全文获取类型
收费全文 | 2208篇 |
免费 | 490篇 |
国内免费 | 700篇 |
专业分类
测绘学 | 155篇 |
大气科学 | 723篇 |
地球物理 | 621篇 |
地质学 | 986篇 |
海洋学 | 282篇 |
天文学 | 120篇 |
综合类 | 273篇 |
自然地理 | 238篇 |
出版年
2024年 | 9篇 |
2023年 | 26篇 |
2022年 | 102篇 |
2021年 | 111篇 |
2020年 | 98篇 |
2019年 | 102篇 |
2018年 | 98篇 |
2017年 | 120篇 |
2016年 | 106篇 |
2015年 | 106篇 |
2014年 | 128篇 |
2013年 | 125篇 |
2012年 | 128篇 |
2011年 | 177篇 |
2010年 | 114篇 |
2009年 | 138篇 |
2008年 | 117篇 |
2007年 | 116篇 |
2006年 | 122篇 |
2005年 | 94篇 |
2004年 | 70篇 |
2003年 | 75篇 |
2002年 | 83篇 |
2001年 | 65篇 |
2000年 | 90篇 |
1999年 | 97篇 |
1998年 | 114篇 |
1997年 | 105篇 |
1996年 | 96篇 |
1995年 | 72篇 |
1994年 | 71篇 |
1993年 | 76篇 |
1992年 | 40篇 |
1991年 | 41篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 27篇 |
1987年 | 20篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1958年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3398条查询结果,搜索用时 15 毫秒
981.
Against the background of climate change, the global carbon and water cycle has undergone significant changes, and it is of great significance to explore the interrelationships of the carbon and water cycles in different regions to cope with future climate change. In this study, based on gross primary productivity (GPP) and precipitation (PRE) data, the precipitation use efficiency (PUE) of the Loess Plateau (LP) was calculated, and the Sen trend analysis and Mann-Kendall test were used to analyse the temporal and spatial variation characteristics of PUE, as well as the first-order difference method was used to derive the relative contributions to quantify the impact of vegetation growth and meteorological factors on PUE. The results show that (1) from 2001 to 2018, the spatial distribution pattern of vegetation PUE exhibited an increasing trend from northwest to southeast. On the time scale, the multi-year average value of PUE was 1.17 gC m−2 mm−1, showing an overall upward trend. Among the different land cover types, paddy fields had the highest PUE level, and sparse grassland had the lowest; (2) LAI had the highest relative contribution to vegetation PUE, followed by temperature (Temp), net radiation of the ground surface (RN), specific humidity (Shum), and wind speed (WS). LAI contributes positively to 88.9% of the area. RN positively influences high-altitude areas, while Shum had a larger area with a negative contribution. The contribution of Temp increases from northwest to southeast, and WS has balanced positive and negative contributions; (3) LAI is the dominant factor for the spatial and temporal variation of PUE in the LP, and the size of the areas where different meteorological factors dominate the changes of PUE are as follows: WS > Shum>RN > Temp. At high altitudes, the dominant meteorological driver is WS, while at low altitudes, the dominant climate driver is Shum. This study is of guiding significance for the ecological restoration and management of the LP, and it can also provide a scientific basis for the improvement of ecosystems and the sustainable management of water resources in the context of global climate change. 相似文献
982.
983.
984.
我国洞体应变固体潮调和分析结果 总被引:3,自引:1,他引:2
本文扼要介绍了我国洞体应变观测现状,公布了18个台站的调和分析结果,同时公布了国外同类仪器优质台站的计算结果,以作比较。 相似文献
985.
986.
987.
布袋注浆桩在深厚层软土地基加固中的应用 总被引:2,自引:0,他引:2
布袋注浆桩是一项新的软土地基加固技术,应用于深厚层和夹硬层的软土加固,具有明显的优势。结合甬台温铁路深厚层软土地基加固,介绍了布袋注浆桩的加固机理、设计、施工、质量检测方法和标准等。检测结果表明,布袋注浆桩成桩质量良好,加固后,地基沉降得到有效控制,满足设计要求。 相似文献
988.
Ping Kong Chunguang Na David Fink Feixin Huang Lin Ding 《Journal of Asian Earth Sciences》2007,29(5-6):698-703
Most Tibetan lakes are surrounded by conspicuous regressive shorelines attesting to high-water levels in the past. Concentrations of the in situ produced cosmogenic radionuclide 10Be in bedrock from the three highest terraces surrounding Sumxi Co, situated in Western Kunlun, indicate that the highest lake-level appeared before 10,000–11,500 yr, and most likely between 11,000 and 12,800 yr. Younger ages for the two lower terraces imply regression of Sumxi Co during the early-mid Holocene. The concurrency of the highest lake-level with orbitally induced maximum northern hemisphere summer insolation suggests that the increase in water supply to Sumxi Co was most likely associated with increased recharge from melting glaciers. We conclude that the enhanced Indian monsoon during the early Holocene did not penetrate the Tibetan plateau and affect the northwestern part of Tibet significantly. 相似文献
989.
This paper investigates single epoch ambiguity resolution performance using Galileo four frequency data. Two commonly used
ambiguity resolution methods are used in the tests, including the Cascade Ambiguity Resolution (CAR) and the Least-Squares
Ambiguity Decorrelation Adjustment (LAMBDA) methods. For CAR method, four optimal combinations are carefully selected according
to their wavelength to noise ratios and success rate for ambiguity fixing. The test results show, in general, the LAMBDA method
performs better than the CAR method. The speed of ambiguity resolution is closely related to the carrier phase measurement
precision. With carrier phase measurement precision of 3 mm, single epoch ambiguity resolution can be achieved at every epoch
with simulated 1-s interval 24-h Galileo data (total epochs 86,400). With the increase of carrier phase noise, ambiguity resolution
performances become worse. When the noise level is increased to 12 mm, single epoch ambiguity resolution can only be achieved
about 50% of epochs. 相似文献
990.
Introduction Major tectonic activities occur in collisions zones between plates or intra-plate continental blocks. Therefore, it is significant to investigate collision processes. We know that orogenic and seismic belts in plate margins are closely relate… 相似文献