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   111篇
  免费   7篇
林业   12篇
农学   1篇
  22篇
综合类   11篇
农作物   8篇
水产渔业   5篇
畜牧兽医   49篇
园艺   1篇
植物保护   9篇
  2024年   2篇
  2022年   1篇
  2020年   4篇
  2019年   3篇
  2018年   2篇
  2017年   7篇
  2016年   5篇
  2015年   5篇
  2014年   5篇
  2013年   10篇
  2012年   8篇
  2011年   10篇
  2010年   5篇
  2009年   4篇
  2008年   7篇
  2007年   3篇
  2006年   7篇
  2005年   12篇
  2004年   5篇
  2003年   1篇
  2002年   3篇
  2001年   2篇
  1992年   2篇
  1991年   1篇
  1990年   1篇
  1988年   1篇
  1984年   1篇
  1972年   1篇
排序方式: 共有118条查询结果,搜索用时 0 毫秒
111.
112.
Major revisions of the Finnish Forest Act were carried out in 1994–1996 and 2010–2013. The need for revision emerged from societal changes and changes in the forest sector’s operational environment that related to the globalisation of markets and influences of international policies. This study analysed the influences of global and European Union forest and environmental policies on the revision of the Forest Act by combining advocacy coalition framework with the four pathways of influence framework introduced by Bernstein and Cashore. The results show that the three identified advocacy coalitions, namely Forestry administration, Private forestry and Environmental coalition remained rather stable over the two revision processes from 1990s to 2010s. The importance of the different pathways of international influence differed between the coalitions. Private forestry and Forestry administration coalitions, which represented forestry paradigm, stressed market-related arguments, whereas Environmental coalition representing environmental paradigm mainly referred to international legally binding rules and non-legally binding initiatives. The argumentation of the actors indicated that international rules and international norms and discourse were regarded to be as equally important.  相似文献   
113.
在过去的20年里,亚洲林业经历了引人注目的转型,包括从计划经济到市场经济的转变,从天然林供给木材到人工林供给木材的转变,木材替代品与非木质林产品的增加,地方分权与当地群众的参与,生态时代的发展与生态系统管理。在促进亚洲可持续森林资源管理中,市场工具、社区参与和环境服务都得到了应用。亚洲林业的转型表现出多样化,其森林、社会与环境之间的联系是丰富多彩的。  相似文献   
114.
The ability of skeletal dipeptides (carnosine and anserine) and a sarcoplasmic protein (myoglobin) to interact with key flavor compounds (hexanal, octanal, methional, 2-pentanone, 2-methylbutanal, and 3-methylbutanal) has been studied using the solid phase microextraction (SPME) technique. Conditions for SPME analysis (fiber coating, sampling time, and linearity of detection) were optimized. The effect of pH on the binding was also investigated. Thermodynamic models were applied to evaluate the binding parameters n (number of binding sites), K (affinity constant), and DeltaG (Gibb's free energy) to all of the flavor compounds studied, and they showed an absence of cooperative effect. Carnosine was the peptide with the highest affinity for all of the volatile compounds except 2-pentanone. Its interaction with hexanal and methional was significantly affected by pH. Anserine showed a lower level of interactions with hexanal, methional, 2-methylbutanal, and 3-methylbutanal, whereas myoglobin interacted with only hexanal and 2-methylbutanal. Differences in aroma retention can thus result in different sensory perceptions of muscle foods.  相似文献   
115.
Soil salinity imposes an unprecedented risk to the soil fertility and availability of plant nutrients. The present proposal is designed to address the effect of salt stress on photosynthetic apparatus of maize including chlorophyll a fluorescence and how silicon nutrition helps to overcome this issue. In a sand culture experiment, two maize cultivars were sown in small pots with two levels of silicon (0 and 2 mM H2SiO3) and two levels of salinity stress (0 and 60 mM NaCl). Salinity stress reduced dry matter yield and potassium (K) concentration in both maize cultivars and also induced inefficient working of photosynthetic apparatus including photochemical efficiency of photosystem II. Silicon addition alleviated NaCl stress on maize crop by improving the dry matter yield and water use efficiency (WUE). It decreased shoot Na concentration by increasing root and shoot K concentration of maize plants. It enhanced maximum quantum yield of primary photochemistry which leads to smooth electron transport chain. It also significantly enhanced shoot silicon concentration and has a significant positive correlation with WUE. Therefore, silicon-treated maize plants have better chance to survive under salt stress conditions as their photosynthetic apparatus is working far better than non-silicon-treated plants.  相似文献   
116.
The influence of a change from daily to weekly sampling of bulk precipitation on the obtained deposition values was studied with parallel sampling for 8 months at the station of Virolahti in 2004. Due to dry deposition, the deposition values of the whole period were found to be 5–70% higher from weekly sampling than from daily sampling, the biggest difference being for K+, Ca2+, Mg+ and Na+. The collection efficiencies of the summer sampler and the winter sampler compared to the standard rain gauge were studied from daily sampling in 1991–2003 and weekly sampling in 2004–2008. The performance was best in summer and in winter with rain samples (median value 85–88%), while the median value for daily snow samples was 72%. In winter, the total sum of precipitation collected in the daily sampler and the weekly sampler was 78% and 69%, respectively. The deficit in the weekly sampler in winter was concluded to be due to evaporation, while from the summer sampler no evaporation seemed to occur. Use of the precipitation amount measured by the standard rain gauge when calculating annual precipitation-weighted mean values gave higher mean concentrations than the use of the precipitation measured by the deposition sampler itself, the biggest difference of 8–11% being in the sea-salt ions Cl?, Mg+ and Na+. It was concluded that the concentration and deposition values measured by daily and weekly bulk sampling are incompatible, and should not be combined into the same time series.  相似文献   
117.
118.

Background  

Immunosenescence is a process that affects all cell compartments of the immune system and the contribution of the immune system to healthy aging and longevity is still an open question. Lymphocyte subpopulations present different patterns of circadian variation and in the elderly alteration of circadian rhythmicity has been evidenced. The aim of our study was to analyze the dynamics of variation of specific cytotoxic lymphocyte subsets in old aged subjects.  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