全文获取类型
收费全文 | 3890篇 |
免费 | 191篇 |
国内免费 | 46篇 |
专业分类
化学 | 2849篇 |
晶体学 | 39篇 |
力学 | 144篇 |
综合类 | 2篇 |
数学 | 423篇 |
物理学 | 670篇 |
出版年
2024年 | 42篇 |
2023年 | 66篇 |
2022年 | 383篇 |
2021年 | 343篇 |
2020年 | 201篇 |
2019年 | 195篇 |
2018年 | 159篇 |
2017年 | 144篇 |
2016年 | 221篇 |
2015年 | 151篇 |
2014年 | 168篇 |
2013年 | 293篇 |
2012年 | 248篇 |
2011年 | 285篇 |
2010年 | 168篇 |
2009年 | 142篇 |
2008年 | 167篇 |
2007年 | 159篇 |
2006年 | 107篇 |
2005年 | 99篇 |
2004年 | 61篇 |
2003年 | 62篇 |
2002年 | 45篇 |
2001年 | 18篇 |
2000年 | 16篇 |
1999年 | 7篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 3篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 7篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1971年 | 2篇 |
1970年 | 3篇 |
排序方式: 共有4127条查询结果,搜索用时 15 毫秒
91.
Muhammad Ahsan Shafique G. Murtaza Shahzad Saadat Muhammad K H Uddin Riaz Ahmad 《辐射效应与固体损伤》2017,172(7-8):590-599
Stainless steel 306 is implanted with various doses of nitrogen ions using a 2?MV pelletron accelerator for the improvement of its surface biomedical properties. Raman spectroscopy reveals incubation of hydroxyapatite (HA) on all the samples and it is found that the growth of incubated HA is greater in higher ion dose samples. SEM profiles depict uniform growth and greater spread of HA with higher ion implantation. Human oral fibroblast response is also found consistent with Raman spectroscopy and SEM results; the cell viability is found maximum in samples treated with the highest (more than 300%) dose. XRD profiles signified greater peak intensity of HA with ion implantation; a contact angle study revealed hydrophilic behavior of all the samples but the treated samples were found to be lesser hydrophilic compared to the control samples. Nitrogen implantation yields greater bioactivity, improved surface affinity for HA incubation and improved hardness of the surface. 相似文献
92.
93.
The advances in recording, editing, and broadcasting multimedia contents in digital form motivate to protect these digital contents from illegal use, such as duplication, manipulation, and redistribution. However, watermarking algorithms are designed to satisfy requirements of applications, as different applications have different concerns. We intend to design a watermarking algorithm for applications which require high embedding capacity and imperceptibility, to maintain the integrity of the host signal as well as embedded information. Reversible watermarking is a promising technique which satisfies our requirements. In this paper, we concentrate on improving the watermark capacity and reducing the perceptual degradation of an image. We investigated the Luo's [1] additive interpolation-error expansion algorithm and enhanced it by incorporating with two intelligent techniques: genetic algorithm (GA), and particle swarm optimization (PSO). Genetic algorithm is applied to exploit the correlation of image pixel values to obtain better estimation of neighboring pixel values, which results in optimal balance between information storage capacity and imperceptibility. Particle swarm optimization (intelligent technique) is also applied for the same purpose. Experimental results show that PSO and GA nearly give the same results, but GA outperforms the PSO. Experimental results also reveal that the proposed strategy outperforms the state of art works in terms of perceptual quality and watermarking payload. 相似文献
94.
95.
Muhammad Saleem Anser Ali Chang-Shik Choi Bong Joo Park Eun Ha Choi Ki Hwan Lee 《Journal of fluorescence》2014,24(4):995-1001
In recent years, fluorescent probes for the detection of environmentally and biologically important metal cations have received extensive attention for designing and development of fluorescent chemosensors. Herein, we report the photophysical results of 2-(2-fluorobenzoyl)-N-(2-methoxyphenyl) hydrazinecarbothioamide (4) functionalized as Ni (II) sensor in micromolar concentration level. Through fluorescence titration at 488 nm, we were confirmed that ligand 4 showed the remarkable emission by complexation between 4 and Ni (II) while it appeared no emission in case of the competitive ions (Cr3+, Fe2+, Co2+, Ba2+, Cu2+, Ca2+, Na+, K+, Cu+, Cs+). Furthermore, ligand 4 exhibited no toxicity with precise cell permeability toward normal living cells using L929 cell lines in bio imaging experiment investigated through confocal fluorescence microscope. The non-toxic behavior of ligand 4 (assessed by MTT assay) and its ability to track the Ni2+ in living cells suggest its possibility to use in biological system as nickel sensor. Figure
? 相似文献
96.
Fission cross sections strongly depend on the ratio of the level density parameter in fission to neutron emission, af/an. In this work, a cascade-exciton model implemented in the code CEM95 has been used to observe this effect for proton induced fission cross sections of tungsten, lead and bismuth. The method was employed using different level density parameter ratios for each fission cross section calculation. The calculated fission cross sections are compared with the available experimental data in the literature. It has been observed that a change of the ratio of the level density parameter, af/an, is necessary with the incident energy of the proton, to best estimate the fission cross sections in CEM95. 相似文献
97.
Muhammad Danial Hisham Abdul Rauf Dumitru Vieru Aziz Ullah Awan 《Chinese Journal of Physics (Taipei)》2018,56(6):3020-3032
Unsteady flows of two immiscible Maxwell fluids in a rectangular channel bounded by two moving parallel plates are studied. The fluid motion is generated by a time-dependent pressure gradient and by the translational motions of the channel walls in their planes. Analytical solutions for velocity and shear stress fields have been obtained by using the Laplace transform coupled with the finite sine-Fourier transform. These analytical solutions are new in the literature and the method developed in this paper can be generalized to unsteady flows of n-layers of immiscible fluids. By using the Laplace transform and classical method for ordinary differential equations, the second form of the Laplace transforms of velocity and shear stress are determined. For the numerical Laplace inversion, two accuracy numerical algorithms, namely the Talbot algorithm and the improved Talbot algorithm are used. 相似文献
98.
99.
Muhammad Irfan 《Numerical Methods for Partial Differential Equations》2023,39(2):1030-1041
The aspects of activation energy in magnetized Maxwell nanofluid flow with Brownian movement and thermophoretic diffusion have been elaborated here. Furthermore, Joule heating, variable conductivity and chemical reaction are scrutinized. The Buongiorno nanofluid thought is ratify to incorporate the importance of thermophoretic and Brownian diffusion. The attained ODEs have been solved via homotopic algorithm. The performance of operational variables is inspected. The Maxwell temperature field for Eckert number and variable conductivity factor have similar trend. The fluid concentration exaggerates for activation energy and decelerates for Brownian motion parameter. Furthermore, the brilliant outcomes attained and associated with possible existing prose accurately. 相似文献
100.
Muhammad Taher Abuelma’atti 《Applied Acoustics》2010,71(3):269-275
A mathematical model for the input-output functions of the hearing aids is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the amplitudes of the harmonic and intermodulation components of the output when the input is formed of multitone large sound pressure levels. The special case of two-tone equal-amplitude incident pressure level is considered in detail. The results show that the third-order intermodulation component is always higher than the third-harmonic component. The results also show that the input-output functions exhibiting peak clipping exhibit the worst harmonic and intermodulation performance for large sound pressure levels. The simple wide-dynamic range compression (WDRC) input-output function exhibits the best harmonic and intermodulation distortion performance under large sound pressure levels. These results are consistent with the previously reported observations and reveal that there is a correlation between intelligibility of high-level speech and the harmonic and intermodulation performance of the hearing aid under large sound pressure levels. 相似文献