全文获取类型
收费全文 | 3287篇 |
免费 | 573篇 |
国内免费 | 731篇 |
专业分类
测绘学 | 130篇 |
大气科学 | 720篇 |
地球物理 | 726篇 |
地质学 | 1794篇 |
海洋学 | 391篇 |
天文学 | 165篇 |
综合类 | 343篇 |
自然地理 | 322篇 |
出版年
2024年 | 14篇 |
2023年 | 51篇 |
2022年 | 158篇 |
2021年 | 170篇 |
2020年 | 115篇 |
2019年 | 123篇 |
2018年 | 167篇 |
2017年 | 157篇 |
2016年 | 180篇 |
2015年 | 152篇 |
2014年 | 201篇 |
2013年 | 180篇 |
2012年 | 169篇 |
2011年 | 179篇 |
2010年 | 203篇 |
2009年 | 192篇 |
2008年 | 166篇 |
2007年 | 148篇 |
2006年 | 106篇 |
2005年 | 94篇 |
2004年 | 56篇 |
2003年 | 85篇 |
2002年 | 80篇 |
2001年 | 92篇 |
2000年 | 107篇 |
1999年 | 162篇 |
1998年 | 119篇 |
1997年 | 141篇 |
1996年 | 129篇 |
1995年 | 114篇 |
1994年 | 106篇 |
1993年 | 87篇 |
1992年 | 77篇 |
1991年 | 60篇 |
1990年 | 51篇 |
1989年 | 44篇 |
1988年 | 40篇 |
1987年 | 14篇 |
1986年 | 25篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1969年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有4591条查询结果,搜索用时 640 毫秒
521.
Taotao Zhang Yang Xiao Dongfang Liang Hongwu Tang Junzeng Xu Saiyu Yuan Nairu Wang Bin Luan 《水文研究》2021,35(5):e14152
Dissolved pollutants in stormwater are a main contributor to water pollution in urban environments. However, many existing transport models are semi-empirical and only consider one-dimensional flows, which limit their predictive capacity. Combining the shallow water and the advection–diffusion equations, a two-dimensional physically based model is developed for dissolved pollutant transport by adopting the concept of a ‘control layer’. A series of laboratory experiments has been conducted to validate the proposed model, taking into account the effects of buildings and intermittent rainfalls. The predictions are found to be in good agreement with experimental observations, which supports the assumption that the depth of the control layer is constant. Based on the validated model, a parametric study is conducted, focusing on the characteristics of the pollutant distribution and transport rate over the depth. The hyetograph, including the intensity, duration and intermittency, of rainfall event has a significant influence on the pollutant transport rates. The depth of the control layer, rainfall intensity, surface roughness and area length are dominant factors that affect the dissolved pollutant transport. Finally, several perspectives of the new pollutant transport model are discussed. This study contributes to an in-depth understanding of the dissolved pollutant transport processes on impermeable surfaces and urban stormwater management. 相似文献
522.
Journal of Oceanology and Limnology - Jellyfish blooms occur worldwide and have resulted in serious problems in tourism, fisheries, coastal industries, and the marine ecosystem. The life cycle of... 相似文献
523.
Liu Zhankun Chen Jin Mao Xiancheng Tang Lei Yu Shuyan Deng Hao Wang Jinli Liu Yuqiao Li Shoulei Bayless Richard C. 《Natural Resources Research》2021,30(6):3987-4007
Natural Resources Research - The Xiadian orogenic deposit with?~?100 t of gold resources, located in the Jiaodong Peninsula, Eastern China, shows an economically attractive gold... 相似文献
524.
Relationships Between Community Structure and Environmental Factors in Xixiakou Artificial Reef Area
Haolin Yu Wenzhao Yang Changdong Liu Yanli Tang Xiefa Song Guangjie Fang 《中国海洋大学学报(英文版)》2020,19(4):883-894
The construction of artificial reefs has unparallelly developed for a few decades in China. Artificial reefs can be used to manage and conserve commercially exploited fish and crustacea. However, their suitability as ecological niche is poorly characterized. Therefore, in this study, we detected the seasonal variation of community biodiversity and the corresponding driving environmental factors. We also explored the relationships between dominant species and environmental factors to identify appropriate ecological niche areas. Different statistical analysis methods were used to assess species distribution within an artificial reef area in Xixiakou during nine sampling events in four seasons between 2017 and 2018. Non-metric multidimensional scaling(NMDS) and cluster analysis results indicated that the components of community can be divided into two clusters. Complexity of community, which is exhibited by species number, biodiversity, and catch per unit effort(CPUE), was significantly higher in summer than in other seasons. Generalized additive model(GAMs) results revealed the significant effects of temperature and chlorophyll a on the community structure. Sebastes schlegelii, Hexagrammos otakii, Conger myriaster and Charybdis japonica were the dominant species in four seasons. GAMs results indicated that temperature, dissolved oxygen(DO), pH and chlorophyll a affect the CPUE of dominant species significantly. The distinct suitable ecological niche for each dominant species was found in this study. For example, Charybdis japonica preferred to live in the area with 20.7–22.1℃, dissolved oxygen 7.07–7.15 mg L~(-1) and salinity 31.8–31.9. The results of this study are beneficial to resource conservation and fishery management. 相似文献
525.
GPS Solutions - We discuss the impact of a traveling ionospheric disturbance (TID) on cycle slip detection for the geometry-free (GF) combination. Based on the GF combination algorithm, we deduce... 相似文献
526.
Spatial co‐location pattern mining aims to discover a collection of Boolean spatial features, which are frequently located in close geographic proximity to each other. Existing methods for identifying spatial co‐location patterns usually require users to specify two thresholds, i.e. the prevalence threshold for measuring the prevalence of candidate co‐location patterns and distance threshold to search the spatial co‐location patterns. However, these two thresholds are difficult to determine in practice, and improper thresholds may lead to the misidentification of useful patterns and the incorrect reporting of meaningless patterns. The multi‐scale approach proposed in this study overcomes this limitation. Initially, the prevalence of candidate co‐location patterns is measured statistically by using a significance test, and a non‐parametric model is developed to construct the null distribution of features with the consideration of spatial auto‐correlation. Next, the spatial co‐location patterns are explored at multi‐scales instead of single scale (or distance threshold) discovery. The validity of the co‐location patterns is evaluated based on the concept of lifetime. Experiments on both synthetic and ecological datasets show that spatial co‐location patterns are discovered correctly and completely by using the proposed method; on the other hand, the subjectivity in discovery of spatial co‐location patterns is reduced significantly. 相似文献
527.
总结国外土地配置研究的特点与经验,可以为我国土地配置工作面临的诸多新问题与新挑战提供参考与借鉴。利用文献资料法与定性分析法,对国外有关土地配置的研究进行了梳理和分析。国外土地配置研究对维持生态系统正常运行、保护土地景观、阻止生态用地向工业用地过度转化以及确保土地利用社会整体利益最大化等问题非常关注,对土地适宜性评判、不同因素对土地配置的影响及土地配置调控手段效率检验与改进等方面也进行了比较深入的研究。与国外土地配置研究相比,我国土地配置研究应从扩展研究视角、注重多维度土地利用类型的适宜性评判、重视利益主体诉求以及探析土地配置新途径等方面完善相关研究体系。 相似文献
528.
529.
泥石流学科的发展和对策 总被引:2,自引:0,他引:2
泥石流研究首先要积极投身于国民经济建设主战场,并以泥石流综合防治为契机,促进山区生态经济系统的良性循环,使得根治泥石流灾害与社会、经济、生态环境协调发展。其次,要突破学科的前沿问题——泥石流起动理论和阻力规律。初步提出了实现目标的措施。 相似文献
530.
不同带宽的防风固沙林流场结构及防风效能风洞实验 总被引:3,自引:1,他引:2
林带宽度是防风固沙林建植时要考虑的基本参数,研究不同带宽林带的防护效果对防风固沙林配置及构建具有重要的指导意义。通过风洞模拟实验,在7、10、15 m·s-1风速条件下,对单行一带(Ⅰ型)、三行一带(Ⅱ型)、六行一带(Ⅲ型)和九行一带(Ⅳ型)共4种带宽的林带的迎风面、带中和背风面的风速进行了测定,分析了4种林带的风速流场、风速加速率和防风效果。结果表明:(1)4种林带流场结构和垂直风速变化规律相似,沿来风向均形成了林带上方和迎风面林缘附近的小范围高风速区及其后的风影区相互组合的流场结构;依据风速垂直变化规律划分为上部变化层(高度30~60 cm,受林带的影响最小)、中间变化层(高度5~20 cm,风速受林冠遮蔽作用,影响最大,且为风影区形成层)和近床面变化层(高度1~3 cm)。(2)4种林带在垂直纵剖面上的平均风速加速率随林带宽度的增大而减小,即Ⅰ型(0.90) > Ⅱ型(0.87) > Ⅲ型(0.79) > Ⅳ型(0.78)。(3)4种林带的防风效果为Ⅰ型和Ⅱ型林带相同,Ⅲ型和Ⅳ型林带相同,后2种林带的防风效果优于前2种林带,且4种林带的防风效能均随着风速的增大而减小。 相似文献