全文获取类型
收费全文 | 91809篇 |
免费 | 1261篇 |
国内免费 | 800篇 |
专业分类
测绘学 | 2443篇 |
大气科学 | 6633篇 |
地球物理 | 17086篇 |
地质学 | 35045篇 |
海洋学 | 7815篇 |
天文学 | 19983篇 |
综合类 | 352篇 |
自然地理 | 4513篇 |
出版年
2022年 | 459篇 |
2021年 | 802篇 |
2020年 | 871篇 |
2019年 | 920篇 |
2018年 | 4168篇 |
2017年 | 3884篇 |
2016年 | 3523篇 |
2015年 | 1399篇 |
2014年 | 2338篇 |
2013年 | 4015篇 |
2012年 | 3253篇 |
2011年 | 5229篇 |
2010年 | 4589篇 |
2009年 | 5484篇 |
2008年 | 4605篇 |
2007年 | 5148篇 |
2006年 | 3021篇 |
2005年 | 2587篇 |
2004年 | 2489篇 |
2003年 | 2438篇 |
2002年 | 2245篇 |
2001年 | 1854篇 |
2000年 | 1789篇 |
1999年 | 1411篇 |
1998年 | 1423篇 |
1997年 | 1405篇 |
1996年 | 1184篇 |
1995年 | 1159篇 |
1994年 | 1058篇 |
1993年 | 905篇 |
1992年 | 907篇 |
1991年 | 869篇 |
1990年 | 924篇 |
1989年 | 778篇 |
1988年 | 787篇 |
1987年 | 833篇 |
1986年 | 750篇 |
1985年 | 962篇 |
1984年 | 1018篇 |
1983年 | 969篇 |
1982年 | 905篇 |
1981年 | 808篇 |
1980年 | 827篇 |
1979年 | 763篇 |
1978年 | 724篇 |
1977年 | 627篇 |
1976年 | 585篇 |
1975年 | 572篇 |
1974年 | 543篇 |
1973年 | 558篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Cluster analysis is discussed in the context of its application to map various test areas in the sea. By analysing the correspondence of the identified categories to areas with specific hydrological conditions, an attempt is made to relate the types of fine structure to diverse background conditions. With two test areas mapped, a conclusion is made as to the possible application of cluster analysis to this end.Translated by Vladimir A. Puchkin. 相似文献
982.
Digital underwater acoustic voice communications 总被引:2,自引:0,他引:2
This paper describes the design of an underwater acoustic diver communication system controlled by a digital signal processor. The speech signal transmission rate is compressed by using linear predictive coding (LPC) and the extracted parameters are transmitted through the water to a synchronized receiver by employing digital pulse position modulation (DPPM). The pulse position in each time frame is estimated by an energy detection and decision algorithm which enables the received LPC parameters to be recovered and used to synthesize the speech signal 相似文献
983.
984.
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
985.
Determination of characteristics of atmospheric motions from satellite multiwave remote sensing data
A. F. Nerushev E. K. Kramchaninova V. I. Solov’ev 《Izvestiya Atmospheric and Oceanic Physics》2007,43(4):442-450
A method of determination of atmospheric dynamic characteristics from the data of remote sensing from a geostationary satellite is described. The method is based on the use of inhomogeneities in the concentration field of a conservative additive as tracers and on the application of correlation-extreme algorithms. Unlike the common methods used abroad, this method is able to determine not only the vector field of wind velocity but also the coefficient of turbulent diffusion and vorticity. Results of computations of the fields of the horizontal component of wind velocity and the effective coefficient of horizontal mesoscale turbulent diffusion from the Meteosat-8 SEVIRI water-vapor channel data are presented. It is shown that the average values of the effective coefficient of mesoscale horizontal turbulent diffusion in the areas with a predominantly turbulized air-mass motion are 1.5 times greater than in the areas where a laminar motion dominates. Specific features of the calculated values of the upper-troposphere dynamic characteristics in different stages of the North Atlantic TC Helene (September 2006) are analyzed. 相似文献
986.
987.
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
988.
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
989.
990.