全文获取类型
收费全文 | 2052篇 |
免费 | 67篇 |
国内免费 | 17篇 |
专业分类
化学 | 1447篇 |
晶体学 | 22篇 |
力学 | 24篇 |
数学 | 165篇 |
物理学 | 478篇 |
出版年
2023年 | 13篇 |
2022年 | 12篇 |
2021年 | 23篇 |
2020年 | 19篇 |
2019年 | 32篇 |
2018年 | 25篇 |
2017年 | 22篇 |
2016年 | 40篇 |
2015年 | 41篇 |
2014年 | 50篇 |
2013年 | 103篇 |
2012年 | 133篇 |
2011年 | 162篇 |
2010年 | 67篇 |
2009年 | 71篇 |
2008年 | 131篇 |
2007年 | 112篇 |
2006年 | 119篇 |
2005年 | 123篇 |
2004年 | 94篇 |
2003年 | 100篇 |
2002年 | 90篇 |
2001年 | 32篇 |
2000年 | 45篇 |
1999年 | 22篇 |
1998年 | 22篇 |
1997年 | 26篇 |
1996年 | 25篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 13篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 20篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 27篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1981年 | 23篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1972年 | 12篇 |
排序方式: 共有2136条查询结果,搜索用时 15 毫秒
151.
152.
The reaction between a hydroquinone aqueous solution and manganese dioxide has been investigated by electron paramagnetic resonance spectroscopy. A very stable p-benzosemiquinone anion is formed when an aqueous solution of hydroquinone is passed through a column of manganese dioxide. The kinetics for the reaction between hydroquinone and manganese dioxide follow the equation where A0 is the initial concentration of hydroquinone, C is the concentration of p-benzosemiquinone anions, W is the amount of manganese dioxide, F is the feed rate of a hydroquinone aqueous solution, and k10 and k20 are constants; k10 = 3.1 × 10?2 (cm3/g MnO2· min), k20 = 3.2 (cm3/g MnO2·min). A mechanism for the reaction is proposed such that Mn(IV) in manganese dioxide is reduced to Mn (II) with hydroquinone from which the semiquinone anion is formed via a neutral semiquinone. The formation of semiquinone anions from several substituted hydroquinones is also discussed. 相似文献
153.
Toshimasa Hashimoto Tetsuya Sakai Seizo Miyata 《Journal of Polymer Science.Polymer Physics》1978,16(11):1965-1971
Thermally stimulated current (TSC) has been observed in extended-chain crystals of polyethylene above room temperature. The TSC spectra exhibit two current peaks of opposite polarity. The peaks were separated into separate components by curve fitting. The position of the negative peak, which appears at 123°C, is independent of charging conditions. The positive current increases after γ irradiation or aging of the samples. 相似文献
154.
155.
A novel cyclization of 1,1-diethyl 2-tert-butyl ethenetricarboxylate (1a) in the presence of a Lewis acid afforded a 5,5-dimethyl-gamma-lactone derivative 2a. The reaction process has been shown to arise from formation by trapping of isobutylene generated in situ. Lewis acid-promoted intermolecular reactions of 1,1-diethyl 2-hydrogen ethenetricarboxylate (5) and various alkenes to afford highly functionalized gamma-lactones were also developed. [reaction: see text] 相似文献
156.
N-Phenethylhexadecanamide was isolated from the MeOH extract of the fruiting bodies of the mushroom Laetiporus sulphureus together with eburicoic acid. Their structures were elucidated by spectroscopic methods. 相似文献
157.
Johnston M Lee JJ Chottiner GS Miller B Tsuda T Hussey CL Scherson DA 《The journal of physical chemistry. B》2005,109(22):11296-11300
The voltammetric characteristics of polycrystalline Au and W electrodes cleaned (thermal annealing at 1100 K) and characterized (Auger electron spectroscopy) in ultrahigh vacuum (UHV) have been examined in ultrapure AlCl(3)/1-ethyl-3-methylimidazolium chloride (EtMeImCl) melts in UHV. These experiments were performed using a custom-designed transfer system that allows for the all-Al electrochemical cell to be filled with EtMeImCl in an auxiliary UHV chamber and later transferred under UHV to the main UHV chamber that houses the Auger electron spectrometer. The results obtained for the underpotential (UPD) and bulk deposition of Al on Au were found to be very similar to those reported in the literature for measurements carried out under 1 atm of an inert gas in a glovebox. For the far more reactive W surfaces, voltammetric features ascribed to the stripping of underpotential-deposited Al could be observed following a single scan from 1.0 V vs Al(3+)/Al to a potential negative enough for bulk deposition of Al to ensue. This behavior is unlike that reported in the literature for experiments performed in a glovebox, which required either extensive potential cycling in the Al bulk deposition and stripping region or excursions to potentials positive enough for chlorine evolution to ensue for Al UPD features to be clearly discerned. These observations open new prospects for fundamental electrochemical studies of well-characterized, highly reactive metals, including single crystals, in a variety of low vapor pressure ionic liquids. 相似文献
158.
An optical atomic clock scheme is proposed that utilizes two lasers to establish coherent coupling between the 5s2 1S0 ground state of 88Sr and the first excited state, 5s5p 3P0. The coupling is mediated by the broad 5s5p 1P1 state, exploiting the phenomenon of electromagnetically induced transparency. The effective linewidth of the clock transition can be chosen at will by adjusting the laser intensity. By trapping the 88Sr atoms in an optical lattice, long interaction times with the two lasers are ensured; Doppler and recoil effects are eliminated. Based on a careful analysis of systematic errors, a clock accuracy of better than 2 x 10(-17) is expected. 相似文献
159.
Naruse M Miyazaki T Kubota F Kawazoe T Kobayashi K Sangu S Ohtsu M 《Optics letters》2005,30(2):201-203
A nanoscale data summation architecture is proposed and experimentally demonstrated based on the optical near-field interaction between quantum dots. Based on local electromagnetic interactions between a few nanometric elements via optical near fields, we can combine multiple excitations at a certain quantum dot, which allows construction of a summation architecture. Summation plays a key role for content-addressable memory, which is one of the most important functions in optical networks. 相似文献
160.
Subwavelength optical imaging through a metallic nanorod array 总被引:1,自引:0,他引:1
We propose a subwavelength imaging system without a lens or a mirror but with an array of metallic nanorods. The near-field components of dipole sources were plasmonically transferred through the rod array to reproduce the source distribution in the other side. We calculated the field distribution at the different planes of imaging process using the finite-difference time-domain algorithm and found that the spatial resolution was 40 nm given by the rod size and spacing. A typical configuration is a hexagonal arrangement of silver rods of 50 nm height and 20 nm diameter. We also show that the image formation highly depends on the coherence and the polarization of the source distribution and the source-array distance. 相似文献