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   1613篇
  免费   95篇
林业   111篇
农学   55篇
基础科学   21篇
  493篇
综合类   55篇
农作物   95篇
水产渔业   180篇
畜牧兽医   521篇
园艺   45篇
植物保护   132篇
  2024年   4篇
  2023年   17篇
  2022年   37篇
  2021年   69篇
  2020年   59篇
  2019年   76篇
  2018年   51篇
  2017年   59篇
  2016年   67篇
  2015年   49篇
  2014年   66篇
  2013年   106篇
  2012年   134篇
  2011年   121篇
  2010年   73篇
  2009年   64篇
  2008年   101篇
  2007年   99篇
  2006年   84篇
  2005年   92篇
  2004年   75篇
  2003年   65篇
  2002年   45篇
  2001年   14篇
  2000年   15篇
  1999年   9篇
  1998年   8篇
  1997年   7篇
  1996年   4篇
  1995年   5篇
  1994年   3篇
  1993年   8篇
  1992年   2篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1984年   1篇
  1983年   1篇
  1981年   1篇
  1979年   1篇
  1978年   3篇
  1963年   1篇
  1944年   1篇
  1939年   1篇
排序方式: 共有1708条查询结果,搜索用时 15 毫秒
1.
Urinary tract diseases are among the main reasons for consultation in veterinary clinics and hospitals. It affects animals of any age, breed and gender. Among the diseases that affect this system, urolithiasis is the second largest cause of clinical signs compatible with feline urinary tract disease. The term urolithiasis refers to the presence of uroliths in any region of the urinary tract, but it is more commonly seen in the bladder and urethra. Uroliths are classified based on the type of mineral present in their composition, therefore, quantitative and qualitative analyzes are important for a better therapeutic approach. The animals may suffer from the disease and be asymptomatic, or show nonspecific clinical signs, making the diagnosis difficult. The disease should not be seen as a single problem, but as a consequence of various disorders. As dietary, metabolic, genetic and infectious causes, as well as factors that potentiate the chance of development of uroliths such as breed, age, sex, age range, obesity, sedentary lifestyle, geographic region and climate. Thus, the knowledge of the factors that influence the formation of uroliths, as well as the understanding of the pathophysiology, are key elements for better alternatives of therapy and prevention. The recognition of these factors helps to identify susceptible populations, minimizing exposure and increasing the protection factors, which facilitates the diagnosis and treatment of patients with urolithiasis. The objective of this paper is to present the main risk factors involved in the formation of urinary lithiasis in felines.  相似文献   
2.
3.
Tyzzer disease (TD) is caused by Clostridium piliforme, a gram-negative and obligate intracellular bacterium. The disease occurs in multiple species. A triad of lesions, namely colitis, hepatitis, and myocarditis, is described in cases of TD in some species, such as rats and mice. We carried out a retrospective analysis of 25 equine cases with a diagnosis of TD; 24 of 25 cases occurred in foals <45 d old; the remaining foal was 90 d old. There were 12 males and 12 females; no sex information was available for one foal. The affected breeds were Quarter Horse, Thoroughbred, Arabian, Paint, and Hanoverian. Most of the cases (19 of 25) occurred in the spring. There were 9 cases of sudden death; the remaining animals had diarrhea, fever, distended abdomen, depression, weakness, non-responsiveness, and/or recumbency. Gross findings included icterus, hepatomegaly with acinar pattern, serosal hemorrhages, pulmonary edema, and/or fluid content in small and large intestine. Microscopically, all foals had severe, multifocal, necrotizing hepatitis. Necrotizing lymphohistiocytic colitis was observed in 10 of 25 foals, and multifocal necrotizing myocarditis was found in 8 of 25. Gram-negative, Steiner-positive, intracytoplasmic filamentous bacteria were observed in hepatocytes, enterocytes, and myocardiocytes, respectively. PCR detected C. piliforme DNA in the liver (24 of 24), colon (20 of 24), and heart (5 of 25). Our results indicate that necrotic hepatitis is the hallmark of TD in horses; the so-called triad of lesions is not a consistent characteristic of the disease in this species.  相似文献   
4.
Global distribution of platyhelminth parasites and their host specificities are not well known. Our hypothesis was that platyhelminth parasites of large pelagic fishes are common around the world. We analysed molecular variation in three different taxa of platyhelminth parasites infecting four species of tunas: yellowfin tuna (Thunnus albacares, Scombridae) from Western Australia, southern bluefin tuna (Thunnus maccoyii, Scombridae) from South Australia, Pacific bluefin tuna (Thunnus orientalis, Scombridae) from Pacific Mexico and northern bluefin tuna (T. thynnus, Scombridae) from two localities in the Mediterranean (Spain and Croatia). Comparisons of ITS2 and partial 28S rDNA demonstrated two congeneric species of blood flukes (Digenea: Sanguinicolidae) from multiple hosts and localities: Cardicola forsteri from southern bluefin and northern bluefin tunas, and Cardicola sp. from Pacific bluefin and northern bluefin tunas; and a gill fluke, Hexostoma thynni (Polyopisthocotylea: Hexostomatidae), from yellowfin, southern bluefin and northern bluefin tunas. Partial 28S rDNA indicates that a second type of fluke on the gills, Capsala sp. (Monopisthocotylea: Capsalidae), occurs on both southern bluefin and Pacific bluefin tunas. This appears to be the first report of conspecific platyhelminth parasites of teleosts with a wide‐ranging geographical distribution that has been confirmed through molecular approaches. Given the brevity of the free‐living larval stage of both taxa of flukes on the gills (H. thynni and Capsala sp.), we conclude that the only feasible hypothesis for the cosmopolitan distribution of these flatworms is migrations of host tunas. Host migration also seems likely to be responsible for the widespread occurrence of the two species of blood flukes (Cardicola spp.), although it is also possible that these were translocated recently by the spread of infected intermediate hosts.  相似文献   
5.
Modern hyperprolific sows must deal with large litters (16–20 piglets) which reduce piglet birthweight with a concomitant increase in the proportion of small and intrauterine growth retarded piglets. However, larger litters do not only have a greater variation of piglet weights, but also a greater variation in colostrum and milk consumption within the litter. To further understand the impact that body weight has on piglets, the present study aimed to evaluate the degree of physiological weakness of the smallest piglets at birth and during the suckling period (20 d) compared to their middle-weight littermates through their jejunal gene expression. At birth, light piglets showed a downregulation of genes related to immune response (FAXDC2, HSPB1, PPARGC1α), antioxidant enzymes (SOD2m), digestive enzymes (ANPEP, IDO1, SI), and nutrient transporter (SLC39A4) (P < 0.05) but also a tendency for a higher mRNA expression of GBP1 (inflammatory regulator) and HSD11β1 (stress hormone) genes compared to their heavier littermates (P < 0.10). Excluding HSD11β1 gene, all these intestinal gene expression differences initially observed at birth between light and middle-weight piglets were stabilized at the end of the suckling period, when others appeared. Genes involved in barrier function (CLDN1), pro-inflammatory response (CXCL2, IL6, IDO1), and stress hormone signaling (HSD11β1) over-expressed compared to their middle-weight littermates (P < 0.05). In conclusion, at birth and at the end of suckling period, light body weight piglets seem to have a compromised gene expression and therefore impaired nutrient absorption, immune and stress responses compared to their heavier littermates.  相似文献   
6.
Anthracnose, caused by Colletotrichum spp., is a major disease of cultivated strawberry, Fragaria × ananassa. This study identifies the Colletotrichum spp. which causes strawberry anthracnose in the southwest of Spain. A survey of the region was carried out, and the strains isolated were identified as C. acutatum by using the polymerase chain reaction (PCR) with genus and species-specific primers, demonstrating that this species is currently the causal agent of strawberry anthracnose in the studied region. The pathogenicity of C. acutatum and C. gloeosporioides strains was evaluated on two principal strawberry cultivars (cvs Camarosa and Ventana) under field conditions, the latter being more pathogenic than the former.  相似文献   
7.
BACKGROUND: Fifteen novel derivatives of D‐DIBOA, including aromatic ring modifications and the addition of side chains in positions C‐2 and N‐4, had previously been synthesised and their phytotoxicity on standard target species (STS) evaluated. This strategy combined steric, electronic, solubility and lipophilicity requirements to achieve the maximum phytotoxic activity. An evaluation of the bioactivity of these compounds on the systems Oryza sativa–Echinochloa crus‐galli and Triticum aestivum–Avena fatua is reported here. RESULTS: All compounds showed inhibition profiles on the two species Echinochloa crus‐galli (L.) Beauv. and Avena fatua L. The most marked effects were caused by 6F‐4Pr‐D‐DIBOA, 6F‐4Val‐D‐DIBOA, 6Cl‐4Pr‐D‐DIBOA and 6Cl‐4Val‐D‐DIBOA. The IC50 values for the systems Echinochloa crus‐galliOryza sativa and Avena fatua–Triticum aestivum for all compounds were compared. The compound that showed the greatest selectivity for the system Echinochloa crus‐galliOryza sativa was 8Cl‐4Pr‐D‐DIBOA, which was 15 times more selective than the commercial herbicide propanil (Cotanil‐35). With regard to the system Avena fatua–Triticum aestivum, the compounds that showed the highest selectivities were 8Cl‐4Val‐D‐DIBOA and 6F‐4Pr‐D‐DIBOA. The results obtained for 6F‐4Pr‐D‐DIBOA are of great interest because of the high phytotoxicity to Avena fatua (IC50 = 6 µM , r2 = 0.9616). CONCLUSION: The in vitro phytotoxicity profiles and selectivities shown by the compounds described here make them candidates for higher‐level studies. 8Cl‐4Pr‐D‐DIBOA for the system Echinochloa crus‐galliOryza sativa and 6F‐4Pr‐D‐DIBOA for Avena fatuaTriticum aestivum were the most interesting compounds. Copyright © 2010 Society of Chemical Industry  相似文献   
8.
The effects of water and salt stress on rate of germination and seedling growth were investigated under laboratory conditions in 46 soya bean genotypes from Central-West region of Brazil to verify how these stresses may limit crop establishment during the initial growth stage and also to identify the most tolerant genotypes to drought and salinity. Mild water and salt stresses were imposed by seed exposure to –0.20 MPa iso-osmotic solutions with polyethylene glycol—PEG 6000 (119.57 g/L) or NaCl (2.357 g/L) for 12 days at 25°C. The germination percentage, seedling length and seedling dry matter were measured, and then, salt or drought tolerance indexes were calculated. The “NS 5909 RG,” “NS 7000 IPRO,” “NS 7338IPRO,” “FPS Solimões RR,” “NS 5151 IPRO,” “SYN 13610 IPRO,” “LG 60177 IPRO,” “NS 6909 IPRO” and “BMX Desafio RR” were identified as the most drought-tolerant genotypes, whereas under salinity conditions, the genotypes “5D 615 RR,” “BMX Desafio RR,” “5D 6215 IPRO” and “BMX Ponta IPRO” were identified as tolerant. The “BMX Desafio RR” is the genotype most adapted to both stress conditions and, therefore, should be used under conditions of water shortage and excess salt in the soil at sowing time.  相似文献   
9.
The aim of this study was to identify possible effects of different vaccination strategies (concomitantly or not) against brucellosis and clostridia on intake, performance, feeding behavior, blood parameters, and immune responses of dairy heifers calves. Fifty heifers calves were enrolled [38 Gyr (Zebu, Bos taurus indicus) and 12 5/8 Holstein Gyr]. At 120 d of age, animals were randomly distributed among 3 groups: B (n = 18), vaccinated against brucellosis; C (n = 14), vaccinated against clostridia and CB (n = 18), vaccinated concomitantly for both. Rectal and thermographic temperatures were evaluated on days 1, 0, 1, 2, 3, 5, 7,10, 14, and 28 relatives to the vaccination day. Feed and water intake, body weight (BW), and feeding behavior were monitored daily by an electronic feeding system. Blood was sampled on days 0, 3, 7, 14, and 28, relative to the vaccination day for determination of glucose and -hydroxybutyrate (BHBA) concentrations. Blood sampled on day 0 (prevaccination) and on days 28 and 42 were used to evaluate the immune response against Brucella abortus and clostridia. There was an increase in rectal temperature between the first and the third day postvaccination in the 3 groups. The thermography revealed an increase of local temperature for 7 d on groups B and CB. Group C had increased local temperature for a longer period, lasting for up to 14 d. Dry mater intake was reduced for groups B and CB, but no alteration was observed for group C. No alterations regarding initial BW, final BW, average daily weight gain, and feed efficiency were observed. No differences were observed for the 3 vaccination groups for blood parameters throughout the evaluation period. The concomitant vaccination against brucellosis and clostridia led to lower neutralizing antibody titers against epsilon toxin of Clostridium perfringens and botulinum toxin type C of C. botulinum (C > CB > B). When cellular proliferation assay and serological tests to B. abortus were evaluated, no differences were observed between groups B and CB. The present results indicate that the concomitant vaccination against brucellosis and clostridia has no relevant impact on the intake, performance, and feeding behavior of dairy calves. However, the concomitant vaccination of vaccines against these 2 pathogens impacts animal immunity against clostridial infections.  相似文献   
10.
The use of live animals for educational purposes is an old practice that is still employed in teaching and research institutions. However, there are several objections to this practice, whether for ethical or humanitarian reasons. Surgical techniques teaching using anatomical pieces and/or preserved cadavers promotes greater learning efficiency, provides exercise repetition and increases the confidence and satisfaction of the students when compared to the use of live animals. The current work aimed to analyse the feasibility of using fresh swine urinary bladder and small intestines (jejunum), obtained from slaughterhouses, fixed in 99.8% ethyl alcohol (EA) and preserved in sodium chloride hypersaturated solution (SCHS) at 30%, for 7, 14 and 21 days, as an alternative method for surgical skills training (SST). Swine viscera, fixed in EA and preserved in SCHS, presented a realistic appearance, absence of odour and maintained the viable morphological characteristics during the performance of the operative techniques. Preservation solutions had low cost, were easy to acquire and did not offers risks to human health. Therefore, urinary bladders and small intestines fixed in 99.8% EA for 30 days and maintained in 30% SCHS at different periods were demonstrated as a good viable option as a preservation method for surgical skills training.  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