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   2193篇
  免费   155篇
林业   161篇
农学   88篇
基础科学   19篇
  596篇
综合类   77篇
农作物   144篇
水产渔业   269篇
畜牧兽医   745篇
园艺   66篇
植物保护   183篇
  2024年   7篇
  2023年   28篇
  2022年   57篇
  2021年   100篇
  2020年   108篇
  2019年   121篇
  2018年   98篇
  2017年   102篇
  2016年   108篇
  2015年   75篇
  2014年   95篇
  2013年   143篇
  2012年   169篇
  2011年   157篇
  2010年   102篇
  2009年   102篇
  2008年   122篇
  2007年   114篇
  2006年   103篇
  2005年   110篇
  2004年   85篇
  2003年   79篇
  2002年   58篇
  2001年   19篇
  2000年   17篇
  1999年   9篇
  1998年   7篇
  1997年   10篇
  1996年   5篇
  1995年   6篇
  1994年   3篇
  1993年   5篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   4篇
  1988年   2篇
  1986年   1篇
  1983年   3篇
  1978年   2篇
  1969年   1篇
  1963年   1篇
  1944年   1篇
  1939年   1篇
排序方式: 共有2348条查询结果,搜索用时 218 毫秒
991.
992.
A four-year-old Appaloosa brood mare was referred for evaluation of a colic episode of 24 hours' duration. Physical examination revealed a distended cecum filled predominantly with fluid. A tentative diagnosis of cecal dysfunction was determined, and surgical intervention was performed by means of typhlotomy and ileocolostomy techniques through a complete bypass of the cecum. Postanaesthetic myopathy and incisional infection developed as postoperative complications. The mare was discharged 13 days after surgery. Follow-up information obtained from the owner and referring veterinarian 4 months after discharge revealed full recovery of the mare.  相似文献   
993.
Veterinarians play a unique role in emergency preparedness and response, and federal agencies and academic institutions therefore allocate considerable resources to provide training to enhance their readiness. However, the level of preparedness of veterinarians in many rural regions is yet to be improved. This article reports an assessment of the bioterrorism preparedness, specifically the experience and training needs, of rural veterinarians in North Texas. The study employed a cross-sectional design with a study population that included all veterinarians (N = 352) in the 37 counties within Texas Department of State Health Services Regions 2 and 3. Data on veterinarians practicing or residing in the target region were obtained from the Texas State Board of Veterinary Medical Examiners. The response rate was 35% (n = 121). Results indicate that chemical exposure was the condition most frequently seen and treated, followed by botulism and anthrax. The majority (80%) of respondents indicated that they had not previously participated in training related to bioterrorism preparedness, and many (41%) also indicated a willingness to participate in a state health department-initiated bioterrorism response plan. However, only 18% were confident in their ability to diagnose and treat bioterrorism cases. These results suggest that many North Texas veterinarians practicing in rural regions could benefit from additional training in bioterrorism preparedness and response. An area in particular need of further training is the diagnosis and treatment of Category A agents. Federal, state, and local health agencies are urged to increase training opportunities and to make additional efforts to involve veterinarians in bioterrorism preparedness and response.  相似文献   
994.
995.

Context

Agricultural intensification is a leading cause of landscape homogenization, with negative consequences for biodiversity and ecosystem services. Conserving or promoting heterogeneity requires a detailed understanding of how farm management affects, and is affected by, landscape characteristics.

Objectives

We assessed relationships between farming systems and landscape characteristics, hypothesising that less-intensive systems act as landscape takers, by adapting management to landscape constraints, whereas more intensive systems act as landscape makers, by changing the landscape to suit farming needs.

Methods

We mapped dominant farming systems in a region of southern Portugal: traditional cereal-grazed fallow rotations; specialization on annual crops; and specialization on either cattle or sheep. We estimated landscape metrics in 241 1-km2 buffers representing the farming systems, and analysed variation among and within systems using multivariate statistics and beta diversity metrics.

Results

Landscape composition varied among systems, with dominance by either annual crops (Crop system) or pastures (Sheep), or a mixture between the two (Traditional and Cattle). There was a marked regional gradient of local landscape heterogeneity, but this contributed little to variation among systems. Landscape beta diversity declined from the Sheep to the Crop system, and it was inversely related to agriculture intensity.

Conclusions

Less intensive farming systems appeared compatible with a range of landscape characteristics (landscape takers), and may thus be particularly suited to agri-environmental management. More intensive systems appeared less flexible in terms of landscape characteristics (landscape makers), likely promoting regional homogenization. Farming systems may provide a useful standpoint to address the design of agri-environment schemes.
  相似文献   
996.
997.
We investigated if probiotic supplementation could improve the health and reproductive performance of unvaccinated lactating sows infected with porcine epidemic diarrhea (PED) virus. Twenty unvaccinated pregnant sows were equally allocated to probiotic‐supplemented (P) and control (C) groups. For the experiment, 15 g/day of probiotic compound BIO‐THREE PZ was given to P sows. Reproductive performance was checked daily. The number of neonates fostered by each sow was maintained at eight throughout the experiment. Individual milk production post‐parturition was measured twice. Milk protein and fat ratios were determined by a milk analyzer. Total immunoglobulin (Ig) A and G concentrations were measured by ELISA. At day 7 post‐parturition, the body weight of P sows was 10 kg higher than that of C sows, and at day 3 post‐parturition, P sows produced more milk (+2 kg) and had a higher IgA concentration in whey than did C sows (< .05). Finally, unlike C sows, P sows tended to return to estrus faster, and had larger piglets at birth with a lower mortality percentage during early days of suckling. In conclusion, probiotic compound BIO‐THREE PZ helped strengthen the immune system of unvaccinated, PED‐infected sows and improved their reproductive performance.  相似文献   
998.
The pupillary light reflex (PLR) is a routinely utilized clinical test to quickly assess integrity of subcortical light perception pathways in patients. While interpretation is simple for ophthalmologists, interestingly discrepancy occurs in annotation of the test results, especially for the consensual response. An email survey sent to diplomates of either the American or European Colleges of Veterinary Ophthalmologists (ACVO and ECVO, respectively), requesting use of a ‘direct/consensual’ annotation convention, showed 58% of respondents preferred one convention while 39% preferred a different convention. The majority preferred convention was different between ACVO and ECVO respondents. Standardization of PLR annotation convention across specialists is recommended for clarity in medical record keeping and communication among colleagues.  相似文献   
999.

Objective

To study the effect of alternating the order of midazolam and alfaxalone administration on the incidence of behavioural changes, alfaxalone induction dose and some cardiorespiratory variables in healthy dogs.

Study design

Prospective, randomized, controlled, clinical trial.

Animals

A total of 33 client-owned dogs undergoing elective procedures.

Methods

Following intramuscular acepromazine (0.02 mg kg?1) and morphine (0.4 mg kg?1) premedication, anaesthesia was induced intravenously (IV) with a co-induction of either midazolam (0.25 mg kg?1) prior to alfaxalone (0.5 mg kg?1; group MA), or alfaxalone followed by midazolam at identical doses (group AM). The control group (CA) was administered normal saline IV prior to alfaxalone administration. Additional alfaxalone (0.25 mg kg?1 increments) was administered as required in all groups until orotracheal intubation was possible. Changes in behaviour, quality of induction, ease of intubation and incidence of adverse events at induction were recorded. Heart rate (HR), respiratory rate (fR) and systolic arterial blood pressure (SAP) were measured before treatments (baseline values), 30 minutes after premedication and at 0, 2, 5 and 10 minutes postintubation.

Results

The incidence of excitement was higher in group MA compared with groups CA (p = 0.005) and AM (p = 0.013). The mean induction dose of alfaxalone was lower in group AM compared with group CA (p = 0.003). Quality of induction and ease of intubation were similar among groups. Mean HR values decreased after premedication and increased after alfaxalone administration in all groups. Mean SAP values were similar between groups. The number of animals that required manual ventilation was higher in the MA group.

Conclusions and clinical relevance

Despite a lower occurrence of adverse events at induction in group AM compared with group MA and a reduction of alfaxalone dose requirement in group AM compared with group CA, the use of an alfaxalone–midazolam co-induction does not seem to produce any cardiovascular or respiratory benefits in healthy dogs.  相似文献   
1000.
Tropical Animal Health and Production - This study aimed to evaluate the impact of subarachnoid anesthesia with ketamine during transcervical artificial insemination (TCAI) on the welfare of ewes...  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