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   287862篇
  免费   16251篇
  国内免费   662篇
林业   24081篇
农学   14095篇
基础科学   2984篇
  44552篇
综合类   34848篇
农作物   17358篇
水产渔业   17376篇
畜牧兽医   118634篇
园艺   6384篇
植物保护   24463篇
  2020年   2876篇
  2019年   3683篇
  2018年   4115篇
  2017年   4526篇
  2016年   4851篇
  2015年   4386篇
  2014年   5726篇
  2013年   16337篇
  2012年   6922篇
  2011年   9065篇
  2010年   7654篇
  2009年   8115篇
  2008年   8460篇
  2007年   7493篇
  2006年   7970篇
  2005年   7218篇
  2004年   7164篇
  2003年   6878篇
  2002年   6209篇
  2001年   7504篇
  2000年   7274篇
  1999年   6385篇
  1998年   4285篇
  1997年   4327篇
  1996年   4077篇
  1995年   4748篇
  1994年   4171篇
  1993年   3845篇
  1992年   5363篇
  1991年   5635篇
  1990年   5342篇
  1989年   5250篇
  1988年   4734篇
  1987年   4854篇
  1986年   4861篇
  1985年   5012篇
  1984年   4478篇
  1983年   4195篇
  1982年   3233篇
  1981年   3105篇
  1980年   3044篇
  1979年   3894篇
  1978年   3421篇
  1977年   3010篇
  1976年   2893篇
  1975年   2802篇
  1974年   3202篇
  1973年   3225篇
  1972年   2974篇
  1971年   2888篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
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   
112.
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   
113.
114.
115.
    
Ohne Zusammenfassung  相似文献   
116.
117.
118.
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   
119.
Thirteen mixed-breed beef bulls, 1 to 4 years old, were used to determine the effect of live and dead filarial nematodes, Setaria labiatopapillosa, placed in the vaginal cavity of the testes. When dead worms were used, granulomatous lesions developed on the tunica vaginalis parietalis in 7 of 8 testes. The lesions were similar to those seen in some clinical cases of periorchitis. Similar lesions developed in 5 of 6 testes after live worms were implanted in the vaginal cavity of the testes and tetramisole (8 mg/kg) was injected subcutaneously 6 days after implantation. When live worms were implanted and tetramisole was not given, lesions developed in 3 of 6 testes. It was concluded that the granulomatous reaction was a local response to dead or killed S labiatopapillosa.  相似文献   
120.
GRAY  S. J.; PRICE  COLIN 《Forestry》1990,63(2):161-175
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints.  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