全文获取类型
收费全文 | 9044篇 |
免费 | 940篇 |
国内免费 | 1018篇 |
专业分类
测绘学 | 2706篇 |
大气科学 | 779篇 |
地球物理 | 2071篇 |
地质学 | 2161篇 |
海洋学 | 856篇 |
天文学 | 117篇 |
综合类 | 863篇 |
自然地理 | 1449篇 |
出版年
2024年 | 30篇 |
2023年 | 115篇 |
2022年 | 370篇 |
2021年 | 441篇 |
2020年 | 429篇 |
2019年 | 474篇 |
2018年 | 250篇 |
2017年 | 365篇 |
2016年 | 361篇 |
2015年 | 383篇 |
2014年 | 478篇 |
2013年 | 564篇 |
2012年 | 580篇 |
2011年 | 544篇 |
2010年 | 406篇 |
2009年 | 443篇 |
2008年 | 469篇 |
2007年 | 588篇 |
2006年 | 505篇 |
2005年 | 440篇 |
2004年 | 394篇 |
2003年 | 368篇 |
2002年 | 301篇 |
2001年 | 294篇 |
2000年 | 220篇 |
1999年 | 191篇 |
1998年 | 195篇 |
1997年 | 155篇 |
1996年 | 120篇 |
1995年 | 116篇 |
1994年 | 119篇 |
1993年 | 78篇 |
1992年 | 54篇 |
1991年 | 25篇 |
1990年 | 29篇 |
1989年 | 28篇 |
1988年 | 34篇 |
1987年 | 18篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
41.
42.
Unlike in the open sea, the use of wind information for forecasting waves may encounter more ambiguous uncertainties in the coastal or harbor area due to the influence of complicated geometric configurations. Thus this paper attempts to forecast the waves based on learning the characteristics of observed waves, rather than the use of the wind information. This is reported in this paper by the application of the artificial neural network (ANN), in which the back-propagation algorithm is employed in the learning process for obtaining the desired results. This model evaluated the interconnection weights among multi-stations based on the previous short-term data, from which a time series of waves at a station can be generated for forecasting or data supplement based on using the neighbor stations data. Field data are used for testing the applicability of the ANN model. The results show that the ANN model performs well for both wave forecasting and data supplement when using a short-term observed wave data. 相似文献
43.
This paper reports a study of the field measurements and monitoring of wastewater discharge in sea water at Bari East (Italy). A wastewater sea outfall system is an integral and fundamental part of each wastewater treatment with ultimate sink in the sea water. The design of a water treatment plant and wastewater outfall must take into account the use of the environmental water, the values of physicochemical parameters to be respected in order to safeguard the use itself and the quality of the environmental water where wastewater is issued. In the present study measurements of sea current velocity components were carried out with a VM-ADP (Vessel-Mounted Acoustic Doppler Profiler). Salinity, wind directions and velocities were assessed with, for one survey, the total faecal coliforms and other biochemical parameters. It was emphasized that the measurements necessary for monitoring cannot be concentrated in the wastewater outfall pipe zone only, but should be extended to a neighbouring area of the outfall pipe, with an extension depending on the wastewater discharge, the polluting charge and the magnitude of the sea currents and the winds typical of the zone of interest. The analyses presented in this paper confirm that the sea zones close to the wastewater outfall pipe are particularly sensitive and vulnerable. Such results must be considered in the planning of a wastewater outfall pipe. 相似文献
44.
海底油气集输管网可靠性评估 总被引:1,自引:0,他引:1
对海底油气集输管网进行了可靠性评估,提出了一种适用于树状海底油气集输管网可靠性评价的方法,将流可靠度和单元重要度的概念引入到海底油气集输管网可靠性的分析中,该方法能够有效地评价海底油气集输管网的可靠性。 相似文献
45.
在综合的科学考察船上以异步通讯口实现的IBM-PC局部网具有较好的性能价格比。本文介绍了该网的联网环境、网络系统的组成及其拓扑结构、网络的服务功能以及网络软、硬件的安装和配置。 相似文献
46.
可靠性约束下的海底油气集输管网系统优化 总被引:1,自引:0,他引:1
在管网系统满足一定可靠度的基础上,以费用最小为优化目标,对系统进行了优化,求出了满足一定可靠度指标的费用最小的管网布置方案。对树状网络可靠性进行了评估,提出了一个0-l规划模型,并运用图论和网络理论将管网系统的优化问题转变为求可靠度至少为α的网络固的最小生成树问题。 相似文献
47.
48.
49.
A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment for more than 10 years, were tested in the laboratory. Comprehensive tests, including flexural test, strength test for corroded concrete and rusty rebar, and pullout test for bond strength between concrete and rebar, were condueted. The flexural test results of CRCBs reveal that the distribution of surface cracks on the beams shows a fractal behavior. The relationship between the fractal dimensions and mechanical properties of CRCBs is then studied. A prediction model based on artificial neural network (ANN) is established by the use of the fractal dimension as the corrosion index, together with the basic intbrmation of the beam. The validity of the prediction model is demonstrated through the experimental data, and satisfactory resuits are achieved. 相似文献
50.