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   150827篇
  免费   7499篇
  国内免费   91篇
林业   6397篇
农学   4328篇
基础科学   1027篇
  16228篇
综合类   31985篇
农作物   6037篇
水产渔业   6405篇
畜牧兽医   75605篇
园艺   1711篇
植物保护   8694篇
  2018年   1605篇
  2017年   1738篇
  2016年   1688篇
  2014年   1660篇
  2013年   5265篇
  2012年   3422篇
  2011年   4199篇
  2010年   2771篇
  2009年   2708篇
  2008年   4210篇
  2007年   3908篇
  2006年   3819篇
  2005年   3624篇
  2004年   3677篇
  2003年   3693篇
  2002年   3568篇
  2001年   4265篇
  2000年   4228篇
  1999年   3268篇
  1997年   1459篇
  1995年   1666篇
  1994年   1564篇
  1993年   1502篇
  1992年   3177篇
  1991年   3439篇
  1990年   3427篇
  1989年   3483篇
  1988年   3210篇
  1987年   3289篇
  1986年   3407篇
  1985年   3317篇
  1984年   2691篇
  1983年   2467篇
  1982年   1681篇
  1981年   1603篇
  1980年   1494篇
  1979年   2536篇
  1978年   2065篇
  1977年   1757篇
  1976年   1676篇
  1975年   1825篇
  1974年   2326篇
  1973年   2353篇
  1972年   2386篇
  1971年   2295篇
  1970年   2148篇
  1969年   1904篇
  1968年   1531篇
  1967年   1710篇
  1966年   1498篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Synovial hemangioma was diagnosed in an 8-year-old castrated male Belgian Sheepdog with lameness of 3 months' duration. Pain, soft-tissue swelling, and hemarthrosis were localized to the left stifle joint. Projections of synovial membrane with reddish-purple nodules, excised via arthrotomy, were composed histologically of variably sized vascular channels that were lined by well-differentiated endothelial cells and separated by fibrous septa. Distension of some channels resulted in endothelial disruption, thrombosis, hemorrhage, necrosis, and focal spindle-cell proliferation. The limb was amputated to remove remaining neoplastic tissue. The hemangioma extended focally into the joint capsule and popliteal soft tissue but did not invade skeletal muscle or bone. The dog was free of detectable neoplasia 6 months after amputation. Synovial hemangioma is a rare benign vascular proliferation in people, most commonly in the knee, and should be included in the differential diagnosis for canine synovial tumors.  相似文献   
992.
A technique of high-performance thin-layer chromatography (HPTLC plates) by which to identify the anabolic substance of trenbolone acetate (TBA) and its metabolite trenbolone is described in this paper. Plasma, bile, urine, faeces, liver, and meat can be used for testing. The sensitivity of the method is 1 ng. Additional reliability criteria are enumerated. Semiquantitative TBA determination has proved to be suitable in random sampling for residual analysis.  相似文献   
993.
Malignant catarrhal fever was induced in four groups of hamsters by the inoculation of cells infected with either the C/500 isolate of alcelaphine herpes-virus-1 (AHV-1) or the sheep-associated agent derived from cattle, red deer or Père David's deer. Using an indirect immunofluorescence assay, antibody to AHV-1 was detected in sera of clinically affected animals of all four groups. The reaction of sera from hamsters affected with malignant catarrhal fever induced by AHV-1 caused diffuse cytoplasmic staining while that from sera of hamsters with the sheep-associated form of the disease stained particulate nuclear antigens. Tests employing three other bovid herpesviruses were negative and no reaction was found with sera from normal hamsters. These studies provide convincing evidence that a virus antigenically related to AHV-1 is the cause of sheep-associated malignant catarrhal fever and that the same virus probably causes this form of the disease in both cattle and deer.  相似文献   
994.
Clinical experience of 73 cases of necrobacillosis in red-necked wallabies (Macropus rufogriseus) over a 6-year period is reviewed. Diagnostic methods and the medical and surgical treatment options are detailed. It is suggested that survival curves are necessary to assess the outcome of treatment.  相似文献   
995.
This study was designed to evaluate the ontogeny of serum IGF-I (SI) concentrations and its relationship to animal performance in a 140-d postweaning feeding trial. Ninety-eight progeny representing six sires (three high and three low feed conversion) and two sexes (43 bulls and 55 heifers) with ad libitum access to feed were allocated by sire and sex to monitor individual weights and pen feed consumption. Blood serum samples were obtained at the beginning of test (average age of 230 d) and every 28 d thereafter until each animal reached a fat thickness (estimated by sonoray) of 8.9 mm. Individual serum samples were acid-ethanol extracted and measured for IGF-I peptide by heterologous RIA. Serum IGF-I concentrations differed (P less than .10) between high (H) and low (L) feed conversion progeny groups at the end of the first 28-d period (125.12 vs 89.52 ng/ml) and tended to differ at the conclusion of the second 28-d period (P less than .15). Weight gains of H and L groups tended to differ in the second and third 28-d periods (P = .11 and .10, respectively). Serum IGF-I concentrations differed (P less than .05) between bulls and heifers for the first through fourth 28-d periods (P less than .01, P less than .05, P less than .10 and P less than .01, respectively). Phenotypic correlations indicated that pens with higher mean SI concentrations at the beginning of the test consumed less feed and had lower cumulative feed:gain ratios.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
996.
A procedure established for the selective isolation of the species of Streptococcus responsible for rainbow trout streptococcosis in South Africa, consisted of the inoculation of samples into nutrient broth which had been supplemented with 100 micrograms/ml of nalidixic acid, 160 micrograms/ml of oxolinic acid or 200 micrograms/ml of sodium azide. After incubation, the sample was plated onto tetrazolium agar on which the rainbow trout pathogenic Streptococcus species grew as a red colony. The colonies were isolated from the tetrazolium agar and identified as rainbow trout pathogenic isolates by biochemical and serological tests. In the laboratory the selective procedure is capable of detecting about 2 bacteria per ml. This procedure was used in the field and biochemically identical Streptococcus species were found in the mud and a freshwater crab from the water source of a site with a history of streptococcosis.  相似文献   
997.
998.
999.
1000.
The effect of colostrum on endocrine and metabolic factors affecting glucose homeostasis was evaluated in 60 neonatal pigs that were fasted, fed (nursed ad libitum) or limit-fed colostrum (25% ad libitum, 4-hr interval feeding). Plasma acquired at birth (t0), and after 10, 20 and 30 hr (t10, t20 and t30, respectively) was analyzed for glucose, non-esterified fatty acids (NEFA), and the glucoregulatory hormones--insulin, glucagon, cortisol, growth hormone and catecholamines. The concentration of glucose and NEFA was similar among treatment groups at birth and increased in proportion to the quantity of colostrum consumed. Pigs fed ad libitum achieved and maintained a higher (greater than or equal to 40%; P less than .01) glucose concentration when compared to fasted neonates. Limit-fed counterparts also achieved and maintained higher levels, with glucose concentration being approximately 20% higher throughout (P less than .05). Fed pigs maintained NEFA concentrations which were approximately 2.5-fold to 4-fold greater than that of fasted pigs (P less than .05). Likewise, limit-fed pigs tended (P = .19) to have elevated NEFA concentrations and a lower (P less than .05) insulin:glucagon molar ratio. An inverse relationship was observed between colostrum intake and plasma concentrations of cortisol and growth hormone. Concentrations of epinephrine and norepinephrine tended (P greater than .10) to be elevated in fed pigs, relative to those of fasted counterparts. Provision of even limited quantities of colostrum is therefore beneficial to the glucoregulatory response in newborn pigs.  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