全文获取类型
收费全文 | 31206篇 |
免费 | 501篇 |
国内免费 | 335篇 |
专业分类
测绘学 | 1219篇 |
大气科学 | 2433篇 |
地球物理 | 6028篇 |
地质学 | 11049篇 |
海洋学 | 2483篇 |
天文学 | 7285篇 |
综合类 | 142篇 |
自然地理 | 1403篇 |
出版年
2021年 | 273篇 |
2020年 | 276篇 |
2019年 | 321篇 |
2018年 | 813篇 |
2017年 | 777篇 |
2016年 | 1000篇 |
2015年 | 567篇 |
2014年 | 945篇 |
2013年 | 1675篇 |
2012年 | 1009篇 |
2011年 | 1262篇 |
2010年 | 1052篇 |
2009年 | 1366篇 |
2008年 | 1192篇 |
2007年 | 1128篇 |
2006年 | 1157篇 |
2005年 | 971篇 |
2004年 | 852篇 |
2003年 | 851篇 |
2002年 | 840篇 |
2001年 | 757篇 |
2000年 | 708篇 |
1999年 | 633篇 |
1998年 | 575篇 |
1997年 | 583篇 |
1996年 | 517篇 |
1995年 | 523篇 |
1994年 | 497篇 |
1993年 | 418篇 |
1992年 | 370篇 |
1991年 | 407篇 |
1990年 | 402篇 |
1989年 | 375篇 |
1988年 | 349篇 |
1987年 | 421篇 |
1986年 | 350篇 |
1985年 | 434篇 |
1984年 | 466篇 |
1983年 | 450篇 |
1982年 | 434篇 |
1981年 | 353篇 |
1980年 | 356篇 |
1979年 | 304篇 |
1978年 | 299篇 |
1977年 | 285篇 |
1976年 | 243篇 |
1975年 | 247篇 |
1974年 | 274篇 |
1973年 | 304篇 |
1972年 | 192篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Water Resources - The factors of phytoplankton development in the stratified Mozhaisk Reservoir are analyzed on the basis of long-term observations and model calculations. To analyze the... 相似文献
2.
Codie Wilson Stephanie K. Kampf Sandra Ryan Tim Covino Lee H. MacDonald Hunter Gleason 《水文研究》2021,35(1):e13975
Wildfire increases the potential connectivity of runoff and sediment throughout watersheds due to greater bare soil, runoff and erosion as compared to pre-fire conditions. This research examines the connectivity of post-fire runoff and sediment from hillslopes (< 1.5 ha; n = 31) and catchments (< 1000 ha; n = 10) within two watersheds (< 1500 ha) burned by the 2012 High Park Fire in northcentral Colorado, USA. Our objectives were to: (1) identify sources and quantify magnitudes of post-fire runoff and erosion at nested hillslopes and watersheds for two rain storms with varied duration, intensity and antecedent precipitation; and (2) assess the factors affecting the magnitude and connectivity of runoff and sediment across spatial scales for these two rain storms. The two summer storms that are the focus of this research occurred during the third summer after burning. The first storm had low intensity rainfall over 11 hours (return interval <1–2 years), whereas the second event had high intensity rainfall over 1 hour (return interval <1–10 years). The lower intensity storm was preceded by high antecedent rainfall and led to low hillslope sediment yields and channel incision at most locations, whereas the high intensity storm led to infiltration-excess overland flow, high sediment yields, in-stream sediment deposition and channel substrate fining. For both storms, hillslope-to-stream sediment delivery ratios and area-normalised cross-sectional channel change increased with the percent of catchment that burned at high severity. For the high intensity storm, hillslope-to-stream sediment delivery ratios decreased with unconfined channel length (%). The findings quantify post-fire connectivity and sediment delivery from hillslopes and streams, and highlight how different types of storms can cause varying magnitues and spatial patterns of sediment transport and deposition from hillslopes through stream channel networks. 相似文献
3.
Orlov A. M. Gorbatenko K. M. Benzik A. N. Rybakov M. O. Nosov M. A. Orlova S. Yu. 《Oceanology》2021,61(2):295-296
Oceanology - The article presents the results of hydrobiological, ichthyological, trophological, acoustic, and genetic research aboard the R/V Professor Levanidov in the Chukchi, East Siberian,... 相似文献
4.
Oceanology - The data assimilation (DA) of satellite observations of the ocean level from the Archiving Validating and Interpolating Satellite Observations (AVISO) into the IWM model (G.I. Marchuk... 相似文献
5.
Astronomy Letters - To explain the presence of early X-ray emission from the object AT2018cow, we have studied a scenario with the presence of dense ejecta in the system in the equatorial plane.... 相似文献
6.
Cheptsov V. S. Belov A. A. Vorobyova E. A. Pavlov A. K. Tsurkov D. A. Frolov D. A. Lomasov V. N. Chumikov A. E. 《Solar System Research》2021,55(5):383-388
Solar System Research - Ionizing radiation is one of the main factors that destroy biomolecules in extraterrestrial conditions. The effects of radiation depend on the conditions of the exposure... 相似文献
7.
Extending the Capture Map Concept to Estimate Discrete and Risk-Based Streamflow Depletion Potential
A popular and contemporary use of numerical groundwater models is to estimate the discrete relation between groundwater extraction and surface-water/groundwater exchange. Previously, the concept of a “capture map” has been put forward as a means to effectively summarize this relation for decision-making consumption. While capture maps have enjoyed success in the environmental simulation industry, they are deterministic, ignoring uncertainty in the underlying model. Furthermore, capture maps are not typically calculated in a manner that facilitates analysis of varying combinations of extraction locations and/or reaches. That is, they are typically constructed with focus on a single reach or group of reaches. The former of these limitations is important for conveying risk to decision makers and stakeholders, while the latter is important for decision-making support related to surface-water management, where future foci may include reaches that were not the focus of the original capture analysis. Herein, we use the concept of a response matrix to generalize the theory of the capture-map approach to estimate spatially discrete streamflow depletion potential. We also use first-order, second-moment uncertainty estimation techniques with the concept of “risk shifting” to place capture maps and streamflow depletion potential in a stochastic, risk-based framework. Our approach is demonstrated for an integrated groundwater/surface-water model of the lower San Antonio River, Texas, USA. 相似文献
8.
Benjamin K. Norris Julia C. Mullarney Karin R. Bryan Stephen M. Henderson 《地球表面变化过程与地形》2021,46(3):573-592
Within a wave-exposed mangrove forest, novel field observations are presented, comparing millimeter-scale turbulent water velocity fluctuations with contemporaneous subtidal bed elevation changes. High-resolution velocity and bed level measurements were collected from the unvegetated mudflat, at the mangrove forest fringe, and within the forest interior over multiple tidal cycles (flood–ebb) during a 2-week period. Measurements demonstrated that the spatial variability in vegetation density is a control on sediment transport at sub-meter scales. Scour around single and dense clusters of pneumatophores was predicted by a standard hydraulic engineering equation for wave-induced scour around regular cylinders, when the cylinder diameter in the equations was replaced with the representative diameter of the dense pneumatophore clusters. Waves were dissipated as they propagated into the forest, but dissipation at infragravity periods (> 30 s) was observed to be less than dissipation at shorter periods (< 30 s), consistent with the predictions of a simple model. Cross-wavelet analysis revealed that infragravity-frequency fluctuations in the bed level were occasionally coherent with velocity, possibly indicating scour upstream of dense pneumatophore patches when infragravity waves reinforced tidal currents. Consequently, infragravity waves were a likely driver of sediment transport within the mangrove forest. Near-bed turbulent kinetic energy, estimated from the turbulent dissipation rate, was also correlated with bed level changes. Specifically, within the mangrove forest and over the unvegetated mudflat, high-energy events were associated with erosion or near-zero bed level change, whereas low-energy events were associated with accretion. In contrast, no single relationship between bed level changes and mean current velocity was applicable across both vegetated and unvegetated regions. These observations support the theory that sediment mobilization scales with turbulent energy, rather than mean velocity, a distinction that becomes important when vegetation controls the development of turbulence. 相似文献
9.
Water Resources - Piano Key Weirs (PKW) is a free-flowing weir, and an improvement over the labyrinth weir family. PKW has higher discharge for the same head as compared to other types of weirs.... 相似文献
10.
Oceanology - The article presents the results of investigations conducted by members of SSC RAS on the Dolgaya Spit in 2019–2020. The following types of data are analyzed: satellite imagery,... 相似文献