全文获取类型
收费全文 | 72082篇 |
免费 | 1450篇 |
国内免费 | 660篇 |
专业分类
测绘学 | 1732篇 |
大气科学 | 5176篇 |
地球物理 | 14485篇 |
地质学 | 25543篇 |
海洋学 | 6274篇 |
天文学 | 16541篇 |
综合类 | 208篇 |
自然地理 | 4233篇 |
出版年
2022年 | 401篇 |
2021年 | 711篇 |
2020年 | 794篇 |
2019年 | 835篇 |
2018年 | 1923篇 |
2017年 | 1784篇 |
2016年 | 2270篇 |
2015年 | 1350篇 |
2014年 | 2220篇 |
2013年 | 3831篇 |
2012年 | 2303篇 |
2011年 | 3178篇 |
2010年 | 2655篇 |
2009年 | 3581篇 |
2008年 | 3314篇 |
2007年 | 3101篇 |
2006年 | 2933篇 |
2005年 | 2400篇 |
2004年 | 2288篇 |
2003年 | 2161篇 |
2002年 | 1948篇 |
2001年 | 1822篇 |
2000年 | 1741篇 |
1999年 | 1394篇 |
1998年 | 1484篇 |
1997年 | 1400篇 |
1996年 | 1114篇 |
1995年 | 1156篇 |
1994年 | 979篇 |
1993年 | 886篇 |
1992年 | 862篇 |
1991年 | 771篇 |
1990年 | 863篇 |
1989年 | 723篇 |
1988年 | 660篇 |
1987年 | 826篇 |
1986年 | 675篇 |
1985年 | 872篇 |
1984年 | 943篇 |
1983年 | 883篇 |
1982年 | 855篇 |
1981年 | 715篇 |
1980年 | 684篇 |
1979年 | 618篇 |
1978年 | 612篇 |
1977年 | 558篇 |
1976年 | 540篇 |
1975年 | 503篇 |
1974年 | 509篇 |
1973年 | 471篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
992.
N. A. Bond J. M. Adams 《Deep Sea Research Part II: Topical Studies in Oceanography》2002,49(26):5869-5887
The atmospheric forcing of the Bering Sea over its eastern shelf is estimated using the 40-year record of daily data from the NCEP/NCAR Reanalysis. This data set includes estimates of the processes responsible for the atmospheric forcing, namely the surface fluxes of momentum, sensible and latent heat, and longwave and shortwave radiation, and therefore permits quantifying effects that previously could be inferred only from the large-scale nature of the flow. The forcing in 1995–1999 is described in detail using daily time series; historical context for these results is provided with seasonal averages for the years 1959–1999.The analysis for winter concentrates on aspects related to the formation and advection of sea ice. Results indicate that the presence of sea ice is strongly related to the net surface-heat fluxes as well as the cross-shelf component of the wind. The 40-year record lacks any discernible long-term trend in the winter forcing and response. There was a notably cold period in the early to middle 1970s, and a warm period from the late 1970s into the early 1980s, but conditions during the 1990s are similar to those in the late 1950s and 1960s.The analysis for the warm season focuses on the mechanisms responsible for the variability in SST warming. Much of the intraseasonal and interannual variability in this warming can be attributed to variations in the downward shortwave radiation (solar heating). The 40-year record does indicate a long-term trend toward increased solar heating, and reduced surface latent-heat fluxes (evaporative cooling). These changes have led to August SSTs in the 1990s that are roughly 1°C warmer than in the 1960s. 相似文献
993.
Vibracores and auger samples collected from the lower (tidal) delta plain of the Ganges-Brahmaputra River in Bangladesh were examined to determine whether the area is a significant sink for riverine sediments. Measurements of 137Cs activity and radiocarbon in the sediments indicate sediment accumulation is taking place on decadal and millennial time scales at rates reaching 1.1 cm/year. The sediment of the lower delta plain is primarily derived from an offshore source after having originally been supplied by the Ganges-Brahmaputra river system, carried westward by prevailing currents and advected inland by monsoonal coastal setup and cyclonic events. 相似文献
994.
995.
996.
997.
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
998.
The Blake Outer Ridge is a 480–kilometer long linear sedimentary drift ridge striking perpendicular to the North American
coastline. By modeling free-air gravity anomalies we tested for the presence of a crustal feature that may control the location
and orientation of the Blake Outer Ridge. Most of our crustal density models that match observed gravity anomalies require
an increase in oceanic crustal thickness of 1–3 km on the southwest side of the Blake Outer Ridge relative to the northeast
side. Most of these models also require 1–4 km of crustal thinning in zone 20–30 km southwest of the crest of the Blake Outer
Ridge. Although these features are consistent with the structure of oceanic fracture zones, the Blake Outer Ridge is not parallel
to adjacent known fracture zones. Magnetic anomalies suggest that the ocean crust beneath this feature formed during a period
of mid-ocean ridge reorganization, and that the Blake Outer Ridge may be built upon the bathymetric expression of an oblique
extensional feature associated with ridge propagation. It is likely that the orientation of this trough acted as a catalyst
for sediment deposition with the start of the Western Boundary Undercurrent in the mid-Oligocene. 相似文献
999.
Multi-AUV Control and Adaptive Sampling in Monterey Bay 总被引:3,自引:0,他引:3
Edward Fiorelli Naomi Ehrich Leonard Pradeep Bhatta Derek A. Paley Ralf Bachmayer David M. Fratantoni 《Oceanic Engineering, IEEE Journal of》2006,31(4):935-948
Operations with multiple autonomous underwater vehicles (AUVs) have a variety of underwater applications. For example, a coordinated group of vehicles with environmental sensors can perform adaptive ocean sampling at the appropriate spatial and temporal scales. We describe a methodology for cooperative control of multiple vehicles based on virtual bodies and artificial potentials (VBAP). This methodology allows for adaptable formation control and can be used for missions such as gradient climbing and feature tracking in an uncertain environment. We discuss our implementation on a fleet of autonomous underwater gliders and present results from sea trials in Monterey Bay in August, 2003. These at-sea demonstrations were performed as part of the Autonomous Ocean Sampling Network (AOSN) II project 相似文献
1000.
We apply the second-order moment (SOM) advection scheme of (Prather, M.J. 1986. Numerical advection by conservation of second-order moments. J. Geophys. Res. 91, 6671–6681.) to the simulation of the large-scale circulation of the Arctic Ocean with a coupled ocean–sea-ice model. Compared to three other advection schemes commonly employed in ocean simulations (centred differences, flux corrected transport, and multidimensional positive definite advection transport), the SOM method helps preserve the vertical structure of Arctic water masses. The depth, thickness and hydrographic properties of the Arctic Surface Water and the Arctic Atlantic Layer are better represented with SOM than with any of the other three advection algorithms. We also present a convenient method for calculating the implicit numerical diffusivity of upstream based schemes, such as the SOM method, and discuss three approaches for improving the monotonicity properties of the SOM algorithm. 相似文献