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   5477篇
  免费   344篇
  国内免费   9篇
林业   463篇
农学   126篇
基础科学   45篇
  1018篇
综合类   866篇
农作物   223篇
水产渔业   492篇
畜牧兽医   2033篇
园艺   161篇
植物保护   403篇
  2023年   49篇
  2022年   80篇
  2021年   118篇
  2020年   161篇
  2019年   216篇
  2018年   191篇
  2017年   164篇
  2016年   175篇
  2015年   133篇
  2014年   184篇
  2013年   286篇
  2012年   358篇
  2011年   461篇
  2010年   253篇
  2009年   231篇
  2008年   364篇
  2007年   350篇
  2006年   307篇
  2005年   277篇
  2004年   265篇
  2003年   279篇
  2002年   234篇
  2001年   57篇
  2000年   40篇
  1999年   51篇
  1998年   36篇
  1997年   31篇
  1996年   26篇
  1995年   22篇
  1994年   26篇
  1993年   17篇
  1992年   28篇
  1991年   32篇
  1990年   24篇
  1989年   23篇
  1988年   19篇
  1987年   12篇
  1986年   22篇
  1985年   18篇
  1984年   21篇
  1983年   13篇
  1982年   15篇
  1981年   12篇
  1980年   12篇
  1979年   7篇
  1978年   13篇
  1977年   10篇
  1976年   10篇
  1974年   10篇
  1971年   8篇
排序方式: 共有5830条查询结果,搜索用时 11 毫秒
21.
Motility of the rumen and abomasum during hypocalcaemia.   总被引:3,自引:0,他引:3       下载免费PDF全文
The relationship between plasma calcium level and rumen motility in cows and sheep and abomasal motility in cows was investigated by inducing hypocalcaemia in seven cows and five sheep by the infusion of Na2 EDTA over a period of approximately two hours. Rates and amplitudes of rumen and abomasal contractions were markedly reduced by the reduction of plasma calcium level to approximately 50% of normal. There were significant positive linear relationships (P less than 0.05) between rate and amplitude of rumen contractions in both sheep and cows over a plasma calcium range of 1-3 mmol/L. There was also a significant linear relationship (P less than 0.05) between plasma calcium and abomasal rate of contraction over the same range in cows, but the relationship with amplitude of abomasal contraction was not quite significant (P less than 0.1 greater than 0.05).  相似文献   
22.
23.
OBJECTIVE To describe the use of intralesional amphotericin B in localised lesions for the treatment of 26 cats from Rio de Janeiro, Brazil, with sporotrichosis refractory to oral itraconazole. DESIGN Uncontrolled intervention study. METHOD The 26 cats in this study were diagnosed with sporotrichosis, confirmed by isolation of Sporothrix schenckii, and presented residual localised skin lesions refractory to treatment with oral itraconazole for a minimum period of 8 weeks. The animals received weekly applications of intralesional amphotericin B in conjunction with oral itraconazole. In cases of owner unavailability, a maximum of 2 weeks between the infiltrations was accepted. RESULTS Twenty-two (84.6%) of the 26 treated cats achieved clinical remission, 16 (72.7%) of which were cured, and in the remaining six (27.3%) the lesions recurred at the same site. Lack of clinical response was observed in one animal and three owners abandoned treatment. CONCLUSION The proposed therapeutic regimen is an adjunctive treatment option for cats with sporotrichosis presenting as residual skin lesions refractory to itraconazole.  相似文献   
24.
猪萎缩性鼻炎免疫和疫苗研究进展   总被引:1,自引:0,他引:1  
猪萎缩性鼻炎(atrophic rhinitis,AR)是猪群的一种重要呼吸系统传染病,最初的临床症状表现为打喷嚏,抽鼻息,眼睛分泌物与灰尘固结形成泪斑,鼻腔出现分泌物,根据疾病发生的不同阶段,分泌物表现为浆液性甚至脓性,部分严重发病猪鼻腔出血(见图1),特别严重的情况下甚至在猪舍的栏圈、墙壁或其他猪身上发现喷出的鼻腔分泌物。  相似文献   
25.
26.
This study was performed to determine if a peripheral sample of lung from the site where biopsy is conducted is representative of the rest of the lung and to investigate the relationship between airway inflammation and intraepithelial mucous production in the peripheral airways. Lung parenchyma samples were collected from five different regions of the lung in five control and five heaves-affected horses. Horse groups were defined by clinical response to stabling. Tissue sections were used for semi-quantitative scoring of lesions, to count the number of airways, to quantify the amount of stored mucosubstances (Vs) within the epithelium, and to count the number of epithelial cells in terminal airways. No significant differences were found between lung regions or between groups of horses. Lack of regional differences in airway structures means that a biopsy sample can be used for diagnosis and investigation of diffusely distributed diseases. Airway inflammation was correlated with mucous cell metaplasia and Vs. Therefore, in horses, mucus accumulation is partly caused by increased number of mucous cells and is associated with airway inflammation. Therapy targeted to reduce airway inflammation will help reduce the excessive mucous accumulation in horses.  相似文献   
27.
28.
BACKGROUND: Knowledge of breed associations is valuable to clinicians and researchers investigating diseases with a genetic basis. HYPOTHESIS: Among symptomatic dogs tested for exocrine pancreatic insufficiency (EPI) by canine trypsin-like immunoreactivity (cTLI) assay, EPI is common in certain breeds and rare in others. Some breeds may be overrepresented or underrepresented in the population of dogs with EPI. Pathogenesis of EPI may be different among breeds. ANIMALS: Client-owned dogs with clinical signs, tested for EPI by radioimmunoassay of serum cTLI, were used. METHODS: In this retrospective study, results of 13,069 cTLI assays were reviewed. RESULTS: An association with EPI was found in Chows, Cavalier King Charles Spaniels (CKCS), Rough-Coated Collies (RCC), and German Shepherd Dogs (GSD) (all P < .001). Chows (median, 16 months) were younger at diagnosis than CKCS (median, 72 months, P < .001), but not significantly different from GSD (median, 36 months, P = .10) or RCC (median, 36 months, P = .16). GSD (P < .001) and RCC (P = .015) were younger at diagnosis than CKCS. Boxers (P < .001), Golden Retrievers (P < .001), Labrador Retrievers (P < .001), Rottweilers (P = .022), and Weimaraners (P = .002) were underrepresented in the population with EPI. CONCLUSIONS AND CLINICAL IMPLICATIONS: An association with EPI in Chows has not previously been reported. In breeds with early-onset EPI, immune-mediated mechanisms are possible or the disease may be congenital. When EPI manifests later, as in CKCS, pathogenesis is likely different (eg, secondary to chronic pancreatitis). Underrepresentation of certain breeds among dogs with EPI has not previously been recognized and may imply the existence of breed-specific mechanisms that protect pancreatic tissue from injury.  相似文献   
29.
The objective of these experiments was to establish the relationship of plasma ghrelin concentrations with feed intake and hormones indicative of nutritional state of cattle. In Exp.1, 4 steers (BW 450 +/- 14.3 kg) were used in a crossover design to compare plasma ghrelin concentrations of feed-deprived steers with those of steers allowed to consume feed and to establish the relationship of plasma ghrelin concentrations with those of GH, insulin (INS), glucose (GLU), and NEFA. After adaptation to a once-daily feed offering (0800), 2 steers continued the once-daily feeding schedule (FED), whereas feed was withheld from the other 2 steers (FAST). Serial blood samples were collected via indwelling jugular catheter from times equivalent to 22 h through 48 h of feed deprivation. Average plasma ghrelin concentrations were greater (P < 0.001) in FAST compared with FED (690 and 123 +/- 6.5 pg/mL) steers. Average plasma ghrelin concentrations for FED steers prefeeding were elevated (P < 0.001) when compared with those postfeeding (174 and 102 +/- 4.2 pg/mL, respectively). Average plasma GH concentration was elevated (P < 0.05) for FAST steers compared with FED steers. Plasma GLU concentrations were not different; however, for FAST steers, NEFA concentrations were elevated (P < 0.001) and INS concentrations were decreased (P < 0.001). In Exp. 2, 4 steers (BW 416 +/- 17.2 kg) were used in a crossover design to determine the effects of i.v. injection of bovine ghrelin (bGR) on plasma GH, INS, GLU, and NEFA concentrations; length of time spent eating; and DMI. Steers were offered feed once daily (0800). Serial blood samples were collected from steers via indwelling jugular catheter. Saline or bGR was injected via jugular catheter at 1200 and 1400. A dosage of 0.08 microg/kg of BW bGR was used to achieve a plasma ghrelin concentration similar to the physiological concentration measured in a FAST steer in Exp. 1 (1,000 pg/mL). Injection of bGR resulted in elevated (P < 0.005) plasma GH concentrations after the 1200 but not the 1400 injection. Plasma INS, GLU, and NEFA concentrations were not affected by bGR injection. For the combined 1-h periods postinjection, length of time spent eating was greater (P = 0.02) and DMI tended to be increased (P = 0.06) for bGR steers. These data are consistent with the hypothesis that ghrelin serves as a metabolic signal for feed intake or energy balance in ruminants.  相似文献   
30.
Beef cattle from a herd in north Alabama were examined because of an outbreak of nonfatal skin disease characterized by discrete circumscribed areas of inflammation that developed on the skin from the neck to the hips. Areas of inflammation, which tended to be superficial, underwent necrosis and scabbed over. The scabs eventually dropped off leaving discrete, round, whitish, hairless lesions that were 1.2 to 2.5 cm diameter. Because clinical signs were consistent with those expected with pseudo-lumpy skin disease (PLSD) caused by bovine herpesvirus type 2 (BHV-2), samples from 16 representative animals were submitted for BHV-2 testing. All 16 animals were seropositive for BHV-2, but the virus could not be isolated from skin biopsy specimens or buffy coat samples. Results of a polymerase chain reaction assay incorporating primers designed to amplify 2 DNA sequences from BHV-2 were positive for 3 of the 10 cattle, suggesting that skin lesions in these cattle were a result of PLSD. Our findings suggest that PLSD may be more common and widespread in the United States than suggested by the frequency with which BHV-2 has been isolated from cattle with PLSD-like skin lesions.  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