全文获取类型
收费全文 | 28126篇 |
免费 | 4820篇 |
国内免费 | 5150篇 |
专业分类
测绘学 | 916篇 |
大气科学 | 2627篇 |
地球物理 | 8918篇 |
地质学 | 11753篇 |
海洋学 | 5273篇 |
天文学 | 2815篇 |
综合类 | 1297篇 |
自然地理 | 4497篇 |
出版年
2024年 | 146篇 |
2023年 | 348篇 |
2022年 | 823篇 |
2021年 | 1003篇 |
2020年 | 1099篇 |
2019年 | 1310篇 |
2018年 | 1032篇 |
2017年 | 1037篇 |
2016年 | 1084篇 |
2015年 | 1139篇 |
2014年 | 1456篇 |
2013年 | 1556篇 |
2012年 | 1437篇 |
2011年 | 1605篇 |
2010年 | 1332篇 |
2009年 | 1862篇 |
2008年 | 1860篇 |
2007年 | 2007篇 |
2006年 | 1902篇 |
2005年 | 1603篇 |
2004年 | 1595篇 |
2003年 | 1469篇 |
2002年 | 1207篇 |
2001年 | 1080篇 |
2000年 | 1023篇 |
1999年 | 968篇 |
1998年 | 1017篇 |
1997年 | 692篇 |
1996年 | 599篇 |
1995年 | 506篇 |
1994年 | 474篇 |
1993年 | 418篇 |
1992年 | 368篇 |
1991年 | 243篇 |
1990年 | 186篇 |
1989年 | 146篇 |
1988年 | 115篇 |
1987年 | 90篇 |
1986年 | 60篇 |
1985年 | 45篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1954年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The 33 086 ha mixed land use Fall Creek watershed in upstate New York is part of the Great Lakes drainage system. Results from more than 3500 water samples are available in a data set that compiles flow data and measurements of various water quality analytes collected between 1972 and 1995 in all seasons and under all flow regimes in Fall Creek and its tributaries. Data is freely accessible at https://ecommons.cornell.edu/handle/1813/8148 and includes measurements of suspended solids, pH, alkalinity, calcium, magnesium, potassium, sodium, chloride, nitrate nitrogen (NO3-N), sulphate sulphur (SO4-S), phosphorus (P) fractions molybdate reactive P (MRP) and total dissolved P (TDP), percent P in sediment, and ammonium nitrogen (NH4-N). Methods, sub-watershed areas, and coordinates for sampling sites are also included. The work represented in this data set has made important scientific contributions to understanding of hydrological and biogeochemical processes that influence loading in mixed use watersheds and that have an impact on algal productivity in receiving water bodies. In addition, the work has been foundational for important regulatory and management decisions in the region. 相似文献
2.
Reservoirs of lowland floodplain rivers with eutrophic backgrounds cause variations in the hydrological and hydraulic conditions of estuaries and low-dam reservoir areas, which can promote planktonic algae to proliferate and algal bloom outbreaks. Understanding the ecological effects of variations in hydrological and hydraulic processes in lowland rivers is important for algal bloom control. In this study, the middle and lower reaches of the Han River, China, a typical regulated lowland river with a eutrophic background, are selected. Based on the effect of hydrological and hydraulic variability on algal blooms, a hydrological management strategy for river algal bloom control is proposed. The results showed that (a) differences in river morphology and background nutrient levels cause significant differences in the critical threshold flow velocities for algal bloom outbreaks between natural river and low-dam reservoir sections; there is no uniform threshold flow velocity for algal bloom control. (b) There are significant differences in the river hydrological/hydraulic conditions between years with and without algal blooms. The average river flow, water level and velocity in years with algal blooms are significantly lower than those in years without algal blooms. (c) For different river sections where algal blooms occur and to meet the threshold flow velocities, the joint operation of cascade reservoirs and diversion projects is an effective method to prevent and control algal blooms in regulated lowland rivers. This study is expected to deepen our understanding of the ecological significance of special hydrological processes and guide algal bloom management in regulated lowland rivers. 相似文献
3.
4.
5.
6.
7.
The Cassini spacecraft, en route to Saturn, passed close to Jupiter while the Galileo spacecraft was completing its 28th and 29th orbits of Jupiter, thus offering a unique opportunity for direct study of the solar wind-Jovian interaction. Here evidence is given of response of the Jovian magnetopause and bow shock positions to changes of the north-south component of the solar wind magnetic field, a phenomenon long known to occur in equivalent circumstances at Earth. The period analyzed starts with the passage over Cassini of an interplanetary shock far upstream of Jupiter. The shock's arrival at Galileo on the dusk-flank of the magnetosphere caused Galileo to exit into the solar wind. Using inter-spacecraft timing based on the time delay established from the shock arrival at each spacecraft, we point out that Galileo's position with respect to the Jovian bow shock appears to correlate with changes in the disturbed north-south reversing field seen behind the shock. We specifically rule out the alternative of changes in the shape of the bow shock with rotations of the interplanetary magnetic field as the cause. 相似文献
8.
9.
平衡剖面的制作流程及其地质意义 总被引:9,自引:0,他引:9
平衡剖面技术是地质思维和计算机技术的结晶,使对断层构造的研究提高到定量阶段,其依据是在垂直构造走向的剖面上,地层长度和面积(2D)或体积(3D)是均衡的。在此原理基础上利用数学手段对盆地的构造发育史进行正演和反演模拟,直观地再现地下构造的原始几何形态,迅速提供地震剖面的构造解释方案,并对解释结果进行检验(不平衡的剖面其解释一般有问题),为深刻认识构造发育史、分析油气运移及聚集规律提供依据,提高了工作效率。其结果也为盆地模拟、油藏模拟、定量计算构造伸缩量等地质研究打下了坚实的基础[1]。 相似文献
10.