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   4235篇
  免费   168篇
  国内免费   54篇
测绘学   95篇
大气科学   321篇
地球物理   998篇
地质学   1403篇
海洋学   406篇
天文学   760篇
综合类   18篇
自然地理   456篇
  2022年   12篇
  2021年   59篇
  2020年   61篇
  2019年   69篇
  2018年   78篇
  2017年   83篇
  2016年   118篇
  2015年   109篇
  2014年   112篇
  2013年   251篇
  2012年   173篇
  2011年   240篇
  2010年   183篇
  2009年   214篇
  2008年   213篇
  2007年   217篇
  2006年   203篇
  2005年   160篇
  2004年   157篇
  2003年   144篇
  2002年   142篇
  2001年   118篇
  2000年   113篇
  1999年   86篇
  1998年   88篇
  1997年   69篇
  1996年   65篇
  1995年   58篇
  1994年   52篇
  1993年   48篇
  1992年   45篇
  1991年   36篇
  1990年   46篇
  1989年   42篇
  1988年   45篇
  1987年   51篇
  1986年   43篇
  1985年   42篇
  1984年   52篇
  1983年   38篇
  1982年   39篇
  1981年   46篇
  1980年   31篇
  1979年   44篇
  1978年   28篇
  1977年   26篇
  1976年   14篇
  1975年   14篇
  1974年   12篇
  1972年   10篇
排序方式: 共有4457条查询结果,搜索用时 15 毫秒
981.
982.
The single most prominent lake associated with the retreat phase of the last British–Irish Ice Sheet (BIIS) was Proglacial Lake Humber. The present research elucidates a revised regional history of Proglacial Lake Humber from its maximum elevation to its demise using a combination of landscape mapping and luminescence dating. The results of mapping multiple Lake Humber strandlines are now best described by an eight‐stage recessional model. Erosional highstands of the lake can be shown to post‐date the BIIS advance that deposited the Skipsea Till at around 17 ka whereas new OSL ages show that Lake Humber was nearing its demise by 15.5±0.8 ka, indicating a possible short‐lived lake. Multiple lake level stands are attributed to the switching of lake outlets from the Lincolnshire Gap to the Humber Gap and to oscillations of the BIIS blocking the latter on more than one occasion and subsequently at a lower elevation with till. The horizontal or near‐horizontal shorelines confirm that isostatic adjustment did not occur during the demise of Lake Humber, indicating that BIIS advances in the North Sea region and Vale of York were not only dynamic but of short duration.  相似文献   
983.
984.
985.
986.
Cedar Bayou, a natural tidal inlet, was recently dredged to allow for direct water exchange between the Gulf of Mexico and Mesquite Bay, TX, USA. We quantified changes in densities of juvenile nekton (fish, shrimps, and crabs) and community structure in Mesquite Bay after Cedar Bayou was reopened by collecting samples at both control and impact sites using an epibenthic sled 1 year before (October 2013–April 2014) and after (October 2014–April 2015) opening. Significantly higher densities of total nekton were observed at the impact sites after opening using a before-after control-impact design. Red Drum (Sciaenops ocellatus), Atlantic Croaker (Micropogonias undulatus), post-larval penaeid shrimps (Farfantepenaeus aztecus, F. duorarum, and Litopenaeus setiferus), and Blue Crabs (Callinectes sapidus) were significantly more abundant at impact sites after Cedar Bayou was opened. Multivariate analysis showed a significant change in impact site communities after opening and was driven by an increased presence of estuarine-dependent species. Overall, this study demonstrates that opening tidal inlets, such as Cedar Bayou, and reconnecting Mesquite Bay to the Gulf of Mexico increased the presence of numerous estuarine-dependent species, many of which were not present or occurred at very low densities prior to reopening. Thus, reestablishing the historical connectivity between a productive estuary and the open Gulf of Mexico via Cedar Bayou should reinstitute natural nekton recruitment processes important to the Aransas, Mesquite, and San Antonio Bay regions.  相似文献   
987.
988.
989.
Using a space-for-time substitution design, we investigated the response of structural instream habitat and fish populations to different riparian management practices throughout a Dairy Best Practice Catchment. We found a significant negative correlation between the upstream area of stock exclusion fencing and deposited instream fine sediment cover. Furthermore, we determined that this relationship emerges when ≥300?m lengths of upstream riparian area were included in the analysis, indicating the scale at which stock exclusion fencing results in a positive instream habitat response. Specifically, for this historically degraded spring-fed stream, our findings indicate that riparian segments with 5 m wide stock exclusion fences (both banks) are required to achieve instream fine sediment cover below 20% in downstream reaches. Fish were sparse and evenly spread throughout the catchment. Fish distributions were not correlated with reach-scale riparian or instream habitat variables, possibly because the available habitat quality gradient was too narrow.  相似文献   
990.
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