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   84201篇
  免费   5282篇
  国内免费   767篇
林业   3676篇
农学   2521篇
基础科学   677篇
  10300篇
综合类   16541篇
农作物   3090篇
水产渔业   3814篇
畜牧兽医   43464篇
园艺   1166篇
植物保护   5001篇
  2021年   742篇
  2020年   833篇
  2019年   994篇
  2018年   1429篇
  2017年   1635篇
  2016年   1443篇
  2015年   1374篇
  2014年   1572篇
  2013年   3053篇
  2012年   2993篇
  2011年   3589篇
  2010年   2354篇
  2009年   2230篇
  2008年   3197篇
  2007年   3084篇
  2006年   2786篇
  2005年   2692篇
  2004年   2417篇
  2003年   2468篇
  2002年   2308篇
  2001年   2553篇
  2000年   2607篇
  1999年   1975篇
  1998年   809篇
  1997年   728篇
  1995年   776篇
  1993年   678篇
  1992年   1542篇
  1991年   1722篇
  1990年   1658篇
  1989年   1603篇
  1988年   1482篇
  1987年   1532篇
  1986年   1584篇
  1985年   1407篇
  1984年   1196篇
  1983年   1026篇
  1982年   684篇
  1979年   1060篇
  1978年   840篇
  1977年   679篇
  1976年   718篇
  1975年   754篇
  1974年   1004篇
  1973年   988篇
  1972年   954篇
  1971年   881篇
  1970年   858篇
  1969年   808篇
  1967年   704篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
141.
142.
Rabies virus is able to infect in vitro a wide range of homeothermic and poikilothermic cells but little is known about its multiplication in arthropod cells. In this research the infection of rabies virus in Aedes pseudoscutellaris cells, a mosquito cell line susceptible to mosquito-borne viruses, was studied. After 60 days of incubation at 26 degrees C up to 70% of infected cells showed the synthesis of both viral nucleocapsid and envelope antigens, although viral yield and cell damage could not be detected. Research performed in order to investigate the role of membrane carbohydrate moieties in rabies virus-mosquito cell interaction suggested the participation of galactose and N-acetylglucosamine whereas sialic acid, known to be a rabies binding site in many homeothermic cell lines, was not involved.  相似文献   
143.
Abstract. Nitrous oxide (N2O) is involved in both ozone destruction and global warming. In agricultural soils it is produced by nitrification and denitrification mainly after fertilization. Nitrification inhibitors have been proposed as one of the management tools for the reduction of the potential hazards of fertilizer-derived N2O. Addition of nitrification inhibitors to fertilizers maintains soil N in ammonium form, thereby gaseous N losses by nitrification and denitrification are less likely to occur and there is increased N utilization by the sward. We present a study aimed to evaluate the effectiveness of the nitrification inhibitor dicyandiamide (DCD) and of the slurry additive Actilith F2 on N2O emissions following application of calcium ammonium nitrate or cattle slurry to a mixed clover/ryegrass sward in the Basque Country. The results indicate that large differences in N2O emission occur depending on fertilizer type and the presence or absence of a nitrification inhibitor. There is considerable scope for immediate reduction of emissions by applying DCD with calcium ammonium nitrate or cattle slurry. DCD, applied at 25 kg ha–1, reduced the amount of N lost as N2O by 60% and 42% when applied with cattle slurry and calcium ammonium nitrate, respectively. Actilith F2 did not reduce N2O emissions and it produced a long lasting mineralization of previously immobilized added N.  相似文献   
144.
145.
Abnormally high or low blood glucose and insulin concentrations after standardized glucose tolerance tests can reflect disorders such as pituitary dysfunction, polysaccharide storage myopathies, and other clinical disorders. Glucose and insulin responses, however, are modified by the diet to which the animal has adapted, time since it was last fed, and what it was fed. Body fat (obesity), fitness level, physiologic status, and stress also alter glucose and insulin metabolism. Therefore, it is important to consider these factors when evaluating glucose and insulin tests, especially if only one sample it taken. This article describes the factors affecting glucose and insulin metabolism in horses and how they might influence the interpretation of standardized tests of glucose tolerance.  相似文献   
146.
Hematology and serum biochemistry values are reported for 33 Attwater's prairie chickens (Tympanuchus cupido attwateri) that were captive-reared at the San Antonio Zoo as part of a federal reintroduction program in Texas. Hematologic values include packed cell volume, and total and differential white blood cell counts. The biochemical values include concentrations of serum calcium, total protein, albumin, phosphorus, glucose, uric acid, and cholesterol. Mathematic computation of globulin concentration and albumin: globulin ratios were conducted. Also, determination of the serum activities of creatine kinase and aspartate aminotransferase was done.  相似文献   
147.
148.
The humoral and cellular immunological reactivity of sheep were studied throughout the first 32 weeks following experimental infection with bovine leukemia virus (BLV). Seroconversion of BLV-inoculated sheep occurred within 4 weeks, but infection was not transmitted to contact control sheep. Despite the persistence of the viral infection, no differences were demonstrated in leukograms, serum IgG concentrations, humoral response to immunization with an irrelevant antigen (rabbit red blood cells), phytomitogen (Concanavalin A and Pokeweek mitogen)-induced lymphocyte blastogenesis, or chemical (1-chloro, 2-4 dinitrobenzene) skin contact hypersensitivity, between BLV-infected and uninfected contact control sheep. These results demonstrate the absence of a nonspecific immunosuppressive effect of BLV and further negate the influence of a generalized immunological deficit on the development of clinical disease in BLV-infected animals.  相似文献   
149.
150.
Magnetic resonance imaging (MR) was used to make a diagnosis of equine nigropallidal encephalomalacia in a horse. Equine nigropallidal encephalomalacia is a neurodegenerative disease that has many characteristics with Parkinson-like diseases in humans. Historically, horses were euthanized based on clinical signs and exposure to the toxic weed, yellow star thistle (Centaurea solstitialis). Previously, the disease has only been confirmed on necropsy. MR imaging can provide accurate and sensitive visualization of typical lesions seen in the brain of horses affected with equine nigropallidal encephalomalacia. Lesions were seen on T1-weighted, T2-weighted and proton density images. There was no contrast enhancement following Gd-DTPA administration. Lesions seen on MR were confirmed at necropsy. Using MR to confirm a diagnosis of equine nigropallidal encephalomalacia will prevent unnecessary suffering of horses and expense to owners that would otherwise incur, while further diagnostics are performed.  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