全文获取类型
收费全文 | 278篇 |
免费 | 30篇 |
国内免费 | 23篇 |
专业分类
化学 | 224篇 |
晶体学 | 3篇 |
力学 | 16篇 |
综合类 | 3篇 |
数学 | 34篇 |
物理学 | 51篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 21篇 |
2012年 | 24篇 |
2011年 | 38篇 |
2010年 | 23篇 |
2009年 | 17篇 |
2008年 | 22篇 |
2007年 | 7篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1990年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有331条查询结果,搜索用时 0 毫秒
311.
烧结是"高炉-转炉"流程中的重要环节,在钢铁工业生态化进程中,烧结生态技术的开发和应用具有重要的意义.本文阐述了烧结生产常用的污染物控制措施,分析了存在的问题及对策.指出:烧结清洁生产的推行和生态化技术的开发将涉及如下方面:提高资源、能源的利用效率,从源头削减、控制污染物和排放物的无害化处理,合理有效利用副产品和废弃物以及开发生态化链接技术,以促进"零排放"生产体系的建立. 相似文献
312.
The self-assembly processes of the rod-coil diblock oligomer thin film of tetra-aniline (TANI)-block-poly(L-lactide) (PLLA) with different film thicknesses induced in the coil-selective solvent of acetone vapor at room temperature were studied. The morphologies of the oligomer films were determined by the film thickness. For the thicker film (232 nm), the nonextinct concentric ring-banded textures could form. While for the thinner and appropriate film (about 6 nm), multistacked diamond-shaped appearances with the periodic thickness being about 8.5 nm(6-nm-thick extended PLLA chain and 2.5-nm-thick p-pi conjugating TANI bimolecular layer) formed. The possible formation models of those two regular morphologies were presented in detail. 相似文献
313.
314.
Chunxia LongJianyu Guan 《Experimental Thermal and Fluid Science》2011,35(6):1162-1168
A method is introduced to determine the valve flow coefficient and resistance coefficient with the experiment of air discharging from a reservoir, and with the least squares method to fit the cumulative molar quantities discharged. The test valve is an angle-seat valve (Type 2632, Bürkert) with different apertures. At pressure difference of about 6 bar, the choked flow occurs when the valve aperture over 60%. Both the valve coefficient and resistance coefficient model can exactly predict the flowrate for the non-choked flow, while there are larger deviations for the choked flow. The modified equation for the choked flow can improve the prediction. In the resistance coefficient model, the value of resistance coefficient and the discharged cumulative molar quantities obtained with both the compressible and incompressible assumption are very close. The compressibility of air is negligible within the experimental pressure difference of about 6 bar. The additivity of the resistance coefficient makes the model more convenient to use. 相似文献
315.
Let G=(V,E) be a graph and let r≥1 be an integer. For a set D⊆V, define Nr[x]={y∈V:d(x,y)≤r} and Dr(x)=Nr[x]∩D, where d(x,y) denotes the number of edges in any shortest path between x and y. D is known as an r-identifying code (r-locating-dominating set, respectively), if for all vertices x∈V (x∈V?D, respectively), Dr(x) are all nonempty and different. Roberts and Roberts [D.L. Roberts, F.S. Roberts, Locating sensors in paths and cycles: the case of 2-identifying codes, European Journal of Combinatorics 29 (2008) 72-82] provided complete results for the paths and cycles when r=2. In this paper, we provide results for a remaining open case in cycles and complete results in paths for r-identifying codes; we also give complete results for 2-locating-dominating sets in cycles, which completes the results of Bertrand et al. [N. Bertrand, I. Charon, O. Hudry, A. Lobstein, Identifying and locating-dominating codes on chains and cycles, European Journal of Combinatorics 25 (2004) 969-987]. 相似文献
316.
317.
运动员头发中微量元素与运动项目的关系 总被引:1,自引:0,他引:1
采用原子吸收光谱法对专业运动员头发中的Ni、Fe、Mn、Cu、Zn、Sr、K和Ca 8种微量元素进行了测定,对这8种微量元素在不同运动项目和性别的运动员头发中含量差异进行了比较.结果表明,运动员头发中一些微量元素与运动项目和性别之间存在比较密切的关系,可为运动员的训练提供参考. 相似文献
318.
He F Yang P Wang D Li C Niu N Gai S Zhang M 《Langmuir : the ACS journal of surfaces and colloids》2011,27(9):5616-5623
Hollow La(2)O(3):Ln (Ln = Yb/Er, Yb/Ho) microspheres with up-conversion (UC) luminescence properties were successfully synthesized via a facile sacrificial template method by employing carbon spheres as hard templates followed by a subsequent heating process. The structure, morphology, formation process, and fluorescent properties are well investigated by various techniques. The results indicate that the hollow La(2)O(3):Ln microspheres can be well indexed to the hexagonal La(2)O(3) phase. The hollow La(2)O(3):Ln microspheres with uniform diameter of about 270 nm maintain the spherical morphology and good dispersion of the carbon spheres template. The shell of the hollow microspheres consists of numerous nanocrystals with the thickness of approximately 40 nm. Moreover, the possible formation mechanism of evolution from the carbon spheres to the amorphous precursor and to the final hollow La(2)O(3):Ln microspheres has also been proposed. The Yb/Er and Yb/Ho codoped La(2)O(3) hollow spheres exhibit bright up-conversion luminescence with different colors derived from different activators under the 980 nm NIR laser excitation. Furthermore, the doping concentration of the Yb(3+) is optimized under fixed concentration of Er(3+)/Ho(3+). This material may find potential applications in drug delivery, hydrogen and Li ion storage, and luminescent displays based on the uniform hollow structure, dimension, and UC luminescence properties. 相似文献
319.
STRICT STABILITY OF IMPULSIVE SET VALUED DIFFERENTIAL EQUATIONS 总被引:1,自引:0,他引:1
In this paper, we develop strict stability concepts of ODE to impulsive hybrid set valued differential equations. By Lyapunov’s original method, we get some basic strict stability criteria of impulsive hybrid set valued equations. 相似文献
320.
Chunxia Xiao Lei Gao Mingjing Lu Han Chen 《Journal of Dispersion Science and Technology》2013,34(8):1145-1150
The effect of polyvinylpyrrolidone (PVP) on rheology of aqueous SiC suspensions stabilized with polyacrylic acid (PAA) was investigated. At pH 6.0, as the total amount of dispersants was fixed at 0.3 wt%, the suspensions with co-addition of PAA and PVP obtained much lower viscosity than those added separately, displaying Newtonian behavior. The improvement in rheology of SiC suspensions arose from enhanced steric hindrance, which was caused by the presence of PVP molecules in association with PAA molecules adsorbed on SiC particle surfaces. However, this effect was relatively weak in alkaline condition because of complete dissociation of PAA. 相似文献