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   107367篇
  免费   6151篇
  国内免费   633篇
林业   4079篇
农学   3241篇
基础科学   832篇
  13521篇
综合类   19764篇
农作物   4010篇
水产渔业   4765篇
畜牧兽医   56078篇
园艺   1446篇
植物保护   6415篇
  2021年   904篇
  2020年   1026篇
  2019年   1251篇
  2018年   1802篇
  2017年   2056篇
  2016年   1806篇
  2015年   1584篇
  2014年   1910篇
  2013年   4348篇
  2012年   3536篇
  2011年   4292篇
  2010年   2932篇
  2009年   2798篇
  2008年   3946篇
  2007年   3819篇
  2006年   3385篇
  2005年   3129篇
  2004年   2862篇
  2003年   2884篇
  2002年   2670篇
  2001年   3062篇
  2000年   3117篇
  1999年   2390篇
  1998年   1003篇
  1997年   890篇
  1995年   968篇
  1992年   1864篇
  1991年   2086篇
  1990年   2004篇
  1989年   1959篇
  1988年   1781篇
  1987年   1826篇
  1986年   1896篇
  1985年   1693篇
  1984年   1474篇
  1983年   1284篇
  1979年   1474篇
  1978年   1119篇
  1977年   1004篇
  1976年   1110篇
  1975年   1176篇
  1974年   1471篇
  1973年   1398篇
  1972年   1345篇
  1971年   1199篇
  1970年   1181篇
  1969年   1180篇
  1968年   1036篇
  1967年   1113篇
  1966年   1043篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
251.
Reference is made to work undertaken by Stehle (1983) on rapid semiquantitative determination of urinary protein in pigs for slaughter to identify premortal strain and stress, with additional studies being conducted into the suitability of the method. The investigations performed for this study covered urinary protein samples from 59 living and 762 slaughtered pigs. The Biophan E paper strip test was applied to groups of animals, and, when compared to high-accuracy laboratory determination of urinary protein, it provided sufficiently accurate information on the presence of stress-related proteinuria. Its accuracy, however, proved to be insufficient, when individual animals were examined. The number of clearly stressed slaughter pigs was unexpectedly high, although the same animals had been rated clinically inconspicuous prior to slaughter. Brief rest period resulted in significant rise of stress. The Biophan E paper strip test was found to be suitable for instantaneous determination of stress and strain on pigs for slaughter.  相似文献   
252.
The laminar epidermis (epidermis parietis) of hooves from 14 clinically normal horses, 6 months to 15 years old, was examined by light and electron microscopy and immunofluorescence to measure the contributions of this region to the formation of the hoof wall. By their progressive keratinization to form primary epidermal laminae, the secondary epidermal laminae ultimately contributed about 20% of the thickness of the hoof wall (as revealed in the white line [zona alba]). The keratinized, primary epidermal laminae were developed to a height of 4 mm during their proximodistal-course, much of this obscured because of their basal portion being embedded in the cap horn epidermis. From evaluation of structural changes accompanying keratinogenesis in the cell and determination of the contribution of the laminar epidermis to the formation of laminar horn, cap horn, connecting horn, terminal horn, and the white line, we concluded that the sterile bed concept of a nongerminative role for the secondary epidermal laminae is no longer tenable.  相似文献   
253.
Nineteen hen turkeys (10 to 12 kg each) were used in a feeding study to determine sulfadimethoxine and sulfaquinoxaline concentrations in blood serum, liver, and skeletal muscle, as well as the respective ratios at selected withdrawal intervals. Two feeds were prepared by use of premixes to achieve 60 mg of sulfadimethoxine/kg and 100 mg of sulfaquinoxaline/kg, respectively. Each of the medicated feeds was given to 9 turkeys for 7 days. The turkeys were then fed nonmedicated feed at intervals from 24 to 56 hours and were slaughtered. One turkey was used as control. The serum/liver and serum/muscle ratios for sulfaquinoxaline were 60 to 70% higher than for sulfadimethoxine. However, the liver/muscle ratio for both sulfonamides was equivalent, approximately 3. Disposition of both sulfonamides approximated first-order pharmacokinetics. The calculated half-life of sulfadimethoxine was half that of sulfaquinoxaline, approximately 16 vs 30 hours. The coefficients of variation in the serum/tissue ratios for both sulfonamides were between 13% and 25% for serum/liver and less than 15% for serum/muscle, indicating excellent potential for using serum as a predictor of actionable concentrations of sulfonamide residues.  相似文献   
254.
An ELISA was developed to detect circulating antigens of Toxoplasma gondii in the serum of cats. For the experiment, toxoplasmosis was induced in a group of cats by oral administration of bradyzoites. An ELISA that detects anti-Toxoplasma IgG, an ELISA to detect circulating antigens, and fecal examinations were performed on samples from each cat for 1 year after inoculation. When coupled with IgG-class antibody measurement, antigen detection can aid in the diagnosis of some cases of subclinical feline toxoplasmosis.  相似文献   
255.
256.
Immunogenicity of Brucella abortus salt-extractable proteins   总被引:5,自引:0,他引:5  
The immunogenic properties of salt-extractable proteins and chromatographic fractions thereof from Brucella abortus were evaluated in lemmings (Dicrostonyx rubricatus). The efficacy of the Brucella proteins as immunogens was determined after challenge with virulent B. abortus strain 2308 and was based on protection against clinical signs and gross lesions of brucellosis, as well as on numbers of viable Brucella in the spleen. Vaccination of lemmings with as little as 0.1 microgram of salt-extractable proteins (CSP) suppressed splenic infection, resulting in reduced numbers of viable organisms per spleen of 5-6 logs compared to non-vaccinated controls. Protein fractions separated by column chromatography were generally effective in reducing splenic infection, and contained proteins with molecular weights of 30,000, 20,000 and 12,000. Vaccines containing chemically modified dodecanoyl-CSP offered no additional advantage over unmodified CSP vaccines.  相似文献   
257.
Oxidized copper wire, commonly referred to as copper oxide needles (CuON), was evaluated using purebred Hereford cows and their calves. Thirty-seven cows were allocated to Cu treatments of 0, 25 or 50 g CuON (79.9% Cu in CuON) with 12, 12 and 13 cows per treatment, respectively; calves within cow treatments were allocated to treatment of 0 and 20 g CuON. Single oral doses of CuON were given at the start of a grazing trial that lasted 92 d. Cows and calves were weighed and blood samples were taken on d 0, 28, 63 and 92; liver biopsies were taken on d 0, 28 and 92 of the grazing trial. Cattle were consuming grass forage with mean concentrations on d 0, 28, 63 and 92 of the grazing trial ranging from 1.6 to 5.5 mg/kg DM for Cu, 2.5 to 5.5 mg/kg DM for Mo and 1.3 to 1.5 g/kg DM for total S. The water consumed by cattle contained 947 mg sulfate per liter (SE = 13.2, n = 4). Body weight of cows and calves was not influenced (P greater than .05) by CuON. Liver Cu was higher (P less than .01) in treated cows and calves but was not different (P greater than .05) between cows dosed with 25 or 50 g CuON. Treatment of cows and calves with CuON had no influence (P greater than .05) on the concentration of Fe or Mo in liver or plasma, the concentration of Cu and ceruloplasmin activity in plasma, or the concentration of Zn in liver. Plasma Zn did not differ (P greater than .05) in cows, but it was higher (P less than .05) in the calves suckling cows treated with CuON. It was concluded that dosing cows and calves with CuON resulted in a higher Cu content of liver but did not adversely influence the metabolism of Fe or Zn or modify the concentration of Mo in the plasma or liver of cows or calves.  相似文献   
258.
Twelve hundred and twenty-eight goats (Capra hircus L.) from a sub-tropical and humid zone of India were examined for gastrointestinal nematodes. The species encountered in the region were: Haemonchus contortus, Bunostomum trigonocephalum, Oesophagostomum columbianum, Trichuris globulosa, O. aspersum, and T. ovis. The overall infection rate was 86.8%. Among various species found, H. contortus emerged as the most prevalent, although B. trigonocephalum and O. columbianum were also significantly in evidence. The seasonal fluctuation in infection was assessed by monitoring the faecal egg count of 1638 goats slaughtered during the 1-year period. The maximum values for the prevalence and overall mean eggs g-1 of faeces (EPG) were observed after the heavy rainfall season and remained at a relatively high level from July to December. H. contortus and O. columbianum appear to be of major importance as parasites in the goats of this climatic zone; the role of climatic factors in their prevalence is discussed.  相似文献   
259.
Recently we reported elimination of radioactivity from [14C]heptachlor from body stores of lactating ovines, mainly into excreta rather than milk, contrasting sharply with bovines. To further assess heptachlor metabolism and clearance by ovines, 12 fine-wool wether lambs (41 +/- 3 kg) housed in metabolism stalls were fed pelleted alfalfa hay (96%) plus molasses (3%) ad libitum and were dosed i.p. once with [14C]heptachlor (1.643 mg/kg body wt; sp. act. = .89 microCi/mg). Feces and urine were collected separately and quantitatively. Light mineral oil was mixed with feed (5 g/100 g) of six lambs and trans-stilbene oxide, an inducer of biotransformational enzymes, was administered i.p. (4 g/hd initially; 2 g/hd daily thereafter) through 20 d to three lambs given each mineral oil treatment, in 2 x 2 factorial arrangement. Feces, urine, blood, bile and body tissues were assayed for total 14C activity. Radioactivity (heptachlor and [or] metabolites) eliminated into excreta during 21 d amounted to 34 to 36% of dose administered, of which 67% appeared in urine and 33% in feces. Biological half-time for elimination into excreta was 11.3 d [Kel = -.061/d], similar to 11.7 d we reported for lactating ewes. Clearance from blood had T1/2 = 14 d. Neither mineral oil nor trans-stilbene oxide altered rate or route of 14C activity excreted or concentrations of 14C activity in blood. Results confirmed that ovines eliminate heptachlor much more rapidly than bovines.  相似文献   
260.
The effects of ionophores on liver weight and function were determined in finishing steers (n = 24; avg weight 440 kg). Steers were group-fed one of three treatments (control, lasalocid or monensin at 33 mg/kg feed) for 46 d prior to slaughter. Three days prior to slaughter, blood was collected for the determination of serum Ca and Mg. At slaughter, the liver was removed, weighed, sampled, frozen in liquid nitrogen and subsequently analyzed for concentrations of carbohydrate metabolites and minerals. Liver weight (5.9 kg) was unaffected by treatment. Serum and hepatic Ca and Mg were not affected by ionophore treatment. Hepatic glycogen levels in steers fed ionophores were unaffected by treatment. Fructose 1,6-bisphosphate was 21% lower (P less than .10) in hepatic tissue of steers fed ionophores, whereas dihydroxyacetone phosphate was 15 to 37% greater in hepatic tissue of steers fed monensin (P less than .20) or lasalocid (P less than .10). Glyceraldehyde 3-phosphate was elevated more extensively by lasalocid than by monensin with increases of 72 (P less than .05) and 132% (P less than .001), respectively, over controls. Glycerol 3-phosphate levels were 37% (P less than .05) and 12% (NS) greater with these ionophores. Hepatic levels of pyruvate were elevated 12 (NS) to 36% (P less than .17) for monensin and lasalocid. Fructose 2,6-bisphosphate levels were 25% lower (P less than .25) in hepatic tissue of steers fed ionophores than in hepatic tissue from control steers. Other metabolites of carbohydrate metabolism in hepatic tissue were not altered appreciably. Changes in levels of intermediary metabolites of carbohydrate metabolism suggest alterations in hepatic carbohydrate metabolism favoring gluconeogenesis in steers fed ionophores.  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