全文获取类型
收费全文 | 154篇 |
免费 | 2篇 |
国内免费 | 12篇 |
专业分类
林业 | 3篇 |
农学 | 19篇 |
基础科学 | 20篇 |
33篇 | |
综合类 | 34篇 |
农作物 | 19篇 |
水产渔业 | 7篇 |
畜牧兽医 | 15篇 |
园艺 | 9篇 |
植物保护 | 9篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有168条查询结果,搜索用时 15 毫秒
101.
102.
为了更加全面的建立中国土壤类型系统,了解中国土壤地域差异,从而提高土地资源的利用率,以及根据土壤类型指导农业科学生产。该研究利用激光诱导击穿光谱(laser-induced breakdown spectroscopy,LIBS)技术结合化学计量学方法对土壤类型进行判别分析研究。从6种标准土壤样品出发,分析所采集6种土壤的LIBS光谱谱线特征,结合其主要成分物质(SiO2,Al2O3,Fe2O3,FeO,MgO,CaO,Na2O,K2O)的含量,针对每种主要物质选取了Si I 390.55 nm、Al I 394.40 nm、Fe I 422.74 nm、Mg I 518.36 nm、Na I 588.96 nm、Ca II 393.37 nm、K I 766.49 nm为特征分析谱线。结合所选的7条特征谱线下的300个标准土壤样品的光谱(200个为训练集,100个为预测集),对训练集光谱进行主成分分析(principal component analysis,PCA),6种土壤有明显的聚类。然后根据训练集光谱值和预先赋予土壤类型的虚拟等级值分别建立最小二乘判别分析(partial least squares discriminant analysis,PLS-DA)和最小二乘支持向量机(least-squares support vector machine,LS-SVM)判别模型,分析预测结果二者总的判别准确率分别为98%和100%。用受试者工作特征曲线(receiver operating characteristic curve,ROC)评价这2个模型的性能,结果表明LS-SVM判别模型性能优于PLS-DA模型。基于以上结果,选取不同于标准土壤的另7种不同类型土壤进行试验验证所选特征谱线和判别模型,建立7种不同类型土壤的LS-SVM预测模型,其预测准确率达100%,ROC曲线对其评价的性能很好。研究证明,LIBS技术结合化学计量学方法能够实现对土壤类型的判别分析,这为土壤质量的正确评价,土壤的整治、规划和合理利用提供理论基础。 相似文献
103.
Summary The F2 generation of interspecific crosses of Vitis were examined for symptoms of incongruity, manifested as morphological abnormalities in the seedlings. Dwarfing, achlorophyllic variegation, deformed leaves, yellow mottling, sparse roots, and enation were documented. Most comparisons between classed of crosses were significantly different. The V. riparia x V. vinifera class exhibited the greatest frequency of abnormalities, the V. riparia x V. riparia class displayed the lowest frequency of abnormalities, and the highly-intercrossed V. riparia x French Hybrid class demonstrated an intermediate frequency of abnormal plants. When incongruity was viewed as a syndrome, or collection of symptoms, differences between classed were consistently evident. The highly-intercrossed nature of the French Hybrid ancestry appears to have been responsible for attenuating incongruity.Minnesota Agricultural Experiment Station, Scientific Journal Series No. 20834 相似文献
104.
《Soil Science and Plant Nutrition》2013,59(6):911-916
Laser-induced breakdown spectroscopy (LIBS) has been developed as a rapid and easy in situ technique for the analysis of inorganic elements. Qualitative and quantitative determinations of an inorganic element can be achieved by analyzing the wavelength and intensity of the light emitted from the excited atoms arising from breakdown phenomena. Because the energy threshold of breakdown phenomena increases in the order of solid<liquid<gas, preferential breakdown of solid particles in liquid is possible by adjusting the energy of laser radiation. This rapid and easy in situ technique for the selective determination of soil particles or sediments suspended in water may enhance the effectiveness of environmental monitoring systems. In the present study, we applied LIBS to selective analyses of Al particles suspended in water. In addition, particle size effects that limit the performance of LIBS for the application of suspensions in the environment were investigated. Selective quantitative analysis of Al of gibbsite and alumina particles that were suspended in water was performed when the laser pulse energy was lower than that required for the breakdown of aqueous Al ions dissolved in water. When the Al concentration in the suspension was identical, the intensity of atomic emission from an Al particle increased with the particle size. This result was ascribed to the fact that larger particles contain more Al atoms per particle. There was a linear relationship between the cross-section area of the alumina particles and the intensity of the atomic emission per particle when the particles were small enough to exceed the threshold of breakdown. This suggested that both the particle size and Al concentration could be roughly estimated when simultaneous counting of the number of particles was accomplished by the use of laser-induced breakdown detection (LIBD). 相似文献
105.
为实现应用激光诱导击穿光谱(LIBS)技术准确检测农业生物炭中主要金属元素含量,并提高检测灵敏度,提出采用高温处理法去除水分、固定碳和有机基体效应的影响。首先获取灰分质量分数在28%~42%范围内具有代表性的66个农业生物炭样品,并选用不同灰分区间间距(14%、7%、3. 5%和2%)对样品集进行划分。当间距设为7%时,样品集的灰分区间被划分为28%~35%(38个样品)和35%~42%(28个样品),对应的高温处理前后各元素含量平均决定系数均大于0. 96。理论上表明,可以利用高温处理后样品光谱信息,并结合原始样品化学信息,构建农业生物炭中主要金属元素含量的连续灰分区间定标模型。通过比较原始样品和高温处理后样品数据集所构建模型的效果,得出高温处理后样品偏最小二乘回归(PLSR)模型的交互验证相对标准偏差明显较低,其预测集的成对T检验显示,LIBS和电感耦合等离子体质谱(ICP-MS)测定结果无显著性差异。结果表明,高温处理结合连续灰分区间定标模型能够实现农业生物炭中主要金属元素的LIBS同步精确定量分析。 相似文献
106.
Four parents [P. acutifolius var.acutifolius (A19), P. a.var. latifolius `Serowi' (A9),P. a. var. latifolius(A10), and P. vulgaris `Red Cloud' kidney (V1)] were used to create six interspecific recurrent and congruity backcross pedigrees (V1 × A9, A9 × V1, V1 × A10, A10 × V1, V1 × A19, A19 × V1) for evaluation of Rhizobium, Bradyrhizobium nodulation affinities and root peroxidase banding patterns. Most primary hybrids nodulated with all Rhizobium, Bradyrhizobium strains, while recurrent generations nodulated with strains of the recurrent parent, suggesting a number of independent loci
and random assortment for strain-specific nodulation. A proximity matrix of nodulation phenotypes produced a cluster with
V1, two recurrent and two congruity backcross hybrids with V1 as the cytoplasmic parent; a separate cluster with all primary interspecific and balanced, congruity backcross hybrids. A9 and A10were clustered the farthest away from V1. Root peroxidase zymograms of primary hybrids were the summation of the parents and controlled by independent loci. Advanced
hybrids exhibited new root peroxidases, matching those found for otherPhaseolus spp., including ancestralP. coccineus. A proximity matrix of root peroxidase phenotypes produced a cluster with only A9
3V1F1, a cluster containing only A19
3V1 F2, and a large cluster with all P. acutifoliusparents and hybrids with P. acutifolius as the cytoplasmic parent in balanced hybrids or the majority parent in unbalanced hybrids. Estimation of genetic distances
showed primary, interspecific hybrids to be more closely related with the cytoplasmic parent. Recurrent and congruity backcross
generations varied in genetic distances between each respective parent. This is the first report of congruity backcrossing
creating hybrids with biochemical traits of nonparental species.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
107.
作为维护国家内部稳定的生力军,武警部队运输装备的优劣直接关系到任务能否顺利完成。武警部队任务多发性、突然性的特点及未来作战的新要求,决定我们对车辆的保障必须符合新时期的新要求。基于武警部队信息网络的车辆故障诊断系统开发,对于提高部队的装备保障有着重要意义。 相似文献
108.
Hybrid breakdown (HB) is an important type of post-zygotic reproductive barrier that inhibits hybrid production during the process of cross-breeding. A novel low temperature-dependent HB was identified in a chromosomal segment substitution line (CSSL) library derived from a cross of two rice (Oryza sativa L. japonica) cultivars, Yukihikari and Kirara397. A set of weakness symptoms in a target CSSL was observed at 23°C, but was rescued at 27°C and/or 30°C. Genetic analysis of HB using an F2:3 population of a cross between a target CSSL and Kirara397 found that a recessive temperature sensitive hybrid breakdown1 (thb1) gene from Yukihikari caused HB in the genetic background of Kirara397. Molecular mapping showed that thb1 was located within a 199-kb fragment on chromosome 6. A genetic study of F2 populations of reciprocal crosses between Yukihikari and Kirara397 confirmed that this HB was induced by the interaction of two recessive genes. These results provide important clues to further dissect the mechanism of generation of a novel temperature sensitive HB in rice intrasubspecific crosses and suggest that these linked markers will useful in rice breeding. 相似文献
109.
黄丽芳 《拖拉机与农用运输车》2005,(5):94-95
机械的结构强度的破坏,大约有80%以上是由于疲劳破坏造成的。曲轴是典型的疲劳破坏零件,本文从金属疲劳破坏机理及疲劳分析的理论,分析了汽车内燃机曲轴断裂的原因,并对曲轴的安全使用与维护提出了有实际意义的措施。 相似文献
110.
玉米C型胞质雄性不育系花药发育的细胞学观察 总被引:5,自引:0,他引:5
对3个 C 型不育系及其同型保持系和4个恢复系与这3个不育系组配的12个 F_1的花药发育过程进行了观察,以了解 C 型不育系雄性败育的细胞学机理。观察结果表明,不同核背景的不育系,其雄性败育的细胞学特点各异。Cms-C Mo17的花药绒毡层细胞为双核型。该层细胞在减数分裂的四分体时期开始液泡化,并呈辐射状膨大,至小孢子的单核前 相似文献