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   173237篇
  免费   9614篇
  国内免费   823篇
林业   7620篇
农学   5370篇
基础科学   1328篇
  21491篇
综合类   33451篇
农作物   6876篇
水产渔业   8388篇
畜牧兽医   86272篇
园艺   2294篇
植物保护   10584篇
  2019年   1801篇
  2018年   2600篇
  2017年   2929篇
  2016年   2697篇
  2015年   2463篇
  2014年   2780篇
  2013年   6668篇
  2012年   5328篇
  2011年   6325篇
  2010年   4214篇
  2009年   4045篇
  2008年   5943篇
  2007年   5530篇
  2006年   5156篇
  2005年   4920篇
  2004年   4712篇
  2003年   4642篇
  2002年   4429篇
  2001年   5092篇
  2000年   5076篇
  1999年   3862篇
  1998年   1659篇
  1997年   1647篇
  1995年   1808篇
  1994年   1653篇
  1993年   1606篇
  1992年   3348篇
  1991年   3641篇
  1990年   3508篇
  1989年   3567篇
  1988年   3274篇
  1987年   3359篇
  1986年   3558篇
  1985年   3353篇
  1984年   2766篇
  1983年   2494篇
  1982年   1667篇
  1981年   1582篇
  1979年   2528篇
  1978年   2034篇
  1977年   1681篇
  1976年   1678篇
  1975年   1720篇
  1974年   2253篇
  1973年   2340篇
  1972年   2269篇
  1971年   2130篇
  1970年   1988篇
  1969年   1847篇
  1967年   1615篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
22.
23.
24.
25.
26.
A brief discussion of those aspects of neonatal physiology that pertain to anesthetic risk and selection of anesthetic techniques is followed by discussion of suggested techniques for anesthetic management in healthy foals. Preoperative preparation and management of foals with selected serious surgical conditions are also considered.  相似文献   
27.
Disseminated Aspergillus terreus infection was diagnosed in ten previously healthy adult dogs--nine German shepherds and one dalmatian. The disease was characterized by the presence of multiple granulomas and infarcts in a wide range of organs. The kidney, spleen, and skeletal system were most commonly and severely affected. Fungal hyphae were demonstrated in large numbers within granulomas and thrombi, and A. terreus was readily isolated by culture. This disseminated mycosis appears unique; in this series of cases there was no apparent predisposing factor, portal of entry, or primary focus for dissemination of the infection.  相似文献   
28.
The association of tumor-associated antigen (TAA) on the proliferation of BLV-infected lymphoblastoid B-cell lines (BL2M3 and BL312) was investigated. Flow cytometric analysis of the expression of TAA with monoclonal antibody (mAb) c143 showed high expression of TAA on the surfaces of BL2M3 and BL312 cells. A large amount of TAA was found in the culture supernatant of BL2M3 and BL312 cells as well as in the lysates of BL2M3 and BL312 cells. Culture supernatant but not lysates of BL2M3 and BL312 cells promoted the growth of either BL2M3 cells or BL312 cells. Furthermore, this growth promoting activity in culture supernatants of BL2M3 and BL312 cells was inhibited in a dose-dependent manner when cultured with mAb c143. These results suggested that TAA may be involved in the growth factor-mediated cell growth of bovine B-lymphoblastoid cell lines expressing TAA on their cell surface.  相似文献   
29.
The uterine and umbilical vessels of 12 pregnant ponies were catheterised to study foetal metabolism. The effects of this procedure on maternal and foetal cardiovascular, respiratory, metabolic and adrenocortical activity were monitored during and after surgery. Premedication with acepromazine-butorphanol-detomidine was followed by induction of anaesthesia with detomidine and ketamine and maintenance, using mechanical ventilation, with halothane in oxygen and nitrous oxide. Mean maternal arterial blood pressure was greater than 70 mmHg during anaesthesia and arterial oxygen tension remained over 100 mmHg. The foetuses were adequately oxygenated but were hypercapnic and lactic acidaemic. Most maternal and foetal blood gases and metabolites had returned to normal by 24 h, although foetal plasma lactate fell more slowly. The maternal adrenocortical discharge was less severe than reported previously and plasma cortisol had fallen to basal levels by 48 h after surgery. Foetal plasma cortisol remained low and did not change during or after surgery. Arterio-venous metabolite and gas tension differences across the uterine and umbilical circulations were slightly greater at operation than in the recovery period, suggesting that uteroplacental perfusion may have been impaired during surgery. Post-operative recovery of the mare and foetus was satisfactory and subsequent problems associated with the foetal catheters were not related to the anaesthesia or surgery.  相似文献   
30.
A technique is described for biopsy of the bovine udder, employing sedation and local anaesthesia. Tissue samples of approximately 5 g were obtained by electrocautery from two quarters of the udder of a cow laterally recumbent. Care was taken to ensure complete haemostasis which was achieved by electrocoagulation and ligation. Postoperative recovery was rapid, and loss of yield was no greater in biopsied glands than in control glands of the same cow. Yield from all quarters returned to preoperative levels within 48 h.  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