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   78846篇
  免费   4247篇
  国内免费   93篇
林业   3184篇
农学   2043篇
基础科学   463篇
  8573篇
综合类   15397篇
农作物   3128篇
水产渔业   3427篇
畜牧兽医   41679篇
园艺   852篇
植物保护   4440篇
  2019年   719篇
  2018年   1094篇
  2017年   1211篇
  2016年   1051篇
  2015年   905篇
  2014年   1189篇
  2013年   2627篇
  2012年   2115篇
  2011年   2575篇
  2010年   1617篇
  2009年   1733篇
  2008年   2595篇
  2007年   2405篇
  2006年   2283篇
  2005年   2136篇
  2004年   2075篇
  2003年   2139篇
  2002年   1924篇
  2001年   2385篇
  2000年   2439篇
  1999年   1868篇
  1998年   719篇
  1997年   711篇
  1996年   711篇
  1995年   805篇
  1993年   740篇
  1992年   1553篇
  1991年   1750篇
  1990年   1634篇
  1989年   1646篇
  1988年   1472篇
  1987年   1534篇
  1986年   1596篇
  1985年   1548篇
  1984年   1184篇
  1983年   1057篇
  1982年   704篇
  1979年   1152篇
  1978年   894篇
  1977年   755篇
  1975年   774篇
  1974年   1024篇
  1973年   1024篇
  1972年   1043篇
  1971年   993篇
  1970年   987篇
  1969年   903篇
  1968年   810篇
  1967年   799篇
  1966年   732篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Using a highly sensitive and selective analytical method and careful stability control, plasma concentrations of ascorbic acid were determined in German Shepherd Dogs, Labrador Retrievers and Siberian Huskies, a total 99 animals. Mean concentration was 35.9 micromol l(-1)(range 18.2-50.7), and no significant variation was observed neither between breeds nor between females and males. These and previous reported data on plasma ascorbic acid levels in dogs are discussed in the light of methodological aspects.  相似文献   
972.
Comprehensive bacterial cultures were made on samples from 20 pigs that had died of porcine dermatitis and nephropathy syndrome after a short clinical illness. Eleven species of porcine bacterial pathogens and a range of commensal organisms were isolated. Pasteurella multocida was isolated from 16 of the 20 cases but the other pathogens occurred much less commonly. P. multocida was isolated from between one and five sites per case and from the tonsils, retropharyngeal lymph node or lungs in 14 of the 16 cases. Immunohistochemical investigations of kidneys from 30 cases of the syndrome (including the 20 cases in the bacteriological study) revealed P. multocida-specific staining in 26 of the cases, primarily in the renal tubular epithelial cells of the proximal convoluted tubules, but also in the glomeruli, in lesions of renal vasculitis and in the cytoplasm of interstitial mononuclear cells.  相似文献   
973.
974.
A growth trial was carried out to test the effect of organic, trivalent chromium and L-carnitine on the body composition of growing rats. At the same time, an evaluation of different measurement methods (weight of epididymal fat pad, adipocyte morphometry, total body electrical conductivity) was performed. Outbred Wistar rats of 30 days of age were fed diets of different (0, 10 and 20%) protein level. The diets were supplemented with 4 mg/kg Cr as chromium nicotinate, and 100 mg/kg L-carnitine. The experimental feeding lasted 15 days, after a 5-day-long adjustment period. It was found that Cr addition increased feed intake. Both treatments caused changes in body composition, increasing fat and protein deposition. Organic chromium had no effect at either protein level, while L-carnitine improved the protein retention only at an optimum (20%) protein supply. No statistically significant correlation was found between total body electrical conductivity (TOBEC) and body composition, which could be attributed to the great individual differences. A close correlation was found among total body fat percentage, weight of epididymal fat pad and the adipocyte surface. The data suggest that there is an interaction between dietary protein supply and the effect of repartitioning agents.  相似文献   
975.
The effects of feeding two fibre-rich diets with contrasting solubility and a concentrated low dietary fibre on the rate of gastric emptying were examined in six gastric cannulated pregnant sows. Additionally, it was examined whether any effect could be related to the physico-chemical properties of digesta, i.e. viscosity and/or water binding capacity. The sows were fed each diet for one week in a 3 x 3 Latin Square design and the samples were taken in a randomised order 0.5, 1, 2, 3, 5 and 15.5 h after the morning meal. The stomach contents were evacuated through the gastric cannula once daily. The evacuated gastric digesta was quantified and a representative sample was taken to determine its viscosity, water binding capacity and its content of dry matter, dietary components and solid (Cr2O3) and liquid (polyethylene glycol) phase markers. The flow of liquid digesta was calculated as the difference between digesta and dry matter. Increasing the content of dietary fibre in the diet led to higher recovery of liquid digesta but did not have any significant effect on the gastric emptying of dry matter and dietary components. The effect of dietary fibre could not be attributed to the viscosity of the liquid phase of digesta but might be related to the ability of the increased gastric dietary fibre content to hold water. The stomach selectively retained the insoluble dietary fibre components most noticeably seen with the bran-supplemented diet where the concentration of insoluble NSP in digesta increased significantly from 2 hours and onward.  相似文献   
976.
The clinical, gross necropsy, and histopathology findings in two unrelated desert grassland whiptail lizards (Cnemidophorus uniparens) with teratoma are described. The desert grassland whiptail is a parthenogenic lizard species with a polyploid chromosomal complement. The chromosome composition of the teratomas from these lizards was not determined.  相似文献   
977.
978.
Toltrazuril sulfone (Ponazuril®) is a triazine-based anti-protozoal agent with highly specific actions against apicomplexan group of organisms, which are undergoing intensive investigation. Toltrazuril sulfone may have clinical application in the treatment of Neospora. caninum and other protozoal infections in cattle. To evaluate absorption, distribution, and elimination characteristics of toltrazuril sulfone in cattle, a sensitive validated quantitative high-pressure liquid chromatography method for toltrazuril sulfone in bovine biological fluids was developed. After a single oral dose of toltrazuril sulfone at 5 mg/kg (as 150 mg/g of Marquis®; Bayer HealthCare, Shawnee Mission, KS, USA), samples from six cows showed good plasma concentrations of toltrazuril sulfone, which peaked at 4821 ng/mL ± 916 (SD) at 48 h postadministration. Thereafter, plasma concentration declined to 1950 ng/mL ± 184 (SD) at 192 h after administration with an average plasma elimination half-life of ∼58 h. Following oral dose of toltrazuril sulfone, the observed peak plasma concentrations were in relatively close agreement ranging from the lowest 3925 ng/mL to the highest of 6285 ng/mL with the mean peak plasma concentration being 4821 ng/mL. This study shows that toltrazuril sulfone is relatively well absorbed after oral dose in cattle. These results are therefore entirely consistent with and support the reported clinical efficacy of toltrazuril sulfone in the treatment of experimentally induced clinical cases of N. caninum and other protozoal-mediated bovine diseases.  相似文献   
979.
The aim of this study was to determine the effects of early feed restriction on performance, carcass characteristics, meat and liver composition, some blood parameters, H-L ratio, antibody titers against SRBC and tonic immobility duration in broilers. One hundred ninety male chicks (Ross 308) were randomly allocated into two treatment groups each of 95 chicks. Broilers in one treatment fed ad libitum until 42 day of age, however in other treatment, broilers were deprived of feed for 4 h per day from 7 to 21 day. Body weight, feed consumption, feed to gain ratio, carcass characteristics and the percentage of examined organs except heart were not statistically significant in groups. Percentage of heart was higher (p < 0.05) in broilers fed ad libitum. At 41 d of age, H-L ratio (p < 0.05) and TI duration (p = 0.001) were higher, serum glucose (p < 0.05) and triglyceride (p < 0.001) levels were lower in broilers fed ad libitum. Chemical composition of breast and thigh and also fat and ash of liver were not affected by early feed restriction. Moisture of liver (p = 0.001) was lower and protein of liver (p < 0.01) was higher in broilers fed ad libitum  相似文献   
980.
This epidemiological survey on canine babesiosis was carried out in three distinct rural regions (Lavras, Belo Horizonte and Nanuque) of the State of Minas Gerais, Brazil. Ticks and blood samples were collected during a dry season (Lavras, n = 92; Belo Horizonte, n = 50; Nanuque, n = 102) and the subsequent rainy season (Lavras, n = 71; Belo Horizonte, n = 28; Nanuque, n = 66) from dogs living on farms. Plasma samples were analyzed by the indirect fluorescent antibody test for detection of anti-Babesia canis vogeli antibodies. DNA was extracted from blood of serologically positive dogs and molecular characterization of Babesia species was performed. Rhipicephalus sanguineus, Amblyomma cajennense and Boophilus microplus were the tick species identified in all regions. In Lavras, in addition to those tick species, A. tigrinum and A. ovale were also identified. The most prevalent tick species was A. cajennense (35.3%), followed by R. sanguineus (19%) and B. microplus (4.0%). Dogs living in Nanuque region were more heavily infested with ticks than dogs living in Belo Horizonte and Lavras regions. The overall frequency of anti-B. c. vogeli antibodies in the canine population in rural areas of Minas Gerais was 28.7%, with prevalence rates of 49.0% in Nanuque, 34.0% in Belo Horizonte and 3.3% in Lavras. The age of the animals and tick infestation were associated with seroprevalence of B. c. vogeli. The sequence analysis showed that B. c. vogeli was the only Babesia species present in all three regions. This study showed different rates of prevalence and incidence of canine babesiosis among the three rural regions sampled in Minas Gerais State. The results point to the importance of canine babesiosis in rural areas and to the need for further studies related to its transmission and maintenance in nature.  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