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   304篇
  免费   5篇
林业   30篇
农学   6篇
基础科学   2篇
  56篇
综合类   21篇
农作物   21篇
水产渔业   22篇
畜牧兽医   142篇
园艺   3篇
植物保护   6篇
  2022年   4篇
  2021年   9篇
  2020年   6篇
  2019年   11篇
  2018年   12篇
  2017年   3篇
  2016年   11篇
  2015年   7篇
  2014年   7篇
  2013年   19篇
  2012年   41篇
  2011年   14篇
  2010年   7篇
  2009年   9篇
  2008年   15篇
  2007年   15篇
  2006年   12篇
  2005年   13篇
  2004年   12篇
  2003年   5篇
  2002年   8篇
  2001年   3篇
  2000年   5篇
  1999年   6篇
  1998年   4篇
  1997年   5篇
  1996年   5篇
  1995年   6篇
  1994年   4篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1989年   2篇
  1988年   2篇
  1987年   3篇
  1984年   1篇
  1983年   3篇
  1982年   3篇
  1981年   2篇
  1980年   1篇
  1974年   1篇
  1968年   1篇
  1966年   1篇
  1962年   1篇
  1956年   1篇
  1955年   1篇
  1949年   1篇
  1948年   1篇
  1946年   1篇
  1945年   1篇
排序方式: 共有309条查询结果,搜索用时 0 毫秒
301.
Staple meat and milk provide excellent nutrition, but when traditional foods and ingredients are tailored to meet the particular nutritional or lifestyle demands of a population they become even more attractive and valuable. These foods can be considered as delivery systems for health-promoting nutrients. Nutritional improvement of meat and milk can be achieved several ways, preferably by making desirable changes on-farm to directly improve the food without subsequent manipulations. Scope for these changes is limited by animal homeostasis, but alternatives may be less desirable. Methods in vivo that suit typical pastoral farming practice and can complement the solving of animal health and production problems include: selection of traits or phenotypes; specialty diets; long-acting parenteral supplements; and modification of ruminal microflora. Successful techniques to increase the concentration of calcium, selenium, iodine and iron in milk or meat are described.

Manipulations to change composition are only one part of bringing tailored foods to market. Commercial realisation of these new products needs the initiative and collaboration of scientists, veterinarians, growers and producers responding to market pull. The uptake of future biotechnologies to capture more value inside the farm gate will also be required if the pastoral industry in New Zealand is to sustain a global competitive advantage.  相似文献   
302.
303.
Polybrominated diphenyl ethers (PBDEs) have been found at high levels, up to 7.6?×?106?pg/g, in biosolids commonly applied to agricultural soils. A field investigation was carried out in this study to measure concentrations of PBDEs in biosolid-amended agricultural soils in which various amounts of biosolids (20 and 80?t/ha) had been applied. Concentrations of PBDEs in surface soils that had received a single application of 80?t/ha biosolids were one to two orders of magnitude greater than that in soil, which had received a single application of 20?t/ha of biosolids. Assessment of PBDEs levels at different depths, between 0.05 and 1.05?m, in soils that received 80?t/ha biosolids, showed that PBDEs were mobilized from the surface soil to lower depths. Total PBDEs concentrations decreased from 10,250?pg/g dry weight basis (dw) in the 0.05?m soil layer to 220?pg/g dw at a depth of 1?m. The distribution of PBDEs with depth and cation exchange capacity of the soil could be described as exponential functions. The coefficients of correlation ranged from 0.47 to 0.57 and 0.47 to 0.67, respectively. Despite the deviation in the experimental measurements induced by variables, such as non-uniform biosolid application, heterogeneity of the soil, and the uneven surface of the field, variations of PBDEs along the soil profile in the biosolid-amended soil were clearly demonstrated.  相似文献   
304.
305.
We developed a model of 545 components (nodes) and 1259 interactions representing signaling pathways and cellular machines in the hippocampal CA1 neuron. Using graph theory methods, we analyzed ligand-induced signal flow through the system. Specification of input and output nodes allowed us to identify functional modules. Networking resulted in the emergence of regulatory motifs, such as positive and negative feedback and feedforward loops, that process information. Key regulators of plasticity were highly connected nodes required for the formation of regulatory motifs, indicating the potential importance of such motifs in determining cellular choices between homeostasis and plasticity.  相似文献   
306.
307.
308.
309.
Bain  Daniel J.  Brush  Grace S. 《Landscape Ecology》2004,19(8):843-856
Recent research shows that land use history is an important determinant of current ecosystem function. In the United States, characterization of land use change following European settlement requires reconstruction of the original property mosaic. However, this task is difficult in unsystematically surveyed areas east of the Appalachian Mountains. The Gwynns Falls watershed (Baltimore, MD) was originally surveyed in the 1600-1700s under a system of warrants and patents (commonly known as ‘metes and bounds’). A method for the reconstruction and mapping of warrant and patent properties is presented and used to map the original property mosaic in the Gwynns Falls watershed. Using the mapped mosaic, the persistence of properties and property lines in the current Gwynns Falls landscape is considered. The results of this research indicate that as in agricultural areas, the original property lines in the Gwynns Falls watershed are persistent. At the same time, the results suggest that the property mosaic in heavily urbanized/suburbanized areas is generally ‘reset.’ Further, trends in surveying technique, parcel size, and settlement patterns cause property line density and property shape complexity to increase in the less urbanized upper watershed. The persistence of original patterns may be damping expression of heterogeneity gradients in this urban landscape. This spatial pattern of complexity in the original mosaic is directly opposite of hypothesized patterns of landscape heterogeneity arising from urbanization. The technique reported here and the resulting observations are important for landscape pattern studies in areas settled under unsystematic survey systems, especially the heavily urbanized areas of the eastern United States. This revised version was published online in July 2006 with corrections to the Cover Date.  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