全文获取类型
收费全文 | 10722篇 |
免费 | 1462篇 |
国内免费 | 678篇 |
专业分类
林业 | 1114篇 |
农学 | 799篇 |
基础科学 | 497篇 |
1889篇 | |
综合类 | 5163篇 |
农作物 | 359篇 |
水产渔业 | 857篇 |
畜牧兽医 | 1206篇 |
园艺 | 294篇 |
植物保护 | 684篇 |
出版年
2024年 | 28篇 |
2023年 | 286篇 |
2022年 | 439篇 |
2021年 | 450篇 |
2020年 | 533篇 |
2019年 | 363篇 |
2018年 | 327篇 |
2017年 | 489篇 |
2016年 | 585篇 |
2015年 | 597篇 |
2014年 | 724篇 |
2013年 | 719篇 |
2012年 | 920篇 |
2011年 | 904篇 |
2010年 | 696篇 |
2009年 | 684篇 |
2008年 | 582篇 |
2007年 | 675篇 |
2006年 | 518篇 |
2005年 | 445篇 |
2004年 | 343篇 |
2003年 | 274篇 |
2002年 | 215篇 |
2001年 | 176篇 |
2000年 | 143篇 |
1999年 | 121篇 |
1998年 | 90篇 |
1997年 | 85篇 |
1996年 | 66篇 |
1995年 | 76篇 |
1994年 | 65篇 |
1993年 | 46篇 |
1992年 | 31篇 |
1991年 | 47篇 |
1990年 | 25篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 14篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The priority of management factors for reducing the yield gap of summer maize in the north of Huang-Huai-Hai region,China 下载免费PDF全文
Yue-e LIU Yu-xin LI Tian-fang LÜ Jin-feng XING Tian-jun XU Wan-tao CAI Yong ZHANG Jiu-ran ZHAO Rong-huan WANG 《农业科学学报》2021,20(2):450-459
Understanding yield potential, yield gap and the priority of management factors for reducing the yield gap in current intensive maize production is essential for meeting future food demand with the limited resources. In this study, we conducted field experiments using different planting modes, which were basic productivity(CK), farmer practice(FP), high yield and high efficiency(HH), and super high yield(SH), to estimate the yield gap. Different factorial experiments(fertilizer, planting density, hybrids, and irrigation) were also conducted to evaluate the priority of individual management factors for reducing the yield gap between the different planting modes. We found significant differences between the maize yields of different planting modes. The treatments of CK, FP, HH, and SH achieved 54.26, 58.76, 65.77, and 71.99% of the yield potential, respectively. The yield gaps between three pairs: CK and FP, FP and HH, and HH and SH, were 0.76, 1.23 and 0.85 t ha~(–1), respectively. By further analyzing the priority of management factors for reducing the yield gap between FP and HH, as well as HH and SH, we found that the priorities of the management factors(contribution rates) were plant density(13.29%)fertilizer(11.95%)hybrids(8.19%)irrigation(4%) for FP to HH, and hybrids(8.94%)plant density(4.84%)fertilizer(1.91%) for HH to SH. Therefore, increasing the planting density of FP was the key factor for decreasing the yield gap between FP and HH, while choosing hybrids with density and lodging tolerance was the key factor for decreasing the yield gap between HH and SH. 相似文献
2.
2000-2018年广西植被时空变化及其对地形、气候和土地利用的响应 总被引:6,自引:5,他引:1
广西是典型的喀斯特地区,其生态系统非常脆弱。为评估广西植被时空变化特征及其影响因素,该研究基于2000-2018年MODIS数据,利用最大值合成和趋势分析等方法,分析广西植被NDVI时空变化特征;基于相关分析等方法,结合地形因子、气候因子和土地利用数据,探讨了植被NDVI对地形、气候变化和土地利用的响应。结果表明:1)2000-2018年广西植被NDVI呈增加趋势,但空间差异显著,表现为北高南低,边缘高中间低。2)随着高程的增加植被NDVI呈现先增加再减少的趋势;随着坡度的增加植被NDVI呈先增加至稳定再减小的趋势;除无坡向以外,坡向的不同对植被NDVI影响不大。3)广西2000-2018年气温和降水对植被NDVI为正影响,复相关系数达到0.32。在不同土地利用类型上,植被NDVI对气候的响应是不同的。研究结果揭示了广西植被时空变化特征及其对地形、气候和土地利用的响应,能够为广西可持续发展和生态环境建设提供决策支持。 相似文献
3.
This study used two different collectors made of polypropylene (PP) rope and polyethylene (PE) fishing net to determine Mediterranean mussel's settlement, growth, condition index (CI), meat yield (MY) and shell thickness index (STI) during the period spent between June 2017 and November 2018. With this regard, chlorophyll a, water temperature, salinity, pH and particulate matter were defined through water samples that were collected on monthly basis triplicate. The mean chlorophyll a level was recorded as 0.32 ± 0.31 μg/L, while water temperature was 19.73 ± 5.14°C, salinity was 35 ± 2.070‰, pH was 8.12 ± 0.04, and TPM was 14.91 ± 10.48 mg/L. As a result of the cultivation period of 8 months spent following the first intense grip, the length of the mussels is measured as 31.79 ± 6.20 mm. Based on the Pearson correlation analysis results, the most important environmental parameter affecting Mediterranean mussels growth in length on PP rope collectors is the temperature (p < .05). The STI and CI were determined to be related with environmental temperature parameters, while no determinations could be obtained concerning the correlation of MY with environmental parameters. Assessment of Mediterranean mussels’ growth rate in PP rope collectors proved significant differences (p < .05) between March and November 2018. As no Mediterranean mussels are observed on PE fishing nets during the samplings performed throughout the study period, it is determined that PE fishing nets are not suitable collector types for Mediterranean mussel cultivation. 相似文献
4.
具有较好环保性能的包膜材料用于缓控释肥生产,可防止膜材料对土壤造成的潜在危害。本文以明胶、聚乙烯醇为原料复合共混制备膜材料,利用红外光谱(FTIR),扫描电镜(SEM)表征材料结构,并研究了膜材料拉伸强度和断裂伸张率力学性能,受控堆肥条件下的生物降解行为,明胶/PVA复合材料包膜尿素的养分缓释性及对小鼠的急性经口毒性。结果表明:当复合膜材料配比为m(PVA):m(Gel)=4:1时,组分相容性最好,并表现出良好力学性能、养分缓释性能和生物降解性能,复合材料包膜的肥料对小鼠无毒性作用,具有较好安全性。因此明胶/PVA复合膜材料具有较好的环保性能,其作为缓控释肥料的包膜材料具有较好应用前景。 相似文献
5.
翅多型现象在昆虫中广泛存在,比如蚜虫有有翅蚜和无翅蚜,无翅蚜无翅不能飞行。翅型分化是蚜虫对不良生态环境的适应策略。有翅蚜能飞行,使其逃离不良环境并找到新的栖息地;而无翅蚜繁殖周期短、繁殖量大,有助于维持一定的种群数量。影响蚜虫翅发育的因素有遗传因素和环境因素,由环境因素决定的翅的多型现象被称为翅的非遗传多型性。本文就蚜虫翅型分化的生态学意义、影响因素,以及蚜虫翅型分化的生理和分子机制进行了综述。关于影响蚜虫翅型分化的遗传因素的研究较少,部分研究发现豌豆蚜翅型由X染色体上的一对等位基因所控制。更多的研究表明蚜虫翅型分化受环境因素影响,影响蚜虫翅型分化的环境因素有光周期、温度、种群密度、共生微生物、天敌、杀虫剂及抗生素等,事实上这些环境因素往往不是单方面存在的。保幼激素、蜕皮激素等外源激素会影响包括蚜虫在内昆虫的翅型分化,蚜虫的拥挤效应最终可能也是通过激素调控发挥作用。外源激素可以作用于出生后的低龄若虫也可作用于预产期的成虫,比如给豆蚜中龄若蚜施加保幼激素处理后,会出现超龄若虫,而不是无翅蚜。相反,反-β-法尼烯(EBF)的刺激会诱导有翅蚜后代的产生。另有研究发现,上一代豌豆蚜注射蜕皮激素可以减少有翅后代数量,而通过RNA干扰(RNA interference, RNAi)EcR受体或施加EcR抑制物也会导致后代有翅个体增加。蚜虫翅型分化分子机制的研究起始于对同一基因型蚜虫有翅、无翅成虫个体的差异表达基因或差异表达蛋白。 相似文献
6.
农业转基因生物环境安全检测标准是农业转基因生物安全管理必不可少的技术保障。截至2021年1月,农业部/农业农村部共发布了农业转基因生物环境安全检测标准47项。本文对我国农业转基因生物环境安全检测标准体系现状进行初步总结,对国内外农业转基因生物环境安全检测标准的发展现状进行比较,探讨了今后一段时间内农业转基因生物环境安全检测标准的发展方向,以期为我国农业转基因生物环境安全检测标准的进一步完善提供借鉴,使其更好地为农业转基因生物安全管理工作提供技术支撑。 相似文献
7.
8.
阿维菌素类药物是一种常用的杀虫剂,现有报道的食品和环境基质样品中阿维菌素残留分析最为常用的检测仪器为液相色谱-串联质谱。基于此,已建立了一系列的不同样基质中多种阿维菌素类药物残留量的检测方法,本研究除了关注常见的多种阿维菌素残留量的测定方法,也关注了食品和环境样品中单种阿维菌素化合物的专一性检测方法。本研究从阿维菌素在食品和环境领域的应用以及赋存状态、前处理方式(提取和净化方法)、检测方法(液相色谱法、酶联免疫法和液相色谱-串联质谱法)及定量方式和基质干扰等方面,综述了2010—2020年不同检测技术在食品和环境样品基质中阿维菌素类化合物残留分析中的研究与应用进展。最后,综述了多残留量检测方法的局限性,未来的关注点以及对阿维菌素残留分析方法的发展趋势。本研究可为开展烟草中阿维菌素类化合物残留分析技术研究提供参考。 相似文献
9.
为稳定烟农队伍,引导烟农高质量生产,促进烟草行业的可持续发展,运用二元Logistic模型和攀枝花市3个烤烟主产区242户烟农的调查数据,分析农户种植烟草的意愿及其影响因素。结果表明,户主的年龄及参加农业专业知识培训的经历对烟农种植意愿具有正向的显著性影响,农户是否兼业、农户的家庭人口数量及非烟作物收入对烟农种植意愿具有负向的显著性影响。由此建议加强专业知识培训、引导烟农专业化生产、优化农村农业从业人口结构,这将有利于正向强化烟农生产积极性,进而通过种植经济作物达到农民收入持续增长、地区农业稳步发展的效果。 相似文献
10.
Wei WANG Xue ZHANG Yuhui ZHANG Xin MI Run WANG Huilan SHI Chunli LI Ziwen DU Youming QIAO 《土壤圈》2021,31(4):596-605
The widespread use of sodium p-perfluorous nonenoxybenzene sulfonate(OBS), a typical alternative to perfluorooctane sulfonate, has resulted in potential threats to the environment, but the adsorption behavior of OBS in soils has not yet been reported. In this study, the adsorption behaviors of OBS on five soils with different physicochemical properties were investigated. The rate of OBS adsorption was fast, and most of the OBS uptake was completed within 12 h. The good model fit of OBS adsorption to the pseudo-second-order and Elovich models indicated the occurrence of chemical adsorption. The adsorption isotherms of OBS on the soils were better described by the Freundlich model than by the Langmuir model, suggesting that the OBS adsorption sites on the soils were heterogeneous. This is possibly associated with various adsorption mechanisms including hydrophobic, π-π, hydrogen bonding, and electrostatic interactions,further confirmed by the good model fit to the D-R isotherm. Adsorption of OBS occurred on the soils, and the adsorption process was spontaneous and endothermic. In addition, the soils were more suitable for OBS adsorption at lower pH values due to the stronger electrostatic adsorption. The OBS adsorption on the soils decreased with the increase of soil depth from 0 to 30 cm. Moreover, the presence of organic matter and ammonia nitrogen in the soils was favorable for OBS adsorption, and these parameters decreased with increasing soil depth, making OBS adsorption less prominent in the deeper soil. This study indicates that OBS is easily enriched in surface soils, and that soil organic matter and ammonia nitrogen significantly affect OBS migration in soil. 相似文献