全文获取类型
收费全文 | 241607篇 |
免费 | 14686篇 |
国内免费 | 717篇 |
专业分类
林业 | 23482篇 |
农学 | 14033篇 |
基础科学 | 2974篇 |
42217篇 | |
综合类 | 17229篇 |
农作物 | 17300篇 |
水产渔业 | 16853篇 |
畜牧兽医 | 93161篇 |
园艺 | 6249篇 |
植物保护 | 23512篇 |
出版年
2021年 | 2498篇 |
2020年 | 2866篇 |
2019年 | 3660篇 |
2018年 | 3997篇 |
2017年 | 4294篇 |
2016年 | 4776篇 |
2015年 | 4352篇 |
2014年 | 5679篇 |
2013年 | 16305篇 |
2012年 | 6064篇 |
2011年 | 7912篇 |
2010年 | 7328篇 |
2009年 | 7881篇 |
2008年 | 7202篇 |
2007年 | 6292篇 |
2006年 | 6907篇 |
2005年 | 6143篇 |
2004年 | 5957篇 |
2003年 | 5722篇 |
2002年 | 5075篇 |
2001年 | 6050篇 |
2000年 | 5687篇 |
1999年 | 5304篇 |
1998年 | 4130篇 |
1997年 | 4174篇 |
1996年 | 3908篇 |
1995年 | 4423篇 |
1994年 | 3824篇 |
1993年 | 3546篇 |
1992年 | 4130篇 |
1991年 | 4406篇 |
1990年 | 4061篇 |
1989年 | 3993篇 |
1988年 | 3557篇 |
1987年 | 3612篇 |
1986年 | 3391篇 |
1985年 | 3706篇 |
1984年 | 3517篇 |
1983年 | 3259篇 |
1982年 | 2757篇 |
1981年 | 2661篇 |
1980年 | 2626篇 |
1979年 | 2986篇 |
1978年 | 2677篇 |
1977年 | 2474篇 |
1976年 | 2347篇 |
1975年 | 2172篇 |
1974年 | 2287篇 |
1973年 | 2217篇 |
1971年 | 1969篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
991.
Blackmore DK 《New Zealand veterinary journal》1983,31(10):167-169
992.
993.
This paper concerns the taxonomic status of the F38-like group (MacOwan), a prime determinant of contagious caprine pleuropneumonia (CCPP). Extensive biochemical and serological investigations on strain F38 are reported. Some complex serological relationships with other mycoplasma species are revealed. The results, taken in conjunction with earlier published work on geno-typic characters, lead to the conclusion that final classification of these organisms should await further comparative studies of a number of field strains with a related group of strains classified as M. capri-colum.The characterization of F38 confirms its partial relationship to the “M. mycoides group” of ovine/caprine/bovine mycoplasmas, and has also revealed a very close phenotypic relationship to the bovine mycoplasma serogroup 7, a finding of potential diagnostic and epidemiological importance.Key words: mycoplasmas, classification, F38-like group 相似文献
994.
Endocrine effects of heat stress in boars 总被引:1,自引:0,他引:1
K. Larsson S. Einarsson K. Lundstrm J. Hakkarainen 《Acta veterinaria Scandinavica》1983,24(3):305-314
The purpose of this study was to describe the temporal changes in peripheral plasma levels of testosterone and Cortisol in boars during and after heat stress. A total of 8 boars were utilized, 4 of them were exposed to 35°C, for 100 h in a climatic room, and 4 served as controls and were kept at 20 °C for 100 h in the climatic room.Blood samples were obtained via permanent vein catheters 3 times daily from 5 days before heat stress until 20 days after termination of heat stress. Testestorone levels were determined by radioimmunoassay and Cortisol by a competitive protein binding technique.For both hormones the pre-exposure levels were similar in both groups of boars. The control boars had significantly higher testosterone levels, while being in the climatic room, than during any other period. The experimental boars had slightly increased testosterone levels during the first day of heat stress and thereafter continuously decreased levels. In the control boars the testosterone levels returned to pre-exposure levels immediately after removal from the climatic room, whereas in the experimental boars the testosterone levels were dramatically increased during the first 5 days after exposure. The differences in Cortisol levels, between the 2 groups of boars were restricted to the period spent in the climatic room. During this period the experimental boars had significantly higher Cortisol levels.Key words: boars, heat stress, testosterone, cortisol 相似文献
995.
Selenium and glutathione peroxidase levels in lambs receiving feed supplemented with sodium selenite or selenomethionine 总被引:1,自引:0,他引:1
Twenty-one 6 months old female lambs were divided into 7 groups and fed a basal diet containing 0.13 mg Se/kg. The basal diet was further supplemented with 0, 0.1, 0.5 or 1.0 mg Se/kg either as sodium selenite or as selenomethionine, and was fed for 10 weeks. Both feed additives produced an increase in the selenium concentration in the tissues analysed. Significant correlations were found between the concentrations of selenomethionine or sodium selenite added to the feed and the subsequent tissue levels. However, the selenium levels seemed to plateau at approximately 0.5 mg Se/kg of supplemented sodium selenite. The total glutathione peroxidase (GSH-Px) activity of the tissues increased when the selenium supplementation increased from 0 to 0.1 mg/kg for both selenium compounds. With further increase in selenium supplementation the GSH-Px activity in the tissues plateaued except in the blood where the activity continued to rise with increasing selenomethionine supplementation. The selenium dependent GSH-Px activity in the liver rose with increasing selenomethionine supplementation, but approached a plateau when 0.1 mg Se/kg as sodium selenite was added to the feed. The selenium concentration in whole blood responded more rapidly to the selenium supplementation than did GSH-Px activity. The experiment indicates that the optimal selenium concentration in the feed is considerably higher than 0.1 mg Se/kg, and that selenium levels of 1.0 mg/kg in the feed do not result in any risk for the animals or the consumers of the products.Key words: dietary selenium, lambs, selenium concentrations, glutathione peroxidase activities, tissues 相似文献
996.
Using 12 years of data from the common grazing areas at Store Vildmose on the incidence of foot rot in cattle, it was shown that the disease incidence varied significantly between the sections in which the animals were grazing. Differences also existed between breeds in their foot rot incidence. Extraordinarily wet summers were noted to influence foot rot in cattle, and a possible effect of soil pH was also observed.Key words: foot rot, cattle, incidence, epidemiology, breed differences, climatic factors, lameness 相似文献
997.
Skerman TM Millar KR Sheppard AD Herceg M Hughes JM 《New Zealand veterinary journal》1983,31(4):54-57
Two groups of adult Merino sheep, initially grazed on pasture, were dosed daily with zinc sulphate (1 mg Zn/kg LW) or zinc oxide (15 mg Zn/kg LW) for six and seven weeks, respectively. On the 18th day, both groups were transferred to indoor pens together with unmedicated control sheep, and five days later the feet of all animals were infected artificially with a virulent strain of Bacteroides nodosus. By the fourth week after challenge, 85% or more of the feet challenged had developed advanced footrot, and no significant differences in the incidence and severity of lesions between dosed and un-dosed groups were recorded. Plasma zinc concentrations, monitored throughout the experiment, remained at similar levels in sheep receiving the lower dose rate and in the controls. At the higher dose rate, plasma zinc levels increased till Day 23, but thereafter declined to values comparable to those of undosed animals. At post mortem, no evidence of zinc toxicosis was found, and only the kidneys of sheep receiving the higher dosage showed a significant accumulation of zinc compared with the controls. 相似文献
998.
Latimer CA Wyman M Szymanski C Werling K 《Journal of the American Veterinary Medical Association》1983,183(9):1003-5, 965
A cyst involving the gland of the 3rd eyelid was removed from an 8-year-old dog. Clinically the circumscribed mass resembled a pigmented neoplasm. Histologically the cyst was multiloculated, with homogeneous eosinophilic periodic acid-Schiff-positive content. Melanin pigment was present in epithelial cells and cystic lumens. Protective functions of the 3rd eyelid were retained following excisional biopsy. 相似文献
999.
1. Broilers were fed on wheat‐casein or wheat‐soyabean meal diets and the excreta collected after 12 and 24 h. Samples of excreta were freeze dried or dried in a force draught oven at 60 or 80 °C.
2. Drying procedure and collection time significantly influenced the determined energy and nitrogen concentrations of the excreta.
3. Drying excreta in an oven at 60 °G proved at least as effective as freeze drying for the majority of amino acids. 相似文献
1000.
White leghorn chickens on five farms were given a bivalent Marek's disease (MD) vaccine consisting of turkey herpesvirus (HVT) and SB-1 (a nononcogenic MD virus); other chickens received only HVT. The farms had histories of "vaccination failures," presumably owing to an exceptionally virulent challenge MD virus. The bivalent vaccine uniformly protected chickens better than HVT alone between 12 and 16-20 weeks of age, when serious MD losses occurred. During that period, total mortality in groups given both viruses ranged from 0.39 to 1.26% (mean 0.86%), whereas that in HVT-vaccinated groups not exposed to SB-1 varied from 1.92 to 7.44% (mean 3.43%). Chickens in pens or rows with close contact to those given bivalent vaccine also had low MD mortality rates (0.46-1.06%, mean 0.77%), probably from the spread of SB-1. 相似文献