全文获取类型
收费全文 | 511篇 |
免费 | 79篇 |
国内免费 | 36篇 |
专业分类
化学 | 263篇 |
晶体学 | 17篇 |
力学 | 35篇 |
综合类 | 26篇 |
数学 | 149篇 |
物理学 | 136篇 |
出版年
2023年 | 5篇 |
2022年 | 15篇 |
2021年 | 41篇 |
2020年 | 28篇 |
2019年 | 18篇 |
2018年 | 25篇 |
2017年 | 28篇 |
2016年 | 27篇 |
2015年 | 19篇 |
2014年 | 28篇 |
2013年 | 57篇 |
2012年 | 34篇 |
2011年 | 22篇 |
2010年 | 17篇 |
2009年 | 17篇 |
2008年 | 27篇 |
2007年 | 28篇 |
2006年 | 28篇 |
2005年 | 24篇 |
2004年 | 21篇 |
2003年 | 16篇 |
2002年 | 14篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有626条查询结果,搜索用时 31 毫秒
1.
The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information. 相似文献
2.
随着经济的飞速发展,社会对能源的需求日益扩大,对工业废水的无害化处理也提出了更高的要求。光催化燃料电池 (photocatalytic fuel cell, PFC) 在燃料电池中引入半导体光催化材料作为电极,实现了有机污染物高效降解和同步对外产电的双重功能,在废水无害化与资源化利用方面具有潜在的应用价值。半导体光催化电极是PFC系统高效运行的核心组件,增强其可见光响应和光生载流子分离是提高PFC性能的关键策略。反应器结构设计和运行参数优化也有利于改善PFC性能。本文从PFC基本原理和应用入手,综述了PFC在环境污染物资源化处理中的研究进展,并详细阐述了提高PFC的污染控制性能和产电效率的优化手段,为进一步设计高效稳定的PFC系统并实现其在水污染控制和清洁能源生产中的应用提供理论指导。 相似文献
3.
区域经济的发展受许多不同因素的影响,本结合西藏社会经济发展的特点,选取了总产值指标、第一产业指标、第二产业指标和第三产业指标等四大类指标体系,采用灰色关联分析法对西藏的区域经济系统进行了简要的分析评价,以研究西藏区域经济的发展状况,从社会经济的角度探讨西藏经济发展落后的原因,以期能为西藏经济发展政策提供参考依据。 相似文献
4.
5.
Three procedures, matrix matching, plasma optimisation and single-point standard-addition, have been evaluated to ascertain the best procedure for simultaneous multi-element analysis of industrial soils by ICP-AES with CCD detection. A standard reference material, CRM143 from the Bureau Communautaire de Réference (BCR), has been analysed for Cd, Cr, Cu, Mn, Ni and Pb using the three different matrix interference correction procedures. All three procedures give comparable results which are in good agreement with the BCR values, except for Cr. The single-point standard addition procedure was chosen, on the basis of economy and ease of implementation, to correct for matrix interferences in the determination of Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sn and V in soil samples collected from an industrial site in England. Concentrations of some of the elements were found to vary greatly with sampling depth. For example, the concentration of Mn, determined using the atomic line at 279.920 nm, increased from 426 ± 3 g/g at a depth of 18–28 cm to 5996 ± 144 g/g at 60–85 cm. 相似文献
6.
粘土矿物的结构特征及其应用研究 总被引:2,自引:0,他引:2
阐述了贮量巨大、用途广泛的粘土矿物,其充分开发应用的关键,在于根据其结构特征,并通过适当的物理、化学方法加以改造、以适应各种不同工业应用的要求。并以我们对粘土矿物进行活化、改性、层间插入及其工业应用产品开发的初步研究成果,阐明利用粘土硅酸盐多层次结构的可变性,开拓新的应用性能的可能性及粘土矿物充分开发应用的途径。 相似文献
7.
8.
水淬渣-累托石颗粒吸附材料的制备及应用 总被引:1,自引:0,他引:1
研究了水淬渣-累托石颗粒吸附材料制备工艺条件、再生方法及其去除铜冶炼工业废水中重金属的条件.试验结果表明,累托石与水淬渣的比例为1∶1,另加入10%的添加剂(IS)和50%的水,焙烧温度为400℃时,制成的颗粒吸附材料体积密度为1.06kg/m3,显气孔率为62.29%,吸水率为58.82%,抗压强度为2.22Mpa,吸附效果好,散失率较低.在未调节铜冶炼工业废水pH值的条件下,颗粒吸附材料用量为0.05g/cm3,反应时间为40min,吸附温度为25℃(常温)时,Cu2 、Pb2 、Zn2 、Cd2 、Ni2 的去除率分别为98.2%、96.3%、78.6%、86.2%、64.2%,处理后的水符合国家污水综合排放标准(GB8978-1996)一级标准.颗粒吸附材料对Zn2 、Cu2 有很好的选择性.吸附饱和的颗粒吸附材料用1mol/L氯化钠溶液再生效果好.该颗粒吸附材料具有分离容易、可重复使用、处理效果好、应用前景广阔的优点. 相似文献
9.
Samuel Melaku Rita Cornelis Frank Vanhaecke Richard Dams Luc Moens 《Mikrochimica acta》2005,150(3-4):225-231
A simple, sensitive and inexpensive method for the speciation of Cr(VI) and Cr(III) in river and industrial wastewater was developed, optimized and validated. Samples were collected, filtered and then chromium species were determined in the filtrate. In the filtrate, total Cr was determined directly by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). A portion of the filtered sample was buffered to pH 6.4, extracted with Amberlite LA-2/MIBK and finally Cr(VI) was determined in the organic extract and Cr(III) in the aqueous phase using GFAAS. The method was evaluated by analysis of the certified reference material, CRM 544, and good accuracy was obtained. The limit of detection for Cr(VI) and Cr(tot)/Cr(III) was found to be 0.30 and 0.08 µg L−1, respectively, and a precision expressed as relative standard deviation of better than 11% was achieved for nine replicates. A number of water samples from the Tinishu Akaki River, Ethiopia, and wastewater samples from a chemical plant in Germany, were analysed. In addition to the GFAAS method, Cr(tot) was also determined using ICP-MS (in CRM 544, lyophilized water, and Tinishu Akaki River water samples) and Cr(tot) and Cr(VI) using UV-VIS spectrophotometry (in CRM 544 and industrial wastewater samples). Good agreement between the different methods was found. 相似文献
10.
Fundamental understanding of aerosol formation and particle transport are important aspects of understanding and improving
laser-ablation ICP–MS. To obtain more information about particles entering the ICP, laser aerosols generated under different
ablation conditions were collected on membrane filters. The particles and agglomerates were then visualised using scanning
electron microscope (SEM) imaging. To determine variations between different sample matrices, opaque (USGS BCR-2G) and transparent
(NIST SRM 610) glass, CaF2, and brass (MBH B26) samples were ablated using two different laser wavelengths, 193 and 266 nm. This study showed that the
condensed nano-particles (∼10 nm in diameter) formed by laser ablation reach the ICP as micron-sized agglomerates; this is
apparent from filters which contain only a few well-separated particles and particle agglomerates. Ablation experiments on
different metals and non-metals show that the structure of the agglomerates is matrix-dependent. Laser aerosols generated
from silicates and metals form linear agglomerates whereas particle-agglomerates of ablated CaF2 have cotton-like structures. Amongst other conditions, this study shows that the absorption characteristics of the sample
and the laser wavelength determine the production of micron-sized spherical particles formed by liquid droplet ejection. 相似文献