首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   31206篇
  免费   501篇
  国内免费   335篇
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
  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.
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.
Deinego  I. D.  Ansorge  I.  Belyaev  K. P. 《Oceanology》2021,61(5):613-624
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.
Urvachev  E. M.  Blinnikov  S. I.  Nomoto  K. 《Astronomy Letters》2021,47(11):738-745
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.
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.
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.
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.
Abhash  Amiya  Pandey  K. K. 《Water Resources》2021,48(2):235-244
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.
Matishov  G. G.  Polshin  V. V.  Kovalenko  E. P.  Grigorenko  K. S. 《Oceanology》2021,61(4):533-542
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号