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   168篇
  免费   12篇
林业   20篇
基础科学   2篇
  29篇
综合类   35篇
农作物   2篇
水产渔业   14篇
畜牧兽医   63篇
园艺   1篇
植物保护   14篇
  2023年   2篇
  2021年   3篇
  2020年   2篇
  2018年   7篇
  2017年   5篇
  2016年   5篇
  2015年   4篇
  2014年   4篇
  2013年   3篇
  2012年   7篇
  2011年   7篇
  2010年   6篇
  2009年   5篇
  2008年   8篇
  2007年   9篇
  2006年   2篇
  2005年   6篇
  2004年   4篇
  2003年   3篇
  2002年   6篇
  2001年   5篇
  2000年   3篇
  1999年   4篇
  1998年   4篇
  1997年   3篇
  1996年   5篇
  1995年   2篇
  1992年   4篇
  1991年   6篇
  1990年   5篇
  1989年   2篇
  1988年   2篇
  1987年   2篇
  1985年   2篇
  1982年   1篇
  1981年   2篇
  1978年   1篇
  1977年   2篇
  1975年   1篇
  1974年   3篇
  1971年   1篇
  1970年   1篇
  1963年   1篇
  1950年   1篇
  1949年   1篇
  1941年   1篇
  1934年   2篇
  1926年   1篇
  1919年   2篇
  1918年   8篇
排序方式: 共有180条查询结果,搜索用时 15 毫秒
1.
Cercospora leaf spot (CLS) poses a high economic risk to sugar beet production due to its potential to greatly reduce yield and quality. For successful integrated management of CLS, rapid and accurate identification of the disease is essential. Diagnosis on the basis of typical visual symptoms is often compromised by the inability to differentiate CLS symptoms from similar symptoms caused by other foliar pathogens of varying significance, or from abiotic stress. An automated detection and classification of CLS and other leaf diseases, enabling a reliable basis for decisions in disease control, would be an alternative to visual as well as molecular and serological methods. This paper presents an algorithm based on a RGB‐image database captured with smartphone cameras for the identification of sugar beet leaf diseases. This tool combines image acquisition and segmentation on the smartphone and advanced image data processing on a server, based on texture features using colour, intensity and gradient values. The diseases are classified using a support vector machine with radial basis function kernel. The algorithm is suitable for binary‐class and multi‐class classification approaches, i.e. the separation between diseased and non‐diseased, and the differentiation among leaf diseases and non‐infected tissue. The classification accuracy for the differentiation of CLS, ramularia leaf spot, phoma leaf spot, beet rust and bacterial blight was 82%, better than that of sugar beet experts classifying diseases from images. However, the technology has not been tested by practitioners. This tool can be adapted to other crops and their diseases and may contribute to improved decision‐making in integrated disease control.  相似文献   
2.
ABSTRACT Production of cacao in tropical America has been severely affected by fungal pathogens causing diseases known as witches' broom (WB, caused by Moniliophthora perniciosa), frosty pod (FP, caused by M. roreri) and black pod (BP, caused by Phytophthora spp.). BP is pan-tropical and causes losses in all producing areas. WB is found in South America and parts of the Caribbean, while FP is found in Central America and parts of South America. Together, these diseases were responsible for over 700 million US dollars in losses in 2001 (4). Commercial cacao production in West Africa and South Asia are not yet affected by WB and FP, but cacao grown in these regions is susceptible to both. With the goal of providing new disease resistant cultivars the USDA-ARS and Mars, Inc. have developed a marker assisted selection (MAS) program. Quantitative trait loci have been identified for resistance to WB, FP, and BP. The potential usefulness of these markers in identifying resistant individuals has been confirmed in an experimental F(1) family in Ecuador.  相似文献   
3.
The major tuber sugars—glucose, fructose and sucrose — in tubers of the Red Pontiac, Kennebec and Monona potato varieties harvested five times during the 1970 growing season were determined quantitatively by a gas-liquid Chromatographic technique. Also, chips were made from tubers and chip color was measured objectively and reported as Rd values. Red Pontiac tubers produced the darkest-colored chips (Rd-15.5), and its tubers tended to accumulate the highest levels of the three sugars. The major difference between Monona, which produced chips with the lightest color (Rd-21.1), and Kennebec (Rd-19.5) was the very low level of glucose found in the tubers of Monona. Varieties produced chips lightest in color at the second (8/31) or third (9/15) harvest dates. Conversely, darkest-colored chips were obtained from each variety at the fourth harvest date (9/28). This was attributed to the cool, wet weather. Sugar content also varied during the harvesting schedule. Glucose content changed little until late in the season when an increase occurred. Fructose tended to decline until the final harvest when a distinct increase was obtained. Sucrose declined significantly through the third harvest, but changed little thereafter.  相似文献   
4.
5.
From 1 January 2007, requirements concerning animal welfare were introduced with effect to cross-compliance. Farmers receiving single payment as well as agri-environmental payments (payments of second pillar) shall respect the statutory management requirements of the following 3 directives in the area of animal welfare: Council Directive 91/629/EEC laying down minimum standards for the protection of calves; Council Directive 91/630/EEC laying down minimum standards for the protection of pigs; Council Directive 98/58/EC concerning the protection of animals kept for farming purposes. The competent authority shall carry out annual systematic inspections on at least 1% of all farmers submitting payments on the basis of a risk analysis and partly at random. In case of non-compliance with the conditions due to specific rules, there will be a reduction or cancellation of the payments to be granted in the calendar year in which non-compliance occurs. Cross-compliance controls should take place on the basis of documented procedures so as to ensure that these controls are carried out uniformly and are of a consistently high quality. For this purpose, a working group composed of representatives from the Federal Ministry of Food, Agriculture and Consumer Protection and from the Lander developed uniform control reports in order to monitor compliance and a guidance booklet for control execution of animal welfare requirements. In the control report (Level 1), the outcomes of inspections of all systematic testable animal welfare requirements are summarized in 6 items. Furthermore, the non-systematically testable requirements are integrated in the control report as a independent item. The guidance booklet (Level 2) with a matrix of validation serves as a specification for on-the-spot checks. Where appropriate, on-the-spot checks provided for cross-compliance and any other checks in animal welfare rules as well as requirements to animal identification and registration shall be carried out at the same time in Baden-Württemberg (integrated control system). Farmers subjected to on-the-spot checks shall be selected on the basis of a centralized common risk analysis and partly at random. This is the best way of safeguarding that the control rate will not be much higher than the established 1% with a minimum administrative burden and costs for farmers and competent control authorities. Integrated check lists for on-the-spot checks were established which take into account systematic cross compliance inspections to improve compliance with 3 existing standards in the area of animal welfare and official controls as proved in Council Directives concerning animal welfare and Regulation (EC) No 882/2004. All staff of the competent authorities performing controls received, for their area of competence, appropriate training enabling them to make their duties competently and to carry out controls in a consistent manner. Integrated systematic controls are very time-consuming and a burden for farmers and the competent authorities. For the beginning of this year, we will expect a discharge by Decision (EC) 2006/778. A controlling system was installed to ensure that cross compliance rules are applied consistently, for example by making subsequent controls by controlling institutions.  相似文献   
6.
Edwardsiellosis is an important bacterial infection of freshwater and marine fishes. Edwardsiella ictaluri causes enteric septicemia of catfish, and E. tarda causes emphysematous putrefactive disease of catfish and fish gangrene in various species; these diseases have considerable economic effects on the aquaculture industry. In addition, E. tarda is an important zoonotic pathogen. Thus, the reduction or elimination of these pathogens from an aquarium or aquaculture facility is imperative. This study examined a variety of commercially available chemicals for their ability to reduce or eliminate E. ictaluri and E. tarda from the aquatic environment. The various concentrations of chemicals were tested in vitro in microcentrifuge tubes with a known concentration of bacteria at room temperature. In this study, ethyl alcohol (30, 50, or 70%), benzyl-4-chlorophenol/phenylphenol (1%), sodium hypochlorite (50, 100, 200, or 50,000 mg/L), n-alkyl dimethyl benzyl ammonium chloride (1:256), povidone iodine (50 or 100 mg/L), glutaraldehyde (2%), and potassium peroxymonosulfate/sodium chloride (1%) were effective disinfectants, as each reduced or eliminated the number of detectable organisms within 1 min of contact time. However, neither Chloramine-T (15 mg/L) nor formalin (250 mg/L) substantially reduced bacterial counts even after 60 min of contact time.  相似文献   
7.
8.
9.
Paraoxonase‐1 (PON1) is an enzyme found in serum and follicular fluid that protects cell membrane and circulating lipids against oxidative damage. The aims of this study were to measure the direct effects of recombinant PON1 (rPON1) on bovine oocyte maturation at the molecular level (gene expression) and to measure the carry‐over effects of PON1 on pre‐implantation embryo development in vitro. COCs were submitted to IVM with the addition of 0.0, 0.02, 0.04 and 0.08 mg ml?1 of rPON1, corresponding to an average PON1 arylesterase enzyme activity of 2.2 ± 0.4, 15.5 ± 1.5, 30.2 ± 3.0 and 57.9 ± 5.0 U ml?1, respectively. The results indicated that addition of rPON1 during IVM improved embryo development in a dose‐dependent manner as D7 embryo development was 22.2%, 29.4%, 32.2% and 37.0% for the treatment groups, respectively (p = 0.02). In conclusion, addition of PON1 enzyme during IVM exerted dose‐related positive effects on embryo development rates to blastocysts.  相似文献   
10.
While articular cartilage changes are considered to be one of the initial events in the pathological cascade leading to osteoarthritis, these changes remain difficult to detect using conventional diagnostic imaging modalities such as plain radiography. The aim of this prospective, experimental, methods comparison study was to compare the sensitivity of magnetic resonance imaging (MRI), magnetic resonance arthrography, computed tomography (CT), and CT arthrography in the detection of artificially induced articular cartilage defects in the equine carpal joints. Defects were created in the antebrachiocarpal and middle carpal joint using curettage by a board‐certified equine surgeon. Normal articular cartilage thickness varied from a maximum of 1.22 mm at the level of the distal aspect of the radius to a minimum of 0.17 mm in the proximal articular surface of the third carpal bone. Regarding cartilaginous defect measurements the remaining cartilaginous bed range from a maximum of 0.776 mm in the partial thickness defects, and 0 mm (defect reaches the subchondral bone) when total thickness defect were made. Computed tomography and magnetic resonance imaging were performed followed by CT arthrography and magnetic resonance arthrography after antebrachiocarpal and middle carpal intraarticular contrast administration. All images were reviewed by two board‐certified veterinary radiologists, both of whom were blinded to the location, presence of, and thickness of the cartilage defects. A total number of 72 lesions in nine limbs were created. Mean sensitivity for localizing cartilage defects varied between imaging modalities with CT arthrography showing the best sensitivity (69.9%), followed by magnetic resonance arthrography (53.5%), MRI (33.3%), and CT (18.1%) respectively. The addition of contrast arthrography in both magnetic resonance and CT improved the rate of cartilage lesion detection although no statistical significance was found. Computed tomographic arthrography displayed the best sensitivity for detecting articular cartilage defects in the equine antebrachiocarpal and middle‐carpal joints, compared to magnetic resonance arthrography, MRI, and CT.  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