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   124130篇
  免费   7142篇
  国内免费   802篇
林业   5477篇
农学   3745篇
基础科学   862篇
  14671篇
综合类   24958篇
农作物   4650篇
水产渔业   5654篇
畜牧兽医   63008篇
园艺   1609篇
植物保护   7440篇
  2019年   1343篇
  2018年   1875篇
  2017年   2107篇
  2016年   1890篇
  2015年   1781篇
  2014年   2055篇
  2013年   4354篇
  2012年   3999篇
  2011年   4790篇
  2010年   3154篇
  2009年   3118篇
  2008年   4391篇
  2007年   4318篇
  2006年   3949篇
  2005年   3776篇
  2004年   3436篇
  2003年   3480篇
  2002年   3280篇
  2001年   3668篇
  2000年   3675篇
  1999年   2909篇
  1998年   1167篇
  1997年   1107篇
  1996年   1046篇
  1995年   1190篇
  1994年   1062篇
  1993年   1074篇
  1992年   2241篇
  1991年   2459篇
  1990年   2355篇
  1989年   2300篇
  1988年   2171篇
  1987年   2264篇
  1986年   2267篇
  1985年   2129篇
  1984年   1783篇
  1983年   1554篇
  1982年   1048篇
  1979年   1593篇
  1978年   1302篇
  1977年   1087篇
  1976年   1116篇
  1975年   1167篇
  1974年   1607篇
  1973年   1488篇
  1972年   1533篇
  1971年   1454篇
  1970年   1346篇
  1969年   1290篇
  1967年   1141篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Subgroup-specific peptide-based enzyme-linked immunosorbent assays from the G-protein of the ovine and bovine respiratory syncytial virus (RSV), respectively, were used to determine the prevalence of the ovine and bovine subgroup strains of RSV infections in cattle. A total of 1,102 bovine serum samples were obtained from 6 diagnostic laboratories located in the northwestern and the southeastern USA and were tested for antibody to either the bovine or ovine subgroups of RSV. Antibody to viruses from each subgroup was present in samples from each region and all states tested. The Southeast had a higher prevalence of the bovine subgroup strains (69.5%). Then did the Northwest (40.9%). The prevalence of the ovine strain was similar for the two regions (16.7% in the southeast, 14.9% in the northwest). The overall prevalence was 56.6% for the bovine strain and 15.9% for the ovine strain. These results suggest members of the ovine subgroup of RSV circulate in the cattle population but with less frequency than those viruses of the bovine subgroup.  相似文献   
52.
Hege  Kippenes  DVM  Patrick R.  Gavin  DVM  PhD  Susan L.  Kraft  DVM  PhD  Ronald D.  Sande  DVM  MS  PhD  Russell L.  Tucker  DVM 《Veterinary radiology & ultrasound》2001,42(2):130-133
The pituitary gland was measured from transverse magnetic resonance T1-weighted images after Gadolinium administration in 96 dogs weighing from 13 to 45 kg. The measurements were done by hand with calipers. The mean (+/- standard deviation) pituitary gland height was 5.1 mm (+/-0.9 mm). The mean width was 6.4 mm (+/- 1.1 mm). The correlation coefficient between pituitary and brain measurements, between pituitary measurement and body weight, and brain measurements and body weight was 0.0 to 0.3. A hyperintense region was present on T1-weighted images in the center of the pituitary gland in 64% of the dogs. At necropsy the pituitary glands were grossly and histologically normal. No pituitary gland measurements were performed at necropsy.  相似文献   
53.
54.
55.
The medical records of 38 horses with puncture wounds of the navicular bursa were reviewed. Only 12 horses had a satisfactory outcome (breeding or riding). Of the remaining 26 horses, 19 were euthanized, five were sold due to persistent severe lameness, one died, and one was lost to long-term follow-up. Different combinations of conservative management prior to surgical debridement and drainage of the navicular bursa were unsuccessful in resolving the condition. Horses that were treated surgically within 1 week of the injury and had a hind leg affected had the best chance of a satisfactory outcome. Additional wound debridement was necessary in 15 horses after initial surgical treatment. The most common complications encountered were navicular bone osteomyelitis and sepsis of the deep digital flexor tendon. Thirteen of 14 horses that had rupture of the deep digital flexor tendon and subluxation of the distal interphalangeal joint had an unsatisfactory outcome. One mare subsequently developed ankylosis of the distal interphalangeal joint and was a useful brood mare. Two horses that had biaxial palmar digital neurectomy because of persistent lameness were later euthanized because of navicular bone fracture and rupture of the deep digital flexor tendon. Results from limited numbers of bacterial cultures and antibiotic sensitivities suggest that penicillin and an aminoglycoside antibiotic should be used as initial antibiotic therapy. Immediate surgical debridement and appropriate antibiotic treatment are recommended as the minimum therapy for penetrating wounds of the navicular bursa in horses.  相似文献   
56.
57.
58.
59.
60.
以传统栽培为对照,研究畦式好气栽培对水稻根系、群体消长、产量构成因素及产量的影响。结果表明,畦式好气栽培显著提高了整个生育期水稻根系的生物量,与传统栽培相比,增幅达5.46%-11.18%;显著增加了抽穗后10cm以下土层的根系比例和根系活力,提高了根冠比,促进了水稻分蘖的发生,显著提高了水稻有效穗数、结实率和产量,每公顷可比传统栽培增产稻谷637.5kg,增产9.48%。  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