全文获取类型
收费全文 | 2395篇 |
免费 | 506篇 |
国内免费 | 605篇 |
专业分类
测绘学 | 245篇 |
大气科学 | 361篇 |
地球物理 | 720篇 |
地质学 | 1311篇 |
海洋学 | 283篇 |
天文学 | 47篇 |
综合类 | 281篇 |
自然地理 | 258篇 |
出版年
2024年 | 13篇 |
2023年 | 59篇 |
2022年 | 134篇 |
2021年 | 167篇 |
2020年 | 174篇 |
2019年 | 161篇 |
2018年 | 190篇 |
2017年 | 180篇 |
2016年 | 164篇 |
2015年 | 172篇 |
2014年 | 169篇 |
2013年 | 168篇 |
2012年 | 158篇 |
2011年 | 149篇 |
2010年 | 151篇 |
2009年 | 171篇 |
2008年 | 132篇 |
2007年 | 140篇 |
2006年 | 109篇 |
2005年 | 86篇 |
2004年 | 81篇 |
2003年 | 68篇 |
2002年 | 86篇 |
2001年 | 73篇 |
2000年 | 61篇 |
1999年 | 61篇 |
1998年 | 42篇 |
1997年 | 26篇 |
1996年 | 19篇 |
1995年 | 19篇 |
1994年 | 23篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1958年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有3506条查询结果,搜索用时 734 毫秒
51.
52.
Introduction The observation records of strong ground motion previously, on the one hand, supplied basicdata both to research on earthquake engineering and to constitute the criterion of aseismatic de-signing of all project structures; on the other hand, it provided important information for the re-search on the process of epicenter burst in seismology. With the development of research on strongground motion observation, especially the development of the new generation accelerograph,which… 相似文献
53.
54.
Spatial information on soil properties is an important input to hydrological models. In current hydrological modelling practices, soil property information is often derived from soil category maps by the linking method in which a representative soil property value is linked to each soil polygon. Limited by the area‐class nature of soil category maps, the derived soil property variation is discontinuous and less detailed than high resolution digital terrain or remote sensing data. This research proposed dmSoil, a data‐mining‐based approach to derive continuous and spatially detailed soil property information from soil category maps. First, the soil–environment relationships are extracted through data mining of a soil map. The similarity of the soil at each location to different soil types in the soil map is then estimated using the mined relationships. Prediction of soil property values at each location is made by combining the similarities of the soil at that location to different soil types and the representative soil property values of these soil types. The new approach was applied in the Raffelson Watershed and Pleasant Valley in the Driftless Area of Wisconsin, United States to map soil A horizon texture (in both areas) and depth to soil C horizon (in Pleasant Valley). The property maps from the dmSoil approach capture the spatial gradation and details of soil properties better than those from the linking method. The new approach also shows consistent accuracy improvement at validation points. In addition to the improved performances, the inputs for the dmSoil approach are easy to prepare, and the approach itself is simple to deploy. It provides an effective way to derive better soil property information from soil category maps for hydrological modelling. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
55.
New magnetostratigraphic and pedostratigraphic investigations of loess deposits in north‐east China and their implications for regional environmental change during the Mid‐Pleistocene climatic transition
下载免费PDF全文
![点击此处可从《第四纪科学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
56.
Peatland initiation and carbon dynamics in northeast China: links to Holocene climate variability
下载免费PDF全文
![点击此处可从《Boreas: An International Journal of Quaternary Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wei Xing Kunshan Bao Wenyong Guo Xianguo Lu Guoping Wang 《Boreas: An International Journal of Quaternary Research》2015,44(3):575-587
Throughout northeast China, the widely distributed peatlands have formed a large carbon (C) pool. However, the relationship between peatland initiation and climate controls is still poorly documented and understood. Understanding the responses of these C‐rich ecosystems to past climate change will provide useful insights into projecting the fate of peatland C in the future. In this study, we present a detailed historical reconstruction of peatland development in northeast China based on 312 basal peat dates, and examine the relationship between Holocene peatland dynamics and climate sensitivity. Our results indicate that peatland initiation started in the early Holocene, and that the majority of peatlands were initiated by and developed during the late Holocene. After the most intensive initiation period of 4.2–0.8 ka, the rate of peatland development slowed, which was concomitant with decreasing insolation and monsoon intensity. The widespread peatland initiation in the late Holocene might have been caused by the cool and moist climate patterns. The optimum timing of the peatland development was not uniform across northeast China, and these spatio‐temporal differences indicate the influences of regional climate and terrain on peatland initiation. Peat‐core data show variations in the long‐term apparent rate of C accumulation (LORCA) during the Holocene, with an average rate of 37.2 g C m?2 a?1. The peak LORCA occurred during 10.5–9.0 ka, probably in response to higher temperatures and stronger East Asia summer monsoon intensities. Both temperature and humidity are important factors influencing the peatland initiation and C dynamics in this region. 相似文献
57.
An analytical solution is developed in this paper to investigate the dynamic response of a large‐diameter end‐bearing pipe pile subjected to torsional loading in viscoelastic saturated soil. The wave propagation in saturated soil and pile are simulated by Biot's two‐phased linear theory and one‐dimensional elastic theory, respectively. The dynamic equilibrium equations of the outer soil, inner soil, and pile are established. The solutions for the outer and inner soils in frequency domain are obtained by Laplace transform technique and the separation of variables method. Then, the dynamic response of the pile is obtained on the basis of the perfect contacts between the pile and the outer soil as well as the inner soil. The results in this paper are compared with that of a solid pile in elastic saturated soil to verify the validity of the solution. Furthermore, the solution in this paper is compared with the classic plane strain solution to verify the solution further and check the accuracy of the plane strain solution. Numerical results are presented to analyze the vibration characteristics and illustrate the effect of the soil parameters and the geometry size of the pile on the complex impedance and velocity admittance of the pile head. Finally, the displacement of the soil at different depth and frequency is analyzed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
58.
Watershed delineation is a required step when conducting any spatially distributed hydrological modelling. Automated approaches are often proposed to delineate a watershed based on a river network extracted from the digital elevation model (DEM) using the deterministic eight‐neighbour (D8) method. However, a realistic river network cannot be derived from conventional DEM processing methods for a large flat area with a complex network of rivers, lakes, reservoirs, and polders, referred to as a plain river network region (PRNR). In this study, a new approach, which uses both hydrographic features and DEM, has been developed to address the problems of watershed delineation in PRNR. It extracts the river nodes and determines the flow directions of the river network based on a vector‐based hydrographic feature data model. The river network, lakes, reservoirs, and polders are then used to modify the flow directions of grid cells determined by D8 approach. The watershed is eventually delineated into four types of catchments including lakes, reservoirs, polders, and overland catchments based on the flow direction matrix and the location of river nodes. Multiple flow directions of grid cells are represented using a multi‐direction encoding method, and multiple outflows of catchments are also reflected in the topology of catchments. The proposed approach is applied to the western Taihu watershed in China. Comparisons between the results obtained from the D8 approach, the ‘stream burning’ approach, and those from the proposed approach clearly demonstrate an improvement of the new approach over the conventional approaches. This approach will benefit the development of distributed hydrological models in PRNR for the consideration of different types and multiple inlets and outlets of catchments. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
59.
60.