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   354篇
  免费   27篇
  国内免费   3篇
林业   27篇
农学   33篇
基础科学   4篇
  67篇
综合类   42篇
农作物   28篇
水产渔业   41篇
畜牧兽医   114篇
园艺   12篇
植物保护   16篇
  2024年   1篇
  2022年   16篇
  2021年   8篇
  2020年   12篇
  2019年   9篇
  2018年   9篇
  2017年   16篇
  2016年   15篇
  2015年   17篇
  2014年   6篇
  2013年   21篇
  2012年   15篇
  2011年   23篇
  2010年   25篇
  2009年   27篇
  2008年   17篇
  2007年   16篇
  2006年   22篇
  2005年   16篇
  2004年   18篇
  2003年   16篇
  2002年   11篇
  2001年   8篇
  2000年   5篇
  1999年   4篇
  1998年   5篇
  1997年   7篇
  1996年   2篇
  1995年   1篇
  1993年   7篇
  1992年   4篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1983年   1篇
  1980年   1篇
排序方式: 共有384条查询结果,搜索用时 62 毫秒
281.
AIM: To determine the prevalence of beak and feather disease virus (BFDV) infection in exotic parrots and cockatoos in the wild in New Zealand. METHODS: Eastern rosellas (Platycercus eximius, n=162) were caught from Te Puke, Wellington and Dunedin, using mistnets, between April 2004 and February 2006, and sulphur crested cockatoos (Cacatua galerita, n=255) were captured for pet-trading from November 2001 to September 2004. Feathers from both species were tested for BFDV, using an established polymerase chain reaction (PCR) test. Post-mortem examinations were conducted on some of the eastern rosellas, and selected tissues from 24 birds positive for BFDV were examined using routine histological methods for the presence of characteristic inclusion bodies. RESULTS: Of the eastern rosellas, 24/162 (14.8%) were positive for BFDV, and the 95% confidence interval (CI) for true prevalence was estimated as 8.6-20.4%, which varied between regions. Eastern rosellas that were positive for BFDV showed no clinical or histological signs of disease or inclusion bodies. Of the sulphur-crested cockatoos, 70/255 (28%) were positive for BFDV, and the 95% CI for true prevalence was calculated as 22-33%. CONCLUSIONS: The surprisingly high prevalence of BFDV in wild eastern rosellas and sulphur-crested cockatoos has serious implications for the conservation of native parrots and the export of wild-trapped parrots and cockatoos from New Zealand. Serological studies for BFDV in wild exotic parrots, and molecular studies of virus genotype, are recommended to further characterise the origin and epidemiology of the disease in populations of wild exotic parrots and cockatoos in New Zealand.  相似文献   
282.
Mulches can improve soil properties, but little is known about nutrient availability in mulched soil that contains plant residues and the effect of mulching with manures. The aim of this study was to determine the effects of mulching with high or low C/N organic materials, in which low C/N materials differed in decomposability, and the presence of wheat straw in the soil on plant growth and N uptake, soil N availability and microbial biomass N within about four months after mulching. Three organic materials were used: mature wheat straw (W, C/N 80), young faba bean shoots (FB, C/N 7), and sheep manure (SM, C/N 8). There were eight treatments differing in amendment methods (mulching or mixing with W or both) and mulching materials (W, FB or SM). Treatments that were only mulched with W, FB or SM are referred to as m‐treatments. In m/s‐treatments, after W was mixed into the soil, W, FB or SM were placed on the soil surface as mulch. Two other treatments included an unamended control and soil mixed with W. Wheat was planted 0, 35 or 70 days after mulching (referred to as 0, 35, and 70 DAM) and grown for 35 days. Faba bean mulch increased shoot dry weight, shoot N uptake and available N compared to wheat or sheep manure mulch, particularly in the m‐treatments. Shoot dry weight was higher in m‐treatments than corresponding m/s‐treatments with the same mulch type. Shoot N uptake was higher in 70 DAM than in 0 DAM in all treatments and 0.3 to three‐fold higher in m‐treatments than the corresponding m/s‐treatments. Microbial biomass N was higher in 0 DAM than in 35 and 70 DAM in most treatments and up to two‐fold higher in m/s‐treatments than the corresponding m‐treatments. Available N in m/s‐treatments was two to six‐fold higher than m‐treatments in 0 DAM, but differed little in older mulch ages of W and SM. It can be concluded that compared to soil with only mulch, mixing of wheat straw into soil reduced plant growth and N uptake, particularly in the early stages of mulching (0 and 35 DAM). However, the presence of wheat in mulched soil may provide a longer lasting source of N for plants and reduce the risk of N leaching from rapidly decomposing low C/N mulch due to greater microbial biomass N uptake than only soil with mulch.  相似文献   
283.
Aquaponics is rapidly developing as the need for sustainable food production increases and freshwater and phosphorous reserves shrink. Starting from small-scale operations, aquaponics is at the brink of commercialization, attracting investment. Arising from integrated freshwater aquaculture, a variety of methods and system designs has developed that focus either on fish or plant production. Public interest in aquaponics has increased dramatically in recent years, in line with the trend towards more integrated value chains, greater productivity and less harmful environmental impact compared to other production systems. New business models are opening up, with new customers and markets, and with this expansion comes the potential for confusion, misunderstanding and deception. New stakeholders require guidelines and detail concerning the different system designs and their potentials. We provide a definitive definition of aquaponics, where the majority (>?50%) of nutrients sustaining the optimal plant growth derives from waste originating from feeding aquatic organisms, classify the available integrated aquaculture and aquaponics (open, domestic, demonstration, commercial) systems and designs, distinguish four different scales of production (≤?50, >?50–≤?100 m2, >?100–≤?500 m2, >?500 m2) and present a definite nomenclature for aquaponics and aquaponic farming allowing distinctions between the technologies that are in use. This enables authorities, customers, producers and all other stakeholders to distinguish between the various systems, to better understand their potentials and constraints and to set priorities for business and regulations in order to transition RAS or already integrated aquaculture into commercial aquaponic systems.  相似文献   
284.
中药复方连翘对感染法氏囊病毒雏鸡免疫功能的影响   总被引:8,自引:0,他引:8  
160只7日龄健康岭南黄鸡随机分为Ⅰ、Ⅱ、Ⅲ和Ⅳ组,每组40只,Ⅰ为正常对照组、Ⅱ为感染病毒组、Ⅲ为中药复方治疗组、Ⅳ为中药复方制剂组,Ⅱ、Ⅲ组均于8日龄感染传染性法氏囊病毒(IBDV),Ⅲ、Ⅳ以20g·kg^-1单剂量灌服中药复方连翘汤。分别于试验后第7、14、21、28日龄采外周血及免疫器官法氏囊和脾脏,测定血细胞的吞噬能力、外周血T淋巴细胞的百分率和T淋巴细胞的转化率,流式细胞仪测定鸡外周血和脾T淋巴细胞亚群CD3^+、CD4^+和CD8^+T细胞的含量;放血致死称体质量、脾和法氏囊质量,计算免疫器官指数。在感染IBDV7d后取脾脏和法氏囊组织,制备组织样品进行组织学及透视电镜观察。结果表明:中药复方连翘制剂可使雏鸡外周血细胞的吞噬能力、T淋巴细胞的百分率和T淋巴细胞的转化率、法氏囊和脾脏的质量明显提高,对感染IBDV后免疫器官法氏囊和脾脏有明显的改善和恢复作用,提高外周血和脾淋巴细胞中CD3^+、CD4^+和CD8^+T细胞百分率,改变CD4^+/CD8^+比值促进对机体免疫系统的调控。感染病毒组的上述指标显著下降,中药复方连翘治疗组与感染病毒组相比能显著提高上述指标。  相似文献   
285.
研究了卵形鲳鲹(Trachinotus ovatus)大规格幼鱼(全长10.53±1.41 cm,体质量15.02±2.46 g)蛋白酶、淀粉酶和脂肪酶活性在不同消化器官中的分布,以及5、15、25、30、35五种盐度对肠、幽门盲囊、胃和肝脏中消化酶活性的影响.结果表明:在不同盐度下,蛋白酶、淀粉酶、脂肪酶活性在各消化...  相似文献   
286.
Aluminum ammonium sulfate was used as a new catalyst for glyoxal to minimize the decrease of physical properties of durable press cotton fabrics, and the optimum treatment conditions such as the concentration of glyoxal, molar ratio of catalyst to glyoxal, curing temperature and time were investigated. The retention of tensile strength and the whiteness of fabrics treated with glyoxal/aluminum ammonium sulfate was increased as much as to the degree of that obtained with glyoxal/aluminum sulfate while wrinkle recovery angles were as good as those of the latter. Some additives such as DEG, polyurethane and softener were used to improve the physical properties. When DEG or polyurethane was added to the glyoxal padding solution, wrinkle recovery angle (WRA) significantly increased while tensile strength and whiteness were not influenced. DEG added to the glyoxal padding solution increased the durability of DP finish. The softener added to the glyoxal padding solution increased the WRA of treated fabrics while it decreased the tensile strength slightly. The whiteness of fabrics treated with glyoxal alone increased while the WRA decreased slightly.  相似文献   
287.
The present study examined the capacity of the mud crab, Scylla serrata to digest experimental diets that contained different animal and plant‐based feed meals or different levels or types of starch. The apparent dry matter digestibility (ADMD) coefficients for all feed meals tested in the first part of this study, except meat meal, were similar (78–88%). Crude protein digestibility (ACPD) coefficients for all feed meals were relatively high, with values ranging from 86% to 96%. Cotton seed meal, poultry meal, canola meal, fishmeal, soybean meal and lupin meal had similar gross energy digestibility (AGED) values (P>0.05) ranging from 84% to 89%. In the second part of this study, the impact of selected starches on the digestibility of fishmeal‐based formulated diets was assessed. The apparent starch digestibility (ASD) of wheat starch decreased significantly as the inclusion level was increased from 15% to 60%, however, there was no significant effect on ACPD values. At a 30% inclusion level, the ASD of diets containing different starches decreased in the order corn>wheat>potato=rice. Moreover, ACPD values were significantly higher (P<0.05) in the diets containing corn or rice starch than in those containing wheat or potato starches.  相似文献   
288.
u| li]? Genotypic variation in wood total and partial shrinkage, basic density and growth traits was estimated in 51÷2 year old Acacia auriculiformis trees in a clonal test. li]? In the tangential, radial and longitudinal directions, the mean values were 2.64%, 1.64% and 0.77% for partial shrinkage, and 5.92%, 3.23%, and 0.96% for total shrinkage, respectively. Total and partial transverse shrinkage were significantly greater in sapwood than in heartwood. li]? Clonal repeatability (H C 2 ) estimates for partial shrinkage were lower than those for total shrinkage, and heartwood shrinkages had lower H C 2 than those for sapwood. Estimates of H C 2 were from 0.32 to 0.38 for total transverse shrinkage, comparable to H C 2 for both total and partial volumetric shrinkages (0.40 and 0.32, respectively). However, H C 2 for longitudinal shrinkages, total and partial coefficients of anisotropy were only from 0.09 to 0.18. li]? The genotypic coefficients of variation of all shrinkage traits varied from 5.45% to 8.02%. Total shrinkage was strongly positively correlated with partial shrinkage in each dimension. Genotypic correlations were not significant between shrinkage and growth traits or density. Strong and significant correlations between transverse shrinkage in heartwood and sapwood (0.87) indicated that juvenile shrinkage is a good genetic indicator of this trait in older trees. Utilisation du retrait du bois dans l’amélioration de l’Acacia auriculiformis A. Cunn. ex Benth à croissance rapide au Vietnam.  相似文献   
289.
The azuki bean in Korea consists of seven domestic varieties which have been developed and registered for the public during last 25 years. Here, we present a simple but reliable method to screen and identify Korean azuki bean varieties. A method based on simple sequence repeat (SSR) markers is widely used for prominent gene identification and variety discrimination. In molecular biology, real-time polymerase chain reaction (PCR) is a laboratory technique based on the polymerase chain reaction that is used to amplify and simultaneously quantify a targeted DNA molecule. It enables easy detection of a specific sequence in a DNA sample without performing electrophoresis and further processes. For separation of seven Korean azuki bean varieties, 110 unique azuki bean SSR markers from an (AG)n-enriched library were selected, synthesized and used for polymerase chain reaction (PCR). Data were taken through acrylamide gel electrophoresis and automated multi-capillary electrophoresis system for selection of specific markers and then changed into proper formats for data mining analysis. Ten primer pairs that showed high polymorphism were chosen for the indepth study. These ten primers were re-amplified with real-time PCR and checked the cycle threshold (Ct) and temperature (Tm) for comparison of amplification sequence in seven varieties. Consequently, a total of 20 alleles and 6 SSR primers were detected from the standard PCR amplification. Within these 6 primers, 7 alleles of 3 SSR primers were isolated for variety identification. From real-time PCR results, 3 SSR primers were selected as efficient markers for discrimination of seven Korean azuki bean varieties. The approach described here could be applied in monitoring our varieties and can be adapted in the azuki bean breeding program.  相似文献   
290.
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