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   596篇
  免费   35篇
林业   79篇
农学   5篇
基础科学   2篇
  39篇
综合类   103篇
农作物   9篇
水产渔业   29篇
畜牧兽医   353篇
园艺   2篇
植物保护   10篇
  2019年   6篇
  2018年   14篇
  2017年   8篇
  2016年   9篇
  2015年   7篇
  2014年   7篇
  2013年   22篇
  2012年   18篇
  2011年   13篇
  2010年   22篇
  2009年   26篇
  2008年   21篇
  2007年   13篇
  2006年   19篇
  2005年   8篇
  2004年   17篇
  2003年   17篇
  2002年   13篇
  2001年   20篇
  2000年   8篇
  1999年   12篇
  1998年   17篇
  1997年   9篇
  1996年   16篇
  1995年   6篇
  1993年   10篇
  1992年   22篇
  1991年   19篇
  1990年   19篇
  1989年   11篇
  1988年   14篇
  1987年   11篇
  1986年   13篇
  1985年   7篇
  1984年   11篇
  1983年   7篇
  1982年   5篇
  1976年   5篇
  1974年   4篇
  1973年   6篇
  1972年   6篇
  1916年   4篇
  1871年   4篇
  1869年   6篇
  1868年   7篇
  1867年   9篇
  1866年   5篇
  1864年   4篇
  1863年   8篇
  1859年   4篇
排序方式: 共有631条查询结果,搜索用时 12 毫秒
1.
2.
In mid-September, 1 month before the insertion of intravaginal pessaries to induce sexual activity, blood samples were collected every 4 days from 16 ewe lambs aged 7 months, in order to determine the incidence of ovulations by measurement of plasma progesterone concentrations. It has been studied whether the response to a progestagen treatment of ewe lambs apparently close to puberty could be modified by the onset of the ovarian events preceding puberty. The effect of the presence or absence of ovulations prior to progestagen treatment on the potential reproductive performance (fertility, litter size and fecundity), embryo development [embryo quality and interferon-tau (IFNτ) secretion], luteal function (progesterone secretion in vitro ) and endometrial progesterone content was studied in seven ovulating (Ov+) and nine nonovulating ewe lambs (Ov−) on day 14 after mating. The best potential reproductive results were obtained with Ov+ animals, although these differences could not be initially attributed to either different progesterone secretion in vitro or concentration of endometrial progesterone. Irrespective of the experimental groups, secretion of progesterone by luteal tissue from ewe lambs with normal embryos was significantly greater (p<0.05) than that of animals with abnormal embryos or with no embryos. Normal embryos secreted a higher amount of IFN-τ than those embryos classified as abnormal (p<0.07). In conclusion, ewe lambs which exhibit luteal activity before puberty have the highest levels of reproductive performances after a progestagen treatment. Corpora lutea from ewe lambs with normal embryos had higher rates of progesterone secretion in vitro and their embryos had a higher IFN-τ production by the embryos, indicating greater capacity for subsequent development.  相似文献   
3.
4.
仔猪断奶后腹泻在猪场的发生率很高,这使养猪生产者遭受了严重的经济损失。有机酸可导致胃内pH值下降,不利于致病菌生存。但由于致病菌的固有抵抗力,含有大量游离有机酸的混合物,与植物化学物质和渗透性物质(Biotronic Top3)的联合使用可以更有效地提高动物的生产性能和控制致病菌。  相似文献   
5.
6.
A 6-year-old female Alaska Malamute dog was presented for evaluation of abdominal enlargement referred by a local veterinarian. On the history, the owner complained of chronic abdominal enlargement initiated more than 4 months ago, reduced appetite, occasional vomiting and general dullness. He also complained of greenish mucous intermittent vaginal discharge starting 10 days ago. The bitch was chronically treated with medroxiprogesterone acetate. A laparatomy was performed and fluid in the abdomen was found and aspirated during the surgery. Also a very fluid-filled distended uterus and a mass in the distal part of the left uterine horn were found. The mass was encapsulated by the omentum, but areas of necrosis and calcification were identified. Histopathological diagnosis was endometrial adenocarcinoma.  相似文献   
7.
Objective To establish the prevalence of intussusceptions involving the caecum in a population of horses admitted to a university hospital for colic. Design Retrospective clinical study Methods Medical records of all horses admitted to the Massey University Veterinary Teaching Hospital between 1991 and 2004 were examined for information of those horses diagnosed with an intussusception involving the caecum. Results A total of 135 horses were admitted for colic surgery during the study period and 61 horses had a diagnosis of ileocaecal (37), caecocaecal (5) or caecocolic intussusception (19) made either at surgery or necropsy. Of the horses with ileocaecal intussusception, 32 had an incomplete hand-sewn ileocaecostomy without reduction and 29 survived to discharge. All the horses with caecocaecal intussusceptions were diagnosed preoperatively via rectal examination and/or transabdominal ultrasound: 2 were euthanased at surgery and 3 survived to discharge. In the 19 horses with caecocolic intussusceptions, manually reduction at surgery was performed in 6 and 5 of them survived to discharge. A typhlectomy was performed via a colotomy in 6 horses, 3 of which survived to discharge. Conclusions The high prevalence of intussusceptions involving the caecum seen at this referral centre may indicate a higher prevalence in New Zealand than is reported elsewhere in the world. Clinical relevance Intussusceptions involving the caecum should be considered as a differential diagnosis in horses presenting with chronic low-grade colic. Transabdominal ultrasound is useful for identifying caecocaecal and caecocolic intussusceptions. Hand-sewn side-to-side incomplete ileocaecostomy is a quick, effective and safe method of surgical treatment of ileocaecal intussusceptions.  相似文献   
8.
9.
10.
Otitic lesions must be evaluated in the context of the whole animal. Accurate historical and clinical assessments are important aids to the pathologist attempting to reach an accurate diagnosis. Primary lesions of the pinna, with or without involvement of the external ear canal, may be an extension of a more generalized dermatologic problem or may specifically involve the ear because of its unique gross and histologic characteristics.  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