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   45946篇
  免费   814篇
  国内免费   705篇
测绘学   1117篇
大气科学   3413篇
地球物理   9005篇
地质学   16151篇
海洋学   4574篇
天文学   10138篇
综合类   184篇
自然地理   2883篇
  2022年   922篇
  2021年   1339篇
  2020年   1295篇
  2019年   1361篇
  2018年   1070篇
  2017年   820篇
  2016年   959篇
  2015年   712篇
  2014年   881篇
  2013年   1997篇
  2012年   1110篇
  2011年   1660篇
  2010年   1385篇
  2009年   2007篇
  2008年   1671篇
  2007年   1609篇
  2006年   1506篇
  2005年   1374篇
  2004年   1466篇
  2003年   1485篇
  2002年   1421篇
  2001年   1238篇
  2000年   1106篇
  1999年   1049篇
  1998年   987篇
  1997年   1040篇
  1996年   719篇
  1995年   675篇
  1994年   625篇
  1993年   539篇
  1992年   564篇
  1991年   536篇
  1990年   517篇
  1989年   478篇
  1988年   450篇
  1987年   489篇
  1986年   528篇
  1985年   560篇
  1984年   631篇
  1983年   629篇
  1982年   534篇
  1981年   506篇
  1980年   464篇
  1979年   415篇
  1978年   436篇
  1977年   379篇
  1976年   337篇
  1975年   355篇
  1974年   405篇
  1973年   380篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Water Resources - For the first time, data are given on cyanobacterial toxins entering tap water, supplied to the population of some cities in Yaroslavl oblast. The detection of microcystins with...  相似文献   
82.
Pavlova  N. A.  Shepelev  V. V.  Galanin  A. A.  Efremov  V. S. 《Water Resources》2020,47(4):581-590
Water Resources - The results of long-term studies of a group of aufeis-forming Buluus groundwater sources are given. A stow, which has been formed by the spring, contains the drainage area of the...  相似文献   
83.
Water Resources - The article presents the results of summer dry-season areal surveys of subsoil water chemistry in the drainage basin of the Ivankovo Reservoir in the Volga segment from Tver City...  相似文献   
84.
The special interest produced by near-field directivity records and their effect on structural response has given a new significance in the velocity time history, its pulse-like content, and relevant parameters and indices. Recent research has shown that directivity pulses inherent in these records govern the linear and the nonlinear response of a wide range of structures. Based on this observation, it is suggested in this paper that a truncated ground motion, limited to the duration of the predominant velocity pulse, can be efficiently used to predict the structural response, instead of the base motion with the total duration, reducing significantly the required runtimes. The proposed methodology is verified for a series of medium to high rise reinforced concrete buildings, for which nonlinear time-history analyses are performed for a vast suite of pulse-like near-field records applied as base excitations with their total duration and the proposed truncated one. Comparison of the results for the response displacements and forces shows very good agreement, permitting the acceptance of the pulse duration as the efficient strong motion time interval of the original record, which determines the response and, thus, it can be used for nonlinear structural analyses.  相似文献   
85.
Springs are the point of origin for most headwater streams and are important regulators of their chemical composition. We analysed solute concentrations of water emerging from 57 springs within the 3 km2 Fool Creek catchment at the Fraser Experimental Forest and considered sources of spatial variation among them and their influence on the chemical composition of downstream water. On average, calcium and acid neutralizing capacity (bicarbonate-ANC) comprised 50 and 90% of the cation and anion charge respectively, in both spring and stream water. Variation in inorganic chemical composition among springs reflected distinct groundwater sources and catchment geology. Springs emerging through glacial deposits in the upper portion of the catchment were the most dilute and similar to snowmelt, whereas lower elevation springs were more concentrated in cations and ANC. Water emerging from a handful of springs in a geologically faulted portion of the catchment were more concentrated than all others and had a predominant effect on downstream ion concentrations. Chemical similarity indicated that these springs were linked along surface and subsurface flowpaths. This survey shows that springwater chemistry is influenced at nested spatial scales including broad geologic conditions, elevational and spatial attributes and isolated local features. Our results highlight the role of overlapping factors on solute export from headwater catchments.  相似文献   
86.
Solar System Research - The ionization-type cosmic dust detector METEOR-L is being developed for the lunar orbiter Luna-26 and is designed to study the distribution of meteoric bodies in space by...  相似文献   
87.
Ermash  A. A.  Pilipenko  S. V.  Lukash  V. N. 《Astronomy Letters》2020,46(5):298-311
Astronomy Letters - The sensitivity of future far-infrared telescopes, such as Millimetron, will be limited by the confusion noise produced by distant galaxies. We have constructed a model of the...  相似文献   
88.
Izvestiya, Atmospheric and Oceanic Physics - A method for retrieving sea wave spectra from space images of high spatial resolution has been developed for various conditions of wave generation based...  相似文献   
89.
Doklady Earth Sciences - The content of plant hormones (brassinosteroids) in oil samples from a number of oilfields in Belarus is determined using an enzyme immunoassay method. Brassinosteroids of...  相似文献   
90.
Doklady Earth Sciences - The results of studying the content and composition of aliphatic hydrocarbons (AHCs) and polycyclic aromatic hydrocarbons (PAHs) in the suspended particulate matter of the...  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