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   125篇
  免费   16篇
  国内免费   1篇
综合类   14篇
农作物   1篇
畜牧兽医   123篇
植物保护   4篇
  2023年   1篇
  2020年   3篇
  2019年   2篇
  2018年   5篇
  2017年   4篇
  2016年   8篇
  2015年   5篇
  2014年   5篇
  2013年   13篇
  2012年   1篇
  2011年   1篇
  2010年   3篇
  2009年   14篇
  2008年   3篇
  2007年   2篇
  2006年   6篇
  2005年   3篇
  2004年   5篇
  2003年   2篇
  2002年   1篇
  1999年   2篇
  1998年   8篇
  1997年   9篇
  1996年   4篇
  1995年   3篇
  1994年   1篇
  1993年   5篇
  1992年   2篇
  1991年   6篇
  1990年   5篇
  1989年   4篇
  1988年   4篇
  1987年   1篇
  1971年   1篇
排序方式: 共有142条查询结果,搜索用时 171 毫秒
91.
Objective   Evaluate the sensitivity and specificity of transrectal ultrasound and transcutaneous ultrasonography across the right flank between days 31 and 196 of pregnancy in the dairy cow.
Procedure   Pregnancy status and stage of gestation at date of pregnancy diagnosis by transcutaneous and transrectal ultrasonography were determined for 1570 dairy cattle. Sensitivity and specificity values and probabilities of a correct diagnosis for both techniques were determined and compared. Possible effects of gestational age, herd, method of transcutaneous ultrasound diagnosis, cow age, cow and bull breed, and calf sex on the determination of a correct diagnosis of pregnancy status were evaluated for both techniques.
Results   The overall sensitivity and probability of a correct diagnosis of pregnancy status from days 31 to 196 of gestation were significantly higher when using transrectal ultrasound relative to transcutaneous ultrasound over the right flank. However, the sensitivity of transcutaneous ultrasound changed over the course of pregnancy: it was low (7–8%) before day 84, increased to 89% between days 141 and 154, and was close to 100% thereafter. The specificity of both methods did not differ significantly. Herd and gestational age at date of pregnancy diagnosis were significantly associated with making a correct test result using transcutaneous ultrasound, although only the latter predictor was significantly associated with making a correct test result using transrectal ultrasound.
Conclusion   Transcutaneous ultrasound can not be recommended as an accurate method for early pregnancy diagnosis in the dairy cow, particularly on a whole-herd basis. However, if pregnancy testing is undertaken in mid to late gestation, this technique could provide an accurate and rapid alternative to transrectal ultrasound or manual palpation per rectum.  相似文献   
92.
Objective   To determine bovine fetal characteristics significantly associated with increasing gestational age as measured via transcutaneous ultrasonography over the right flank.
Methods   The length of gestation at date of pregnancy diagnosis via transcutaneous and transrectal ultrasonography was determined for 224 dairy cattle by estimation from subsequent calving dates. A separate dataset was created for each measurable fetal characteristic (i.e. thoracic diameter, abdominal diameter, umbilical diameter, placentome length and placentome height) and risk factors significantly associated with gestational age at pregnancy diagnosis within each dataset, including the fetal characteristic, were identified.
Results   Abdominal diameter was the most frequently observed fetal characteristic and thoracic diameter was the least. Gestational age at pregnancy diagnosis (d) was significantly associated with fetal thoracic diameter (P < 0.01), abdominal diameter (P < 0.01) and umbilical diameter (P = 0.02) when measured via transcutaneous ultrasound. Within each model, sire breed, dam breed, dam age and/or calf sex were also significantly associated with gestational age. Gestational age at pregnancy diagnosis was not significantly associated with either placentome height or length (P > 0.05).
Conclusion   Fetal thoracic diameter, abdominal diameter and umbilical diameter were found to be significantly associated with gestational age between approximate days 73 to 190 of gestation. Transcutaneous ultrasonography may prove a useful method of estimating gestational age in the absence of accurate breeding records.  相似文献   
93.
A three‐year‐old intact female Old English sheepdog was presented for evaluation of infertility. A uterine biopsy was performed during dioestrus, and the microscopic appearance was inconsistent with progesterone stimulation; the glands were sparse, simple and failed to show coiling, while the glandular epithelium was cuboidal instead of columnar. There was very little evidence of glandular activity. Due to the inappropriate appearance of the glands for the stage of the cycle, immunohistochemistry for progesterone receptors was performed. No progesterone receptor‐positive immunoreactivity was identified in the endometrial luminal epithelium, glandular epithelium or stroma. Weak intranuclear immunoreactivity was identified within the smooth muscle cells of the myometrium. The absence of progesterone receptors within the endometrial glands is the most likely explanation for the abnormal appearance of the endometrium and for this bitch's infertility. To our knowledge, this is the first report of endometrial progesterone receptor absence in a bitch.  相似文献   
94.
The green iguana, Iguana iguana, is used as a model in reptile anesthesia research because of its size, availability, and the body of knowledge characterizing its physiology. Arterial blood gas values in nonanesthetized green iguanas have not been determined because of the technical difficulty involved. Vascular access port (VAP) placement to facilitate blood sampling has been described in other species, but not lacertilians. This abstract describes the technique for placement of VAPs and the values for arterial blood gas parameters in seven 1 kg adult green iguanas. Using sterile technique, a 1.5 cm incision was made on the lateral side of the neck. Blunt dissection ventral to the external jugular vein revealed the internal and external carotid arteries near their bifurcation. The catheter was inserted into the internal carotid artery and then guided to the common carotid artery. The other end of the catheter was tunneled below the skin to a subcutaneous location, caudal‐dorsal to the iSPSilateral scapula. The skin was closed and the port was flushed twice a week with heparinized saline. Post‐operatively, the VAPs were well tolerated by the iguanas. Difficulties included port disconnection (n = 1), inability to aspirate blood after a few weeks (n = 2), and infection (n = 1). The iguanas were breathing room air prior to and during blood collection. From the five functional VAPs, the blood pH, PCO2, PO2, HCO3, and BE (measured at 37 °C) were 7.45 ± 0.06; 37.5 ± 7.0 mm Hg, 99.0 ±16.6 mm Hg, 25.4 ± 2.5 mmol L–1, and 1.5 ±2.4 mmol L–1 respectively (mean ± SD). VAPs can be successfully used to facilitate collection of arterial blood gas samples in green iguanas. These values are similar to those reported for most mammalian species. This technique should facilitate research in anesthesiology and respiratory physiology of iguanas and other lacertilians.  相似文献   
95.
96.
97.
AIMS: To develop an indirect ELISA based on recombinant nucleocapsid (rN) protein of wobbly possum disease (WPD) virus for investigation of the presence of WPD virus in Australian brushtail possums (Trichosurus vulpecula) in New Zealand.

METHODS: Pre- and post-infection sera (n=15 and 16, respectively) obtained from a previous experimental challenge study were used for ELISA development. Sera were characterised as positive or negative for antibody to WPD virus based on western-blot using WPD virus rN protein as antigen. An additional 215 archival serum samples, collected between 2000–2016 from five different regions of New Zealand, were also tested using the ELISA. Bayesian modelling of corrected optical density at 450?nm (OD450) results from the ELISA was used to obtain estimates of receiver operating characteristic (ROC) curves to establish cut-off values for the ELISA, and to estimate the prevalence of antibody to WPD virus.

RESULTS: Western blot analysis showed 5/14 (36%) pre-infection sera and 11/11 (100%) post-infection sera from experimentally infected possums were positive for antibodies to WPD virus. Bayesian estimates of the ROC curves established cut-off values of OD450≥0.41 for samples positive, and OD450<0.28 for samples negative for antibody to WPD virus, for sera diluted 1:100 for the ELISA. Based on the model, the estimated proportion of samples with antibodies to WPD virus was 0.30 (95% probability interval=0.196–0.418). Of the 230 archival serum samples tested using the ELISA, 48 (20.9%) were positive for antibody to WPD virus, 155 (67.4%) were negative and 27 (11.7%) equivocal, using the established cut-off values. The proportion of samples positive for WPD virus antibody differed between geographical regions (p<0.001).

CONCLUSION: The results suggested that WPD virus or a related virus has circulated among possums in New Zealand with differences in the proportion of antibody-positive samples from different geographical regions. Antibodies to WPD virus did not seem to protect possums from disease following experimental infection, as one third of possums from the previous challenge study showed evidence of pre-existing antibody at the time of challenge. These results provide further support for existence of different pathotypes of WPD virus, but the exact determinants of protection against WPD and epidemiology of infection in various regions of New Zealand remain to be established.

CLINICAL RELEVANCE: Availability of the indirect ELISA for detection of WPD virus antibody will facilitate prospective epidemiological investigation of WPD virus circulation in wild possum populations in New Zealand.  相似文献   
98.
AIMS: To investigate the pathophysiology of humeral fractures in first-lactation dairy heifers in the North Island of New Zealand.

METHODS: Ten 2-year-old dairy heifers with humeral fractures were subject to euthanasia and the fractured and non-fractured contralateral humeri were collected. Humeri were also collected from 10 unaffected 2-year-old dairy heifers sent for slaughter. Humeri from heifers with and without fractures were examined using computed tomography (CT), and four slices of the diaphysis and lower metaphysis (D1–4) were analysed using the Bone J plug-in for Image J. The humeri were sectioned sagittally and 5?mm bone slabs were processed for histopathology.

RESULTS: There were no differences in bone length between the humeri from heifers with or without fractures (p=0.31). Median cortical bone mineral density at D1 was increased in humeri from affected compared with unaffected heifers (810 vs. 783?mg/cm3; p=0.03), cortical area at D1 was reduced (816 vs. 1,037?mm2; p=0.04), the median stress strain index, a calculated theoretical measure of bone strength, at D1 was decreased (7,288 vs. 9,072?mm3; p<0.01), and the median ratio of overall bone volume (BV) to total volume (TV) was decreased (0.32 vs. 0.38; p<0.01). The median periosteal circumference at D1 was also reduced in humeri from affected compared with unaffected heifers (151 vs. 173?mm; p<0.01). Using a binary logistic regression model, BV/TV was the only variable associated with humeral fractures (p=0.03).In nine of 10 fractured humeri the fracture appeared to have started just distal to the head of the humerus and spiralled distally down the diaphysis to end just above the humeral condyles. Histopathological findings included a reduction in the number, and thickness, of trabeculae in the metaphysis; metaphyseal growth arrest lines, and osteoclastic resorption in fractured humeri. Concentrations of copper in serum from four of five animals with fractures were within, and one was below, normal reference ranges, while concentration of copper in the livers of three heifers with fractures were below adequate ranges.

CONCLUSIONS: The CT and histological findings were consistent with a diagnosis of osteoporosis. We propose that humeral fractures in dairy heifers are associated with osteoporosis, possibly as a result of insufficient deposition of bone during growth because of protein-calorie malnutrition. Increased osteoclastic resorption of bone associated with calcium mobilisation for lactation, and periods of copper deficiency may contribute to bone weakening.  相似文献   
99.
Many researches describe the embryonic developmental features in domestic animals; however, in farm animals, they are scarce. Most farm animal studies are related to assisted reproduction and embryos transfer techniques. But, morphological features and size measure to estimate the age gestation are rarely reported in literature. Thus, in this study, we described the developmental changes in the bubaline (Bubalus bubali) concepts from 21 to 60 days of gestation. Our results revealed that buffalo embryos similar morphological characteristics similar to other mammalian species. Also, similarities between bovine and bubaline persist; except on foetal stages when buffalos have a faster development than bovine. Therefore, buffalo's gestation period exhibits some varieties and accurate embryo age is more difficult. Yet, when we use a combination of the crown–rump, macroscopic analysis and alizarin red, it is possible to describe better the whole embryogenesis stages of the buffalo and which can contribute for future reproduction researches and applications in veterinary practice.  相似文献   
100.
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