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   254308篇
  免费   5298篇
  国内免费   3303篇
测绘学   6943篇
大气科学   19192篇
地球物理   52937篇
地质学   88345篇
海洋学   21587篇
天文学   54824篇
综合类   1024篇
自然地理   18057篇
  2021年   2168篇
  2020年   2594篇
  2019年   2833篇
  2018年   3713篇
  2017年   3434篇
  2016年   5805篇
  2015年   4215篇
  2014年   6901篇
  2013年   14206篇
  2012年   6547篇
  2011年   8001篇
  2010年   7025篇
  2009年   9680篇
  2008年   8474篇
  2007年   7986篇
  2006年   9668篇
  2005年   7769篇
  2004年   7637篇
  2003年   7117篇
  2002年   6633篇
  2001年   5908篇
  2000年   5584篇
  1999年   4803篇
  1998年   4846篇
  1997年   4641篇
  1996年   4207篇
  1995年   4320篇
  1994年   4002篇
  1993年   3740篇
  1992年   3496篇
  1991年   3530篇
  1990年   3625篇
  1989年   3325篇
  1988年   3166篇
  1987年   3710篇
  1986年   3254篇
  1985年   4117篇
  1984年   4625篇
  1983年   4310篇
  1982年   4224篇
  1981年   3844篇
  1980年   3599篇
  1979年   3439篇
  1978年   3437篇
  1977年   3223篇
  1976年   2966篇
  1975年   2904篇
  1974年   2878篇
  1973年   3066篇
  1972年   1992篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Nikanorova  A. D.  Egorov  S. A. 《Water Resources》2019,46(1):138-142
Water Resources - The study is focused on the step-by-step development of the modern system of legal rules and principles used at the international level to regulate the use of transboundary...  相似文献   
82.
Geomagnetism and Aeronomy - It is possible that the radially independent, spatial-spectral components of the energy and power of the potential part of the main geomagnetic field were determined and...  相似文献   
83.
Water Resources - Hydrogen sulfide, like other sulfides, is formed in aquatic environments due to sulphate reduction processes and putrefactive decomposition of organic matter of bottom sediments,...  相似文献   
84.
Geomagnetism and Aeronomy - The paper presents the results of a study of microwave thermal bremsstrahlung of local sources above sunspots. Special attention is paid to the transition from thermal...  相似文献   
85.
Geomagnetism and Aeronomy - The data from observation of the geomagnetic field variations at the Midlatitude Mikhnevo Geophysical Observatory of Institute of Geosphere Dynamics of the Russian...  相似文献   
86.
Geomagnetism and Aeronomy - The causes of a sharp increase in the radiocarbon content in the Earth’s atmosphere for periods with abnormally low solar modulation of galactic cosmic rays (GCRs)...  相似文献   
87.
Determining sediment transfer times is key to understanding source-to-sink dynamics and the transmission of environmental signals through the fluvial system. Previous work on the Bolivian Altiplano applied the in situ cosmogenic 14C-10Be-chronometer to river sands and proposed sediment storage times of ~10–20 kyr in four catchments southeast of Lake Titicaca. However, the fidelity of those results hinges upon isotopic steady-state within sediment supplied from the source area. With the aim of independently quantifying sediment storage times and testing the 14C-10Be steady-state assumption, we dated sediment storage units within one of the previously investigated catchments using radiocarbon dating, cosmogenic 10Be-26Al isochron burial dating, and 10Be-26Al depth-profile dating. Palaeosurfaces appear to preserve remnants of a former fluvial system, which has undergone drainage reversal, reduction in catchment area, and local isostatic uplift since ~2.8 Ma. From alluvium mantling the palaeosurfaces we gained a deposition age of ~580 ka, while lower down fluvial terraces yielded ≤34 ka, and floodplains ~3–1 ka. Owing to restricted channel connectivity with the terraces and palaeosurfaces, the main source of channel sediment is via reworking of the late Holocene floodplain. Yet modelling a set of feasible scenarios reveals that floodplain storage and burial depth are incompatible with the 14C-10Be disequilibrium measured in the channel. Instead we propose that the 14C-10Be offset results from: (i) non-uniform erosion whereby deep gullies supply hillslope-derived debris; and/or (ii) holocene landscape transience associated with climate or human impact. The reliability of the 14C-10Be chronometer vitally depends upon careful evaluation of sources of isotopic disequilibrium in a wide range of depositional and erosional landforms in the landscape. © 2018 John Wiley & Sons, Ltd.  相似文献   
88.
Zhang  Guanglei  Ranjith  P. G.  Perera  M. S. A.  Lu  Yiyu  Choi  Xavier 《Natural Resources Research》2019,28(4):1639-1660
Natural Resources Research - High-volatile bituminous coal samples were reacted in deionized water with supercritical CO2 (ScCO2–water) under simulated in situ pressure and temperature...  相似文献   
89.
Application of X-ray fluorescence core-scanning(XRF-CS) on both marine and lake sediments has achieved remarkable results. However, its application has not been widely extended to the research on speleothems. In this study, we measure the Sr abundance and the Sr/Ca ratios of three stalagmites(two aragonite stalagmites, one calcite stalagmite) using the state-of-the-art fourth-generation Avaatech high-resolution XRF core scanner. Through comparisons among different scan paths and among different scan resolutions, as well as comparisons with inductively coupled plasma optical emission spectrometer(ICP-OES), Itrax XRF, and Artax XRF results, we confirm that the Avaatech XRF core scanner could precisely, quickly, and nondestructively analyze the high-resolution Sr abundance of speleothems. Furthermore, we combine the stalagmite δ~(18)O records to explore the paleoclimatic significance of the measured stalagmite Sr/Ca.  相似文献   
90.
Izvestiya, Atmospheric and Oceanic Physics - This paper investigates the stability of a jet flow with a piecewise linear velocity profile in a rotating stratified atmosphere. The linearized set of...  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