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   1000篇
  免费   87篇
林业   153篇
农学   38篇
基础科学   4篇
  261篇
综合类   59篇
农作物   73篇
水产渔业   91篇
畜牧兽医   252篇
园艺   29篇
植物保护   127篇
  2023年   11篇
  2022年   14篇
  2021年   26篇
  2020年   29篇
  2019年   38篇
  2018年   59篇
  2017年   75篇
  2016年   73篇
  2015年   32篇
  2014年   56篇
  2013年   61篇
  2012年   59篇
  2011年   88篇
  2010年   50篇
  2009年   48篇
  2008年   42篇
  2007年   57篇
  2006年   35篇
  2005年   21篇
  2004年   31篇
  2003年   24篇
  2002年   18篇
  2001年   10篇
  2000年   8篇
  1999年   8篇
  1998年   8篇
  1997年   5篇
  1996年   4篇
  1995年   7篇
  1994年   3篇
  1992年   4篇
  1990年   4篇
  1989年   4篇
  1988年   5篇
  1987年   4篇
  1985年   3篇
  1979年   2篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1975年   3篇
  1974年   2篇
  1973年   4篇
  1972年   2篇
  1970年   2篇
  1969年   3篇
  1968年   3篇
  1965年   2篇
  1958年   2篇
  1957年   2篇
排序方式: 共有1087条查询结果,搜索用时 125 毫秒
81.
82.
A new type of intestinal re-entrant cannula for the small intestine of pigs is described. It consisted of an intestinal tube joined to a stem bearing a flange and two perspex plugs ("maintenance plug" and "collection plug"). The cannula was inserted in the intestine through the incision on the antimesenteric side of the intestine and no transection of the intestine was required. No outside connection was present and the cannula extended only 1 to 2cm beyond the body. Cannulae were inserted in the duodenum and ileum of 5 pigs and these functioned satisfactorily for up to 3 months.  相似文献   
83.
Two experiments were carried out with sheep that originated from a fauna-free flock and were fed a soybean meal-corn silage diet with or without a bentonite supplement. One-half of the sheep fed each diet in each experiment were faunated with a mixed population of ruminal protozoa, whereas the other half of the sheep remained fauna-free until the end of both experiments. Wool growth and daily gain were measured in Exp. 1. (eight rams per treatment), which lasted 110 d, and the metabolic effects in the rumen and intestinal tract of protozoa and dietary bentonite supplement were tested with cannulated wethers (four wethers per treatment) in Exp. 2. The results of Exp. 1 showed decreased wool growth (P less than .05) due to the presence of protozoa in the rumen. Dietary supplementation with bentonite partly offset the decreased wool growth in sheep with protozoa, but there were no effects of dietary bentonite and no protozoa x bentonite interaction (P greater than .05). Daily gain was decreased by the dietary bentonite (P less than .05) supplement but was not affected (P greater than .05) by the ruminal presence of protozoa. In Exp. 2, protozoa increased (P less than .01) the ruminal concentrations of ammonia and decreased (P less than .05) the acetic:propionic acid molar ratio. Fractionation of N in the duodenal digesta flowing from the stomach to the small intestine showed that protozoa decreased (P less than .05) the flow of nonammonia N and bacterial N, and there was a protozoa x bentonite interaction for these effects (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
84.
Enzootic Bovine Leukosis   总被引:1,自引:1,他引:0       下载免费PDF全文
The author emphasizes the significance of enzootic bovine leukosis in Canada. He describes in detail diagnostic methods, various types of the disease and methods of transmission.

Various aspects of the disease in Canada are compared with those in other countries. Prevention and control are discussed in a Canadian context and include the current policies of the Government of Canada in relationship to this disease. The possibility of developing a certification program for herds free of the disease is also discussed. The paper includes incidence in various parts of Canada.

  相似文献   
85.
Naturally fauna-free crossbred rams approximately 5 mo old, 49.3 +/- 1.88 kg live weight, were allotted to four groups. Two groups remained fauna-free, whereas the other two groups were faunated. A diet based on corn silage-soybean meal containing either a low or a high Cu concentration (7 or 15 micrograms/g dry matter) was fed ad libitum to the two groups for 197 d. The rams were killed at the end of the experiment and livers and ruminal contents were analyzed for Cu. Faunated sheep grew faster (P less than .01) and as a group consumed 1.53 kg diet dry matter daily compared with 1.34 for the fauna-free sheep. Faunated sheep had lower final liver Cu concentrations (P less than .01), total liver Cu per unit of Cu intake and ruminal Cu solubilities (P less than .01) when fed both low and high Cu diets. The relative hepatic Cu uptake was higher by rams fed the low Cu than by those fed the high Cu diet. The results are interpreted to show that faunation decreased the availability of Cu in sheep fed a corn silage-soybean meal diet. The magnitude of the effect was independent of the Cu concentration in the diet.  相似文献   
86.
ELISPOT and ELISA were standardised for pig interferon-gamma (IFN-gamma), interleukin-10 (IL-10) and interleukin-4 (IL-4) with the aim to study the evolution of the immune response in conventional pigs from birth to 6 months of age and also to compare results of both techniques. Five pigs were bled at 1, 6, 9, 12 and 22 weeks of age and peripheral blood mononuclear cells (PBMC) were stimulated with phytohemagglutinin. The frequencies of cytokine secreting cells (CSC) and the levels of secreted cytokines were compared. For IFN-gamma the mean of CSC increased with age (p<0.05) from an average of 486/10(6) PBMC at first week of age to 1256/10(6) PBMC at 22 weeks of age. No correlation was found between the number of IFN-gamma CSC and the cytokine levels obtained by ELISA. For IL-10, frequencies of CSC did not increase with age of pigs, having a low of 315/10(6) PBMC at first week of age and a high of 1485/10(6) PBMC at six weeks. Comparison of ELISA and ELISPOT results for IL-10 showed a certain degree of correlation (r=0.74; p<0.05). Spontaneous secretion was observed in unstimulated cultures. For IL-4, frequencies of CSC were low (50-70/10(6) PBMC). In this case, comparison of ELISA and ELISPOT could not be done because cytokine levels in culture supernatants were often below the detection limit of the IL-4 ELISA. All these values can serve as a reference for future studies and also, our observations suggest that ELISPOT and ELISA should be carefully interpreted and do not necessarily correlate.  相似文献   
87.
Metabolic diseases of cows represent the leading internal pathology in Lithuania in terms of incidence and economic impact. This paper summarizes the mineral metabolic state of milk cows, and details the influence of feeding on serum levels of calcium, nonorganic phosphorus, magnesium, potassium, sodium, glucose, total protein, and urea quantity, and correlationd among them, in healthy dry or post-calving cows as well as in cows with osteomalacia and milk fever after calving. There was less pronounced hypocalcaemia and there were only minor changes in phosphorus, magnesium, potassium and sodium in the serum of healthy dry and post-calving cows that had silage and mineral-vitamin supplements, compared to cows that did not have supplements and silage. There was a fall in calcium and phosphorus (to 1.89 +/- 0.12 mmol/L and 0.71 +/- 0.06 mmol/L, respectively) in the blood of cows sick with milk fever after calving, while levels of magnesium and potassium were increased. The correlation between calcium and phosphorus was r = 0.6993, p < 0.001 in the serum of sick cows. There was a fall in calcium, phosphorus and magnesium (to 1.86 +/- 0.46 mmol/L, 0.75 +/- 0.37 mmol/L, and 0.60 +/- 0.19 mmol/L, respectively) and an increase in sodium level (to 158.90 +/- 19.30 mmol/L) in the blood of cows with osteomalacia in comparison with healthy cows.  相似文献   
88.
OBJECTIVE: To evaluate the use of polyamide bands, manufactured for securing electrical cables, for repair of oblique femoral fractures in rabbits. STUDY DESIGN: Experimental study. ANIMALS: Twelve nulliparous, 21-25-week-old, California female rabbits. METHODS: Rabbits were divided into 3 groups (n=4) and studied for 14, 28, or 56 days. A Z-shaped mid-diaphyseal femoral osteotomy was repaired with a 2.5 mm intramedullary pin and a polyamide 6.6 cerclage band. Healing was evaluated at intervals by physical examination, limb use, femoral radiographs, and callus histology. RESULTS: Rabbits had early limb use with good wound healing. From the 1st day, movement of the hip and stifle joints was satisfactory. Radiographically, fractures were healed at 28 days. Histologically, there was no foreign body reaction and bone healing was normal. CONCLUSION: Nylon cerclage band application was accomplished easily, maintained reduction, and resulted in good healing and limb use. CLINICAL RELEVANCE: Sterilized nylon bands, manufactured for electrical use, can be used for cerclage in rabbits.  相似文献   
89.
Protection of cucumber seedlings against damping off, caused byPythium debaryanum, was obtained by soaking the seeds in a solution of 1 ppm 6-azauracil (AzU), but not by treatment with a 10 or 100 ppm AzU solution. After the 1 ppm AzU treatment of the seeds, the rhizosphere microflora of the developing seedlings was changed; an increase of the bacterial population and a decrease of the fungal population was observed. SinceP. debaryanum is rather insensitive to AzU in vitro, it is suggested that the control of damping off is obtained in an indirect way, possibly via the microflora of the roots.Samenvatting Bescherming van komkommerzaailingen tegen aantasting doorPythium debaryanum werd verkregen na weken der zaden in een oplossing van 1 ppm 6-azauracil (AzU); 10 en 100 ppm AzU waren niet werkzaam. Na behandeling der zaden met 1 ppm AzU traden veranderingen in de rhizosfeermicroflora der kiemplanten op; de bacteriepopulatie nam toe en de schimmelpopulatie nam af. AangezienP. debaryanum in vitro vrijwel ongevoelig is voor AzU, wordt verondersteld dat de bescherming tegen aantasting door deze schimmel op indirecte wijze verkregen wordt, mogelijk via de microflora van de wortels.  相似文献   
90.
A selection of 43 bovine viral diarrhoea viruses isolated from mainly persistently infected cattle on 23 Slovenian farms between 1997 and 2001 were characterised genetically. Viral RNA was extracted from infected cell cultures, reverse transcribed and amplified by PCR with primers targeting the 5'-UTR and the N(pro) gene, followed by direct sequencing of purified PCR products obtained for both genomic regions. The N(pro) sequences provided the best genetic resolution, and gave also higher statistical support for phylogenetic classification of the viruses. Thirty-eight of the Slovenian isolates were of genetic subtypes 1d and 1f, four were 1b, and one subtype 1g. No BVDV type 2 viruses were found. This genetic prevalence matched those previously reported for neighbouring countries, as opposed to findings reported for more distant European countries, e.g. France, Spain and the UK. From eight cattle herds several virus isolates were analysed; with one exception all isolates from each herd were of the same genetic group. Extended sequencing of the N(pro) and part of the C gene of virus isolates with identical 5'-UTR sequences allowed differentiation between isolates obtained at different times from one herd.  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