全文获取类型
收费全文 | 448篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 289篇 |
晶体学 | 8篇 |
力学 | 11篇 |
数学 | 62篇 |
物理学 | 87篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 20篇 |
2013年 | 33篇 |
2012年 | 22篇 |
2011年 | 38篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 18篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 18篇 |
2004年 | 10篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1982年 | 3篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1969年 | 3篇 |
1943年 | 5篇 |
1942年 | 4篇 |
1941年 | 2篇 |
1940年 | 9篇 |
1939年 | 6篇 |
排序方式: 共有457条查询结果,搜索用时 125 毫秒
451.
R Kumar RG Pillai N Pekas Y Wu RL McCreery 《Journal of the American Chemical Society》2012,134(36):14869-14876
A three terminal molecular memory device was monitored with in situ Raman spectroscopy during bias-induced switching between two metastable states having different conductivity. The device structure is similar to that of a polythiophene field effect transistor, but ethylviologen perchlorate was added to provide a redox counter-reaction to accompany polythiophene redox reactions. The conductivity of the polythiophene layer was reversibly switched between high and low conductance states with a "write/erase" (W/E) bias, while a separate readout circuit monitored the polymer conductance. Raman spectroscopy revealed reversible polythiophene oxidation to its polaron form accompanied by a one-electron viologen reduction. "Write", "read", and "erase" operations were repeatable, with only minor degradation of response after 200 W/E cycles. The devices exhibited switching immediately after fabrication and did not require an "electroforming" step required in many types of memory devices. Spatially resolved Raman spectroscopy revealed polaron formation throughout the polymer layer, even away from the electrodes in the channel and drain regions, indicating that thiophene oxidation "propagates" by growth of the conducting polaron form away from the source electrode. The results definitively demonstrate concurrent redox reactions of both polythiophene and viologen in solid-state devices and correlate such reactions with device conductivity. The mechanism deduced from spectroscopic and electronic monitoring should guide significant improvements in memory performance. 相似文献
452.
The stationary phase of alumina adsorbents, prepared by different chemical processes, was used to study the separation behaviour of hydrogen isotopes. Three types of alumina, obtained by conventional hydroxide route alumina coated with silicon oxide and alumina prepared by internal gelation process (IGP), were used as packing material to study the separation of HT and T2 in a mixture at various temperatures. The conventional alumina and silicon oxide coated alumina resolved HT and T2 at 77 K temperature with different retention times. The retention times on SiO2 coated columns were found to be higher than those of other adsorbents. However, the column filled with IGP alumina was found to be ideal for the separation of HT and T2 at 240 K. The peaks were well resolved in less than 5 min on this column. 相似文献
453.
Pai Rajesh V. Pillai K. T. Pathak Sachin Mukerjee S. K. Vinogradov V. V. Agafonov A. V. Vinogradov A. V. Aggarwal S. K. 《Journal of Sol-Gel Science and Technology》2012,61(1):192-196
Mesoporous γ-alumina samples were prepared by the sol–gel process from the boehmite sol having different template solutions.
Copper doped material was also prepared from sol containing template solution along with copper nitrate. Studies were performed
to understand the influence of templates on the morphology of the synthesized samples particularly with respect to specific
surface area and porosity. Synthesized samples were used to study sorption of Pu(IV) from nitric acid–oxalic acid solutions.
Distribution ratios (D) for Pu(IV) were determined using the γ-alumina samples with an objective to employ these for the recovery
of Pu. 相似文献
454.
Universal behavior of the magnetocaloric effect along with structural and critical exponent analysis in mixed manganite La0.67Ca0.33Mn1−xCrxO3 (x = 0.1, 0.25), [LCMCr0.1 and LCMCr0.25] exhibiting second order phase transition are investigated. Structural study using Reitveld refinement of XRD patterns indicates orthorhombic structure with Pnma space group. Modified Arrott plot method has been adopted to study the critical behavior of the compounds at their transition region, which gives values of β = 0.555(6), γ = 1.17(4) and δ = 2.7096(7) at TC = 232.5 K for LCMCr0.1 and β = 0.68 (1), γ = 1.09(3) and δ = 2.9362(4) at TC = 202.5 K for LCMCr0.25. The values are close to those expected for mean field ferromagnets with long range order. With increase in Cr content, the temperature corresponding to the maximum entropy change as well as the magnetic transition temperature gradually shifts to low temperatures. The maximum magnetic entropy change was found to be 3.5 J/kg K for x = 0.1 and 2.2 J/kg K for x = 0.25 for a field change of 5 T. The field dependence of the magnetic entropy change is also analyzed, which shows the power law dependence namely, ?SM ∝ Hn, n = 0.9086(5) at TC = 232.5 K and n = 0.849(7) at TC = 202.5 K for LCMCr0.1 and LCMCr0.25 respectively. Relative cooling power was found to be about 147 J/kg for LCMCr0.1 and 88 J/kg for LCMCr0.25. The field dependence of the relative cooling power for both the compounds shows a H1+1/δ dependence with the δ values in agreement with the mean field model. 相似文献
455.
The known median-based denoising methods tends to work well for restoring the images corrupted by random-valued impulse noise with low noise level, but it fails in denoising highly corrupted images. In this paper, a new noise reduction method based on directional weighted median based fuzzy impulse noise detection and reduction method (DWMFIDRM) has been proposed, which has been specially developed for denoising all categories of impulse noise. The contribution of this paper is threefold. The main contribution of the novel impulse noise reduction technique lies in the unification of three different methods; the impulse noise detection phase utilizing the concept of fuzzy gradient values, edge-preserving noise reduction phase based on the directional weighted median of the neighboring pixels and a final filtering step in order to deal with noisy pixels of non-zero degree. Such a unique combination has improved the efficiency of this method for high density noise removal. The experimental results of our proposed method have a significant improvement when compared to other existing filters for high density noise removal. This paper utilizes the concept of fuzzy gradient values. The noise reduction phase that preserves edge sharpness is based on the directional weighted median of neighboring pixels. Final filtering phase is performed only when there is non-zero degree of noise pixels. This phase makes our method more efficient in high noise density. Experimental results show that DWMFIDRM provides a significant improvement on other existing filters. 相似文献
456.
Varaprasad Bodala Rajitha Lakshmi Podugu Kumari Yettula Dr. Padmarao Gollamudi Dr. Siddaiah Vidavalur Dr. Shyamala Pulipaka 《化学:亚洲杂志》2023,18(1):e202201004
A direct access to unsymmetrical and symmetrical multi-substituted pyridines has been accomplished via iron-catalysed [3+3] annulation of oxime acetates with enaminones. This protocol is featured by easily available starting materials, no requirement of expensive additives and ligands, operational simplicity, and good tolerance with diverse functional groups. 相似文献
457.
Bennie R. Biju Joel C. Raj A. Nirmal Paul Antony A. Jerold Pillai S. Iyyam 《Journal of Solid State Electrochemistry》2023,27(1):271-280
Journal of Solid State Electrochemistry - The growing demand for electricity has increased the interest of the researchers towards exploration of energy storing devices (ESDs). With the motif for... 相似文献