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   29036篇
  免费   612篇
  国内免费   374篇
测绘学   863篇
大气科学   2069篇
地球物理   5808篇
地质学   10025篇
海洋学   2645篇
天文学   6881篇
综合类   71篇
自然地理   1660篇
  2021年   242篇
  2020年   282篇
  2019年   354篇
  2018年   688篇
  2017年   676篇
  2016年   836篇
  2015年   506篇
  2014年   827篇
  2013年   1547篇
  2012年   917篇
  2011年   1262篇
  2010年   1104篇
  2009年   1459篇
  2008年   1346篇
  2007年   1344篇
  2006年   1302篇
  2005年   1005篇
  2004年   963篇
  2003年   913篇
  2002年   843篇
  2001年   683篇
  2000年   686篇
  1999年   579篇
  1998年   585篇
  1997年   547篇
  1996年   430篇
  1995年   437篇
  1994年   454篇
  1993年   345篇
  1992年   351篇
  1991年   289篇
  1990年   333篇
  1989年   295篇
  1988年   282篇
  1987年   313篇
  1986年   266篇
  1985年   364篇
  1984年   376篇
  1983年   370篇
  1982年   360篇
  1981年   304篇
  1980年   312篇
  1979年   254篇
  1978年   250篇
  1977年   245篇
  1976年   205篇
  1975年   215篇
  1974年   207篇
  1973年   195篇
  1972年   135篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
31.
Thanks to its simple division into agricultural and forestry land use, the Corbeira catchment (Galicia, Spain) is used as a case study to build a predictive model using hydrogeochemical signatures. Stream data acquired under recessional flow conditions over a one year period were obtained from a sampling station near the downstream end of the catchment, and using principal component analysis, it is shown that some of the analytical parameters are covariant, and some are negatively correlated. These findings support inferences about the pathways of rainfall in the catchment. Specific signatures may be associated with the dominant hydrological source, either surface runoff or subsurface waters: additionally, the dominant land use in that part of the catchment, where the flow originated, can also be predicted. The dominant runoff shows a strong covariance between suspended solids (SS) and particulate phosphorus (PP), with a clear negative correlation with pH. Dissolved organic carbon (DOC) data are associated with this covariant set when these compounds are available in the soils in question. Dissolved phosphorus, total organic nitrogen and dissolved nitrates are also associated with the same covariant set when the runoff flows through areas of extensive agricultural use. The SS ? PP covariance is less significant at lower flows. Typical base flow regimes show a significant covariance between salinity and pH, with a marked negative correlation with SS ? PP set, confirming the dominance of subsurface waters in the baseflow, as expected. Seasonally divergent DOC ? SS behaviour proves to be a useful tracer for rainfall regimes. The DOC trend shows a sinusoidal annual variation in amplitude, determined by the rainfall regime. As a result, flow from the catchment is dominated by surface water whenever there is synchronicity between the peaks of DOC and SS. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
32.
Bobylev  V. V.  Krisanova  O. I.  Bajkova  A. T. 《Astronomy Letters》2020,46(7):439-448
Astronomy Letters - Based on published data, we have produced a sample of 256 radio sources whose trigonometric parallaxes and proper motions were measured by VLBI. This sample contains Galactic...  相似文献   
33.
Understanding what drives farmers’ voluntary adoption of nutrient and soil best management practices has important consequences for many environmental outcomes including water quality. We build on research revealing the need for simultaneous use of multiple nitrogen best management practices to achieve water quality improvement goals. Using social, economic and attitudinal variables we predict the use of multiple nitrogen best management practices at three time points: current use (2013), past use (before 2013), and likelihood of use on their largest field in the next three years. Our empirical analysis uses structural equation modeling with latent variables and 2014 farmer survey data from three Midwestern US states. Most farmers in our sample used at least one of the six best management practices. Our results reveal that farmers’ attitudes, use of information sources, and conservation program participation affect the number of nitrogen best management practices concurrently in use at multiple time points.  相似文献   
34.
Doklady Earth Sciences - The species composition and structure of bottom communities with a predominance of bivalve mollusks of the Portlandia genus, which are widespread on the shelf of the...  相似文献   
35.
Tasev  G.  Serafimovski  D.  Volkov  A. V.  Boev  B.  Djordjevic  T.  Kolitsch  U.  Serafimovski  T. 《Geology of Ore Deposits》2020,62(5):419-431
Geology of Ore Deposits - The Dudica deposit is located in the southern part of the Republic of North Macedonia (RNM), not far from the border with Greece in the Kozuf–Aridean volcanic...  相似文献   
36.
Doklady Earth Sciences - A structural model of the rare mineral yushkinite [(Mg0.60Al0.30V0.10)Σ1.0(OH)2] [V0.875S2] is studied using the data of electron microdiffraction and the X-ray powder...  相似文献   
37.
Demianski  M.  Doroshkevich  A.  Larchenkova  T.  Pilipenko  S. 《Astronomy Reports》2020,64(11):883-893
Astronomy Reports - A comparison of the virial parameters of galaxies and galaxy clusters (radius, density, and entropy function) in a wide range of masses, $${{10}^{6}} \leqslant...  相似文献   
38.
Gordeev  V. V.  Dara  O. M.  Alekseeva  T. N.  Kochenkova  A. I.  Boev  A. G.  Lokhov  A. S.  Belorukov  S. K. 《Oceanology》2020,60(3):384-392
Oceanology - The paper presents the first results of a study of seasonal variations in the grain size distribution and mineral compositions of suspended particulate matter (SPM) of the Northern...  相似文献   
39.
Zagidullin  A. A.  Usanin  V. S.  Petrova  N. K.  Nefedyev  Yu. A.  Andreev  A. O.  Gudkova  T. V. 《Astronomy Reports》2020,64(12):1093-1106
Astronomy Reports - The work is devoted to the study of the physical libration of the Moon. Interest in the traditional topic related to the rotation of the Moon is stirred up by the activity of...  相似文献   
40.
Doklady Earth Sciences - The content of polycyclic aromatic hydrocarbons (PAHs) in soil and snow cover near the carbon black plants in Moscow, Omsk, and Samara regions was studied. The differences...  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