全文获取类型
收费全文 | 97795篇 |
免费 | 1400篇 |
国内免费 | 569篇 |
专业分类
测绘学 | 2299篇 |
大气科学 | 6594篇 |
地球物理 | 18017篇 |
地质学 | 37130篇 |
海洋学 | 8524篇 |
天文学 | 21714篇 |
综合类 | 337篇 |
自然地理 | 5149篇 |
出版年
2022年 | 620篇 |
2021年 | 1028篇 |
2020年 | 1117篇 |
2019年 | 1241篇 |
2018年 | 4337篇 |
2017年 | 3935篇 |
2016年 | 3654篇 |
2015年 | 1429篇 |
2014年 | 2638篇 |
2013年 | 4487篇 |
2012年 | 3500篇 |
2011年 | 5390篇 |
2010年 | 4827篇 |
2009年 | 5864篇 |
2008年 | 4960篇 |
2007年 | 5450篇 |
2006年 | 3579篇 |
2005年 | 2772篇 |
2004年 | 2669篇 |
2003年 | 2534篇 |
2002年 | 2438篇 |
2001年 | 1966篇 |
2000年 | 1879篇 |
1999年 | 1448篇 |
1998年 | 1499篇 |
1997年 | 1363篇 |
1996年 | 1105篇 |
1995年 | 1213篇 |
1994年 | 1023篇 |
1993年 | 979篇 |
1992年 | 904篇 |
1991年 | 950篇 |
1990年 | 916篇 |
1989年 | 782篇 |
1988年 | 726篇 |
1987年 | 856篇 |
1986年 | 746篇 |
1985年 | 931篇 |
1984年 | 1058篇 |
1983年 | 1016篇 |
1982年 | 939篇 |
1981年 | 891篇 |
1980年 | 801篇 |
1979年 | 734篇 |
1978年 | 718篇 |
1977年 | 613篇 |
1976年 | 620篇 |
1975年 | 609篇 |
1974年 | 583篇 |
1973年 | 653篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Izmailov I. S. Shakht N. A. Polyakov E. V. Gorshanov D. L. Pogodin M. A. 《Astrophysics》2021,64(2):160-171
Astrophysics - This paper is a continuation of our earlier work devoted to determining the orbit and mass of the star 61 Cyg and the changes in the photometric characteristics of its components.... 相似文献
62.
Pavlenko E. P. Sosnovskii A. A. Antonyuk K. A. Antonyuk O. I. Pit’ N. V. Kokhirova G. I. Rakhmatullaeva F. J. Baklanov A. V. 《Astrophysics》2021,64(3):293-305
Astrophysics - Photometric studies of the type SU UMa dwarf nova NY Her were made during 2017 and 2020 at the Crimean Astrophysical Observatory and at the Sanglokh Observatory over a total of 77... 相似文献
63.
Opekunov A. Yu. Mitrofanova E. S. Spasskii V. V. Opekunova M. G. Sheinerman N. A. Chernyshova A. V. 《Water Resources》2020,47(2):282-293
Water Resources - The article gives the results of integrated studies of bottom sediments in four watercourses in the central St. Petersburg: the rivers of Ekateringofka, Okhta, Fontanka, and... 相似文献
64.
Water Resources - The possible input of nutrients-pollutants into water bodies in the Upper Volga basin from agricultural lands is evaluated for the case of the Yakhroma R. with a basin area of... 相似文献
65.
Chia-Yu Chen Sean D. Willett A. Joshua West Simon Dadson Niels Hovius Marcus Christl J. Bruce H. Shyu 《地球表面变化过程与地形》2020,45(3):548-564
Extreme erosion events can produce large short-term sediment fluxes. Such events complicate erosion rates estimated from cosmogenic nuclide concentrations in river sediment by providing sediment with a concentration different from the long-term basin average. We present a detrital 10Be study in southern Taiwan, with multiple samples obtained in a time sequence bracketing the 2009 Typhoon Morakot, to assess the impact of landslide sediment on 10Be concentrations (N10Be) in river sediment. Sediment samples were collected from 13 major basins, two or three times over the last decade, to observe the temporal variation of N10Be. Landslide inventories with time intervals of 5–6 years were used to quantify sediment flux changes. A negative correlation between N10Be and landslide areal density indicates dilution of N10Be by landslide sediment. Denudation rates estimated from the diluted N10Be can be up to three times higher than the lowest rate derived from the same basins. Observed increases imply that, 3 years after the passage of Typhoon Morakot, fluvial channels still contain a considerable amount of sediment provided by hillslope landslides during the event. However, higher N10Be in 2016 samples indicate that the contribution from landslide sediment at the sampled grain size has decreased with time. The correlation between changes in N10Be and landslide area and volume is not strong, likely resulting from the stochastic and complex nature of sediment transport. To simultaneously evaluate the volume of landslide-derived sediment and estimate the background denudation rate, associated with less impulsive sediment supply, we constructed a sediment-mixing model with the time series of N10Be and landslide inventories. The spatial pattern of background erosion rate in southern Taiwan is consistent with the regional tectonic framework, indicating that the landscape is evolving mainly in response to the tectonic forcing, and this signal is modified, but not obscured by impulsive sediment supply. © 2019 John Wiley & Sons, Ltd. 相似文献
66.
Petter Nyman Walter A.C. Box Justin C. Stout Gary J. Sheridan Saskia D. Keesstra Patrick N.J. Lane Christoph Langhans 《地球表面变化过程与地形》2020,45(5):1155-1167
Field studies that investigate sediment transport between debris-flow-producing headwaters and rivers are uncommon, particularly in forested settings, where debris flows are infrequent and opportunities for collecting data are limited. This study quantifies the volume and composition of sediment deposited in the arterial channel network of a 14-km2 catchment (Washington Creek) that connects small, burned and debris-flow-producing headwaters (<1 km2) with the Ovens River in SE Australia. We construct a sediment budget by combining new data on deposition with a sediment delivery model for post-fire debris flows. Data on deposits were plotted alongside the slope–area curve to examine links between processes, catchment morphometry and geomorphic process domains. The results show that large deposits are concentrated in the proximity of three major channel junctions, which correspond to breaks in channel slope. Hyperconcentrated flows are more prominent towards the catchment outlet, where the slope–area curve indicates a transition from debris flow to fluvial domains. This shift corresponds to a change in efficiency of the flow, determined from the ratio of median grain size to channel slope. Our sediment budget suggests a total sediment efflux from Washington Creek catchment of 61 × 103 m3. There are similar contributions from hillslopes (43 ± 14 × 103 m3), first to third stream order channel (35 ± 12 × 103 m3) and the arterial fourth to fifth stream order channel (31 ± 17 × 103 m3) to the total volume of erosion. Deposition (39 ± 17 × 103 m3) within the arterial channel was higher than erosion (31 ± 17 × 103 m3), which means a net sediment gain of about 8 × 103 m3 in the arterial channel. The ratio of total deposition to total erosion was 0.44. For fines <63 μm, this ratio was much smaller (0.11), which means that fines are preferentially exported. This has important implications for suspended sediment and water quality in downstream rivers. © 2019 John Wiley & Sons, Ltd. 相似文献
67.
Meandering river sinuosity increases until the channel erodes into itself (neck cutoff) or forms a new channel over the floodplain (chute cutoff) and sinuosity is reduced. Unlike neck cutoff, which can be measured or modelled without considering overbank processes, chute cutoff must be at least partially controlled by channel-forming processes on the floodplain. Even though chute cutoff controls meandering river form, the processes that cause chute cutoff are not well understood. This study analyses the morphology of two incipient chute cutoffs along the East Fork White River, Indiana, USA, using high temporal and spatial resolution UAS-based LiDAR and aerial photography. LiDAR and aerial imagery obtained between 1998 and 2019 reveals that large scour holes formed in the centre of both chutes sometime after chute channel initiation. A larger analysis within the study watershed reveals that scour holes within incipient chutes can be stable or unstable, and tend to stabilize when the chute is colonized by native vegetation and forest. When the scour holes form in farmed floodplain, they enlarge rapidly after initial formation and contribute to complete chute cutoff. In addition, this study shows that the formation of scour holes can occur in response to common, relatively low-magnitude floods and that the amount of incipient chute erosion does not depend on peak flood magnitude. The role of scour holes in enlarging chute channels could be an important mechanism for chute channel evolution in meandering rivers. This study also confirms that understanding the relationships among flow, land cover, and cutoff morphology is substantially improved with on-demand remote sensing techniques like integrated UAS and LiDAR. © 2020 John Wiley & Sons, Ltd. 相似文献
68.
Zhengcong Yin Daniel W. Goldberg Tracy A. Hammond Chong Zhang Andong Ma Xiao Li 《Transactions in GIS》2020,24(3):656-680
Reverse geocoding, which transforms machine‐readable GPS coordinates into human‐readable location information, is widely used in a variety of location‐based services and analysis. The output quality of reverse geocoding is critical because it can greatly impact these services provided to end‐users. We argue that the output of reverse geocoding should be spatially close to and topologically correct with respect to the input coordinates, contain multiple suggestions ranked by a uniform standard, and incorporate GPS uncertainties. However, existing reverse geocoding systems often fail to fulfill these aims. To further improve the reverse geocoding process, we propose a probabilistic framework that includes: (1) a new workflow that can adapt all existing address models and unitizes distance and topology relations among retrieved reference data for candidate selections; (2) an advanced scoring mechanism that quantifies characteristics of the entire workflow and orders candidates according to their likelihood of being the best candidate; and (3) a novel algorithm that derives statistical surfaces for input GPS uncertainties and propagates such uncertainties into final output lists. The efficiency of the proposed approaches is demonstrated through comparisons to the four commercial reverse geocoding systems and through human judgments. We envision that more advanced reverse geocoding output ranking algorithms specific to different application scenarios can be built upon this work. 相似文献
69.
Solar System Research - Within the framework of Tsallis nonextensive statistics, the criteria for the Jeans gravitational instability are derived for a self-gravitating protoplanetary disk, whose... 相似文献
70.
Tsap Yu. T. Stepanov A. V. Kopylova Yu. G. Khaneichuk O. V. 《Geomagnetism and Aeronomy》2020,60(4):446-451
Geomagnetism and Aeronomy - The propagation of linear Alfvén waves with periods of 10–200 s from the photosphere to the solar chromosphere under the conditions of an isothermal... 相似文献