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   176808篇
  免费   9720篇
  国内免费   92篇
林业   7173篇
农学   5465篇
基础科学   1181篇
  23149篇
综合类   28576篇
农作物   6667篇
水产渔业   9090篇
畜牧兽医   90619篇
园艺   2189篇
植物保护   12511篇
  2018年   2732篇
  2017年   2964篇
  2016年   2793篇
  2015年   2271篇
  2014年   2822篇
  2013年   7258篇
  2012年   5186篇
  2011年   6241篇
  2010年   3959篇
  2009年   3887篇
  2008年   6026篇
  2007年   5743篇
  2006年   5397篇
  2005年   4933篇
  2004年   4781篇
  2003年   4715篇
  2002年   4531篇
  2001年   5308篇
  2000年   5105篇
  1999年   4150篇
  1998年   1671篇
  1997年   1667篇
  1995年   1928篇
  1994年   1731篇
  1993年   1678篇
  1992年   3463篇
  1991年   3579篇
  1990年   3637篇
  1989年   3620篇
  1988年   3277篇
  1987年   3395篇
  1986年   3486篇
  1985年   3316篇
  1984年   2838篇
  1983年   2510篇
  1982年   1735篇
  1981年   1628篇
  1979年   2708篇
  1978年   2194篇
  1977年   1928篇
  1976年   1825篇
  1975年   1954篇
  1974年   2476篇
  1973年   2466篇
  1972年   2399篇
  1971年   2099篇
  1970年   1997篇
  1969年   1943篇
  1968年   1606篇
  1967年   1703篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
981.
Colonic perforation after corticosteroid and surgical treatment of intervertebral disk disease in a dog Perforation of the distal segment of the descending colon, after corticosteroid and neurosurgical treatment for an intervertebral disk herniation, resulted in the death of a 3-year-old, male, Lhasa Apso. Initially, the dog was paraparetic in the hindlimbs, but became paraplegic after 4 days of conservative treatment. Corticosteroids were administered before referral and during decompressive hemilaminectomy. Six days after surgery, the dog had improved neurologically, but was depressed, anorectic, and vomiting. Abdominocentesis revealed septic peritonitis. The dog died shortly after a perforation in the descending colon was surgically corrected.  相似文献   
982.
983.
984.
985.
Field trials with a bivalent vaccine (HVT and SB-1) against Marek's disease   总被引:3,自引:0,他引:3  
White leghorn chickens on five farms were given a bivalent Marek's disease (MD) vaccine consisting of turkey herpesvirus (HVT) and SB-1 (a nononcogenic MD virus); other chickens received only HVT. The farms had histories of "vaccination failures," presumably owing to an exceptionally virulent challenge MD virus. The bivalent vaccine uniformly protected chickens better than HVT alone between 12 and 16-20 weeks of age, when serious MD losses occurred. During that period, total mortality in groups given both viruses ranged from 0.39 to 1.26% (mean 0.86%), whereas that in HVT-vaccinated groups not exposed to SB-1 varied from 1.92 to 7.44% (mean 3.43%). Chickens in pens or rows with close contact to those given bivalent vaccine also had low MD mortality rates (0.46-1.06%, mean 0.77%), probably from the spread of SB-1.  相似文献   
986.
1. Four rearing temperature regimes (15, 20, 25, 30 °C) and three feeding schedules (ad libitum, restricting to the ad libitum intake of the 12th week and feeding 70% of this rate) were carried out with layer replacement pullets to 170 d of age. From this age, during lay, birds were kept at either 21 °C or on a 24‐h cycle of 21 for 18 h and 28 °C for the 6 h before lights out. Both a white and a brown egg‐laying strain were used.

2. Body weight at 169 d of age varied from, on average, 1409 g (15 °C, ad libitum) to 943 g (30 °C, 70% schedule) for the white strain and 1947 to 1250 g for the same treatments respectively for the brown strain. Sexual maturity was considerably delayed by the 70% feeding schedule, only slightly by rearing at 30 °C.

3. Rearing at 30 °C tended to depress subsequent egg output. The 70% feeding schedule at least maintained egg output compared with birds fed ad libitum in rearing.

4. There was a highly significant effect of temperature treatment during lay on food intake. The reduction in food intake due to the 21–28 °C cycle, however, appeared small.  相似文献   

987.
In a study of susceptibilities of sows from 2 herds to experimentally induced Escherichia coli mastitis, a marked difference was seen. The "susceptible" sows were from a conventional herd and "resistant" sows were from a specific-pathogen-free herd. The purpose of the study was to determine whether deficient neutrophil function was associated with increased susceptibility to E coli-induced mastitis. Four in vitro procedures were used to evaluate polymorphonuclear leukocyte (PMN) function: (i) random migration under agarose, (ii) ingestion of 125I-iododeoxyuridine-labeled Staphylococcus aureus, (iii) quantitative nitroblue tetrazolium reduction, and (iv) iodination. After parturition and intramammary inoculation with E coli, sows from the susceptible herd were neutropenic and the neutrophils which were present in the peripheral blood had reduced function. Specifically, there were depressed random migration under agarose, S aureus ingestion, and iodination when compared with PMN function in resistant sows. These data indicate that susceptibility to E coli mastitis was associated with deficiencies in PMN numbers and function. Potential causes of the neutrophil dysfunction are discussed and include possible systemic hormonal aberrations or the presence of an inapparent viral or bacterial infection.  相似文献   
988.
1. A 31P topical magnetic resonance study of whole chicken's eggs in vivo is described.

2. Resonances from adenosine triphosphate, phosphocreatine, inorganic phosphate and phosphorous storage protein were observed. These changed in relative intensity as the embryo developed.

3. No ill effects due to exposure to radiofrequency radiation or magnetic fields were observed.

4. It is concluded that topical magnetic resonance can make a useful contribution to the study of embryonic development in avian eggs.  相似文献   

989.
1. The effect of feeding the detergent, sodium lauryl sulphate at concentrations up to 10 g/kg diet on egg‐shell quality was examined in laying hens at 24, 36 and 48 weeks of age.

2. Lauryl sulphate at 2.5 g/kg or more in the diet significantly increased shell breaking strength, shell thickness and shell weight at 24 and 36 weeks. In 48‐week‐old hens only shell breaking strength was increased significantly. Egg production and egg weight were not affected significantly by lauryl sulphate.

3. Lauryl sulphate might increase these measures of quality by increasing shell deposition and/or shell elasticity.  相似文献   

990.
Five horses were presented because of a dermatitis of the forehead. Unlike previous reports, ventral midline dermatitis was not the major problem, and was present in only two of five cases. All five horses responded to levamisole therapy at a daily dosage of 5.5 g for one week. Owners were cautioned that repeat therapy may be necessary.  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