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   21764篇
  免费   267篇
  国内免费   4篇
林业   3983篇
农学   1461篇
基础科学   171篇
  3787篇
综合类   1599篇
农作物   2312篇
水产渔业   2117篇
畜牧兽医   3100篇
园艺   1262篇
植物保护   2243篇
  2023年   34篇
  2022年   51篇
  2021年   91篇
  2020年   142篇
  2019年   134篇
  2018年   2841篇
  2017年   2781篇
  2016年   1296篇
  2015年   175篇
  2014年   147篇
  2013年   272篇
  2012年   1086篇
  2011年   2490篇
  2010年   2301篇
  2009年   1406篇
  2008年   1615篇
  2007年   1877篇
  2006年   321篇
  2005年   388篇
  2004年   368篇
  2003年   424篇
  2002年   314篇
  2001年   68篇
  2000年   114篇
  1999年   83篇
  1998年   57篇
  1997年   53篇
  1996年   54篇
  1995年   40篇
  1994年   47篇
  1993年   61篇
  1992年   47篇
  1991年   46篇
  1990年   47篇
  1989年   47篇
  1988年   49篇
  1987年   41篇
  1986年   54篇
  1985年   32篇
  1984年   43篇
  1983年   36篇
  1982年   36篇
  1981年   27篇
  1980年   20篇
  1979年   23篇
  1978年   27篇
  1977年   30篇
  1975年   20篇
  1973年   24篇
  1972年   21篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
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   
74.
75.
76.
77.
78.
This study investigates how age at first maturity of two tropical amphidromous species Sicyopterus lagocephalus (Pallas, 1770) and Cotylopus acutipinnis (Guichenot, 1863) varies in relation to their larval and juvenile life history. Reproductive stage was estimated based on histological observation of ovaries of more than 200 females of each species caught monthly over 1 year. The age of fish was estimated by interpreting the daily increments deposited on otoliths during the oceanic larval phase, and the juvenile phase in the river. The age at first maturity was approximately 9 months for S. lagocephalus and 7 months for C. acutipinnis, corresponding to approximately 70–130 and 90–130 days after they returned to freshwater respectively. For both species, the time spent in freshwater before maturity was significantly influenced by the duration of the pelagic larval stage at sea (PLD) and the season of return in freshwater. Individuals with a long PLD, or returning in freshwater during the warmer season, maturated faster once in freshwater. This reproductive advantage may minimise the risk of extirpation due to catastrophic events at each generation and thus probably benefits amphidromous species living in very unpredictable tropical rivers.  相似文献   
79.
80.
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   
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