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   893篇
  免费   107篇
林业   80篇
农学   12篇
基础科学   6篇
  215篇
综合类   92篇
农作物   34篇
水产渔业   44篇
畜牧兽医   401篇
园艺   29篇
植物保护   87篇
  2023年   4篇
  2022年   7篇
  2021年   12篇
  2020年   14篇
  2019年   13篇
  2018年   35篇
  2017年   22篇
  2016年   20篇
  2015年   30篇
  2014年   36篇
  2013年   62篇
  2012年   56篇
  2011年   63篇
  2010年   39篇
  2009年   29篇
  2008年   75篇
  2007年   54篇
  2006年   45篇
  2005年   42篇
  2004年   51篇
  2003年   43篇
  2002年   31篇
  2001年   21篇
  2000年   26篇
  1999年   22篇
  1998年   14篇
  1997年   7篇
  1996年   7篇
  1995年   6篇
  1994年   7篇
  1993年   13篇
  1992年   12篇
  1991年   13篇
  1990年   3篇
  1989年   13篇
  1988年   9篇
  1987年   2篇
  1986年   2篇
  1984年   3篇
  1983年   4篇
  1981年   2篇
  1979年   2篇
  1976年   3篇
  1973年   2篇
  1968年   4篇
  1966年   2篇
  1945年   1篇
  1930年   2篇
  1923年   1篇
  1921年   1篇
排序方式: 共有1000条查询结果,搜索用时 15 毫秒
21.
OBJECTIVE: To describe and evaluate subtotal ostectomy of dorsal spinous processes (DSP) performed in standing horses. STUDY DESIGN: Retrospective study. SAMPLE POPULATION: Nine adult horses. METHODS: The diseased portions of the DSP were removed with the horses standing and sedated after infiltrating a local anesthetic agent around the affected DSP. Medical records of affected horses were reviewed to determine history, findings of physical and radiographic examination, surgical technique, postoperative complications, and outcome. RESULTS: Five horses had subtotal ostectomy of DSP because of osteomyelitis, and 4 because of impingement and/or fracture of DSP. Affected portions of DSP were removed safely and effectively, with no apparent discomfort to the horses; hemorrhage was minimal. CONCLUSIONS: Subtotal ostectomy of DSP can be performed safely in standing, conscious horses and the risks associated with general anesthesia are eliminated. Hemorrhage is minimal compared to that which occurs when the procedure is performed with horses anesthetized and in lateral recumbency. CLINICAL RELEVANCE: Access and visibility are better when subtotal ostectomy of the DSP is performed with the horse standing rather than anesthetized and in lateral recumbency. Performing subtotal ostectomy of diseased DSP with the horse standing avoids the expense and risks of general anesthesia.  相似文献   
22.
A novel proximity ligation assay (PLA) using a pan-serotype reactive monoclonal antibody was developed and evaluated for the detection of foot-and-mouth disease virus (FMDV) in clinical samples collected from field cases of disease. The FMDV-specific PLA was found to be 100 times more sensitive for virus detection than the commonly used antigen capture-ELISA (AgELISA). As few as five TCID50 were detected in individual assays, which was comparable with the analytical sensitivity of real-time RT-PCR. Although this assay was capable of detecting diverse isolates from all seven FMDV serotypes, the diagnostic sensitivity of the PLA assay was lower than real-time RT-PCR mainly due to a failure to detect some SAT 1, SAT 2 and SAT 3 FMDV strains. In conclusion, this new PLA format has high analytical sensitivity for the detection of FMDV in clinical samples and may prove valuable as a rapid and simple tool for use in FMD diagnosis.  相似文献   
23.
The purpose of this study was to develop a percutaneous lung biopsy technique to be used on steers in a commercial feedlot setting. Thirty-four crossbred steer and heifer calves from a commercial feedlot in southern Alberta were used in this study. The calves originated from the auction market and all were chronically affected with bovine respiratory disease (BRD). A technique was developed to obtain a lung sample from the right cranioventral lung lobe, intercostal space (ICS) 2, using a manual or an automatic biopsy instrument with a 14- or 12-gauge (ga) biopsy needle. Overall, lung parenchyma was successfully harvested in 55.9% of experimental animals and in 55.0% of lung biopsy trials. Compared with postmortem diagnosis, the biopsy resulted in the same pathologic diagnosis for 75% of biopsy samples when evaluated using standardized criteria by the same veterinary pathologist. The success rate was 61.5% and 42.9% in a hospital or field setting, respectively. With an automatic instrument, lung was recovered from 57.9% and 37.5% of samples obtained using a 12- or 14-ga biopsy needle, respectively. One experimental animal or 2.9% of the total had fatal complications from the procedure. In a commercial feedlot setting, the procedure took 20 min for each animal. Percutaneous lung biopsy of the right cranioventral lung lobe may be a viable technique when used on feedlot steers affected with chronic pneumonia. These findings suggest that using an automatic instrument with either a 14- or 12-ga biopsy needle may yield lung samples that are suitable for histopathological evaluation. However, this technique needs to be further evaluated in a field setting.  相似文献   
24.
Bats are hosts of diverse coronaviruses (CoVs) known to potentially cross the host–species barrier. For analysing coronavirus diversity in a bat species‐rich country, a total of 421 anal swabs/faecal samples from Costa Rican bats were screened for CoV RNA‐dependent RNA polymerase (RdRp) gene sequences by a pancoronavirus PCR. Six families, 24 genera and 41 species of bats were analysed. The detection rate for CoV was 1%. Individuals (n = 4) from four different species of frugivorous (Artibeus jamaicensis, Carollia perspicillata and Carollia castanea) and nectivorous (Glossophaga soricina) bats were positive for coronavirus‐derived nucleic acids. Analysis of 440 nt. RdRp sequences allocated all Costa Rican bat CoVs to the α‐CoV group. Several CoVs sequences clustered near previously described CoVs from the same species of bat, but were phylogenetically distant from the human CoV sequences identified to date, suggesting no recent spillover events. The Glossophaga soricina CoV sequence is sufficiently dissimilar (26% homology to the closest known bat CoVs) to represent a unique coronavirus not clustering near other CoVs found in the same bat species so far, implying an even higher CoV diversity than previously suspected.  相似文献   
25.
猪的回肠炎及其控制   总被引:1,自引:0,他引:1  
猪的增生性回肠病 (回肠炎 )最早在 1 931年被发现 ,但直到约 60年后 ,本病的病原体由爱丁堡大学的 lawson等人命名为 lawsonia intracellu-laris。随后的 1 0年中由于许多特有技术的发展 ,使得人们可进一步研究这种细菌感染的流行病学和它的各种临床表现 -即地方性回肠炎 ( RI)、增生性肠病 ( PE)、坏死性肠炎 ( NE)和急性出血增生性肠病 ( AHPE)。所有疾病的控制方案都是以流行病学为基础的。有关病原体和传播方式的许多问题仍待解决。1 流行病学分子诊断技术可用于整个畜群抽查并可检测它们粪便中的 L intracellularis。西班牙对 7…  相似文献   
26.
Sperm reservoirs in South American Camelids would be crucial for successful fertilization. Since ovulation occurs approximately 36 h after mating, the maintenance of the sperm viability in the oviduct waiting for the ovum is a critical reproductive event. Our study aimed at determining whether the isthmus or the utero tubal junction (UTJ) could function as a sperm reservoir in llama by means of in vivo and in vitro experiments. For the in vivo experiments, the oviducts of adult females with a dominant follicle bigger than 7 mm were examined for the presence of sperm at 6, 18, 24, 28 and 35 h after mating. The results using scanning and transmission electron microscopy showed ultrastructural differences between isthmus and UTJ with respect to (1) predominance of secretory cells in the UTJ and ciliated cells in the isthmus epithelium and (2) cytoplasmic bulbous projection of the secretory cells in the UTJ. Sperm adhered by a mucus‐like substance were seen only in the UTJ at 6, 18, 24 and 28 h post‐mating. Lack of sperm adhered to oviductal mucosa was observed around ovulation (35 h). In vitro experiments demonstrated higher ability of UTJ epithelial cell explants with respect to isthmus explants to bind sperm in a co‐cultured system. The anatomical features and the presence of a sperm bonding agent in the UTJ together with the in vitro differential binding of sperm to UTJ explants strongly suggest that both may be feasible mechanisms that facilitate sperm storage in this oviductal region in llama.  相似文献   
27.
The goal of this study was to confirm the vasopressor and cardiac effects of POTENAY® INJETÁVEL (POT), a mephentermine‐based product, given to cattle with induced vascular/cardiac depression. Ten healthy Holstein cattle (206 ± 13 kg) followed a randomized‐complete‐block design (RCBD) utilizing crossover study design. Each animal randomly received (1 ml/25 kg, IM) of either POT (= 10) or volume‐matched placebo control (0.9%NaCl, CP,= 10). A subset of animals (= 5) received POT first (day 0) while the remaining (= 5) received CP; after a six‐day washout period, cattle received the opposite compound. Animals were anesthetized and catheterized for systemic/left ventricular hemodynamic monitoring. Myocardial dysfunction/hypotension was induced by increasing the end‐tidal isoflurane concentration until arterial blood pressure was 20% lower than at baseline and remained stable. Once the animal was determined to be hypotensive and hemodynamically stable, steady‐state hypotensive baseline data (BL2) were acquired, and treatment with either POT or CP was given. Data were acquired post‐treatment at every 15 min for 90 min. POT improved cardiac output (+68 L/min, ±14%, < 0.05), MAP (+14 mmHg, ±4%, < 0.05), HR (+22 bpm, ±8%, < 0.05), and peak rates of ventricular pressure change during both systole (dP/dtmax: +37 mmHg/s ±13%, < 0.05) and diastole (dP/dtmin: +31 mmHg/s, ±7%, < 0.05). No improvements were noted following placebo‐control administration. Results indicate that POT improves cardiac performance and systemic hemodynamics in cattle with induced cardiovascular depression when given as single intramuscular injection.  相似文献   
28.
This study aimed to evaluate the hypothesis that mixed sequential grazing of dairy cows and breeding ewes is beneficial. During the seasons of spring–summer 2013 and autumn–winter 2013–2014, 12 (spring–summer) and 16 (autumn–winter) Holstein Friesian cows and 24 gestating (spring–summer) and lactating (autumn–winter) Pelibuey ewes grazed on six (spring–summer) and nine (autumn–winter) paddocks of alfalfa and orchard grass mixed pastures. The treatments “single species cow grazing” (CowG) and “mixed sequential grazing with ewes as followers of cows” (MixG) were evaluated, under a completely randomized design with two replicates per paddock. Herbage mass on offer (HO) and residual herbage mass (RH) were estimated by cutting samples. The estimate of herbage intake (HI) of cows was based on the use of internal and external markers; the apparent HI of ewes was calculated as the difference between HO (RH of cows) and RH. Even though HO was higher in CowG, the HI of cows was higher in MixG during spring–summer and similar in both treatments during autumn–winter, implying that in MixG the effects on the cows HI of higher alfalfa proportion and herbage accumulation rate evolving from lower residual herbage mass in the previous cycle counteracted that of a higher HO in CowG. The HI of ewes was sufficient to enable satisfactory performance as breeding ewes. Thus, the benefits of mixed sequential grazing arose from higher herbage accumulation, positive changes in botanical composition, and the achievement of sheep production without negative effects on the herbage intake of cows.  相似文献   
29.
The adrenal cortex is believed to be implicated in the high incidence of abortion in the Angora goat. Stimulation testing with adrenocorticotrophic hormone (ACTH) was used to assess the adrenal cortical function in 5 Angora does from herds with a history of abortion and 5 non-Angora does. An acute test involving a single intramuscular (i.m.) injection of 0.25 mg of synthetic ACTH was given during anoestrus, at mid-oestrus, on day 90 and on day 120 of gestation. Blood samples were collected from the jugular vein at 30 min intervals for 1 h before and 5 h after injection. Cortisol concentrations rose within 30 min and returned to baseline values within 3.5 h. Cortisol production was lower (p<0.01) in the pregnant state compared to the non-pregnant state in both groups. Production of cortisol was consistently lower (p<0.05) in the Angora does compared to the non-Angora does during anoestrus and pregnancy and marginally so at mid-oestrus. A chronic stimulation test involving once daily injections of 0.5 mg of a depot form of ACTH i.m. for 7 days commencing on day 90 of pregnancy was also conducted. Cortisol concentrations rose to reach a peak on the third day of treatment in both groups. The values then declined in the Angora does despite continued ACTH treatment, while those for the non-Angora does exhibited a second peak. During and following this treatment, two non-Angora does delivered live kids (day 95, day 120). Out of 7 Angora pregnancies, one Angora doe aborted two dead fetuses at day 116. No significant difference in the cortisol response in the acute test was detected between the animals that aborted and their respective cohorts, but the two non-Angora does that aborted had significantly lower cortisol concentrations during depot ACTH administration. Progesterone and oestradiol levels did not differ between Angora and non-Angora animals during pregnancy or on the test days. The results suggest that the steroidogenic response of the adrenal cortex to ACTH stimulation is significantly less in Angora does with a history of abortion than it is in non-Angora does and support the view that the Angora goat would make a more limited adrenal cortical response to a stressful occurrence during pregnancy.  相似文献   
30.
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