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   753篇
  免费   22篇
  国内免费   1篇
林业   18篇
农学   12篇
基础科学   2篇
  82篇
综合类   111篇
农作物   32篇
水产渔业   29篇
畜牧兽医   435篇
园艺   25篇
植物保护   30篇
  2021年   5篇
  2020年   9篇
  2019年   16篇
  2018年   9篇
  2017年   9篇
  2016年   10篇
  2015年   8篇
  2014年   19篇
  2013年   50篇
  2012年   25篇
  2011年   38篇
  2010年   10篇
  2009年   21篇
  2008年   22篇
  2007年   28篇
  2006年   31篇
  2005年   33篇
  2004年   27篇
  2003年   26篇
  2002年   18篇
  2001年   19篇
  2000年   23篇
  1999年   18篇
  1998年   9篇
  1997年   8篇
  1996年   5篇
  1995年   5篇
  1992年   27篇
  1991年   18篇
  1990年   12篇
  1989年   13篇
  1988年   9篇
  1987年   11篇
  1986年   12篇
  1985年   11篇
  1984年   7篇
  1983年   6篇
  1978年   11篇
  1977年   9篇
  1974年   5篇
  1973年   5篇
  1972年   7篇
  1971年   6篇
  1970年   9篇
  1969年   10篇
  1968年   8篇
  1967年   5篇
  1966年   7篇
  1936年   4篇
  1935年   4篇
排序方式: 共有776条查询结果,搜索用时 16 毫秒
741.
Intrammary inoculation of 70 colony forming units (cfu) of Mycoplasma bovis into one quarter of four previously non-infected cows resulted in severe mastitis in inoculated and uninoculated quarters. Hematogenous spread of the infection was most likely, as mycoplasma was isolated from the peripheral blood of three of four cows and the milking machine was designed to prevent quarter to quarter communication of milk and air. The presence of large numbers of mycoplasma exceeding 106 cfu/ml of milk preceded the onset of overt sero-purulent mastitis by 1–3 days. In general, the severity, duration of the infection and within cow spread of mastitis to adjacent quarters after the inoculation of 70 cfu was indistinguishable from naturally occurring mycoplasma mastitis.The pathology of the chronically infected quarters consisted of alveolar involution and moderate to severe mononuclear infiltration and an increase in interalveolar and loose connective tissue. The quarters of one cow resolving the infections at the time of slaughter were not as severely affected and contained numerous milk-producing alveoli and many alveoli with hyperplasia of the alveolar cells.  相似文献   
742.
The clinical findings from 30 cases of feline poxvirus infection in the UK are reviewed and some epidemiological observations described and discussed. In most cases the clinical signs consisted of skin lesions only, although systemic signs were also occasionally seen. Over half the cats had a history of a single recent lesion, assumed to be primary, on the head, neck or a forelimb. Twenty-nine of 30 cats developed more widespread secondary skin lesions. Cat-to-cat transmission was apparently rare. More cases were recognised in the autumn than at other times of the year. The possibility of a wild mammal reservoir of infection is discussed.  相似文献   
743.
Calf mortality data were summarized from four experiments, including a total of 15,694 birth records over 39 herd-years. Two experiments at Waikite and Waikeria were long-term, straightbred Angus and Hereford selection trials and the other two, at Goudies and Tokanui stations, were comparisons of 11 sire breeds mated to Angus and Herefore cows. The objective of the analyses was to study the relationship between birth weight (BW) and calf mortality for both calf sexes and for different dam age or parity groups. Overall calf death rates from birth to weaning were greater (P less than .01) from 2-yr-old than from older dams at Waikite (13.4 vs 5.3%) and Waikeria (14.7 vs 5.2%). Sex differences in death rate within 2 d of birth were small for calves from older dams. Death rate of males vs females from 2-yr-old dams were 9.1 vs 3.2% (Waikite) and 17.7 vs 10.5% (Waikeria). Mature Angus dams at Goudies had 3.7% calf deaths at birth (4.9 vs 2.4% for males vs females), a further 1.8% calf deaths to weaning and 4.6% assisted births. The BW of calves at Waikite from Angus 2-yr-old vs older dams averaged, respectively, 6.8 and 6.5% of their dam's precalving live weights. Corresponding figures for Waikeria Angus were 7.8 and 6.6% and for Waikite Herefords, 7.3 and 6.9%. Quadratic regressions revealed that, on a whole-herd basis, a small increase in BW would have no effect on total mortality at Waikeria and would decrease total mortality at Waikite; regression lines were different in shape and minimum value for calves from the two dam age groups. Quadratic models also provided an adequate fit to data from Goudies and Tokanui. There was no particular threshold BW.  相似文献   
744.
Mycoplasma alkalescens-induced arthritis in dairy calves   总被引:1,自引:0,他引:1  
Mycoplasma alkalescens was isolated from 6 of 7 synovial fluid samples taken by arthrocentesis from 3-week- to 4-month-old Holstein-Friesian calves with severe arthritis (tibiotarsal or carpal joints). Approximately 30 of 215 calves in the herd were affected. In one 6-week-old calf, M alkalescens was isolated from the liver, right tibiotarsal joint, right and left popliteal lymph nodes, and an exposed umbilical artery. Intraarticular inoculations of broth cultures of M alkalescens initially induced a febrile response and then severe fibrinopurulent arthritis. Intravenous inoculation of M alkalescens induced only a febrile response. The natural disease may have been a complication of umbilical exposure to M alkalescens, causing omphaloarteritis and subsequent arthritis. Before and during the arthritis problem, the umbilicus of newborn calves was dipped in an organic iodine product with 10% glycerin, marketed as a postmilking teat dip. After the cause of the arthritis was determined, the umbilicus of each newborn calf was treated with 7% tincture of iodine and no new cases of arthritis occurred.  相似文献   
745.
This study explored possible identification of Perpetration-induced Traumatic Stress (PITS) in workers whose occupations required euthanizing nonhuman animals and determining whether event or person-related factors influenced symptoms. The sample included 148 animal workers: veterinarians, veterinary nurses, and research and animal shelter staff. The Impact of Event Scale-Revised (IES-R) assessed traumatic stress. Experimenters constructed additional scales measuring satisfaction with social support, participation in various types of training, and concern over animal death. More than 70% of participants reported affinity toward animals had strongly influenced their occupation selection. Half the sample perceived animal death--particularly euthanasia--as one of the least desirable jobs. Of the sample, 11% reported experiencing moderate levels of traumatic symptoms. The study found lower levels of euthanasia-related stress were associated with increased satisfaction with social support and length of time working with animals. Those who reported high levels of concern about animal death reported higher levels of euthanasia-related stress. The study found occupational context was not associated with different levels of euthanasia-related stress symptoms--even though reasons for administering euthanasia differed significantly between occupations.  相似文献   
746.
There is limited genetic information relating calving difficulty and body weights to other productive and reproductive traits. Such information is useful for specifying selection criteria and for predicting economic consequences of selection. Genetic, maternal, and environmental covariances of six productive and reproductive measurements with calving difficulty, birth weight, 200-d weight, and 168-d postweaning gain were estimated in 12 experimental populations of cattle. Calf (direct) genetic effects resulting in longer gestation length were associated with increased calving difficulty and birth weight. Maternal genetic effects of increased gestation length and heavier birth weight were significantly associated. Lighter birth weight and reduced calving difficulty were associated with earlier heifer age at puberty. Increases in direct genetic effects of calving difficulty, 200-d weight, and postweaning gain were associated with a small increase in direct effect of scrotal circumference. Increased direct genetic effects of scrotal circumference were correlated with maternal effects decreasing calving difficulty and increasing 200-d weight. Direct effects of the skeletal measurements, yearling hip height, and heifer pelvic area were positively correlated with direct effects of calving difficulty, birth weight, 200-d weight, and postweaning gain, positively correlated with maternal effects for birth weight and 200-d weight, and negatively correlated with maternal calving difficulty. Percentage of retail product was positively associated with calving difficulty and negatively associated with 168-d gain. Predicted genetic change in calving difficulty resulting from one standard deviation of selection for either calving difficulty score or birth weight was much larger than for any other traits. Selection for 200-d weight, 168-d postweaning gain, hip height, pelvic area, or scrotal circumference was predicted to have opposite effects on direct and maternal calving difficulty. Estimated genetic correlations indicate some small to moderate relationships between calving difficulty and the measured productive and reproductive traits. However, selection for reduced calving difficulty should be based on calving difficulty score and(or) birth weight because of their superiority in predicted genetic change.  相似文献   
747.
OBJECTIVE: To compare detomidine hydrochloride and romifidine as premedicants in horses undergoing elective surgery. ANIMALS: 100 client-owned horses. PROCEDURE: After administration of acepromazine (0.03 mg/kg, IV), 50 horses received detomidine hydrochloride (0.02 mg/kg of body weight, IV) and 50 received romifidine (0.1 mg/kg, IV) before induction and maintenance of anesthesia with ketamine hydrochloride (2 mg/kg) and halothane, respectively. Arterial blood pressure and blood gases, ECG, and heart and respiratory rates were recorded. Induction and recovery were timed and graded. RESULTS: Mean (+/- SD) duration of anesthesia for all horses was 104 +/- 28 minutes. Significant differences in induction and recovery times or grades were not detected between groups. Mean arterial blood pressure (MABP) decreased in both groups 30 minutes after induction, compared with values at 10 minutes. From 40 to 70 minutes after induction, MABP was significantly higher in detomidine-treated horses, compared with romifidine-treated horses, although more romifidine-treated horses received dobutamine infusions. In all horses, mean respiratory rate ranged from 9 to 11 breaths/min, PaO2 from 200 to 300 mm Hg, PaCO2 from 59 to 67 mm Hg, arterial pH from 7.33 to 7.29, and heart rate from 30 to 33 beats/min, with no significant differences between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Detomidine and romifidine were both satisfactory premedicants. Romifidine led to more severe hypotension than detomidine, despite administration of dobutamine to more romifidine-treated horses. Both detomidine and romifidine are acceptable alpha2-adrenoceptor agonists for use as premedicants before general anesthesia in horses; however, detomidine may be preferable when maintenance of blood pressure is particularly important.  相似文献   
748.
749.
This study describes the ultrasonographic and cytopathological characteristics of malignant neoplasms of the exocrine pancreas and their value in making an antemortem diagnosis. The medical records of eight dogs and five cats were reviewed. The clinical presentations were variable and at times mimicked pancreatitis. Overall, cytopathology of ultrasound or fluoroscopic-guided biopsies or fine-needle aspirates, or impressions from surgical biopsies were helpful in establishing the diagnosis in 10 of 12 animals where it was performed. Histopathology of ultrasound or fluoroscopic-guided biopsies provided a diagnosis in five of six cases where it was performed.  相似文献   
750.
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