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   161篇
  免费   6篇
  国内免费   1篇
林业   8篇
农学   2篇
基础科学   1篇
  26篇
综合类   11篇
农作物   11篇
水产渔业   4篇
畜牧兽医   102篇
植物保护   3篇
  2020年   3篇
  2019年   2篇
  2018年   4篇
  2016年   5篇
  2015年   2篇
  2014年   3篇
  2013年   12篇
  2012年   3篇
  2011年   4篇
  2010年   7篇
  2009年   4篇
  2008年   3篇
  2007年   7篇
  2006年   1篇
  2005年   1篇
  2004年   1篇
  2003年   6篇
  2002年   3篇
  2000年   3篇
  1999年   7篇
  1998年   2篇
  1997年   2篇
  1995年   1篇
  1994年   2篇
  1993年   6篇
  1992年   9篇
  1991年   2篇
  1990年   3篇
  1989年   3篇
  1988年   2篇
  1987年   2篇
  1986年   8篇
  1985年   4篇
  1984年   2篇
  1983年   5篇
  1981年   1篇
  1980年   1篇
  1979年   3篇
  1978年   2篇
  1975年   2篇
  1974年   3篇
  1973年   3篇
  1972年   1篇
  1971年   4篇
  1966年   3篇
  1961年   1篇
  1960年   2篇
  1959年   1篇
  1958年   1篇
  1956年   2篇
排序方式: 共有168条查询结果,搜索用时 15 毫秒
61.
62.
Poland has the largest agricultural area within the Baltic Sea drainage basin and reducing the risk of phosphorus (P) and nitrogen (N) leaching from Polish soils to water is therefore essential. Increased acidity is known to reduce soil fertility and may trigger P leaching from non-calcareous soils. As part of advisor training, 25 farms each in Pomerania and north-western Mazovia were visited and 1500?ha arable soil, including 180?ha grassland soil, were monitored in 2013–2014. The soil was mainly coarse textured, but 25% of the Pomeranian farms were dominated by silty or clayey soils. More or less regular drainage systems were found on 20% of the farms, while 50% had simpler, older (>30 years) systems with a few single pipes. The farmers often used only ammonium sulphate or other acidifying N mineral fertiliser. Median pH on the Pomeranian farms, analysed in potassium chloride solution [pH(KCl)], was 5.2 and liming was advised for fields on most (72%) of these farms. Soil P content, measured by double-lactate extraction (PDL), was positively and significantly correlated (Pearson coefficient 0.57; p?DL (P given in elemental form) tended to be lower on dairy farms and arable farms and was significantly lower (mean 51?mg?PDL?kg?1 soil) on mixed farms (with just a few cows and poultry) than on pig farms (mean 122?mg?PDL?kg?1 soil). Farm-gate balances indicated deficits of P and potassium (K) on many of the small mixed farms in Pomerania and the soil can be expected to be nutrient depleted. In contrast, the pig farms demonstrated surplus farm-gate P balances (mean 27?kg?ha?1). The P leaching risk is discussed relative to soil threshold values and to results from Swedish long-term field experiments.  相似文献   
63.
Chitooligosaccharides (CHOS) are homo- or heterooligomers of N-acetylglucosamine and D-glucosamine. CHOS can be produced using chitin or chitosan as a starting material, using enzymatic conversions, chemical methods or combinations thereof. Production of well-defined CHOS-mixtures, or even pure CHOS, is of great interest since these oligosaccharides are thought to have several interesting bioactivities. Understanding the mechanisms underlying these bioactivities is of major importance. However, so far in-depth knowledge on the mode-of-action of CHOS is scarce, one major reason being that most published studies are done with badly characterized heterogeneous mixtures of CHOS. Production of CHOS that are well-defined in terms of length, degree of N-acetylation, and sequence is not straightforward. Here we provide an overview of techniques that may be used to produce and characterize reasonably well-defined CHOS fractions. We also present possible medical applications of CHOS, including tumor growth inhibition and inhibition of TH2-induced inflammation in asthma, as well as use as a bone-strengthener in osteoporosis, a vector for gene delivery, an antibacterial agent, an antifungal agent, an anti-malaria agent, or a hemostatic agent in wound-dressings. By using well-defined CHOS-mixtures it will become possible to obtain a better understanding of the mechanisms underlying these bioactivities.  相似文献   
64.
The effect of meat cooking was measured on myofibrillar proteins from bovine M. Rectus abdominis. The heating treatment involved two temperatures (100 degrees C during 5, 15, 30, and 45 min and 270 degrees C during 1 min). Protein oxidation induced by cooking was evaluated by the level of carbonyl and free thiol groups. Structural modifications of proteins were assessed by the measurement of their surface hydrophobicity and by their aggregation state. With the aim of evaluating the impact of heat treatment on the digestive process, myofibrillar proteins were then exposed to proteases of the digestive tract (pepsin, trypsin, and alpha-chymotrypsin) in conditions of pH and temperature that simulate stomach and duodenal digestion. Meat cooking affected myofibrillar protein susceptibility to proteases, with increased or decreased rates, depending on the nature of the protease and the time/temperature parameters. Results showed a direct and quantitative relationship between protein carbonylation (p<0.01) and aggregation (p<0.05) induced by cooking and proteolytic susceptibility to pepsin. However, no such correlations have been observed with trypsin and alpha-chymotrypsin.  相似文献   
65.
66.
The importance of iron for survival of Trichinella spiralis larvae in vitro was examined. It was found that iron-deficient media drastically reduce the survival of this larva. Also, molting of the larvae was observed in the control media but not in the iron-deficient media.  相似文献   
67.
In two studies carried out in 1974-75 on 10 eight and 25 two week old piglets obtained from a SPF-herd the endoparasitic status was determined. Samples of faeces were examined by microscopy which revealed the presence of Isospora suis, a finding that was quite unexpected in a SPF-herd. During days 17-23 pp. the 25 piglets were not found to excrete oocysts, the earliest findings of oocysts being made 24-35 days p.p. The 10 piglets being kept isolated in individual pens excreted oocysts up until 88 days p.p. The epidemiology of Isospora suis is discussed.  相似文献   
68.
Pregnancy rates after transfer of frozen/thawed bisected embryos, demiembryos, have until now been very low. In the present study it was attempted to improve the freezability rate of demiembryos by culturing them on a monolayer of bovine oviduct epithelial cells (BOEC) prior to freezing. The cultured frozen/thawed demiembryos showed a lower developmental rate than intact embryos. The pregnancy rate (23%) following transfer was not different from the pregnancy rate after transfer of unfrozen demiembryos (26%). The calving rate (4%), however, was significantly lower than the calving rate after transfer of fresh demiembryos (23%). Although the overall pregnancy rate achieved in this study was low, it can be concluded that a co-culture period upon BOEC prior to freezing does not improve the viability of frozen demiembryos.  相似文献   
69.
籼粳交恢复系万恢88的选育与应用   总被引:5,自引:0,他引:5  
万恢88是采用籼粳亚种间杂交选育而成的籼粳交恢复系,具有恢复力强、配合力高、抗性好、米质较优、综合表现佳的特点.应用该恢复系所配组合郑优88、冈优88、K优88等在1998~2001年已示范、推广13万hm2,其中冈优88于1998年通过重庆市品种审定.  相似文献   
70.
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