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   627篇
  免费   37篇
林业   94篇
农学   29篇
基础科学   4篇
  112篇
综合类   59篇
农作物   16篇
水产渔业   55篇
畜牧兽医   226篇
园艺   21篇
植物保护   48篇
  2024年   1篇
  2023年   2篇
  2022年   6篇
  2021年   13篇
  2020年   9篇
  2019年   6篇
  2018年   19篇
  2017年   30篇
  2016年   19篇
  2015年   17篇
  2014年   29篇
  2013年   27篇
  2012年   58篇
  2011年   64篇
  2010年   22篇
  2009年   27篇
  2008年   36篇
  2007年   54篇
  2006年   40篇
  2005年   41篇
  2004年   31篇
  2003年   34篇
  2002年   33篇
  2001年   3篇
  2000年   2篇
  1999年   3篇
  1998年   2篇
  1997年   1篇
  1996年   3篇
  1995年   3篇
  1994年   4篇
  1993年   1篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   3篇
  1987年   4篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1981年   1篇
  1974年   1篇
  1968年   1篇
  1966年   1篇
  1927年   2篇
排序方式: 共有664条查询结果,搜索用时 15 毫秒
221.
Most mutations in the dystrophin gene create a frameshift or a stop in the mRNA and are associated with severe Duchenne muscular dystrophy. Exon skipping that naturally occurs at low frequency sometimes eliminates the mutation and leads to the production of a rescued protein. We have achieved persistent exon skipping that removes the mutated exon on the dystrophin messenger mRNA of the mdx mouse, by a single administration of an AAV vector expressing antisense sequences linked to a modified U7 small nuclear RNA. We report the sustained production of functional dystrophin at physiological levels in entire groups of muscles and the correction of the muscular dystrophy.  相似文献   
222.
223.
224.
A calcium-soluble protein isolate (CSPI) was prepared from the supernatant obtained after addition of 0.75 M calcium chloride to a pH 5.0 aqueous extract of yellow mustard (Sinapis alba) seed meal. Total amino acid analysis showed that the CSPI has significantly higher (p < 0.05) contents of glutamic acid + glutamine, cysteine, and proline when compared to the precipitated, calcium-insoluble proteins. Peptide mass fingerprinting of tryptic peptides of the major polypeptides by mass spectrometry indicated that the CSPI is composed mainly of cruciferin proteins with a contribution from napins (the major allergenic proteins of S. alba). The S. alba CSPI had significantly higher (p < 0.05) protein solubility and emulsion formation ability in the presence of 0.75 M calcium chloride when compared to similar isolates prepared from Brassica juncea (brown mustard) and soybean seed meals. We suggest that the S. alba CSPI could be used to prepare calcium-fortified high protein liquid products. However, the presence of allergenic proteins in this extract may limit its widespread food use.  相似文献   
225.
The changes in water proton transverse relaxation behavior induced by aggregation of whey proteins are explained in terms of the simple molecular processes of diffusion and chemical exchange. The water self-diffusion coefficient was measured in whey protein solutions and gels by the pulsed field gradient NMR method. As expected, water self-diffusion was reduced with increased protein concentrations. Whatever the concentration, the water molecules were free to diffuse over distances varying from 15 to 47 mum. Water diffusion was constant over these distances, demonstrating that no restrictions were found to explain the water hindrance. The modification in protein structure by gelation induced a decrease in water diffusion. The effects of protein concentration on water diffusion are discussed and modeled. Two approaches were compared, the obstruction effect induced by a spherical particle and the cell model, which considered two water compartments with specific self-diffusion coefficients.  相似文献   
226.
Summary A sample of 50 wild populations of perennial ryegrass (12 from northern Italy and 38 from Corsica) was tested with controls as spaced plant nurseries in two locations in France. Multivariate analyses, such as principal component analysis, hierarchical clustering and factorial discriminant analysis were used to describe the genetic variability of such Mediterranean material.On the whole, Mediterranean populations do not appear to be more promosing than the north European varieties. However, some populations from Corsica could be used to develop genetic resources for the Mediterranean area.The interest of each cluster is discussed and geographical repartition of clusters is shown on country maps.The factorial discriminant analysis gives a linear discriminant Fisher function which clearely discriminates two groups of populations according to their country of origin.  相似文献   
227.
228.

Cocoa is a major crop and income source for most farmers and rural households in the Centre, South and South-West regions of Cameroon, where cocoa is generally produced in agroforestry systems. In this country, cocoa-based agroforestry systems (CBAFS) are undergoing multiple changes alongside the rapid changes underway in the natural, economic and socio-political conditions. This study—carried out in the Akongo subregion in central Cameroon—was designed to gain insight into the CBAFS trends and dynamics in the light of those multiple changes. This semi-structured socioeconomic survey involved interviews and direct observations at plot, farm, household and village scales. Overall, forty cocoa growers from ten villages were interviewed and then fifteen cocoa plots were characterized on the basis of the survey findings. They revealed that cocoa was the major crop in this study area, with cocoa plantations occupying three quarters of the total farming area. Three types of CBAFS were identified, which differed according to their vegetation structure, management practices and age of the plantations. Dynamics affecting the structural characteristics and the spatial extension of these systems emerged and were intimately linked to the dynamics of the cocoa farmer population in relation to their context.

  相似文献   
229.
Agroforestry Systems - In temperate regions, tree leaves could be a source of energy, protein, vitamins and minerals for ruminants. Our objective was to study the diversity in chemical composition...  相似文献   
230.
Histo- and immunohistochemical techniques have recently been used to study the fibre type and myosin expression in fish muscle during development. In the present work, embryonic, larval and adult myosin isozymes (heavy and light chains) and parvalbumin isotypes were analyzed, from fertization to the adult stage, by polyacrylamide gel electrophoresis of barbel (Barbus barbus L.) trunk muscle extracts. The examined myosins display the sequential transitions from embryonic to larval and adult forms characteristic of higher vertebrates. They are characterized by specific heavy chains but their light chains differ only by the LC1/LC3 stoichiometry with LC3 exceeding LC1 after 10 days. Sarcoplasmic parvalbumins show considerable and unforeseen developmental transitions in their isotype distribution: the PA II isotype first appears after hatching and becomes the predominant form until the length reaches about 6 cm. One month after hatching, the amount of PA II then decreases and the synthesis of PA III and IV further increases to reach the typical adult pattern at a size of 18 cm. These observations show that the distribution of parvalbumin isotypes reflects the stage of development. It suggests a specific role for each isotype in relation to muscle activity. Microscopy illustrates the progressive development of somites, muscles cells, and myofibrils, which accelerates at hatching when movements increase.  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