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   466篇
  免费   43篇
林业   25篇
农学   13篇
基础科学   1篇
  94篇
综合类   26篇
农作物   33篇
水产渔业   36篇
畜牧兽医   250篇
园艺   11篇
植物保护   20篇
  2024年   1篇
  2023年   4篇
  2022年   14篇
  2021年   16篇
  2020年   20篇
  2019年   23篇
  2018年   20篇
  2017年   22篇
  2016年   21篇
  2015年   15篇
  2014年   19篇
  2013年   17篇
  2012年   33篇
  2011年   43篇
  2010年   22篇
  2009年   24篇
  2008年   29篇
  2007年   22篇
  2006年   19篇
  2005年   22篇
  2004年   24篇
  2003年   12篇
  2002年   8篇
  2001年   3篇
  2000年   8篇
  1999年   2篇
  1998年   1篇
  1997年   2篇
  1995年   1篇
  1994年   1篇
  1992年   2篇
  1991年   4篇
  1990年   2篇
  1989年   3篇
  1988年   2篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1984年   5篇
  1983年   3篇
  1981年   5篇
  1980年   1篇
  1977年   1篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1973年   3篇
  1972年   1篇
排序方式: 共有509条查询结果,搜索用时 15 毫秒
51.
The effect of transportation on peripheral blood lymphocyte subsets in 24 calves was investigated by flow cytometry. Blood was collected before departure, on arrival, at 24h and 1 week after arrival. Highest leucocyte and neutrophil counts, associated with increased concentrations of cortisol and catecholamines, indicated that stress was maximal upon arrival. At this time, a decrease in the percentages of all T lymphocyte subsets was evident, while they did not decrease as absolute counts. The proportion of CD21(+) cells did not change, indicating that the relative reduction of T lymphocyte subsets was not related to an increase in B lymphocytes. These variations may be due to the increase of a natural killer (NK) cell subset. NK cell expansion, together with increasing lymphocyte count and increasing major histocompatibility complex class II expression, may indicate stress-induced stimulation of the immune system.  相似文献   
52.
Tropical Animal Health and Production - Twenty-seven Nellore cow-calf pairs were submitted for feed efficiency testing. The animals were weighed every 21 ± 5 days to...  相似文献   
53.
54.
Establishment of the temperature-salinity relationship in the ocean has concerned oceanographers for decades because of its importance for understanding ocean circulation. High-resolution measurements in the ocean mixed layer are used to show that temperature and salinity gradients on horizontal scales of 20 meters to 10 kilometers tend to compensate in their effect on density. These observations support the notion of a horizontal mixing in the mixed layer that depends on density gradient.  相似文献   
55.
Fourteen calves were inoculated intranasally (i.n.) with the viral isolates as follows: 5 with 85/BH 16TV, 1 with 85/BH 17TV, 1 with 85/BH 18TV, 2 with 85/BH 231TN and 5 with 85/BH 232TN. Strain 85/BH 16TV was the only one which caused overt respiratory-like disease in all inoculated calves. Onset of the disease was observed after 7-8 days of incubation and was characterized by fever, depression, nasal discharge and coughing. Virus was isolated from the nasal swabbings of calves obtained from post-infection day (PID) 2-10. The other viral strains did not cause any sign of disease although virus was isolated regularly from the nasal swabbings of the inoculated calves. Virus was recovered from central nervous system tissues of calves that were infected with 85/BH 16TV or 85/BH 232TN strains and were killed on PID 4 or 8. Virus was also isolated from other tissues, such as lymph node, nasal mucosa (PID 8), or lung (PID 4). It was speculated that the nervous system could be one of the target areas of the virus of the naturally occurring infection by BHV-4. This might indicate a possible role of the nervous system (site of latency?) in the pathogenesis of BHV-4 as is the case in certain herpesviral infections of man and the lower animals.  相似文献   
56.
Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites.  相似文献   
57.
Walnuts (Juglans regia L.) are relevant components of the Mediterranean diet providing important macronutrients, micronutrients and other bioactive constituents including unsaturated fatty acids, proteins, fiber, vitamins, minerals, phytosterols and polyphenols. Although the walnut beneficial effects in human health are widely recognized by a lot of epidemiologic studies very little is known regarding its effect on damaged DNA. The aim of the present study was to investigate the effect of Juglans regia L. ethanolic extract from kernel on the induction of DNA strand breaks by thiol/Fe3+/O2 mixed function oxidase, tert-butyl hydroperoxide or UVC radiations in acellular and cellular models. Plasmid DNA cleavage and fast Halo assay were used to monitor oxidative damage to DNA. Both approaches showed protection of oxidatively injured DNA. These results agree with a lot of scientific proofs which recommend walnut as dietary adjunct in health promotion and prevention as well as in treatment of lifestyle-related oxidative diseases.  相似文献   
58.
Supply of clear, unstained logs from an export country is important economically as well as in reducing the biosecurity risk to an importing country such as Japan. Although conditions found within the holds of ships containing logs are thought to be ideal for rapid colonization of sapstain fungi, no research has been conducted. Research-focussed log export trials were designed to determine the extent of sapstain colonisation at specific points in the processing of logs from harvesting to arrival at the export destination. Two trials were established, in the austral summer and winter, in which mature Pinus radiata logs were harvested in New Zealand and shipped to export ports in Japan. Data loggers placed above and below deck of the ships recorded microclimatic conditions. Nine species of sapstain fungi were isolated from logs during the summer trial; the most common species isolated were Ophiostoma floccosum, Ophiostoma querci, and Ophiostoma setosum. In contrast, ten sapstain species were detected during the winter trial, with Sphaeropsis sapinea, O. querci, O. floccosum, and O. setosum most commonly isolated. This research was the first successful attempt at measuring visual sapstain development and isolating sapstain fungi from the time of harvesting to arrival at an export destination.  相似文献   
59.
Formalin-fixed, paraffin-embedded sections from 32 canine pairs of testes were immunohistochemically examined for Inhibin-α (INHα). Samples were subdivided into two groups (group 1, neonates; group 2, puppies and adults) and results statistically compared. Inhibin-α was significantly expressed only in Sertoli cells of neonatal testes, while in Leydig cells it was expressed without significant difference between groups. These results suggest that, in dogs, INHα expression switches from Sertoli to Leydig cells during testicular maturation and that, in adult, Leydig cells represent the main source of INHα.  相似文献   
60.
The objective of this paper was to study the changes of some cytokines and neuroendocrine hormones in vaccinated and unvaccinated pigs that were naturally infected by a PRRSV-1 (porcine reproductive and respiratory syndrome virus) heterologous field strain. We analyzed gene expression of pro-inflammatory (TNF-α, IL-1β, MCP-1, IL-6), pro-immune (IFN-γ) and anti-inflammatory cytokines (IL-10) in PBMC, as well as hormonal (GH and cortisol) levels in blood samples of pigs obtained in a field trial previously reported [Martelli P, Gozio S, Ferrari L, Rosina S, De Angelis E, Quintavalla C, et al. Efficacy of a modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine in pigs naturally exposed to a heterologous European (Italian cluster) field strain: clinical protection and cell-mediated immunity. Vaccine 2009;27:3788-99]. All vaccinated pigs showed an increase in pro-inflammatory and pro-immune cytokine gene expression with respect to controls and a prompt increase in GH that could be consistently associated with pro-inflammatory cytokines in sustaining innate immunity; moreover, the higher levels of cortisol indicates the activation of the hypothalamus-pituitary-adrenal (HPA) axis response. In contrast, unvaccinated pigs showed down-regulation of the cortisol and GH responses, and the pro-inflammatory and pro-immune cytokines remained at a basal or low level, with an increase of TNF-α and IL-6 in association with a higher level of IL-10 in the late phase of natural infection. The associated trends of pro-inflammatory and anti-inflammatory cytokines together with the cortisol level demonstrate that a previous vaccination promotes an early immune responsiveness in pigs and a more efficient control of inflammation in the late phase of infection with a heterologous PRRSV isolate; both events could sustain clinical protection.  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