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   147篇
  免费   3篇
  国内免费   1篇
林业   16篇
农学   3篇
  26篇
综合类   40篇
农作物   1篇
水产渔业   4篇
畜牧兽医   56篇
园艺   1篇
植物保护   4篇
  2023年   1篇
  2021年   1篇
  2020年   2篇
  2019年   2篇
  2018年   3篇
  2017年   1篇
  2014年   4篇
  2013年   6篇
  2012年   8篇
  2011年   6篇
  2010年   5篇
  2009年   4篇
  2008年   3篇
  2007年   6篇
  2006年   9篇
  2005年   9篇
  2004年   14篇
  2003年   8篇
  2002年   2篇
  2001年   2篇
  2000年   4篇
  1999年   2篇
  1998年   3篇
  1997年   2篇
  1994年   1篇
  1993年   3篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1989年   3篇
  1988年   3篇
  1987年   1篇
  1985年   2篇
  1984年   7篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   2篇
  1971年   4篇
  1968年   2篇
  1966年   4篇
排序方式: 共有151条查询结果,搜索用时 15 毫秒
91.
92.
Flynn JT 《Science (New York, N.Y.)》1972,176(4040):1184-1186
  相似文献   
93.
94.
In 2006 there was an outbreak of equine infectious anaemia (EIA) in Ireland. This paper describes the use of the diagnosis of clinical and subclinical cases of the disease. In acute cases the ELISAs and the immunoblot were more sensitive than the AGID. In one mare, fluctuating antibody levels were observed in all the serological assays before it seroconverted by AGID. Viral RNA and DNA were detected by RT-PCR and PCR in all the tissues from the infected animals examined postmortem. The PCR detected viral DNA in plasma regardless of the stage of the disease. In contrast, the RT-PCR detected RNA in only 52 per cent of the seropositive animals tested and appeared to be most sensitive for the detection of virus early in infection. Both PCR and RT-PCR demonstrated potential to detect acutely infected horses earlier than some of the official tests. The serological data suggest that the usual incubation/seroconversion period for this strain of the virus was approximately 37 days but may be more than 60 days in a few cases.  相似文献   
95.
Accumulation of surplus phosphorus (P) in the soil and the resulting increased transport of P in land runoff contribute to freshwater eutrophication. The effects of increasing soil P (19–194 mg Olsen‐P (OP) kg−1) on the concentrations of particulate P (PP), and sorption properties (Qmax, k and EPCo) of suspended solids (SS) in overland flow from 15 unreplicated field plots established on a dispersive arable soil were measured over three monitoring periods under natural rainfall. Concentrations of PP in plot runoff increased linearly at a rate of 2.6 μg litre−1 per mg OP kg−1 of soil, but this rate was approximately 50% of the rate of increase in dissolved P (< 0.45 μm). Concentrations of SS in runoff were similar across all plots and contained a greater P sorption capacity (mean + 57%) than the soil because of enrichment with fine silt and clay (0.45–20 μm). As soil P increased, the P enrichment ratio of the SS declined exponentially, and the values of P saturation (Psat; 15–42%) and equilibrium P concentration (EPCo; 0.7–5.5 mg litre−1) in the SS fell within narrower ranges compared with the soils (6–74% and 0.1–10 mg litre−1, respectively). When OP was < 100 mg kg−1, Psat and EPCo values in the SS were smaller than those in the soil and vice‐versa, suggesting that eroding particles from soils with both average and high P fertility would release P on entering the local (Rosemaund) stream. Increasing soil OP from average to high P fertility increased the P content of the SS by approximately 10%, but had no significant (P > 0.05) effect on the Psat, or EPCo, of the SS. Management options to reduce soil P status as a means of reducing P losses in land runoff and minimizing eutrophication risk may therefore have more limited effect than is currently assumed in catchment management.  相似文献   
96.
Immune privileged mesenchymal stem cells (MSCs) can differentiate into multiple cell types and possess great potential for human and veterinary regenerative therapies. This study was designed with an objective to isolate, expand and characterize buffalo bone marrow‐derived MSCs (BM‐MSCs) at molecular and cellular level. Buffalo BM‐MSCs were isolated by Ficoll density gradient method and cultured in Dulbecco’s modified Eagle’s medium supplemented with fetal bovine serum (FBS). These cells were characterized through alkaline phosphatase (AP) staining, colony‐forming unit (CFU) assay, mRNA expression analysis (CD 73, CD 90, CD 105, Oct4 and Nanog), immunolocalization along with flow cytometry (Stro 1, CD 73, CD 105, Oct4, Sox2 and Nanog) and in situ hybridization (Oct4 and Sox2). Multilineage differentiation (osteogenic, adipogenic and chondrogenic) was induced in vitro, which was further assessed by specific staining. Buffalo BM‐MSCs have the capacity to form plastic adherent clusters of fibroblast‐like cells and were successfully maintained up to 16th passage. These cells were AP positive, and further CFU assay confirmed their clonogenic property. RT‐PCR analysis and protein localization study showed that buffalo BM‐MSCs are positive for various cell surface markers and pluripotency markers. Cytoplasmic distribution of mRNA for pluripotency markers in buffalo BM‐MSCs and multilineage differentiation were induced in vitro, which was further assessed by specific staining. To the best of our knowledge, this is the first report of buffalo BM‐MSCs, which suggests that MSCs can be derived and expanded from buffalo bone marrow and can be used after characterization as a novel agent for regenerative therapy.  相似文献   
97.
An experiment was conducted to establish the effect of feeding either refined coconut oil (CO) or copra meal containing CO to beef heifers on DMI, animal performance, enteric CH4 emissions, diet digestibility, and the fatty acid profile of the resulting meat. Forty-one Charolais and Limousin crossbred beef heifers (474 +/- 29 kg; 661 +/- 89 d of age) were blocked by BW before being assigned in a randomized complete block design to 1 of 3 experimental treatments (n = 12) or to a pretrial slaughter group (n = 5) used to determine the initial carcass weight. The experimental period lasted for 93 d. Enteric CH4 output was recorded for 2 periods of 5 consecutive days from d 14 to 18 and from d 70 to 74. The 3 dietary treatments were 1) control, a barley/soybean meal-based concentrate with 0 g of CO/ d; 2) RCO, a barley/soybean meal-based concentrate with 250 g of CO/d from refined coconut oil; and 3) CM, a copra meal-based concentrate with 250 g of CO/d from copra meal. Each diet had a 50:50 forage:concentrate using grass silage as the forage source. There was no effect of diet on DMI (P = 0.734) or GE intake (P = 0.486). The addition of RCO increased ADG (P < 0.05) compared with the control treatment. The CM treatment decreased (P < 0.05) average daily carcass gain compared with the RCO treatment only. There was a decrease (P < 0.05) in the digestibility of the DM, OM, CP, and GE fractions of the diet only with the CM treatment. Both the RCO and CM concentrates decreased (P < 0.001) daily enteric CH4 output when expressed in terms of liters per day, liters per kilogram of DMI, percentage of GE intake, liters per kilogram of ADG, and liters per kilogram of average daily carcass gain. The RCO treatment produced the greatest numerical response for all measures. Ruminal protozoa numbers on the RCO treatment were lower (P < 0.05) than on the control treatment. The concentrations of the fatty acid methyl esters, lauric (P < 0.001) and myristic (P < 0.002) acids, were increased in muscle when either of the CCO treatments was compared with the controls, but the differences were of a magnitude unlikely to influence human health status. Although the CM concentrate decreased CH4 comparable with the RCO concentrate, decreased performance resulted in an extended finishing time with implications for lifetime CH4 emissions.  相似文献   
98.
99.
Impairment of water quality is a major concern for streams and rivers in the central USA. Total maximum daily loads (TMDLs) establish a watershed framework and set management targets to alleviate pollution from both point and nonpoint sources. For this study, we have used a hydrologic modeling approach to holistically examine the effect of land use management, urban development, and agricultural practices on sediment and nutrient loadings in an agricultural watershed. Annualized Agricultural Nonpoint Source (AnnAGNPS) simulation indicates that while point source dischargers contribute 8% of total nitrogen (TN) and 24% of total phosphorus (TP) loadings to the Marmaton River, agricultural nonpoint sources are the leading pollution source contributing 55% of TN and 49% of TP loading. Based on TMDL analysis and model simulation, 3% of the watershed area (3,244 ha) needs to be targeted to control TN loading whereas 1% of the total area (1,319 ha) is required for TP reduction management. Managing the TN areas alone can achieve a 57% reduction in the TP load required for the TMDL, whereas managing the targeted TP areas can only provide 30% of the required TN reduction. Areas required both TN and TP management comprise 469 ha. Targeting these areas can achieve approximately 22% of the required TN reduction and 29% of the required TP reduction. Overall, 4,094 ha will require management to achieve water quality goals. This study demonstrates that a modeling approach is needed to effectively address TMDL issues and help identify targeted areas for management.  相似文献   
100.
The function of many DNA metabolism proteins depends on their ability to coordinate an iron-sulfur (Fe-S) cluster. Biogenesis of Fe-S proteins is a multistep process that takes place in mitochondria and the cytoplasm, but how it is linked to nuclear Fe-S proteins is not known. Here, we demonstrate that MMS19 forms a complex with the cytoplasmic Fe-S assembly (CIA) proteins CIAO1, IOP1, and MIP18. Cytoplasmic MMS19 also binds to multiple nuclear Fe-S proteins involved in DNA metabolism. In the absence of MMS19, a failure to transfer Fe-S clusters to target proteins is associated with Fe-S protein instability and preimplantation death of mice in which Mms19 has been knocked out. We propose that MMS19 functions as a platform to facilitate Fe-S cluster transfer to proteins critical for DNA replication and repair.  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