全文获取类型
收费全文 | 42474篇 |
免费 | 31299篇 |
国内免费 | 27822篇 |
专业分类
测绘学 | 4778篇 |
大气科学 | 19231篇 |
地球物理 | 13563篇 |
地质学 | 38365篇 |
海洋学 | 14946篇 |
天文学 | 1313篇 |
综合类 | 5230篇 |
自然地理 | 4169篇 |
出版年
2025年 | 49篇 |
2024年 | 867篇 |
2023年 | 1056篇 |
2022年 | 1845篇 |
2021年 | 2144篇 |
2020年 | 2799篇 |
2019年 | 5298篇 |
2018年 | 5517篇 |
2017年 | 5131篇 |
2016年 | 5280篇 |
2015年 | 4946篇 |
2014年 | 4585篇 |
2013年 | 5041篇 |
2012年 | 5016篇 |
2011年 | 4789篇 |
2010年 | 4660篇 |
2009年 | 4009篇 |
2008年 | 3363篇 |
2007年 | 3305篇 |
2006年 | 2869篇 |
2005年 | 2600篇 |
2004年 | 2641篇 |
2003年 | 2380篇 |
2002年 | 2189篇 |
2001年 | 1997篇 |
2000年 | 1674篇 |
1999年 | 1738篇 |
1998年 | 1678篇 |
1997年 | 1730篇 |
1996年 | 1384篇 |
1995年 | 1290篇 |
1994年 | 1166篇 |
1993年 | 1101篇 |
1992年 | 928篇 |
1991年 | 691篇 |
1990年 | 649篇 |
1989年 | 540篇 |
1988年 | 458篇 |
1987年 | 342篇 |
1986年 | 276篇 |
1985年 | 238篇 |
1984年 | 242篇 |
1983年 | 155篇 |
1982年 | 167篇 |
1981年 | 126篇 |
1980年 | 94篇 |
1979年 | 93篇 |
1978年 | 39篇 |
1971年 | 39篇 |
1970年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
The Qinghai–Tibet Plateau has a vast area of approximately 70×104 km2 of alpine meadow under the impacts of soil freezing and thawing, thereby inducing intensive water erosion. Quantifying the rainfall erosion process of partially thawed soil provides the basis for model simulation of soil erosion on cold-region hillslopes. In this study, we conducted a laboratory experiment on rainfall-induced erosion of partially thawed soil slope under four slope gradients (5, 10, 15, and 20°), three rainfall intensities (30, 60, and 90 mm h−1), and three thawed soil depths (1, 2, and 10 cm). The results indicated that shallow thawed soil depth aggravated soil erosion of partially thawed soil slopes under low hydrodynamic conditions (rainfall intensity of 30 mm h−1 and slope gradient ≤ 15°), whereas it inhibited erosion under high hydrodynamic conditions (rainfall intensity ≥ 60 mm h−1 or slope gradient > 15°). Soil erosion was controlled by the thawed soil depth and runoff hydrodynamic conditions. When the sediment supply was sufficient, the shallow thawed soil depth had a higher erosion potential and a larger sediment concentration. On the contrary, when the sediment supply was insufficient, the shallow thawed soil depth resulted in lower sediment erosion and a smaller sediment concentration. The hydrodynamic runoff conditions determined whether the sediment supply was sufficient. We propose a model to predict sediment delivery under different slope gradients, rainfall intensities, and thawed soil depths. The model, with a Nash–Sutcliffe efficiency of 0.95, accurately predicted the sediment delivery under different conditions, which was helpful for quantification of the complex feedback of sediment delivery to the factors influencing rainfall erosion of partially thawed soil. This study provides valuable insights into the rainfall erosion mechanism of partially thawed soil slopes in the Qinghai–Tibet Plateau and provides a basis for further studies on soil erosion under different hydrodynamic conditions. 相似文献
104.
通过地层结构、沉积序列与碎屑锆石年代学记录等三方面的成因分析和区域对比,本文进一步探究了中-朝地块新元古代-古生代的构造属性及演化信息。研究指出,朝鲜半岛平南盆地、太白山盆地以及华北地块内部,其地层结构-沉积相序主要以寒武-奥陶系内陆架碳酸盐岩沉积、志留-泥盆系缺失、中上石炭统-二叠系海陆交互相含煤沉积为特征,并具有可对比的1.85Ga、2.5Ga以及1.15Ga、1.6Ga等碎屑锆石年龄峰值。而在临津江带、沃川带以及华北东南缘,则以泥盆-石炭系泥岩/片岩、中基性火山岩及火山碎屑岩、碳酸盐岩(透镜体)混杂发育为特征,总体显示外陆架沉积环境,且具有可对比的与地层时代接近的最小碎屑锆石年龄,这也是对沉积期较强构造-岩浆活动的反映。综合地层结构、相序、碎屑锆石年龄组成以及聚煤记录,提出朝鲜半岛与华北应属于统一的一级构造单元,即"中-朝板块";但朝鲜半岛西南部及华北东南缘毗邻板块边缘,因此其地层-沉积记录与板内存在差异,简单的一致性模式并不适用。 相似文献
105.
During the course of a major sandstorm from April 17 to April 23, 2008 in the Taklimakan Desert, data pertaining to the mass concentrations of different-sized atmospheric particulate matter were observed continuously with Grimm 1.108, Thermo RP 1400a, TSP, and CAWS-600 instruments. The results showed that: (1) during the entire sandstorm process there were some differences between the daily mean particle concentration peaks and the hourly mean particle concentration peaks because the actual sandstorm lasted for only about 4 hr, whereas more particles were accumulated in the floating dust days before and after the actual sandstorm; (2) the intensity of the sandstorm was enhanced with the increase of wind speed, and this was related to the peak mass concentrations of atmospheric particulate matter; the wind speed directly affected the concentration of atmospheric particulate matter: the higher the wind speed, the higher the mass concentration (>0.23 μm was 39,496.5 μg/m3, and >20.0 μm was 5,390.7 μg/m3); (3) the concentration changes of PM10 and TSP were also related to the course and intensity of the sandstorm; and (4) the mass concentration of atmospheric particulate matter had the following sequence during the dust weather: clear day < floating dust < floating and blowing dust < sandstorm. Temperature, relative humidity, and barometric pressure are important factors affecting the strength of storms, which could also indirectly affect the concentration change of atmospheric particulate matter. 相似文献
107.
分频解释技术已经越来越多的应用到地震储层预测和油藏描述中,成为地震解释的一种常规技术手段,分频解释技术中分频RGB颜色融合显示方法因其独有的视觉效果也开始受到关注.本文介绍了分频混色技术在高精度地震解释中的应用以及在应用过程中应注意的几点问题,包括优选高精度频谱分解方法、RGB颜色融合技术应用中频率选择的原则等.在此基础上,进一步探讨了分频数据RGB混色方法能有效解决地震沉积学中地层切片精度不满足薄储层预测的问题.RGB颜色融合显示方法能充分发掘高精度地震数据宽频的优势,得到精度更高的储层预测结果. 相似文献
109.
110.