全文获取类型
收费全文 | 1024篇 |
免费 | 62篇 |
国内免费 | 25篇 |
专业分类
化学 | 425篇 |
晶体学 | 2篇 |
力学 | 119篇 |
综合类 | 43篇 |
数学 | 288篇 |
物理学 | 234篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 38篇 |
2021年 | 74篇 |
2020年 | 40篇 |
2019年 | 42篇 |
2018年 | 40篇 |
2017年 | 52篇 |
2016年 | 63篇 |
2015年 | 32篇 |
2014年 | 69篇 |
2013年 | 83篇 |
2012年 | 50篇 |
2011年 | 53篇 |
2010年 | 37篇 |
2009年 | 40篇 |
2008年 | 44篇 |
2007年 | 56篇 |
2006年 | 53篇 |
2005年 | 40篇 |
2004年 | 33篇 |
2003年 | 24篇 |
2002年 | 25篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1111条查询结果,搜索用时 250 毫秒
51.
有相似产品信息情形下的可靠性评定方法 总被引:1,自引:0,他引:1
两个具有局部相同组成部分的相似设备为模型,建立有相关信息情形下进行可靠性评估的指数模型,并给出了指数模型中的参数估计方法,在此基础上建立了相似设备到目标设备信息的融合算法,进而提出了一种具有相似产品信息情形下的可靠性评定方法. 相似文献
52.
A simple procedure is proposed for the assessment of reinforced rectangular concrete columns under combined biaxial bending
and axial loads and for the design of a correct amount of FRP-strengthening for underdesigned concrete sections. Approximate
closed-form equations are developed based on the load contour method originally proposed by Bresler for reinforced concrete
sections. The 3D failure surface is approximated along its contours, at a constant axial load, by means of equations given
as the sum of the acting/resisting moment ratio in the directions of principal axes of the sections, raised to a power depending
on the axial load, the steel reinforcement ratio, and the section shape. The method is extended to FRP-strengthened sections.
Moreover, to make it possible to apply the load contour method in a more practical way, simple closed-form equations are developed
for rectangular reinforced concrete sections with a two-way steel reinforcement and FRP strengthenings on each side. A comparison
between the approach proposed and the fiber method (which is considered exact) shows that the simplified equations correctly
represent the section interaction diagram.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 443–462, May–June, 2008. 相似文献
53.
区域经济发展的属性模式识别模型 总被引:1,自引:0,他引:1
本将属性模式识别系统应用于区域经济发展优先级别的评价中。在建立评价指标体系的基础上。根据各指标的权重,提出确定区域经济发展中心的属性测度模型。并以黄河流域的12个大城市为样本,给出了一种比较科学的、切实可行的区域经济发展优先级别的评价方法。 相似文献
54.
55.
本文在客户问卷调查的基础上,结合国外有关的物流企业客户服务指标,建立了物流客户服务水平评价的指标体系,同时应用定性与定量分析相结合的方法,建立了属性综合评价的物流客户服务水平评价模型,并给出了具体的应用实例. 相似文献
56.
Theoretical assessment of the errors involved in ultrasonic location and sizing of molten weld pools
Ultrasonic transit times may be used to locate the interface between molten weld metal and parent plate as a weld is formed. These transit times will lead to errors in interpretation of the location of the weld interface if account is not taken of the variation of ultrasonic velocity with temperature. We assess the magnitude of these errors using a theoretical model based on the Green's function to obtain the temperature distribution at any time and then convert the temperatures into elastic constants through empirical fits to high temperature data. A ray tracing method and a semi-analytical approach are used to estimate the effects of the changes in elastic constants on the ray paths and transit times. From these theoretical predictions we conclude that the location errors incurred by assuming ultrasonic velocities appropriate to cold metal are less than 0.5 mm for a 3.5 mm radius weld in austenitic steel or in iron. Experimental values tend to be larger than this, possibly suggesting that the solid-liquid interface is not as perfect as in the theoretical model. Under all of the conditions investigated, predicted errors are smaller with compression waves than with shear waves. 相似文献
57.
敌情威胁程度的判断是定下作战决心的基础.提出利用多级模糊综合评判的方法,首先利用层次分析法(AHP法)综合专家的判断,建立权重集,然后利用模糊综合评判理论对对战场某一指定区域的模糊敌情进行威胁程度判断,从而将两种方法的优点综合起来.并给出了一个应用该方法的海区模糊敌情判断实例,结论说明该方法可行. 相似文献
58.
Xiangwei You Chengcheng Sui Xiuguo Wang Jinli Xu Xiao Zheng 《International journal of environmental analytical chemistry》2017,97(13):1253-1265
A rapid, sensitive, and selective method using a quick, easy, cheap, effective, rugged, and safe procedure in combination with high-performance liquid chromatography and tandem mass spectrometry was developed for the analysis of fenaminstrobin in peanut and soil. The average recoveries in all samples fall within 88.1%–10%, having relative standard deviations of 2.5%–14%. The limits of quantitation of fenaminstrobin in peanut shell, peanut kernels, peanut plant, and soil were 0.005, 0.004, 0.01, and 0.002 mg kg?1, respectively. The field trial results show that the half-lives of fenaminstrobin in peanut plant and soil are 1.3–10 and 5.5–20 days, respectively. Residues in peanut kernels were found to be present at <0.004 mg kg?1 levels, based on good agricultural practices recommended by the manufacturer. The risk posed by fenaminstrobin exposure at the recommended dosage is negligible to humans, depending on the risk quotient. 相似文献
59.
2006年7月至2007年11月采集了大亚湾10个采样点春、夏、秋和冬4季表层沉积物样品,分析了沉积物中的生物硅(BSi)、有机碳(TOC)、总氮(TN)和总磷(TP)含量。结果表明:大亚湾生源要素含量与国内外港湾相比属于中等水平;春季BSi、TP的平均含量分别为1.09%、0.043%;夏季BSi、TOC、TN、TP的平均含量分别为1.21%、1.05%、0.37%、0.043%;秋季BSi、TP的平均含量分别为0.99%、0.038%;冬季BSi、TOC、TN、TP的平均含量分别为1.09%、0.84%、0.11%、0.039%。根据TN/TP和TOC/TN比值判断,大亚湾沉积物为磷限制;夏季TOC主要来源于水生有机碳,冬季为混合来源。夏季表层沉积物中BSi、TOC、TN和TP的平均含量均高于其他季节;其中夏季各站位TN的含量较冬季要高,反映了夏季较高的硅藻生产力以及较丰富的地表径流。大亚湾大部分采样点TOC和TN的污染基本属于Ⅱ类,TP属于Ⅰ类,可能对底栖生物群落具有一定毒害作用。 相似文献
60.
Reinout Heijungs Gjalt Huppes Jeroen B. Guinée 《Polymer Degradation and Stability》2010,95(3):422-1719
There are many approaches to study the environmental and sustainability aspects of production and consumption. Some of these reside at the level of concepts, e.g., industrial ecology, design for environment, and cleaner production. Other approaches are based on the use of quantitative models, e.g., life cycle assessment, material flow accounting and strategic environmental assessment. This paper focuses on the development of a framework that is able to incorporate different models for environmental analysis, with the option of a broader scope that also includes economic and social aspects, thus covering the three pillars of sustainability. This framework builds on the ISO-framework for life cycle assessment, but takes a broader view, and allows us to move from micro questions on specific products, via meso questions on life styles up to macro questions in which the entire societal structure is part of the analysis. 相似文献