全文获取类型
收费全文 | 28371篇 |
免费 | 4238篇 |
国内免费 | 5066篇 |
专业分类
测绘学 | 2919篇 |
大气科学 | 2815篇 |
地球物理 | 5426篇 |
地质学 | 12465篇 |
海洋学 | 3798篇 |
天文学 | 5223篇 |
综合类 | 1877篇 |
自然地理 | 3152篇 |
出版年
2024年 | 74篇 |
2023年 | 283篇 |
2022年 | 698篇 |
2021年 | 996篇 |
2020年 | 1025篇 |
2019年 | 1090篇 |
2018年 | 931篇 |
2017年 | 1069篇 |
2016年 | 1070篇 |
2015年 | 1252篇 |
2014年 | 1680篇 |
2013年 | 2005篇 |
2012年 | 1726篇 |
2011年 | 1952篇 |
2010年 | 1842篇 |
2009年 | 2143篇 |
2008年 | 2080篇 |
2007年 | 2043篇 |
2006年 | 2029篇 |
2005年 | 1706篇 |
2004年 | 1521篇 |
2003年 | 1288篇 |
2002年 | 1125篇 |
2001年 | 986篇 |
2000年 | 846篇 |
1999年 | 745篇 |
1998年 | 678篇 |
1997年 | 481篇 |
1996年 | 368篇 |
1995年 | 355篇 |
1994年 | 326篇 |
1993年 | 282篇 |
1992年 | 191篇 |
1991年 | 152篇 |
1990年 | 121篇 |
1989年 | 131篇 |
1988年 | 77篇 |
1987年 | 51篇 |
1986年 | 46篇 |
1985年 | 52篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 4篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1971年 | 3篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
112.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae. 相似文献
113.
1 INTRODUCTIONThe South China Sea (SCS) is a semi-enclosedmarginal sea in western North Pacific Ocean withvery complex topography and is the important pas-sage connecting the Pacific and Indian Oceans. Ithas great impact to the global climate and a greatinterest of many oceanography researchers. Twodominant surface hydrographic and circulation fea-tures in the northern SCS are a strong fresh waterexpansion and a warm and high-salinity seawaterintrusion such as the SCS Diluted Water… 相似文献
114.
115.
116.
提要 本文详细讨论了一种三维重力位场快速正反演方法。作者在前人工作的基础上,对算法作了行之有效的改进,通过对反演中的不稳定因素进行各种理论模型试算,得出保证迭代反演稳定收敛的准则,编制出可在微型机IBM—PC上运行的人机对话式自动正反演程序。本文还对各种不均质模型进行了模似计算并将该方法应用于某含油气沉积盆地的双层界面构造研究,揭示出了储油有利地段。 相似文献
117.
林菁 《广东海洋大学学报》1996,(1)
分析了分频和CTC计数采样中误读数的原因和解决方法,并利用微机软件实现非线性校正。此传感器用于位移测量系统中,具有0.01mm的分辨率及优于1%的精度,可在-20~60℃温度范围内工作。 相似文献
118.
119.
Yanjun ZHANG Fenglong ZHANG Full QI Fuquan NI 《东北亚地学研究》2006,9(2):199-203
In view of the situation of excavation of open coal mine for the underground water disaster,we should carry out simulation studies for the numerical value of the water lowering project and improve the accuracy and the level of the water lowering project.On the basis of the hydrological geological conditions of certain open mine digging,a more reasonable seepage numerical model was built according to MODFLOW.It was simulated in advance that the process of the confined water level descending with the time,and combining with the actual observations to test the correctness of the model.The calculation showed that the results coincided well with the results of actual measurement.Based on this,different water lowering numerical simulations were built for the open coal mine digging.It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit,and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process,which provide an important basis for the actual water lowering project and the possible project disposal. 相似文献
120.
Natural and agricultural wetlands are considered to be the major sources of global atmospheric methane (CH4). A one‐dimensional model was developed to simulate methane emission and used to examine the influence of various physical processes on the rate of methane emission. Three processes involved in the methane emission are implemented in the model: production, reoxidation and transport. Three transport pathways were considered: diffusion across water–air or soil–air interfaces, ebullition and diffusion through plants. These pathways are influenced by soil properties, plant growth, water‐table conditions, temperature and external inputs (e.g. fertilizer). The model was used to examine the seasonal variation of the methane emission at a rice field in Hunan, China, which was observed during a field experiment for consecutive (early and late) rice seasons in 1992. The observed seasonal variations of methane emission, and role of plants in transporting methane to the atmosphere, are captured by the model simulation. Further model applications were conducted to simulate effects of fertilizer and water‐level condition on the methane emission. The results indicate that unfermented organic fertilizer produces a higher methane emission rate than mineral fertilizer. The simulations with treatments of a deep‐water covering and constant moisture reduced the methane emission. The rice field study provides a framework for further development of the model towards simulations based on spatially distributed variables (e.g. water table, soil temperature and vegetation) at a regional scale. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献