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   1197篇
  免费   109篇
林业   57篇
农学   25篇
基础科学   4篇
  354篇
综合类   71篇
农作物   78篇
水产渔业   94篇
畜牧兽医   538篇
园艺   27篇
植物保护   58篇
  2023年   10篇
  2022年   11篇
  2021年   33篇
  2020年   29篇
  2019年   30篇
  2018年   46篇
  2017年   35篇
  2016年   45篇
  2015年   40篇
  2014年   47篇
  2013年   68篇
  2012年   79篇
  2011年   98篇
  2010年   51篇
  2009年   61篇
  2008年   79篇
  2007年   75篇
  2006年   79篇
  2005年   84篇
  2004年   66篇
  2003年   50篇
  2002年   62篇
  2001年   20篇
  2000年   16篇
  1999年   7篇
  1998年   7篇
  1997年   6篇
  1996年   6篇
  1995年   5篇
  1994年   3篇
  1993年   2篇
  1992年   7篇
  1991年   4篇
  1990年   4篇
  1989年   3篇
  1988年   2篇
  1983年   3篇
  1981年   2篇
  1975年   2篇
  1974年   2篇
  1972年   2篇
  1928年   3篇
  1926年   1篇
  1925年   1篇
  1924年   4篇
  1913年   1篇
  1912年   1篇
  1910年   1篇
  1905年   1篇
  1903年   1篇
排序方式: 共有1306条查询结果,搜索用时 546 毫秒
991.
992.
993.
The diagnosis of bovine genital campylobacteriosis (BGC) presents significant challenges, as traditional methods lack sensitivity when prolonged transport of samples is required. Assays of preputial samples by means of real-time polymerase chain reaction (PCR) provide good sensitivity and high throughput capabilities. However, there is limited information on the acceptable duration of transport and temperature during transport of samples. In addition, the use of pooled samples has proven to be a valuable strategy for the diagnosis of other venereal diseases in cattle. The objectives of the present study were to determine the effect of sample pooling and of transport time and temperature on the clinical sensitivity of a real-time quantitative PCR (qPCR) assay for Campylobacter fetus subsp. venerealis in preputial samples from beef bulls. Eight infected bulls and 176 virgin yearling bulls were used as the source of samples. The qPCR sensitivity was comparable for unpooled samples and pools of 5 samples, whereas sensitivity was decreased for pools of 10 samples. Sensitivity for the various pool sizes improved with repeated sampling. For shorter-term transport (2 and 48 h), sensitivity was greatest when the samples were stored at 4°C and 30°C, whereas for longer-term transport (96 h) sensitivity was greatest when the samples were stored at −20°C. The creation of pools of 5 samples is therefore a good option to decrease costs when screening bulls for BGC with the qPCR assay of direct preputial samples. Ideally the samples should be stored at 4°C and arrive at the laboratory within 48 h of collection, but when that is not possible freezing at −20°C could minimize the loss of sensitivity.  相似文献   
994.
OBJECTIVE:To determine the pharmacokinetics of an orally administered dose of tramadol in domestic rabbits (Oryctolagus cuniculus). ANIMALS: 6 healthy adult sexually intact female New Zealand White rabbits. PROCEDURES: Physical examinations and plasma biochemical analyses were performed to ensure rabbits were healthy prior to the experiment. Rabbits were anesthetized with isoflurane, and IV catheters were placed in a medial saphenous or jugular vein for collection of blood samples. One blood sample was collected before treatment with tramadol. Rabbits were allowed to recover from anesthesia a minimum of 1 hour before treatment. Then, tramadol (11 mg/kg, PO) was administered once, and blood samples were collected at various time points up to 360 minutes after administration. Blood samples were analyzed with high-performance liquid chromatography to determine plasma concentrations of tramadol and its major metabolite (O-desmethyltramadol). RESULTS: No adverse effects were detected after oral administration of tramadol to rabbits. Mean +/- SD half-life of tramadol after administration was 145.4 +/- 81.0 minutes; mean +/- SD maximum plasma concentration was 135.3 +/- 89.1 ng/mL. CONCLUSIONS AND CLINICAL RELEVANCE: Although the dose of tramadol required to provide analgesia in rabbits is unknown, the dose administered in the study reported here did not reach a plasma concentration of tramadol or O-desmethyltramadol that would provide sufficient analgesia in humans for clinically acceptable periods. Many factors may influence absorption of orally administered tramadol in rabbits.  相似文献   
995.
A nested polymerase chain reaction (PCR) using primers from the LipL32 sequence of Leptospira spp. was used to detect shedding of pathogenic leptospires in urine from naturally infected cattle. Amplicons (497bp) were obtained from 21 pathogenic reference serovars belonging to four species (L. interrogans, L. borgpetersenii, L. santarosai, L. kirschneri). DNA was amplified from 26/30 urine samples taken from cattle with suspected leptospirosis and from leptospires cultivated from 10 of these samples. The limit of detection of DNA in the clinical samples was 200pg and the nested PCR detected all pathogenic reference serovars of Leptospira spp. tested. No PCR products were amplified using DNA from other common bacterial species from the bovine urogenital tract or urine, or from the non-pathogenic L. biflexa Andamana serovar. The nested PCR exhibited high specificity and sensitivity for detection of pathogenic serovars in urine from cattle.  相似文献   
996.
Animal population estimates are essential for public health services to ensure the success of zoonoses control programmes. Canine and feline populations vary among different regions mainly because of local human income status and type of human residence. Accordingly, the present study estimated the pet population size living in apartments of a vertical neighbourhood in Curitiba, Brazil. We chose a neighbourhood with a predominance of apartment buildings. All apartment buildings were visited, and questionnaires were completed by doormen or residents. Data were obtained from 120 of 173 apartment buildings. Survey questions included the number of apartments, residents, dogs and cats. Two thousand nine hundred and sixty six apartments with a total of 7429 residents were surveyed. The number of dogs and cats was 569 and 86 respectively. Thus, the human : dog and human : cat ratios were 13.05 : 1 and 86.38 : 1. These ratios were higher than those observed in other neighbourhoods in Curitiba. The present study indicates that the number of pets from apartments may be different from houses, and different among distinct areas within the same city.  相似文献   
997.
Armadillos are primitive mammals used as food, mostly in rural areas. These animals may be sources of toxoplasmosis and leptospirosis infection for humans, but there is little information about their potential risk as reservoirs. In order to determine the prevalence of armadillos infected by Toxoplasma gondii and Leptospira spp., serum samples of 31 nine-banded armadillos (Dasypus novemcinctus), three six-banded armadillos (Euphractus sexcinctus), two naked-tailed armadillos (Cabassous tatouay) and two long-nosed armadillos (D. hybridus), captured in the mid-west region of the state of S?o Paulo, were analyzed for leptospirosis using the Microscopic Agglutination Test (MAT-l), and for toxoplasmosis using the Modified Agglutination Test (MAT-t). Only 4/31 (12.90%) nine-banded armadillos were positive for T. gondii, while 3/31 (9.68%) nine-banded armadillos and 1/3 (33.33%) six-banded armadillos presented antibodies to Leptospira spp., demonstrating the potential risk of T. gondii and Leptospira spp. transmission to humans, mainly due the habit of eating the meat of these animals in rural areas.  相似文献   
998.
In 2001 and 2002, an outbreak of a previously unreported disease, associated with a border disease virus (BDV), caused high mortality in the Southern chamois (Rupicapra pyrenaica) population in the Alt Pallars-Aran National Hunting Reserve in the Catalan Pyrenees (NE Spain). Between 2002 and 2006, sera and/or tissue samples taken from 116 healthy chamois shot during the hunting season, plus 42 from chamois affected by different diseases, were studied. A blocking enzyme-immunosorbent assay (ELISA) was used to study pestivirus seroprevalence in 114 healthy hunted and 31 diseased chamois, yielding positive results in 73.7 and 22.6% of the chamois, respectively. Comparative virus neutralization tests (VNT) performed on 42 seropositive samples with 6 pestivirus strains yielded statistically higher titres to BDV Spain 97, followed by BDV chamois, BDV 137/4, BDV Moredun, Bovine Diarrhoea virus-1 (BVDV-1) NADL and BVDV-2 atypical. Virological investigations for pestivirus detection were performed using an antigen ELISA test in 82 healthy and 18 diseased chamois, RT-PCR in 16 healthy and in all diseased chamois, and virus isolation in 14 diseased chamois. No viral antigen was detected in any of the healthy animals. A pestivirus, characterized as BDV by monoclonal antibodies, was detected in the 10 chamois showing clinical signs consistent with BDV infection. Sequence analysis in the 5' untranslated region (5'-UTR) revealed that they were grouped into the BDV-4 genotype. In the remaining chamois, infectious keratoconjunctivitis, pneumonia, trauma and contagious ecthyma were diagnosed. The cause of death was unknown in five chamois. The results suggest that the infection has become endemic in the population and that it could have a significant impact on chamois population dynamics.  相似文献   
999.
Salmonella spp. (n = 468), isolated from the feces of sows, nursery, and grow-finish pigs in 20 farrow-to-finish herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. No resistance was identified to amikacin, amoxicillin-clavulanic acid, ceftiofur, ceftriaxone, ciprofloxacin or nalidixic acid, and less than 1% of the isolates were resistant to cefoxitin and gentamicin. Isolates were most commonly resistant to tetracycline (35%) and sulfamethoxazole (27%). Overall, 59% of the Salmonella were susceptible to all 16 drugs (pansusceptible). Isolates from sows were more likely to be pansusceptible than isolates from nursery or grow-finish pigs. Resistance to 2 or more drugs occurred in 29% of the isolates and was significantly more likely to occur in Salmonella from nursery pigs than from sows. The odds of resistance to 4 of the drugs, streptomycin, ampicillin, kanamycin and cephalothin, were significantly higher in isolates from nursery pigs than grow-finish pigs, while the odds of resistance to 2 drugs, tetracycline and streptomycin, were higher in Salmonella from nursery pigs than from sows. More age-specific risk factor studies are needed to investigate these differences between production phases.  相似文献   
1000.
BACKGROUND: There are few studies evaluating the natural history and prognostic variables in chronic mitral valve disease (CMVI) in a heterogeneous population of dogs. OBJECTIVES: To estimate survival and prognostic value of clinical and echocardiographic variables in dogs with CMVI of varying severity. Five hundred and fifty-eight dogs belonging to 36 breeds were studied. METHODS: Dogs were included after clinical examination and echocardiography. Long-term outcome was assessed by telephone interview with the owner. RESULTS: The mean follow-up time was 22.7 +/- 13.6 months, and the median survival time was 19.5 +/- 13.2 months. In univariate analysis, age>8 years, syncope, HR>140 bpm, dyspnea, arrhythmias, class of heart failure (International Small Animal Cardiac Health Council), furosemide therapy, end-systolic volume-index (ESV-I)>30 mL/m(2), left atrial to aortic root ratio (LA/Ao)>1.7, E wave transmitral peak velocity (Emax)>1.2 m/s, and bilateral mitral valve leaflet engagement were associated with survival time when all causes of death were included. For the cardiac-related deaths, all the previous variables except dyspnea and EDV-I>100 mL/m(2) were significantly associated with survival time. Significant variables in multivariate analysis (all causes of death) were syncope, LA/Ao>1.7 m/s, and Emax>1.2 m/s. For cardiac-related death, the only significant variable was LA/Ao>1.7. CONCLUSIONS AND CLINICAL IMPORTANCE: Mild CMVI is a relatively benign condition in dogs. However, some clinical variables can identify dogs at a higher risk of death; these variables might be useful to identify individuals that need more frequent monitoring or therapeutic intervention.  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