全文获取类型
收费全文 | 59868篇 |
免费 | 402篇 |
国内免费 | 1048篇 |
专业分类
测绘学 | 2049篇 |
大气科学 | 3999篇 |
地球物理 | 10885篇 |
地质学 | 26385篇 |
海洋学 | 4179篇 |
天文学 | 9358篇 |
综合类 | 2207篇 |
自然地理 | 2256篇 |
出版年
2022年 | 263篇 |
2021年 | 433篇 |
2020年 | 398篇 |
2019年 | 465篇 |
2018年 | 7143篇 |
2017年 | 6357篇 |
2016年 | 4286篇 |
2015年 | 647篇 |
2014年 | 857篇 |
2013年 | 1313篇 |
2012年 | 2481篇 |
2011年 | 5280篇 |
2010年 | 4556篇 |
2009年 | 4940篇 |
2008年 | 4046篇 |
2007年 | 5072篇 |
2006年 | 1160篇 |
2005年 | 1115篇 |
2004年 | 1184篇 |
2003年 | 1248篇 |
2002年 | 983篇 |
2001年 | 574篇 |
2000年 | 491篇 |
1999年 | 346篇 |
1998年 | 343篇 |
1997年 | 329篇 |
1996年 | 254篇 |
1995年 | 263篇 |
1994年 | 236篇 |
1993年 | 183篇 |
1992年 | 209篇 |
1991年 | 181篇 |
1990年 | 195篇 |
1989年 | 188篇 |
1988年 | 156篇 |
1987年 | 183篇 |
1986年 | 170篇 |
1985年 | 205篇 |
1984年 | 198篇 |
1983年 | 197篇 |
1982年 | 188篇 |
1981年 | 192篇 |
1980年 | 185篇 |
1979年 | 183篇 |
1978年 | 158篇 |
1977年 | 142篇 |
1976年 | 140篇 |
1975年 | 136篇 |
1974年 | 125篇 |
1973年 | 166篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
The results of a laboratory experimental program aimed at better understanding the scour around and burial of heavy cylindrical objects under oscillating flow on a sandy bed are described. This study was motivated by its application to the dynamics of isolated cobbles/mines on a sandy floor under nonlinear progressive waves, such as that occur in shallow coastal waters beyond the wave-breaking region. In the experiments, nonlinear progressive waves were generated in a long wave tank of rectangular cross-section with a bottom slope. Model mines (short cylinders) were placed on the sandy bottom and the temporal evolution of the bed profile and the velocity field in the near field of the object were observed. Experiments were conducted at relatively high Reynolds numbers for a range of flow conditions, which can be characterized by the Keulegan–Carpenter number and Shields parameter. Depending on the values of these parameters, four different scour regimes around the cylinder including periodical burial of cylinder under migrating sand ripples were observed; they were classified as: (i) no scour/burial, (ii) initial scour, (iii) expanded scour, and (iv) periodic burial cases. A scour regime diagram was developed and the demarcation criteria between different regimes were deduced. Semi-empirical formulae that permit estimation of the scour depth with time, the equilibrium maximum scour depth and length, and conditions necessary for the burial of the cylinder as a function of main external parameters are also proposed. 相似文献
202.
We have examined wind-induced circulation in the Sea of Okhotsk using a barotropic model that contains realistic topography
with a resolution of 9.25 km. The monthly wind stress field calculated from daily European Centre for Medium-Range Weather
Forecasting (ECMWF) Re-Analysis data is used as the forcing, and the integration is carried out for 20 days until the circulation
attains an almost steady state. In the case of November (a representative for the winter season from October to March), southward
currents of velocity 0.1–0.3 m s−1 occur along the bottom contours off the east of Sakhalin Island. The currents are mostly confined to the shelf (shallower
than 200 m) and extend as far south as the Hokkaido coast. In the July case (a representative for the summer season from April
to September), significant currents do not occur, even in the shallow shelves. The simulated southward current over the east
Sakhalin shelf appears to correspond to the near-shore branch of the East Sakhalin Current (ESC), which was observed with
the surface drifters. These seasonal variations simulated in our experiments are consistent with the observations of the ESC.
Dynamically, the simulated ESC is interpreted as the arrested topographic wave (ATW), which is the coastally trapped flow
driven by steady alongshore wind stress. The volume transport of the simulated ESC over the shelf reaches about 1.0 Sv (1
Sv = 106 m3s−1) in the winter season, which is determined by the integrated onshore Ekman transport in the direction from which shelf waves
propagate.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
203.
Spatial and Temporal Variations of Sound Speed at the PN Section 总被引:3,自引:0,他引:3
Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section
in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are
mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the
upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone.
Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance
are almost equivalent.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
204.
205.
V. I. Valsenko 《Physical Oceanography》1992,3(6):417-424
A numerical model is developed for the generation of internal waves induced by a barotropic tidal wave travelling over large bottom features. Motion equations consider the non-linear terms, as well as the terms responsible for horizontal turbulent exchange. The fluid is assumed to be continuously stratified. In the framework of the developed model, a packet of short non-linear internal waves is shown to occur together with a long baroclinic tide. In the absence of non-linear terms in the equations of motion, the model data are qualitatively and quantitatively consistent with the data provided by known linear models.Translated by V. Puchkin. 相似文献
206.
207.
The expansion of the temperature anomaly field in the North Atlantic is considered using natural orthogonal functions of depth. It is shown that the first few components of this expansion describe the field both at the surface and in the upper 1000 m layer accurately enough. The relation between the water temperature anomaly at some levels and the above components is estimated for various regions of the ocean.Translated by Mikhail M. Trufanov. 相似文献
208.
209.
Some aspects of the upper ocean layer dynamics are considered, including the Ekman transport, the relation of the thickness of the quasi-homogeneous layer to the thickness of the layer of rotation of the drift current vector, and the correlation between the level of the turbulent energy dissipation and the thickness of the quasi-homogeneous layer. 相似文献
210.