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   832篇
  免费   46篇
林业   9篇
农学   13篇
基础科学   4篇
  82篇
综合类   132篇
农作物   31篇
水产渔业   31篇
畜牧兽医   538篇
园艺   15篇
植物保护   23篇
  2023年   8篇
  2021年   6篇
  2020年   11篇
  2019年   9篇
  2018年   6篇
  2017年   7篇
  2016年   6篇
  2015年   8篇
  2014年   13篇
  2013年   41篇
  2012年   27篇
  2011年   24篇
  2010年   34篇
  2009年   17篇
  2008年   33篇
  2007年   38篇
  2006年   25篇
  2005年   22篇
  2004年   34篇
  2003年   35篇
  2002年   40篇
  2001年   24篇
  2000年   27篇
  1999年   20篇
  1998年   8篇
  1997年   7篇
  1996年   20篇
  1995年   8篇
  1993年   9篇
  1992年   16篇
  1991年   14篇
  1990年   23篇
  1989年   15篇
  1988年   14篇
  1987年   16篇
  1986年   11篇
  1985年   11篇
  1984年   6篇
  1982年   9篇
  1981年   9篇
  1974年   8篇
  1972年   11篇
  1971年   11篇
  1970年   8篇
  1968年   6篇
  1967年   6篇
  1966年   7篇
  1965年   6篇
  1961年   5篇
  1946年   9篇
排序方式: 共有878条查询结果,搜索用时 15 毫秒
101.
This case history describes a fatal complication of cardiac catheterization in a dog. A 2-year-old intact female miniature Schnauzer presented with a one month history of coughing, tachypnea, and dyspnea that was unresponsive to medical therapy. On clinical examination, a 4/6 systolic murmur was auscultated over the left and right fourth intercostal spaces. Lung sounds were diffusely increased. Survey radiographs revealed cardiomegaly and pulmonary edema. Cardiac catheterization was undertaken to clarify the cause of congestive cardiac failure but was abandoned when contrast medium was seen in the pericardial sac following an attempted injection of the contrast medium into the left ventricle. During recovery from anesthesia progressive pallor, hemothorax, and respiratory distress developed. The dog died 10 hours later despite aggressive support therapy. Gross necropsy revealed hemorrhage into the pericardial sac and pleural space, thrombus formation around and perforation of the right coronary artery.  相似文献   
102.
103.
This study describes the pharmacokinetics of intravenous hydromorphone in cats and the simultaneous measurement of antinociceptive pharmacodynamic effects using a thermal threshold testing system. Following establishment of a baseline thermal threshold, six adult cats were administered 0.1 mg/kg of hydromorphone intravenously. Thermal threshold testing and blood collection were conducted simultaneously at predetermined time points. Plasma hydromorphone concentrations were determined by a liquid chromatographic-mass spectral method and pharmacokinetic analysis was performed by nonlinear least squares regression analysis. Plasma hydromorphone concentrations declined rapidly over time, and were below the limit of quantification of the assay (LOQ = 1.0 ng/mL) by 360 min. In contrast, thermal thresholds rose from a pretreatment value of 40.9 +/- 0.65 degrees C (mean +/- SEM) to instrument cut-out (55 degrees C) within 15 min and remained significantly elevated from 15-450 min after treatment. Inspection of the data revealed no direct correlation between plasma hydromorphone concentrations and the antinociceptive effect of this drug in cats. These findings support the importance of conducting pharmacokinetic studies in parallel with objective measurements of drug effect.  相似文献   
104.
Cochlosoma anatis is a flagellated intestinal parasite that infects a variety of avian species. C. anatis infections have been associated with decreased weight gain and increased morbidity and mortality. Conditions favoring the growth of this organism in birds are current pathogenic intestinal infections and/or young age. There is little data describing the life cycle of this parasite. In this study, electron microscopy images are presented that document longitudinal binary fission of the trophozoite stage and outline the events of pseudocyst formation, which includes a rounding stage. Evidence provided here indicates that the pseudocyst stage may be a mechanism for transmission of this organism. The observations reported here provide additional evidence of homology between Cochlosoma and members of the trichomonad order.  相似文献   
105.
Faecal samples were collected from 1,190 wild cervids in Norway and analyzed for cysts/oocysts of the protozoan parasites Giardia and Cryptosporidium. Samples were from calves, yearlings and adults of moose (Alces alces), red deer (Cervus elaphus), roe deer (Capreolus capreolus) and reindeer (Rangifer tarandus) shot during the hunting season. Cryptosporidium was found in 15 (3.3%) of 455 moose, 1 (0.3%) of 289 red deer, 18 (6.2%) of 291 roe deer, but was not found in any of 155 reindeer. Giardia was found in 56 (12.3%) moose, 5 (1.7%) red deer, 45 (15.5%) roe deer and 11 (7.1%) reindeer. The calves had the highest prevalence of infection, but this was only statistically significant for Giardia in moose and for Cryptosporidium and Giardia in roe deer. Calves generally had the highest intensity of infection, but this difference was only statistically significant for calves with Giarda and the highest intensity of infection. Both Giardia and Cryptosporidium were found in samples from several geographical areas, indicating that these parasites are distributed among the cervid population in all parts of Norway, especially in moose and roe deer. This is the first published report of Cryptosporidium in moose and of Giardia in reindeer.  相似文献   
106.
OBJECTIVE: To determine the prevalence of postanesthetic hyperthermia [rectal temperature >40 degrees C (104 degrees F)] in a clinical population of cats. STUDY DESIGN: Retrospective study. ANIMAL POPULATION: One hundred and twenty-five cats with an age range of 2 months to 16.1 years, and weighing 3.9 +/- 1.5 kg. MATERIALS AND METHODS: Data were obtained from the medical records of 125 cats that underwent general anesthesia. Information on perioperative rectal temperatures, breed, sex, weight, surgical procedure, anesthetic time, surgery time, anesthetic and analgesic drugs were retrieved. STATISTICAL ANALYSES: Five groups of cats were compared; group 1 (n = 15) received acepromazine and no opioids; group 2 (n = 17) received acepromazine and buprenorphine; group 3 (n = 19) received acepromazine, buprenorphine and ketoprofen; group 4 (n = 45) received acepromazine and hydromorphone and group 5 (n = 29) received acepromazine, hydromorphone and ketoprofen. Data conformed to a split-plot repeated measures analysis of variance and was analyzed using SAS PROC MIXED. Post hoc tests were by means of Bonferroni t-test; < or = 0.05 was considered significant. RESULTS: Rectal temperature was significantly decreased in all groups at the end of anesthesia. Rectal temperature was significantly elevated at 1, 1.5, 2, 3, 4 and 5 hours after the end of anesthesia in group 4, and at 2, 3 and 4 hours in group 5. Sixty-four percent of cats in group 4 and 69% in group 5 had rectal temperatures >40 degrees C (104 degrees F) at one or more times in the postanesthetic period. The highest temperature recorded was 42.5 degrees C (108.5 degrees F) in one cat in group 4. Mean rectal temperature did not exceed the preoperative temperature at any time during the postanesthetic period in group 1, 2 and 3 animals. CONCLUSIONS: This study indicates an association between hyperthermia and perioperative administration of hydromorphone in cats. CLINICAL RELEVANCE: When hydromorphone is used in cats their body temperature should be closely monitored.  相似文献   
107.
The ability to switch the coupling between quantum bits (qubits) on and off is essential for implementing many quantum-computing algorithms. We demonstrated such control with two flux qubits coupled together through their mutual inductances and through the dc superconducting quantum interference device (SQUID) that reads out their magnetic flux states. A bias current applied to the SQUID in the zero-voltage state induced a change in the dynamic inductance, reducing the coupling energy controllably to zero and reversing its sign.  相似文献   
108.
Functional CpG methylation system in a social insect   总被引:1,自引:0,他引:1  
DNA methylation systems are well characterized in vertebrates, but methylation in Drosophila melanogaster and other invertebrates remains controversial. Using the recently sequenced honey bee genome, we present a bioinformatic, molecular, and biochemical characterization of a functional DNA methylation system in an insect. We report on catalytically active orthologs of the vertebrate DNA methyltransferases Dnmt1 and Dnmt3a and b, two isoforms that contain a methyl-DNA binding domain, genomic 5-methyl-deoxycytosine, and CpG-methylated genes. The honey bee provides an opportunity to study the roles of methylation in social contexts.  相似文献   
109.
OBJECTIVE: To evaluate the clinico-pathological findings, response to treatment and prevalence of complications in dogs with primary hypoparathyroidism. DESIGN: Retrospective study of 17 dogs presenting to the University of Melbourne Veterinary Clinical Centre and Murdoch University Veterinary Hospital over a 15 year period (1990 to 2004). Case records were evaluated for signalment, body weight, diet type, historical and clinical findings, serum total calcium, phosphate, albumin and parathyroid hormone concentrations, urinary fractional excretion ratios of calcium and phosphate, electrocardiogram (ECG) results, treatments administered, outcome and period of follow-up. RESULTS: The most common breeds identified were St Bernard (three dogs), Chihuahua (two dogs), German Shepherd (two dogs) and Jack Russell Terrier (two dogs). Three dogs were cross bred. Seizures, muscle tremors and fasciculations, stiff gait, tetany, muscle cramping, behavioural change and hyperventilation were the most common clinical signs. Vomiting, inappetence, diarrhoea, abdominal pain, hyperthermia, facial pruritus, ataxia, weakness, cataracts, and circling also occurred with less frequency. The mean duration of observed clinical signs preceding diagnosis was 33 days (median 13 days, range 1 to 173 days). All dogs had marked hypocalcaemia with normal or mildly increased serum albumin concentrations. Mean phosphate concentrations were significantly higher in inappetent dogs (P = 0.049). Mean serum calcium concentrations were significantly lower in dogs with cataracts compared to those without (P = 0.046). There were no other significant relationships between serum calcium or phosphate concentrations and the clinical presentation or outcome. No significant correlations were identified between the presence of a particular clinical sign and the duration of clinical signs. ECGs were obtained in four dogs and all exhibited QT interval prolongation due to a ST-segment prolongation. Sixteen of 17 dogs were treated successfully for hypocalcaemia and discharged from hospital. Acute management included parenteral calcium gluconate (10 dogs) and intravenous anticonvulsants (five dogs). Chronic therapy included oral vitamin D analogues and calcium supplementation. Treatment complications occurred in two dogs and included acute renal failure (one dog) and iatrogenic tissue necrosis following subcutaneous calcium administration (one dog). The mean follow-up period was 14.5 months (median 13 months, range 0 to 39 months). Twelve dogs were alive at the last follow up and two dogs were euthanased for unrelated reasons. The type of vitamin D analogue used was not associated with outcome. CONCLUSION: Primary hypoparathyroidism was an uncommon diagnosis in dogs. Saint Bernards, cross bred dogs, German Shepherd dogs and Terrier breeds were most commonly affected. Neurological signs were the most common presenting clinical signs, although alimentary signs may have been more common than previously reported. Dogs with primary hypoparathyroidism appeared to have a good prognosis following initiation of calcium supplementation and vitamin D therapy. Complications of treatment were uncommon and could be minimised with regular monitoring.  相似文献   
110.
Serological and clinical studies were conducted between March 2009 and August 2010 to validate the foot-and-mouth disease free status of Tsirang district of Bhutan as determined by the country's passive surveillance system. Randomised (first survey) and targeted (third survey) samplings, with subsequent follow-up samplings (second and fourth), were conducted on FMD-susceptible animals to detect the disease at a design prevalence of 25% and 20% at the individual animal-level and village-level, respectively. Sera from cattle, goats, pigs, and sheep were tested for the presence of non-structural protein (NSP) antibodies using two commercial (PrioCHECK(?) FMDV NS and CHEKIT(?)-FMD-3ABC-bo-ov) and one in-house NSP kit (c-ELISA, AAHL, Australia). The overall seropositivity (all species) at the animal-level was 3% (95% CI: 1.7, 4.8) and 3.5% (95% CI: 2.1, 5.4), for the randomised and targeted surveys, respectively. Except for one goat from the first survey, none of the small ruminants and pigs had NSP antibodies. The seropositives from the first and targeted surveys were distributed among 13 and 16 of 20 villages sampled, respectively. All repeat testing from the initial seropositive animals and their herd mates, for both the first and third surveys, were negative in the NSP tests 6-8 months later. Using the hypergeometric exact probability formula for two-stage analyses, the results enabled rejection of the null hypothesis and supported conclusion that the population was free from disease at the minimum expected prevalence of 20% at the 95.53% and 99.46% confidence levels, for the randomised and targeted surveys, respectively. Clinical surveillance also showed absence of disease or clinical signs suggestive of FMD. The few seropositives were likely to be false positives due to factors such as imperfect specificities of the tests and possible NSP-residues in the vaccines. The study has paved the way for initiation of zoning approaches for the progressive control of FMD in Bhutan.  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