全文获取类型
收费全文 | 96107篇 |
免费 | 2287篇 |
国内免费 | 1457篇 |
专业分类
测绘学 | 2475篇 |
大气科学 | 7116篇 |
地球物理 | 19293篇 |
地质学 | 34616篇 |
海洋学 | 8597篇 |
天文学 | 21306篇 |
综合类 | 431篇 |
自然地理 | 6017篇 |
出版年
2022年 | 609篇 |
2021年 | 1006篇 |
2020年 | 1068篇 |
2019年 | 1152篇 |
2018年 | 2503篇 |
2017年 | 2350篇 |
2016年 | 2917篇 |
2015年 | 1787篇 |
2014年 | 2868篇 |
2013年 | 5164篇 |
2012年 | 3231篇 |
2011年 | 4353篇 |
2010年 | 3735篇 |
2009年 | 4882篇 |
2008年 | 4422篇 |
2007年 | 4240篇 |
2006年 | 4041篇 |
2005年 | 3162篇 |
2004年 | 3043篇 |
2003年 | 2774篇 |
2002年 | 2554篇 |
2001年 | 2349篇 |
2000年 | 2172篇 |
1999年 | 1711篇 |
1998年 | 1846篇 |
1997年 | 1682篇 |
1996年 | 1382篇 |
1995年 | 1511篇 |
1994年 | 1275篇 |
1993年 | 1164篇 |
1992年 | 1135篇 |
1991年 | 1058篇 |
1990年 | 1161篇 |
1989年 | 967篇 |
1988年 | 886篇 |
1987年 | 1103篇 |
1986年 | 905篇 |
1985年 | 1191篇 |
1984年 | 1332篇 |
1983年 | 1205篇 |
1982年 | 1174篇 |
1981年 | 1018篇 |
1980年 | 974篇 |
1979年 | 871篇 |
1978年 | 867篇 |
1977年 | 828篇 |
1976年 | 786篇 |
1975年 | 743篇 |
1974年 | 752篇 |
1973年 | 762篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Geomagnetism and Aeronomy - Diurnal variations in the statistical characteristics of the day-to-day variability in the electron number density NmF2 of the ionospheric F2 layer maximum is studied... 相似文献
2.
Astronomy Letters - The emission from the Crab nebula exhibits a significant gamma-ray variability. In this paper we have analyzed this variability in terms of periodicity. Using the pulsar... 相似文献
3.
Solar System Research - A numerical-analytical method for analyzing the orbital evolution of a planetary satellite under the influence of a perturbing body moving in an elliptical orbit is... 相似文献
4.
Sherri L. Johnson Don Henshaw Greg Downing Steve Wondzell Mark Schulze Adam Kennedy Greg Cohn Stephanie A. Schmidt Julia A. Jones 《水文研究》2021,35(5):e14187
The H. J. Andrews Experimental Forest (HJA) encompasses the 6400 ha Lookout Creek watershed in western Oregon, USA. Hydrologic, chemistry and precipitation data have been collected, curated, and archived for up to 70 years. The HJA was established in 1948 to study the effects of harvest of old-growth conifer forest and logging-road construction on water quality, quantity and vegetation succession. Over time, research questions have expanded to include terrestrial and aquatic species, communities and ecosystem dynamics. There are nine small experimental watersheds and 10 gaging stations in the HJA, including both reference and experimentally treated watersheds. Gaged watershed areas range from 8.5 to 6242 ha. All gaging stations record stage height, water conductivity, water temperature and above-stream air temperature. At nine of the gage sites, flow-proportional water samples are collected and composited over 3-week intervals for chemical analysis. Analysis of stream and precipitation chemistry began in 1968. Analytes include dissolved and particulate species of nitrogen and phosphorus, dissolved organic carbon, pH, specific conductance, suspended sediment, alkalinity, and major cations and anions. Supporting climate measurements began in the 1950s in association with the first small watershed experiments. Over time, and following the initiation of the Long Term Ecological Research (LTER) grant in 1980, infrastructure expanded to include a set of benchmark and secondary meteorological stations located in clearings spanning the elevation range within the Lookout Creek watershed, as well as a large number of forest understory temperature stations. Extensive metadata on sensor configurations, changes in methods over time, sensor accuracy and precision, and data quality control flags are associated with the HJA data. 相似文献
5.
Astrophysics - We study the modulation of galactic cosmic rays due to magnetic clouds observed during solar cycles 23 and 24 (1996-2018). We utilize solar wind plasma and field data together with... 相似文献
6.
Kim I. S. Krusanova N. L. Popov V. V. Osokin A. R. Mironova I. V. 《Geomagnetism and Aeronomy》2020,60(4):441-445
Geomagnetism and Aeronomy - The color of the coronal continuum was determined from observations in order to search for manifestations of coronal expansion. A brief review of studies determining the... 相似文献
7.
Water Resources - The relationships between various hydrological and morphometric characteristics of branch channels in the backwater zone are analyzed in the case of the Chilia channel system in... 相似文献
8.
Water Resources - The study is focused on examining and simulating the formation processes of the runoff and pollution export in the case of Rostov (Rostov Velikii), a town in the Volga basin. The... 相似文献
9.
Carissa A. Raymond Luke A. McGuire Ann M. Youberg Dennis M. Staley Jason W. Kean 《地球表面变化过程与地形》2020,45(6):1349-1360
Wildfire significantly alters the hydrologic properties of a burned area, leading to increases in overland flow, erosion, and the potential for runoff-generated debris flows. The initiation of debris flows in recently burned areas is well characterized by rainfall intensity-duration (ID) thresholds. However, there is currently a paucity of data quantifying the rainfall intensities required to trigger post-wildfire debris flows, which limits our understanding of how and why rainfall ID thresholds vary in different climatic and geologic settings. In this study, we monitored debris-flow activity following the Pinal Fire in central Arizona, which differs from both a climatic and hydrogeomorphic perspective from other regions in the western United States where ID thresholds for post-wildfire debris flows are well established, namely the Transverse Ranges of southern California. Since the peak rainfall intensity within a rainstorm may exceed the rainfall intensity required to trigger a debris flow, the development of robust rainfall ID thresholds requires knowledge of the timing of debris flows within rainstorms. Existing post-wildfire debris-flow studies in Arizona only constrain the peak rainfall intensity within debris-flow-producing storms, which may far exceed the intensity that actually triggered the observed debris flow. In this study, we used pressure transducers within five burned drainage basins to constrain the timing of debris flows within rainstorms. Rainfall ID thresholds derived here from triggering rainfall intensities are, on average, 22 mm h−1 lower than ID thresholds derived under the assumption that the triggering intensity is equal to the maximum rainfall intensity recorded during a rainstorm. We then use a hydrologic model to demonstrate that the magnitude of the 15-min rainfall ID threshold at the Pinal Fire site is associated with the rainfall intensity required to exceed a recently proposed dimensionless discharge threshold for debris-flow initiation. Model results further suggest that previously observed differences in regional ID thresholds between Arizona and the San Gabriel Mountains of southern California may be attributed, in large part, to differences in the hydraulic properties of burned soils. © 2019 John Wiley & Sons, Ltd. 相似文献
10.
Rafael C. Carvalho David M. Kennedy Yakufu Niyazi Chloe Leach Teresa M. Konlechner Daniel Ierodiaconou 《地球表面变化过程与地形》2020,45(11):2540-2555
Historical aerial photographs are an invaluable tool in shoreline mapping and change detection in coastal landscapes. We evaluate the extent to which structure-from-motion (SfM) photogrammetric methods can be applied to quantify volumetric changes along sandy beaches, using archival imagery. We demonstrate the application of SfM-derived digital surface models (DSMs) at East Beach and Lady Bay in southwest Victoria, Australia, using photographic datasets taken in 1969, 1977 and 1986, and compare them to LiDAR-derived DSMs acquired at both sites in 2007. The SfM approaches resulted in two entire and two partial suitable DSMs out of six datasets. Good-quality DSMs were spatially continuous with a good spread of ground control points (GCPs) near the beach at Lady Bay, whereas unsuitable DSMs were mostly restricted by poor distribution and number of GCPs in spatially segmented areas of East Beach, due to limited overlapping of images, possible poor quality of GCPs and also the propagation of errors in the derived point clouds. A volume of approximately 223 000 ± 72 000 m3 was deposited at Lady Bay between 1969 and 2007, despite minimal erosion observed near the breakwater. The partially suitable dataset of East Beach indicated that beach erosion of at least 39 m3 m−1 occurred immediately to the east of the seawall after 1977. We also discuss the drawbacks and strengths of SfM approaches as a benchmark of historical erosion assessments along sandy beaches. © 2020 John Wiley & Sons, Ltd. 相似文献