induced dynamic stresses within the seabed as proposed by Yamamoto et al. [1978. On the response of a poro-elastic bed to water waves. Journal of Fluid Mechanics 87 (1), 193–206.] and Hsu and Jeng [1994. Wane-induced soil response in an unsaturated anisotropic seabed of finite thickness. International Journal for Numerical and Analytical Methods in Geomechanics 18, 785–807], the experimental results show that the pressure on the seabed surface, the pore water pressure within the seabed as well as the vertical and the horizontal stresses are all smaller than their theoretical values. If we were to obtain the characteristics of seabed soil, the analytical solution of Hsu and Jeng [1994. Wane-induced soil response in an unsaturated anisotropic seabed of finite thickness. International Journal for Numerical and Analytical Methods in Geomechanics 18, 785–807] might agree to the simulation of the wave-induced effective stresses and shear stress in the sandy seabed. A different phase shift exists among all the three soil stresses. Their influences on the three dynamic stresses within seabed soil are important for seabed stability, and can be used in the verification of numerical models. In the whole, the non-linear progressive waves and the naturally deposited seabed are found to have a strong interaction, and the behavior of the induced dynamic stresses within the seabed is very complicated, and should be investigated integrally. 相似文献
126.
Bathymetric, gravity, and magnetic data from Antarctic expeditions with RV POLARSTERN and satellite altimeter data from the Geosat Geodetic Mission are analysed using methods from geostatistics and geophysical inverse theory.The Explora Escarpment represents the edge between the Antarctic Continental Shelf and the Weddell Abyssal Plain. It is an important link in the reconstruction of Gondwana breakup, but a feature as large as the 2000 m deep Wegener Canyon was only discovered in 1984, when extensive bathymetric, gravimetric, and magnetic surveys with RV POLARSTERN began.Geostatistics, the theory of regionalized variables, is applied to integrate dense surveys of Wegener Canyon and sparse observations in adjacent areas into maps with full coverage of the 230 km by 330 km area at 10°–20° W/70°–72° S. The resultant highresolution bathymetric and gravity maps reveal detailed structures of the Explora Escarpment. Using geophysical inversion, the gravity terrain effect is calculated. Satellite data are used for their better coverage, but have much lower resolution. Nevertheless, the structures of Wegener Canyon and other more prominent features appear with surprisingly good correlation also in the Geosat altimeter data. While it was initially supposed that Wegener Canyon is purely an erosional structure, the magnetic map now provides evidence of the canyon's tectonic origin. 相似文献
127.
128.
重金属锌,铅对菲律宾蛤仔的急性毒性试验 总被引:14,自引:1,他引:14
本文研究了必需元素Zn及非必需元素Pb对菲律宾蛤仔的急性毒性作用,得到Zn对其的48hLD50和96hLD50分别为147.91、16.40mg/dm^3;Pb对其的48hLD50和96hLD50分别为31.62、14.28mg/dm^3。估算得到Zn、Pb对菲律宾蛤仔的安全浓度分别为0.82、0.71mg/dm^3。 相似文献
129.
State Estimation of the North Pacific Ocean by a Four-Dimensional Variational Data Assimilation Experiment 总被引:1,自引:0,他引:1
Toshiyuki Awaji Shuhei Masuda Yoichi Ishikawa Nozomi Sugiura Takahiro Toyoda Tomohiro Nakamura 《Journal of Oceanography》2003,59(6):931-943
A four-dimensional variational data assimilation system has been applied to an experiment to describe the dynamic state of
the North Pacific Ocean. A synthesis of available observational records and a sophisticated ocean general circulation model
produces a dynamically consistent dataset, which, in contrast to the nudging approach, provides realistic features of the
seasonally-varying ocean circulation with no artificial sources/sinks for temperature and salinity fields. This new dataset
enables us to estimate heat and water mass transports in addition to the qualification of water mass formation and movement
processes. A sensitivity experiment on our assimilation system reveals that the origin of the North Pacific Intermediate Water
can be traced back to the Sea of Okhotsk and the Bering Sea in the subarctic region and to the subtropical Kuroshio region
further south. These results demonstrate that our data assimilation system is a very powerful tool for the identification
and characterization of ocean variabilities and for our understanding of the dynamic state of ocean circulation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
130.