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   310篇
  免费   25篇
  国内免费   55篇
林业   20篇
农学   51篇
基础科学   50篇
  82篇
综合类   92篇
农作物   9篇
水产渔业   52篇
畜牧兽医   22篇
园艺   3篇
植物保护   9篇
  2024年   7篇
  2023年   6篇
  2022年   12篇
  2021年   15篇
  2020年   12篇
  2019年   18篇
  2018年   11篇
  2017年   26篇
  2016年   18篇
  2015年   9篇
  2014年   25篇
  2013年   22篇
  2012年   26篇
  2011年   19篇
  2010年   11篇
  2009年   13篇
  2008年   9篇
  2007年   11篇
  2006年   15篇
  2005年   17篇
  2004年   11篇
  2003年   12篇
  2002年   8篇
  2001年   5篇
  2000年   3篇
  1999年   4篇
  1998年   6篇
  1997年   4篇
  1996年   9篇
  1995年   6篇
  1994年   6篇
  1993年   4篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1988年   2篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1976年   1篇
排序方式: 共有390条查询结果,搜索用时 78 毫秒
1.
ABSTRACT

Aims: To evaluate the outcome of surgical management of entropion of the upper and lower eyelids in Shar Pei dogs which had previously undergone temporary palpebral tacking, using the Stades forced granulation procedure of the upper eyelid only.

Methods: Medical records were retrospectively searched to identify Shar Pei dogs referred for bilateral entropion of both the lower and upper eyelids, and that were treated with the forced granulation procedure of the upper eyelid only. Dogs were included if they had previously undergone unsuccessful temporary palpebral tacking and had at least three follow-up examinations in the 30 days following surgery.

Results: Twenty-seven Shar Pei dogs with a median age of 7.9 (min 4, max 24) months were included in the study. Before surgery, all dogs showed signs of severe ocular discomfort with bilateral keratitis and visual deficit due to blepharospasm, enophthalmos and protrusion of the third eyelid. In 13/54 eyes, keratitis was associated with a corneal ulcer. When re-examined 4 weeks after surgery, correction of the upper eyelid entropion and associated trichiasis resolved ocular signs in 50/54 eyes. Mild bilateral lower entropion remained in two dogs postoperatively, which underwent revision surgery with the Hotz-Celsus technique. There were no cases of long-term recurrence of entropion or ocular irritation in the 38 eyes (19 dogs) which were re-examined 1 year after surgery.

Conclusion and clinical relevance: The forced granulation procedure performed on the upper eyelid only was effective for correction of entropion in the Shar Pei dogs included in this study. In our experience, it is preferable to operate on the upper eyelid alone, rather than attempting to correct upper and lower entropion during the same surgical operation. The dog can then be reassessed a few weeks later to determine whether the lower entropion is anatomical or secondary to the severe blepharospasm resulting from the painful ocular irritation.  相似文献   
2.
The venturi aeration is an effective practice to increase the dissolved oxygen accessibility in the water bodies. This study aims to optimize the various geometrical parameters of the venturi aeration system. A non-dimensional technique was applied to find the optimum performance of various geometric parameters i.e. throat lengths (tl), number of air holes (N), and converging and diverging angles (α and β). These experiments have been carried out using 1124 L capacity of tank having dimensions of 105 cm long, 105 cm wide and 102 cm deep. The experiments were conducted at a constant flow velocity of water (1.096 m/s) with varying throat length (tl = 20–100 mm keeping 20 mm as interval between two consecutive length), number of air holes (N = 1–17 at an equal hole to hole distance of 5 mm between them), and converging and diverging angles (α and β = 10°, 15°, 20° and 25°). Multiple non-linear regression equations were also developed from the linear relation with the dependent variable (Non-dimensional form of standard aeration efficiency, NDSAE) and independent variables (tl and N). With the geometrically optimized venturi aerator the optimum performance was found for tl =100 mm, N = 17, and α and β = 15°. The maximum value of standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) obtained was 0.0216 kgO2/h and 0.611 kgO2/kWh respectively. From the non-dimensional study, it was found that the NDSAE is the function Reynolds number (Re) and Froude number (Fr). The simulation equations were developed on the basis of Re and Fr for NDSAE, and subjected to 7.378 × 10−6 < Re < 3.689 × 10-5 and 0.163 < Fr < 0.817, respectively.  相似文献   
3.
Effects of water‐misting sprays with forced ventilation on post mortem glycolysis, adenosine monophosphate‐activated protein kinase (AMPK) and meat quality of broilers after transport during summer were investigated in the present paper. A total of 105 mixed‐sex Arbor Acres broilers were divided into three treatment groups: (i) 45 min transport without rest (T); (ii) 45 min transport with 1 h rest (TR); and (iii) 45 min transport with 15 min water‐misting sprays with forced ventilation and 45 min rest (TWFR). Each treatment consisted of five replicates with seven birds each. The results indicated that the water‐misting sprays with forced ventilation could mitigate the stress caused by transport under high temperature conditions during summer, which reduced the energy depletion in post mortem Pectoralis major (PM) muscle. This resulted in a higher energy status compared to the T group, which would decrease the expression of phosphorylation of AMPK (p‐AMPK). Furthermore, decreased the expression of p‐AMPK then slowed down the rate of glycolysis in post mortem PM muscle during the early post mortem period, which in turn lessened the negative effects caused by transport on meat quality. In conclusion, water‐misting sprays with forced ventilation may be a better method to control the incidence of the pale, soft and exudative meat in broilers.  相似文献   
4.
The engineering design of sewage treatment plant for the Chongqing city, P. R. China is analyzed in this paper. Considering the situation of China and other projects, the characteristics of falling water reactor for the environment protection project and economy of investment is introduced ; the application and foreground of falling water aeration in the process of sewage treatment is discussed, such as Oxidation - ditch, SBR, and so on. The conclusion indicated that the falling water aeration can be designed and used as an independent aeration, and, it is an upgraded technology of sewage treatment which is adaptive for city water environment control in middle and small towns in China. The falling water aeration may reduce running cost of the sewage treatment plant, is adaptive for foothill and the mountainous areas, and reduces project investment and environments damage.  相似文献   
5.
Through introducing the principle of bubbleless aerated membrane bioreactor, the traditional membrane bioreactor was improved. It could be obtained that the removal efficiency of COD and NH3 - N in bubbleless aerated membrane bioreactor increased 4% and 2% than that in traditional membrane bioreactor, respectively. Adopting bubbleless aeration as reflushing air which not only increased DO in the MBR, but also advanced the oxygen utilization, and the energy consumption decreased as well.  相似文献   
6.
7.
8.
微孔曝气流量与曝气管长度对水体增氧性能的影响   总被引:2,自引:2,他引:2  
为了探究曝气流量与曝气管长度对增氧性能的影响,在不同曝气流量、不同曝气管长度条件下进行了室内水体底部微孔曝气增氧试验。分析了曝气流量与曝气管长度对氧体积传质系数、增氧量和氧利用率的影响。研究结果表明,当曝气流量为0.27~0.55 m3/s、曝气管长为0.9~1.5 m时,所对应的氧体积传质系数在0.63~1.1 h-1变化,增氧量在6.8~12.9 g/h变化,氧利用率在6.87%~9.28%变化,且在一定的曝气管长度下,氧体积传质系数、增氧量均与曝气流量成正比,而氧利用率则与其成反比关系;在一定的曝气流量下,曝气管长度对氧体积传质系数产生的影响表现为先高后低再高的趋势;氧体积传质系数与修正的饱和溶解氧浓度是否作为增氧量的主要影响因子取决于曝气管长度;曝气流量对氧利用率较曝气管长度更为敏感。研究还发现,微孔曝气系统中存在着最优曝气管长度,使得增氧性能最佳,并建立了最优曝气管长度与曝气流量、水深、输入压力、最优初始气泡直径的相关关系式,为低碳经济下微孔曝气系统的设计和运行提供了理论依据。  相似文献   
9.
土壤增氧方式对其氮素转化和水稻氮素利用及产量的影响   总被引:7,自引:3,他引:7  
以3种不同生态型水稻品种中浙优1号(水稻)、IR45765-3B(深水稻)和中旱221(旱稻)为材料,比较研究了不同增氧方式(T1-增施过氧化钙、T2-微纳气泡水增氧灌溉、T3-表土湿润灌溉和CK-淹水对照)下稻田土壤氮素转化和水稻氮素吸收利用特性。结果表明:1)增氧处理明显改善土壤氧化还原状况,3种增氧方式下土壤氧化还原电位均高于CK。稻田增氧促进土壤氮素硝化,在分蘖期和齐穗期T1、T2和T3的土壤硝化强度和脲酶活性均显著高于CK,反硝化强度显著低于CK。2)不同增氧处理对水稻氮素吸收的影响不同,在拔节期、齐穗期和完熟期3品种的植株氮素积累量均表现为T1、T2显著高于CK,而T3显著低于CK;在完熟期,T1处理下中浙优1号、IR45765-3B和中旱221植株氮素积累量分别较CK增加了21.2%、13.2%和17.0%,而T2处理下3品种的植株氮素积累量分别较CK增加了14.3%、6.9%和9.1%。3)与CK相比,T1和T2显著提高水稻籽粒产量和收获指数,氮素籽粒生产效率与CK无显著差异,而T3显著增加水稻氮素干物质生产效率和氮素籽粒生产效率。可见,施用过氧化钙和微纳气泡水增氧灌溉能有效改善稻田土壤氧化还原状况,不仅显著提高水稻产量,而且显著增强稻田氮的硝化而减少氮素损失,从而提高水稻氮素积累量和氮素收获指数。  相似文献   
10.
转速、浸没深度和液位高度对倒伞曝气机曝气性能的影响较大,为了研究各影响参数协同作用下倒伞曝气机曝气性能的变化情况,该文通过试验研究了不同转速、浸没深度和液位高度对曝气性能的影响。研究表明:在相同转速时随着运行时间的增加曝气池溶解氧浓度随之增大,但增幅逐渐降低;随着转速的增加,叶轮对水的做功能力增强,提高了水面的湍动强度及水面下的复氧强度,进而缩短了曝气池达到氧饱和的时间,转速为300 r/min达到氧饱和的时间比150 r/min缩短了约57%。转速、浸没深度和液位高度的改变均会极大地影响倒伞曝气机的性能:转速的增加能够提升倒伞曝气机的标准氧总转移系数和标准充氧能力,但对于标准动力效率的提升有一个上限值,该上限值与浸没深度有关;倒伞曝气机低速运行时,浸没深度和液位高度对标准氧总转移系数和标准充氧能力的影响较小。液位高度的增加会加大倒伞曝气机的标准充氧能力和标准动力效率,但是相同液位高度下,随着转速的增加标准动力效率增幅明显小于标准充氧能力增幅,当液位高度为250 mm时,转速从150增加到300 r/min,标准充氧能力值提高2.91倍而标准动力效率提高1.22倍。该研究可为倒伞曝气机的经济运行提供参考。  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