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   156856篇
  免费   7533篇
  国内免费   104篇
林业   7078篇
农学   4541篇
基础科学   1068篇
  17030篇
综合类   32237篇
农作物   6495篇
水产渔业   6772篇
畜牧兽医   78246篇
园艺   1888篇
植物保护   9138篇
  2018年   1711篇
  2017年   1905篇
  2016年   1840篇
  2015年   1649篇
  2014年   1847篇
  2013年   5404篇
  2012年   3823篇
  2011年   4473篇
  2010年   2870篇
  2009年   2776篇
  2008年   4269篇
  2007年   3944篇
  2006年   3857篇
  2005年   4324篇
  2004年   4293篇
  2003年   4110篇
  2002年   3661篇
  2001年   4360篇
  2000年   4250篇
  1999年   3369篇
  1995年   1663篇
  1994年   1564篇
  1993年   1505篇
  1992年   3238篇
  1991年   3520篇
  1990年   3531篇
  1989年   3581篇
  1988年   3316篇
  1987年   3344篇
  1986年   3484篇
  1985年   3388篇
  1984年   2752篇
  1983年   2519篇
  1982年   1702篇
  1981年   1611篇
  1980年   1509篇
  1979年   2630篇
  1978年   2119篇
  1977年   1819篇
  1976年   1727篇
  1975年   1917篇
  1974年   2431篇
  1973年   2432篇
  1972年   2487篇
  1971年   2385篇
  1970年   2207篇
  1969年   1986篇
  1968年   1630篇
  1967年   1807篇
  1966年   1590篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
The dietary lysine requirement of juvenile red drum Sciaenops ocellatus was reevaluated in two separate experiments. In the first experiment, lyophilized red drum muscle was combined with an L-form crystalline amino acid premix to yield diets containing approximately 35% protein on a dry-matter basis. Gradations (0.25%) of L-lysine HCl were added to the basal diet containing approximately 1.0% lysine. Each diet was fed to triplicate groups of juvenile red drum initially weighing 6–7 g for 8 weeks. Based on growth and feed efficiency data, the lysine requirement (±SE) was determined to be 1.55% (±0.079%) of dry diet or 4.430% of dietary protein. In a second experiment, the lysine requirement of red drum was investigated with diets containing 35% intact protein from zein and red drum muscle. Each of the zein-based diets containing incremental levels of lysine was fed to triplicate groups of juvenile red drum initially weighing 1–2 g for 8 weeks. A crystalline amino acid test diet serving as a control in this experiment significantly outperformed the zein-based diets, and palatability of those diets was questionable due to an obvious change in feeding behavior of the fish. Due to the inferior performance of the fish fed the zein-based diets, the authors were not successful in determining a requirement with these diets. Thus, a lysine requirement of 1.55% of dry diet (4.43% of dietary protein) as determined in the first experiment is recommended for juvenile red drum.  相似文献   
132.
1. Three experiments were designed to determine the response of broiler chickens to dietary isoleucine, and to quantify the antagonistic effects of excess leucine and valine on this response. 2. A dilution technique was used to measure the responses in growth rate and food intake to a range of diets differing in their isoleucine concentrations. A summit diet was formulated to contain isoleucine at 1.14 times the requirement and with leucine (1.76 times the requirement) and valine (1.87 times the requirement) at the minimum possible concentrations, given the ingredients available. A dilution mixture, devoid of protein, was formulated to correspond in all respects, other than in amino acid content, to the summit diet. These two basal diets were blended in different proportions to give a range of diets of decreasing isoleucine and protein content. 3. In experiment 1 the response was measured to isoleucine with leucine and valine remaining in the same proportion to isoleucine throughout the range of diets fed. In experiments 2 and 3, however, L-leucine and L-valine were added to the diets either singly or in combination to give 6 isoleucine concentrations and 3 ratios of each of leucine and valine to isoleucine. 4. Weight gain decreased as the isoleucine content of the diet was reduced, whereas food intake of broilers fed on the marginally deficient diets increased to a maximum and then decreased. FCE decreased curvilinearly as the isoleucine concentration in the food decreased, reflecting a concomitant change in the fat content of the broilers. 5. It is possible that the amount of dietary isoleucine assumed to be available to the broilers in these experiments was overestimated by hydrolysing the food samples for 72 h, and the doubt thus created makes an estimate of the efficiency of retention of isoleucine suspect. 6. Excess valine had no effect on the response to isoleucine, whereas an increase in the leucine to isoleucine ratio depressed food intake and hence weight gain, but only at the lowest concentrations of isoleucine. 7. If the food content of isoleucine is sufficient to meet the requirements of the broiler, relatively large excesses of leucine, of valine, or of both will not depress growth.  相似文献   
133.
134.
Twenty-nine pruritic, atopic dogs were entered into a double-blind, placebo-controlled, crossover study to evaluate the efficacy of an investigational antiallergenic compound, AHR-13268. Fourteen dogs were evaluated by a veterinary dermatologist (at intervals) and the owner (daily). Fifteen dogs were evaluated only by the owner. The mean (+/- SE) owner scores for pruritus, erythema, and lesions with placebo treatment (higher score = worse signs) were 3.24 (+/- 0.12), 2.73 (+/- 0.12), and 2.61 (+/- 0.09), respectively. With drug treatment, the corresponding scores were 2.89 (+/- 0.12), 2.50 (+/- 0.12), and 2.25 (+/- 0.09). Scores for pruritus and lesions (but not erythema) were significantly better with drug treatment than with placebo treatment. Investigator scores showed similar trends, but the differences were not great enough to be statistically significant. Overall, 11/29 (38%) owners reported their dogs had moderate or better improvement from drug capsules, and 4/29 dogs (14%) improved on placebo capsules. A variety of adverse effects were reported following both drug (9/29 dogs) and placebo (8/29 dogs) capsule administration, but were mild and well tolerated. Results of this study indicate that AHR-13268 has potential for empiric treatment of allergic inhalant dermatitis in some dogs.  相似文献   
135.
Meat regulations also involve game inspection. This publication deals with the regulations concerning furred game intended for slaughter and furred game hunted for food.  相似文献   
136.
Two cases of H.c.c. which occurred in winter 1987 in Vienna are described. Case one was a female Chow-Chow, 8 weeks of age, that died from the peracute form of the disease. The diagnosis was confirmed by histology and direct immunofluorescence. Case two, a 9-month old female Kuvacz, showed clinical signs of the subacute form of H.c.c. She was hospitalized and therapy was successful. The disease was diagnosed by the typical clinical signs and the raise of antibodies in paired serum samples. Etiology, clinical signs and immunology of H.c.c. are discussed.  相似文献   
137.
138.
A complete radiographic examination of the equine foot consists of properly exposed, processed, and positioned radiographs. For radiographic interpretation, in addition to knowing radiographic signs of disease, a knowledge of normal radiographic anatomy and possible insignificant anatomic variations is necessary.  相似文献   
139.
The present study shows that milk is an appropriate source for detection of seroreactors to bovine virus diarrhoea virus (BVDV). There was close agreement between antibody titres in serum and in skim milk, as determined by an indirect enzyme-linked immunosorbent assay. The antibody titres were usually lower in skim milk than in serum, but all seropositive cows (n = 84) were also skim milk-positive and all but one seronegative cow (n = 55) proved negative in skim milk. During lactation, the level of antibodies to BVDV in milk showed an inverse relationship to the amount of milk produced. However, there was a sufficient level of antibodies in milk throughout lactation to permit an adequate determination of BVDV antibody status in dairy cows. There was a mutual good agreement between milk antibody titre in the four mammary quarters, irrespective of milk cell count. Milk can be used to detect seroreactors to BVDV. Milk is preferable to blood in large-scale epidemiological studies, since the sampling procedure is much simpler.  相似文献   
140.
The efficacy of a new pelleting process in eliminating naturally occurring Escherichia coli and salmonella from poultry mash was assessed by comparing the microbial load in raw and processed mash. Instead of using steam produced in a boiler, the new process conditioned mash in an Original Vertical Conditioner with steam and other hot gases generated by direct combustion in a Vaporator. E. coli was isolated from 72-100% of samples of raw mash in all trials, and the mean number of colony-forming units of E. coli/g of samples was 6.8 +/- 4.0 X 10(4). Salmonellae (S. senftenberg, S. bredeney, and S. mbandaka) were isolated from 5-10% of samples of raw mash utilized in three of the seven trials. Within limitations of the sampling and analytical tests utilized, the new pelleting process eliminated salmonella from all mash in which the organism was known to be present but eliminated E. coli in only three trials. The process appeared to be 100% effective against both organisms when mash entering the pellet mill from the conditioner had a temperature of 85.7 C and a moisture content of 14.5% and had been retained and treated with steam and hot gases for 4.1 minutes.  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