全文获取类型
收费全文 | 342061篇 |
免费 | 30217篇 |
国内免费 | 28337篇 |
专业分类
林业 | 19553篇 |
农学 | 15119篇 |
基础科学 | 9835篇 |
68247篇 | |
综合类 | 78035篇 |
农作物 | 16693篇 |
水产渔业 | 19466篇 |
畜牧兽医 | 143691篇 |
园艺 | 6092篇 |
植物保护 | 23884篇 |
出版年
2021年 | 2884篇 |
2020年 | 4839篇 |
2019年 | 8777篇 |
2018年 | 9741篇 |
2017年 | 11019篇 |
2016年 | 11522篇 |
2015年 | 10982篇 |
2014年 | 10866篇 |
2013年 | 17723篇 |
2012年 | 14411篇 |
2011年 | 15124篇 |
2010年 | 10769篇 |
2009年 | 10175篇 |
2008年 | 12235篇 |
2007年 | 12014篇 |
2006年 | 11176篇 |
2005年 | 10195篇 |
2004年 | 10037篇 |
2003年 | 9893篇 |
2002年 | 8994篇 |
2001年 | 9964篇 |
2000年 | 9616篇 |
1999年 | 7973篇 |
1998年 | 4007篇 |
1997年 | 3973篇 |
1996年 | 3627篇 |
1995年 | 4216篇 |
1994年 | 3861篇 |
1993年 | 3625篇 |
1992年 | 6332篇 |
1991年 | 6500篇 |
1990年 | 6218篇 |
1989年 | 6206篇 |
1988年 | 5763篇 |
1987年 | 5676篇 |
1986年 | 5747篇 |
1985年 | 5387篇 |
1984年 | 4410篇 |
1983年 | 3972篇 |
1982年 | 2772篇 |
1979年 | 4030篇 |
1978年 | 3264篇 |
1977年 | 2791篇 |
1975年 | 2883篇 |
1974年 | 3543篇 |
1973年 | 3595篇 |
1972年 | 3463篇 |
1971年 | 3236篇 |
1970年 | 3149篇 |
1969年 | 3057篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
993.
Pulmonary responses to intratracheal challenge exposure with Pasteurella haemolytica, with or without Escherichia coli-derived endotoxin, E coli endotoxin alone, or saline solution were compared in anesthetized, mechanically ventilated neonatal calves. Baseline values for dynamic compliance, total pulmonary resistance, functional residual capacity, arterial blood gas tensions, hemogram, leukogram, and systemic and pulmonary arterial pressures were recorded for each calf. After baseline data were obtained, calves were challenge exposed with logarithmic-growth phase P haemolytica organisms with or without E coli endotoxin, E coli endotoxin alone, or saline solution (0.9% NaCl). Physiologic data were obtained immediately after challenge exposure and at various intervals over the next 6 hours. Calves challenge exposed with P haemolytica alone developed sever hypoxemia, had increased alveolar-arterial oxygen difference and threefold increases in total pulmonary resistance, became hypercarbic, had decreased functional residual capacity, and developed systemic hypotension without change in pulmonary arterial pressure. At necropsy, these calves had extensive multifocal areas of necrohemorrhagic and purulent pneumonia. Ratio of extravascular lung water to lung dry weight was not significantly increased in lung specimens obtained from calves challenge exposed with P haemolytica, but ratio of lung wet weight to dry weight was increased, indicating that increased lung wet weight was attributable largely to increased solids and not to fluid alone. (Extravascular lung water measurement excludes fluid from the vascular compartment.) Intratracheal challenge exposure with endotoxin failed to alter lung function and caused minor changes in lung structure consisting of focal areas of hemorrhage and edema.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
994.
Two trials were conducted to determine the effect of induced molt on the reisolation of Mycoplasma gallisepticum (MG) from commercial leghorn hens that had been eyedrop-inoculated with MG at 10 weeks of age. Chickens were maintained in a conventional floored chicken house on dry litter through 100 weeks of age. At age 64 weeks, 4 days (Trial 1), and at 100 weeks (Trial 2), hens were swabbed and cultured for MG and then molted in biological isolation units. Swabs were again taken at the end of each molt. No difference was observed in the number of MG isolations between molted hens and controls that did not undergo molting. However, a significant decrease in MG isolations was observed in both trials from swabs obtained when hens were housed on dry litter floors as compared with swabs taken from the same hens after 18 days (Trial 1) or 21 days (Trial 2) of confinement in isolation units. 相似文献
995.
996.
Destruction of Trichinella spiralis spiralis during the preparation of the "dry cured" pork products proscuitto, proscuittini and Genoa salami 总被引:1,自引:1,他引:0 下载免费PDF全文
Genoa salami, proscuittini and proscuitto were prepared from pork carcasses that were heavily infected experimentally with Trichinella spiralis spiralis. Genoa salami was prepared with salt concentrations of 2.0%, 2.75% and 3.3%. Proscuitto was prepared by two procedures approved by Agriculture Canada. At various times postpreparation, samples of the various cured products were taken and examined by pepsin digestion and rat bioassay for the presence of viable trichinae. Water activity and pH of the cured meat were also determined. Curing of the various products was shown to destroy the Trichinella larvae. Pepsin digestion revealed that larvae progressively became loosely coiled, uncoiled and more subject to digestion (ghost larvae) during the curing process. Rat bioassay revealed the presence of viable trichinae in the proscuitto prepared using a sodium chloride salt mixture at day 34 but not at day 48 postpreparation. All other bioassays carried out on Genoa salami between 13 and 42 days postpreparation, on proscuittini between days 27 and 69 and on proscuitto between days 34 and 69 were negative for viable trichinae. Under the conditions of this study, preparing Genoa salami with salt concentrations as low as 2% did not appear to affect the destruction of Trichinella larvae. 相似文献
997.
998.
C. R. CLARKE † C. R. SHORT ¶ D. W. A. BOURNE‡ § E. A. USENIK 《Journal of veterinary pharmacology and therapeutics》1989,12(3):312-321
The purpose of this study was to characterize the pharmacokinetics of a subcutaneously implanted tissue-chamber model. Thermoplastic tissue chambers were implanted in the paralumbar fossae of six steers. Starting 30 days after implantation, the distribution of intravenously administered antipyrine and phenylbutazone into the tissue chambers was studied. These pharmacokinetic experiments were repeated 10 days later to determine the effect of time after implantation on tissue-chamber distribution. Fifty days after implantation, tissue chambers were drained of transudate, refilled with sterile saline and the rate of influx of endogenous urea, creatinine and albumin was measured. Delayed diffusion of antipyrine and phenylbutazone into tissue chambers was well described using a compartmental model in which tissue-chamber fluid represented the third of three compartments arranged in series. The distribution of antipyrine into tissue chambers was greater than that of phenylbutazone; an observation which is well correlated with the high degree of protein binding of phenylbutazone. There was no effect of time on the penetration of the two agents. Rapid diffusion of urea and creatinine and extremely slow influx of albumin into chambers showed that these chambers formed true interstitial compartments. 相似文献
999.
Antagonism of medetomidine sedation by atipamezole in pigs. 总被引:1,自引:0,他引:1
R Nishimura H Kim S Matsunaga M Sakaguchi N Sasaki H Tamura A Takeuchi 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(6):1237-1240
The efficacy of atipamezole as a medetomidine antagonist was evaluated in pigs. The atipamezole doses (intramuscularly) were 80, 160, 320 and 480 micrograms/kg of body weight, which were one, two, four and six times higher than the preceding medetomidine dose (80 micrograms/kg, intramuscularly). Atipamezole effectively reversed medetomidine-induced sedation, and the optimal action was seen at doses of 160 and 320 micrograms/kg. Recovery from sedation was quick and smooth, and adverse effects such as hyperactivity or tachycardia were minimal with either dose. 相似文献
1000.
1118 Friesian cows and 101 Friesian heifers were investigated in internal pelvic measurements and their relationships to external measurements. The mean of the pelvic vertical and the medium diagonally diameter of the pelvis are 19.8 cm and 18.3 cm. 363.9 square centimetres and 76.3 centimetres were found for the pelvic surface and pelvic circumference. The difference between the biggest and smallest pelvis was 295.0 square centimetres. Medium to high coefficiences of correlation were detected between the internal pelvic measurements but relationships between internal and external pelvic measurements were low. From determined external pelvic measurements only the hip breadth provides usefull informations of the pelvic shape. 相似文献