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Shaw DE Maragakis P Lindorff-Larsen K Piana S Dror RO Eastwood MP Bank JA Jumper JM Salmon JK Shan Y Wriggers W 《Science (New York, N.Y.)》2010,330(6002):341-346
Molecular dynamics (MD) simulations are widely used to study protein motions at an atomic level of detail, but they have been limited to time scales shorter than those of many biologically critical conformational changes. We examined two fundamental processes in protein dynamics--protein folding and conformational change within the folded state--by means of extremely long all-atom MD simulations conducted on a special-purpose machine. Equilibrium simulations of a WW protein domain captured multiple folding and unfolding events that consistently follow a well-defined folding pathway; separate simulations of the protein's constituent substructures shed light on possible determinants of this pathway. A 1-millisecond simulation of the folded protein BPTI reveals a small number of structurally distinct conformational states whose reversible interconversion is slower than local relaxations within those states by a factor of more than 1000. 相似文献
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Hui Qiao Yibing Cai Fang Chen Qufu Wei Foquan Weng Fenglin Huang Lei Song Yuan Hu Weidong Gao 《Fibers and Polymers》2009,10(6):750-755
The Fe-montmorillonite (Fe-MMT) combined catalysis effects of Fe ion with barrier effects of silicate clays, was firstly synthesized
by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The organic-modified Fe-montmorillonite
(Fe-OMT) was dispersed in the N, N-dimethyl formamide (DMF) and then compounded with polyacrylonitrile (PAN) solution which
was dissolved in DMF. The composite solutions were electrospun to form PAN/Fe-OMT nanocomposite fibers. The influences of
the Fe-OMT on the structure, morphology, thermal, flammability and mechanical properties of PAN nanocomposite fibers were
respectively characterized by X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Scanning
electron microscopy (SEM), Thermogravimetric analyses (TGA), Micro Combustion Calorimeter (MCC) and Electronic Single Yarn
Strength Tester. It was found from XRD curves that there was not observable diffraction peak of silicate clay, indicating
that the silicate clay layers were well dispersed within the PAN nanofibers. The HRTEM image indicated that the multilayer
stacks of nanoclays could be found within the nanofibers and were aligned almost along the axis of the nanofibers. The SEM
images showed that the diameters of nanocomposite fibers were decreased with the loading of the Fe-OMT. The TGA analyses revealed
that the onset temperature of thermal degradation and charred residue at 700°C of PAN nanocomposite fibers were notably increased
compared with the pure PAN nanofibers, contributing to the improved thermal stability properties. It was also observed from
MCC analyses that the decreased peak of heat release rate (PHRR) of the PAN nanocomposite fibers reduced the flammability
properties. The loadings of Fe-OMT increased the tensile strength of PAN nanocomposite fibers, but the elongation at break
of PAN nanocomposite fibers was lower than that of the PAN nanofibers. 相似文献
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为研究灵芝孢子粉与大豆异黄酮对110~140日龄文昌鸡生长性能、肉品质与抗氧化能力的影响,试验选取540只110日龄文昌母鸡,随机分成3个处理组,每组6个重复,每个重复30只,试验周期30天,对照组饲喂基础日粮,处理组分别在基础饲粮中添加500 mg/kg灵芝孢子粉和300 mg/kg大豆异黄酮预混剂,试验期满后,测定试鸡生长性能,采集试鸡血浆、胸肌样品,测定血液与胸肌抗氧化指标、胸肌肉质性状、肉感官评定及货架期指标。结果表明,与对照组相比,1)大豆异黄酮组试鸡的生长末重与平均日增重均显著增加(P<0.05),料重比降低(P<0.05);2)灵芝孢子粉显著提高试鸡胸肌宰后24 h的pH(P<0.05)、降低剪切力(P<0.05);大豆异黄酮显著降低胸肌宰后45 min的a*值(P<0.05),提高胸肌宰后24 h的L*值和pH(P<0.05);3)灵芝孢子粉组试鸡的肉汤鲜味评分显著提高(P<0.05);4)灵芝孢子粉可显著降低文昌鸡胸肌宰后24 h的丙二醛(MDA)与宰后45 min的挥发性盐基氮含量(P<0.05);大豆异黄酮显著降低试鸡胸肌宰后45 min和24 h的MDA含量(P<0.05);5)饲粮添加灵芝孢子粉与大豆异黄酮显著降低了文昌鸡血浆MDA含量(P<0.05),灵芝孢子粉还增加了血浆谷胱甘肽含量(P<0.05)。综上,500 mg/kg灵芝孢子粉和300 mg/kg大豆异黄酮预混剂均可提高文昌鸡的抗氧化能力,改善肌肉品质。二者比较,500 mg/kg灵芝孢子粉作用更优。 相似文献
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阿尔泰山位于中国、蒙古和苏联的交界处,分布着较完整的垂直地带性土壤。有关阿尔泰山山地土壤的垂直分布规律,已有报道。本试验研究土壤中铁、锰的形态分布特征及垂直地带性,其结果有助于了解阿尔泰山山地土壤的发生发展过程,为合理开发利用阿尔泰山山地土壤资源的途径提供科学依据。 相似文献
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中国秸秆生物质发电区域适宜度分异评价 总被引:4,自引:0,他引:4
秸秆发电是我国发展生物质能产业的重要组成部分,区域适宜度评价是决定其合理布局的关键.在综合分析秸秆发电产业发展影响因素的基础上,运用层次分析法和多目标线性加权函数法从耕地资源潜力、秸秆原料供应、市场需求状况和产业发展成本四个层面共选取了耕地资源总量、耕地资源量波动水平、秸秆资源总量、秸秆产量波动水平、用电量、用电量增长率、秸秆资源密度和人均GDP等8个指标建立了中国秸秆发电区域适宜度评价指标体系和评价模型,结果显示,我国各省区秸秆发电适宜度存在较大差异,综合适宜度较高的是河南、山东、安徽、江苏、河北、黑龙江、吉林等我国中部和东北粮食主产区;综合适宜度较低的是北京、上海、天津、浙江等东部经济发达区和青海、宁夏、甘肃、陕西等西北农牧区;其余区域秸秆生物质发电的适宜程度一般. 相似文献
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