全文获取类型
收费全文 | 410篇 |
免费 | 18篇 |
国内免费 | 16篇 |
专业分类
林业 | 26篇 |
农学 | 64篇 |
基础科学 | 15篇 |
119篇 | |
综合类 | 179篇 |
农作物 | 7篇 |
水产渔业 | 1篇 |
畜牧兽医 | 18篇 |
园艺 | 8篇 |
植物保护 | 7篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 21篇 |
2015年 | 17篇 |
2014年 | 29篇 |
2013年 | 51篇 |
2012年 | 44篇 |
2011年 | 31篇 |
2010年 | 22篇 |
2009年 | 20篇 |
2008年 | 21篇 |
2007年 | 18篇 |
2006年 | 13篇 |
2005年 | 8篇 |
2004年 | 1篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 3篇 |
排序方式: 共有444条查询结果,搜索用时 15 毫秒
61.
The corrosion and extraction toxicity of heavy metal in ancient smelting slag is analyzed. Leaching behavior of heavy metal in smelting slag is discussed through extraction toxicity test of different pH values. The results show that the pH of smelting slag is alkalescence, the heavy metal content is high and the average content of heavy metal (zinc plus plumbum) is up to 6.97%. However, most of heavy metal in smelting slag is in residual state. Its extraction toxicity is low and potential harm for environment is obviously weakened. It indicates that forecasting heavy metal’s potential harm for environment in smelting slag by totalizing method is not accurate. The leachable quantities of heavy metals significantly increase in extremely acidic and alkaline condition. The leachable quantities of Zn, Pb, Cr and Cd are all up to maximum when pH<3. The leachable quantities of Zn, Pb and Cr all increase when pH>12, but the extracting amount is lower than that in acidic condition. The leachable quantity of Zn, Pb, Cr and Cd is minimal in neutral condition. Under normal rainfall conditions, potential harm for environment of ancient smelting slag is decreased to a lower level. It can be treated according to the requirement for general industrial solid wastes. 相似文献
62.
为破解压煤塌陷区农村移民安置的困境,通过对压煤塌陷区移民风险与特点的分析,借鉴水利水电工程移民安置模式的经验,提出压煤塌陷区农村移民城乡联动安置模式。重点论述了城乡联动安置模式的内涵、运行设计、合理性,并探讨了该模式在实现过程中的约束条件。 相似文献
63.
64.
《Communications in Soil Science and Plant Analysis》2012,43(19-20):2619-2634
Abstract Coal bed natural gas (CBNG) development in the Powder River (PR) Basin produces modestly saline, highly sodic wastewater. This study assessed impacts of wetting four textural groups [0–11%, 12–22%, 23–33%, and >33% clay [(g clay/100 g soil)×100%)] with simulated PR or CBNG water on water retention. Soils received the following treatments with each water quality: a single wetting event, five wetting and drying events, or five wetting and drying events followed by leaching with salt‐free water. Treated samples were then resaturated with the final treatment water and equilibrated to ?10, ?33, ?100, ?500, or ?1,500 kPa. At all potentials, soil water retention increased significantly with increasing clay content. Drought‐prone soils lost water‐holding capacity between saturation and field capacity with repeated wetting and drying, whereas finer textured soils withstood this treatment better and had increased water‐retention capacity at lower matric potentials. 相似文献
65.
PLC在输煤控制系统中的应用 总被引:1,自引:0,他引:1
采用ABControlLogix1756系列产品PLC实现了对输煤过程的控制,通过建立以太网环网和双缆双网的控制层网络ControlNet以及主机的双机热备提高了系统的可靠性。利用GEiFixSCADA上位机监控软件实现了对输煤与配煤系统的监视和控制。 相似文献
66.
腐熟油菜秸秆、煤矸石组合的栽培基质重金属污染及蔬菜安全评价 总被引:1,自引:0,他引:1
以腐熟油菜秸秆、煤矸石等废弃资源为原料, 配制有机生态型无土栽培混合基质, 在人工光照室内以盆栽的方法栽培白菜、生菜、苋菜和菠菜, 采用尼梅罗综合污染指数和Hakanson 潜在生态风险指数法对5 种混合基质以及此基质中生长的 4 种蔬菜的重金属污染和潜在生态风险进行综合评价。结果表明: 5 种混合基质中, 煤矸石含量较少的T1、T2、T3(即煤矸石与腐熟油菜秸秆的体积比分别为 2∶8、3∶7 和4∶6)基质的重金属污染程度较小, 潜在生态风险程度较低, 在这 3 种基质上栽种的蔬菜重金属综合污染评价等级为优良或安全, 符合蔬菜绿色食品标准。重金属对混合基质产生的污染中, Cd 和Hg 是主要的重金属污染及潜在生态风险因子, 其他重金属(Cr、Cu、Pb、Zn、As)的污染能力较低。此外, 影响混合基质重金属生物有效性的主要因子是有机质, 除Cd、As 外, 基质中的有机质含量与有效态重金属含量存在极显著负相关, 基质pH 对其影响较小。 相似文献
67.
通过对材料组成和结构的设计,获得了高炉渣和钢渣用量为55%-60%,抗弯强度大于300MPa,显微硬度达12GPa,耐磨性比GCr15钢高26倍的玻璃陶瓷。探讨了微晶化工艺条件对钢铁废渣玻璃陶瓷的显微结构和性能的影响,在一定工艺条件下所制备的玻璃陶瓷的晶相含量可达90%以上,晶粒大小仅0.1-0.3μm,多为等轴柱状晶,以辉石类为主晶相。 相似文献
68.
The silicic acid adsorption by a soil (Eutric Gleysols) where slag fertilizers were applied was measured by the addition of a silicic acid solution labelled with 30Si after soil incubation, in order to study the effect of slag application on the specific Si adsorption by the soil and to estimate the amount of Si in the soil solid phase which can easily enter the soil solution. It was evident that the application of slags increased the ability of soil to adsorb Si. It was also shown that the 30Si added was diluted with not only the Si present in the soil solution but also the Si dissolved from the soil solid phase. We proposed the use of the term “active” for Si in soil which can take part in the isotopic dilution within 1 h. The amount of active Si in the soil solid and liquid phases (D 60 - value) was calculated from the 30Si content in the soil solution and compared with the amount of Si taken up by rice plant (Oryza sativa L.), which was determined in our previous study. The buffering capacity of the soil for Si, which can reflect the ability of soil to maintain the Si concentration in the soil solution constant when Si is added to or removed from the soil, was also determined. The D 60 - value and the Si buffering capacity of the soil increased by slag application. These increases were large when the alkalinity of the applied slags was high. The correlation study revealed that the D 60 - value was a better index of Si availability of the soil than the amount of Si dissolved from the soil solid phase during the incubation when the slags were previously applied. 相似文献
69.
70.
刘冲 《山东农业大学学报(自然科学版)》2015,(1):132-135
为了对采煤机故障进行准确诊断研究,本文提出了一种基于优化支持向量机的采煤机故障诊断新方法,首先采用主成分分析法(PCA)对采煤机故障特征参数进行特征提取,其次应用特征数据进行基于支持向量机(SVM)的采煤机故障诊断模型训练,再次采用交叉验证方法对SVM模型参数进行优化,建立最优SVM采煤机故障诊断模型,最后通过对比实验,验证了基于优化SVM采煤机故障诊断模型的可行性和优越性。 相似文献