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   18805篇
  免费   153篇
  国内免费   9篇
林业   3756篇
农学   1339篇
基础科学   146篇
  3133篇
综合类   1104篇
农作物   2191篇
水产渔业   1984篇
畜牧兽医   2063篇
园艺   1155篇
植物保护   2096篇
  2023年   12篇
  2022年   17篇
  2021年   40篇
  2020年   64篇
  2019年   72篇
  2018年   2782篇
  2017年   2753篇
  2016年   1244篇
  2015年   114篇
  2014年   81篇
  2013年   125篇
  2012年   950篇
  2011年   2307篇
  2010年   2201篇
  2009年   1330篇
  2008年   1476篇
  2007年   1738篇
  2006年   205篇
  2005年   258篇
  2004年   235篇
  2003年   294篇
  2002年   205篇
  2001年   29篇
  2000年   59篇
  1999年   24篇
  1998年   23篇
  1997年   30篇
  1996年   18篇
  1995年   29篇
  1994年   23篇
  1993年   26篇
  1992年   19篇
  1991年   17篇
  1990年   14篇
  1989年   23篇
  1988年   21篇
  1987年   12篇
  1986年   5篇
  1985年   11篇
  1984年   11篇
  1983年   13篇
  1982年   11篇
  1981年   4篇
  1980年   4篇
  1979年   4篇
  1978年   6篇
  1977年   9篇
  1976年   4篇
  1973年   2篇
  1968年   5篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
51.
52.
Umma Tamima 《林业研究》2016,27(4):853-861
The objective was to evaluate the performance of the co-management of Nishorgo Support Project at Chunati Wildlife Sanctuary in Bangladesh. I adopted the Focus Groups Discussion method for opinion survey and applied the SWOTAHP technique for data analysis. Local people did not participate in the decision-making process of forest management and they perceived co-management as a threat to their livelihoods. Moreover, mistrust and misunderstanding among different stakeholders, political and ethical conflicts, lack of property rights of tribal communities, and lack of accountability and transparency were identified as the drawbacks of co-management.  相似文献   
53.
54.
55.
56.
57.
The spawning success of lithophilic salmonids is strongly influenced by the fine sediment content (“fines”) of spawning substrates, yet knowledge on the impacts of fines on the spawning of non‐salmonid lithophiles remains limited, despite their ecological and socio‐economic importance in European rivers. Consequently, the aim here was to use an ex‐situ experiment to investigate the impact of sand content on egg survival and timing of larval emergence of the surface‐spawning cyprinid European barbel Barbus barbus. Thirty incubator boxes within a recirculating system were filled with one of five experimental sediment mixtures (0%–40% sand by mass) that each contained 300 fertilised eggs at a depth of 50 mm. Emerged, free‐swimming larvae were captured and counted daily to assess grain‐size effects on larval survival and emergence. Specifically, total proportion of emerged larvae, cumulative daily proportion of emerged larvae and time required to reach 50% emergence were measured during the study. Whilst the proportion of sand in the sediments did not have a significant impact on egg‐to‐emergence survival (mean survival per treatment 75%–79%), it significantly affected the timing of larval emergence to the water column; early emergence was detected in treatments with elevated sand content (on average, 50% emergence after 12–13 days versus 19 days in the control). Similar to findings from salmonid studies, these results suggest high sand content in spawning gravels can influence timing of larval emergence and potentially cyprinid lithophilic fish survival.  相似文献   
58.
59.
A new functional porous carbons (PC-WF) is prepared by activation-pyrolysis method use waste cotton fabrics (WF) as an abundant, cheap and available precursor for removal of Brilliant Crocein (BC-GR) and Cationic Red 2GL (CR-GL) from aqueous phase. The PC-WF was characterized by BET, FTIR, SEM, and XRD techniques, the surface area, total pore volume, average pore diameter was found as 1463.5 m2 g-1, 0.783 cm3 g-1 and 2.14 nm, respectively. The influences on BC-GR and CR-GL adsorption of various experimental factors such as initial concentration and temperature were investigated. Adsorption kinetics was found to be best represented by the pseudo-second order model. The adsorption capacity was 319.8 mg g-1 for BC-GR and 842.5 mg g-1 for CR-GL at 30 °C, respectively. The results indicate that for waste cotton fabrics in particular, the practical application of this process to the production of porous carbon would be possible.  相似文献   
60.
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