全文获取类型
收费全文 | 82548篇 |
免费 | 1755篇 |
国内免费 | 1417篇 |
专业分类
测绘学 | 2219篇 |
大气科学 | 6108篇 |
地球物理 | 16038篇 |
地质学 | 29923篇 |
海洋学 | 7521篇 |
天文学 | 18891篇 |
综合类 | 406篇 |
自然地理 | 4614篇 |
出版年
2022年 | 578篇 |
2021年 | 943篇 |
2020年 | 976篇 |
2019年 | 1066篇 |
2018年 | 2226篇 |
2017年 | 2131篇 |
2016年 | 2623篇 |
2015年 | 1510篇 |
2014年 | 2533篇 |
2013年 | 4341篇 |
2012年 | 2858篇 |
2011年 | 3722篇 |
2010年 | 3261篇 |
2009年 | 4182篇 |
2008年 | 3584篇 |
2007年 | 3643篇 |
2006年 | 3497篇 |
2005年 | 2584篇 |
2004年 | 2502篇 |
2003年 | 2352篇 |
2002年 | 2260篇 |
2001年 | 1945篇 |
2000年 | 1861篇 |
1999年 | 1516篇 |
1998年 | 1597篇 |
1997年 | 1487篇 |
1996年 | 1287篇 |
1995年 | 1251篇 |
1994年 | 1072篇 |
1993年 | 956篇 |
1992年 | 941篇 |
1991年 | 920篇 |
1990年 | 1010篇 |
1989年 | 819篇 |
1988年 | 780篇 |
1987年 | 915篇 |
1986年 | 782篇 |
1985年 | 973篇 |
1984年 | 1135篇 |
1983年 | 976篇 |
1982年 | 954篇 |
1981年 | 853篇 |
1980年 | 820篇 |
1979年 | 788篇 |
1978年 | 765篇 |
1977年 | 671篇 |
1976年 | 621篇 |
1975年 | 617篇 |
1974年 | 594篇 |
1973年 | 645篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
961.
The paper is concerned with the evaluation of the drift current parameters derived through the use of an analytical model.
In this model, effective when stratification is stable and indifferent, the vertical turbulence coefficient profile is prescribed
by the power function, and hydrodynamic quantities are prescribed using the external parameters of the problem (wind stress,
the Coriolis parameter, and the dimensionless stratification parameter). Model data are compared with the observations of
the upper mixed layer in the vicinity of the oceanic Station C, conducted during one year. It is shown that, under the spring-summer-time
warming conditions, the model at issue is capable of adequately simulating the upper ocean layer dynamics.
Translated by Vladimir A. Puchkin. 相似文献
962.
963.
The problem of the seasonal variations of temperature and salinity in the intermediate zone located between the West African and the Gulf of Guinea upwellings is considered. The vertical distribution of the phase-amplitude characteristics of the annual and semi-annual variations is examined in good detail and their parameters are defined from the monthly means using the least-squares fit technique. The contribution of isopycnic advection to the formation of seasonal thermohaline variations is studied.Translated by Vladimir A. Puchkin. 相似文献
964.
965.
966.
This paper studies the influence of shelf tidal flows on the structure of surface and near-bottom turbulent boundary layers.Translated by Vladimir A. Puchkin. 相似文献
967.
Cabell S. Davis Scott M. Gallager Martin Marra W. Kenneth Stewart 《Deep Sea Research Part II: Topical Studies in Oceanography》1996,43(7-8)
Traditional methods for determining spatial distributions of planktonic taxa involve net, pump, and bottle collections followed by the tedious and time-consuming task of plankton sample analysis. Thus, plankton ecologists often require months or even years to process samples from a single study. In this paper, we present a method that allows rapid visualization of the distribution of planktonic taxa while at sea. Rapid characterization of plankton distributions is essential in the dynamic physical environment, where biological and physical patterns can change quickly. Such a “sample-and-observe” capability is necessary for mapping ephemeral features (such as patches, eddies, jets, plumes) and determining appropriate locations to conduct more localized sampling, including in situ observational studies. We describe the techniques used in imaging the plankton, analyzing the video, and visualizing the data. We present an example of at-sea data analysis conducted aboard R.V. Columbus Iselin on Georges Bank in May 1994 and visualizations of the 3-dimensional distribution of selected planktonic taxa in a 2 × 2 km × 90 m volume of seawater. A video of the image processing and visualization is included on the CD-ROM accompanying this volume and is an essential part of this paper. 相似文献
968.
969.
970.
Characterization of interface roughness of rippled sand off Fort Walton Beach, Florida 总被引:1,自引:0,他引:1
As part of the environmental characterization to model acoustic bottom scattering during the high-frequency sediment acoustics experiment (SAX99), fine-scale sediment roughness of a medium sand was successfully measured within a 600 /spl times/ 600-m area by two methods: stereo photography and a technique using a conductivity system. Areal coverage of the two methods, representing approximately 0.16 m/sup 2/ of the sea floor, was comparable, resulting in the depiction and quantification of half-meter wavelength sand ripples. Photogrammetric results were restricted to profiles digitized at 1-mm intervals; sediment conductivity results generated gridded micro-bathymetric measurements with 1- to 2-cm node spacing. Roughness power spectra give similar results in the low-spatial-frequency domains where the spectra estimated from both approaches overlap. However, spectra derived from higher resolution photogrammetric results appear to exhibit a multiple-power-law fit. Roughness measurements also indicate that spectrum changes as a function of time. Application of statistical confidence bounds on the power spectra indicates that roughness measurements separated by only 1-2 m may be spatially nonstationary. 相似文献