全文获取类型
收费全文 | 2566篇 |
免费 | 729篇 |
国内免费 | 775篇 |
专业分类
测绘学 | 182篇 |
大气科学 | 285篇 |
地球物理 | 814篇 |
地质学 | 1846篇 |
海洋学 | 606篇 |
天文学 | 9篇 |
综合类 | 122篇 |
自然地理 | 206篇 |
出版年
2024年 | 8篇 |
2023年 | 46篇 |
2022年 | 94篇 |
2021年 | 104篇 |
2020年 | 158篇 |
2019年 | 155篇 |
2018年 | 154篇 |
2017年 | 122篇 |
2016年 | 150篇 |
2015年 | 167篇 |
2014年 | 219篇 |
2013年 | 235篇 |
2012年 | 188篇 |
2011年 | 209篇 |
2010年 | 188篇 |
2009年 | 185篇 |
2008年 | 165篇 |
2007年 | 182篇 |
2006年 | 192篇 |
2005年 | 166篇 |
2004年 | 140篇 |
2003年 | 129篇 |
2002年 | 84篇 |
2001年 | 83篇 |
2000年 | 92篇 |
1999年 | 66篇 |
1998年 | 59篇 |
1997年 | 67篇 |
1996年 | 58篇 |
1995年 | 36篇 |
1994年 | 38篇 |
1993年 | 30篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有4070条查询结果,搜索用时 15 毫秒
101.
土壤水分深层渗漏是陆地近地层水分循环的重要环节。利用土壤水分深层渗漏记录仪对毛乌素沙地典型流动沙丘不同深度土层的土壤渗漏水量连续进行两年定点监测。结果表明:(1)2016年生长季(4月1日至10月31日)降水量为2017年的1.93倍,但50、100、200 cm沙层的渗漏水量分别是2017年同期的4.53、5.53,5.22倍。同时,渗漏水量与降雨量及土壤蓄水量的波峰较一致。(2)强降雨对深层渗漏水量的影响较大,土壤蓄水量的变化也与深层渗漏水量密切相关;降雨量较小时,土壤蓄水量与深层渗漏水量之间的关系更为密切。在连续降雨过程中,越往深处,渗漏的产生通常是多次降雨过程累积的结果,将土壤蓄水量作为中间变量,能更好地分析土壤深层渗漏过程。(3)当天蓄水量与次日渗漏水量的相关系数较高,土层越深,深层渗漏水量与土壤蓄水量的相关系数增加,二者之间的线性拟合的R2也相应增加。 相似文献
102.
Impact of climate change on 24‐h design rainfall depth estimation in Qiantang River Basin,East China
The frequency and magnitude of extreme meteorological or hydrological events such as floods and droughts in China have been influenced by global climate change. The water problem due to increasing frequency and magnitude of extreme events in the humid areas has gained great attention in recent years. However, the main challenge in the evaluation of climate change impact on extreme events is that large uncertainty could exist. Therefore, this paper first aims to model possible impacts of climate change on regional extreme precipitation (indicated by 24‐h design rainfall depth) at seven rainfall gauge stations in the Qiantang River Basin, East China. The Long Ashton Research Station‐Weather Generator is adopted to downscale the global projections obtained from general circulation models (GCMs) to regional climate data at site scale. The weather generator is also checked for its performance through three approaches, namely Kolmogorov–Smirnov test, comparison of L‐moment statistics and 24‐h design rainfall depths. Future 24‐h design rainfall depths at seven stations are estimated using Pearson Type III distribution and L‐moment approach. Second, uncertainty caused by three GCMs under various greenhouse gas emission scenarios for the future periods 2020s (2011–2030), 2055s (2046–2065) and 2090s (2080–2099) is investigated. The final results show that 24‐h design rainfall depth increases in most stations under the three GCMs and emission scenarios. However, there are large uncertainties involved in the estimations of 24‐h design rainfall depths at seven stations because of GCM, emission scenario and other uncertainty sources. At Hangzhou Station, a relative change of ?16% to 113% can be observed in 100y design rainfall depths. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
103.
The governments around the Baltic Sea have agreed on a new set of targets for nutrient load reductions. The major motive for this is new and better knowledge about the link between nutrient loads and water transparency in different parts of the sea. The Baltic Sea Action Plan (BSAP) defines target for transparency in different marine basins, the load reductions necessary to meet transparency targets and a scheme for the distribution of the abatement burden between countries adjacent to the sea. 相似文献
104.
105.
106.
The monsoon reversal winds in different seasons and high influx of freshwater from various rivers make the Bay of Bengal (BoB) a unique region. Thus, the knowledge of the dynamics of the mixed layer over this region is very important to assess the climatic variation of the Indian subcontinent. A comprehensive study of the role of external forcing on the seasonal and interannual mixed layer depth (MLD) variability over the BoB is carried out for 36 years (1980–2015) using reanalysis products. A weak and strong seasonality of MLD is observed over the northern and the southern BoB (NBoB and SBoB) respectively. The partial correlation suggests that the net heat flux (Qnet) is the major contributor to the deepening of MLD over the NBoB, whereas the wind stress controls the deepening over the SBoB. The seasonal variability reveals the deepening of MLD during summer and winter monsoon and the shallowing during pre- and post-monsoon over the BoB. The relation of the interannual MLD variability and the different phases of the Indian Ocean Dipole (IOD) reveals that the negative phase of IOD is associated with deeper MLD over BoB while the positive phase of IOD depicts shallower MLD. In addition, the opposing characteristic of MLD is highly prominent during October-December. This is majorly contributed by variations related to the second downwelling Kelvin and associated Rossby waves over BoB for the opposing phases of the IOD years. 相似文献
107.
中国海岸带分布规律及其海部要素变化检测 总被引:2,自引:1,他引:1
在海岸带图测绘完成后,海部要素的变化是导致海岸带图使用价值降低的重要因素.根据我国海岸的组成物质将其归纳为淤泥质海岸、沙砾质海岸、基岩海岸、红树海岸和珊瑚海岸,并归纳总结了每一种海岸的空间分布规律.分析了影响海岸线、干出滩以及近海水深等海部要素变化的主要因素,海岸要素变化的因素和变化规律,进而提出了海部要素实质性变化的检测统计方法,对提高海岸带图测绘效率、缩短成图周期、确定更新周期和制定更新方案都具有重要的意义. 相似文献
108.
岩石锚桩基础的承压力与抗拔力之应用 总被引:1,自引:0,他引:1
根据“110kV绩溪-旌德”线路现场设计及施工情况,系统总结了岩石锚桩基础在中风化、强风化的山区中的应用经验,分析了工程设计中锚筋内力、锚桩承载力和粘结力之间关系,合理采用计算公式,获得较好效果。 相似文献
109.
ZHANG Jiarui MENG Qingsheng ZHANG Yan FENG Xiuli WEI Guanli SU Xiuting LIU Tao 《中国海洋大学学报(英文版)》2022,21(2):361-374
Partial drainage often occurs during piezocone penetration testing on Yellow River Delta silt because of its intermediate physical and mechanical properties between those of sand and clay.Yet,there is no accurate understanding for the range of penetra-tion rates to trigger the partial drainage of silt soils.In order to fully investigate cone penetration rate effects under partial drainage condi-tions,indoor 1 g penetration model tests and numerical simulations of cavity expansion at variable penetration rates were carried out on the Yellow River Delta silt.The boundary effect of the model tests and the variation of key parameters at the different cavity ex-pansion rates were analyzed.The 1 g penetration model test results and numerical simulations results consistently indicated that the penetration rate to trigger the partially drainage of typical silt varied at least three orders of magnitude.The numerical simulations also provide the reference values for the penetration resistance corresponding to zero dilation and zero viscosity at any given normalized penetration rate for silt in Yellow River Delta.These geotechnical properties can be used for the design of offshore platforms in Yel-low River Delta,and the understanding of cone penetration rate effects under the partially drained conditions would provide some technical support for geohazard evaluation of offshore platforms. 相似文献
110.
Maria Cristina Gambi Maurizio Lorenti Giovanni F. Russo Maria Beatrice Scipione Valerio Zupo 《Marine Ecology》1992,13(1):17-39
Abstract. The taxonomical and trophic structures of the vagile fauna communities of the leaf stratum in a Posidonia oceanica meadow at Ischia (Gulf of Naples, Italy) were investigated at five stations along a depth gradient (1 to 25 m). Sampling was performed in July, November, February, and May. The analyzed groups - polychaetes, molluscs, tanaids, isopods, amphipods, and decapods - exhibited similar distributional trends in all seasons, with coenotic discontinuities occurring at well-defined depths. The same zonation pattern was produced by feeding-guild analysis. Eleven trophic groups were identified. The most abundant groups were: Herbivores, which were found mainly at the shallow stations; Herbivores-deposit feeders, which were widely distributed along the transect; Deposit feeders-carnivores, found mainly at the deep stations.
This study suggests that in the Posidonia leaf stratum, herbivores and herbivores-deposit feeders, as consumers of epiphytic micro- and macroflora and deposited particulate organic matter, play an important role in the energy transfer from producers to higher trophic levels of the system. 相似文献
This study suggests that in the Posidonia leaf stratum, herbivores and herbivores-deposit feeders, as consumers of epiphytic micro- and macroflora and deposited particulate organic matter, play an important role in the energy transfer from producers to higher trophic levels of the system. 相似文献