全文获取类型
收费全文 | 2340篇 |
免费 | 75篇 |
国内免费 | 20篇 |
专业分类
化学 | 1410篇 |
晶体学 | 11篇 |
力学 | 44篇 |
数学 | 425篇 |
物理学 | 545篇 |
出版年
2023年 | 17篇 |
2022年 | 29篇 |
2021年 | 65篇 |
2020年 | 48篇 |
2019年 | 67篇 |
2018年 | 63篇 |
2017年 | 54篇 |
2016年 | 79篇 |
2015年 | 90篇 |
2014年 | 78篇 |
2013年 | 160篇 |
2012年 | 140篇 |
2011年 | 162篇 |
2010年 | 114篇 |
2009年 | 115篇 |
2008年 | 166篇 |
2007年 | 141篇 |
2006年 | 173篇 |
2005年 | 137篇 |
2004年 | 92篇 |
2003年 | 82篇 |
2002年 | 92篇 |
2001年 | 37篇 |
2000年 | 29篇 |
1999年 | 28篇 |
1998年 | 22篇 |
1997年 | 25篇 |
1996年 | 33篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有2435条查询结果,搜索用时 31 毫秒
171.
We investigated the mechanisms of DNA exit during single‐cell gel electrophoresis (the comet assay) by measuring the kinetics of the comet tail formation. In the neutral comet assay, the rate of DNA exit was found to be dependent on the topological state of DNA, which was influenced by either ethidium bromide or a low radiation dose. The results clearly show that the comet tail is formed by extended DNA loops: the loop extension, being reversible when the DNA torsional constraint remains in the loops, is favored when the constraint is relaxed. The kinetics of the comet formation in the case of a high radiation dose points out that accumulation of the single‐strand breaks causes DNA fragmentation. In contrast to the neutral comet assay, the alkaline comet assay is not related to the chromatin loops. Our results imply that the alkaline treatment induces detachment of the loops from the nuclear matrix, and the comet tail is formed by ssDNA fragments, the ends of which are pulled out from the comet head by electric force. We suggest that the kinetic approach can be considered as an important improvement of the comet assay. 相似文献
172.
Marian Vîrgolici Corneliu Ponta Mihaela Manea Daniel Neguţ Mihalis Cutrubinis Ioan Moise Rareş Şuvăilă Eugen Teodor Costel Sârbu Andrei Medvedovici 《Journal of chromatography. A》2010,1217(12):1977-1987
Research on the chemical composition of fossil resins has evolved during the last decades as a multidisciplinary field and is strongly oriented toward the correlation with their geological and botanical origin. Various extraction procedures and chromatographic techniques have been used together for identifying the volatile compounds contained in the fossil resin matrix. Hyphenation between thermal desorption (TD), gas chromatography (GC) and mass spectrometry detection (MS) has been chosen to investigate the volatile compounds fraction from ambers with a focus on Romanite (Romanian amber) and Baltic amber species. A data analysis procedure was developed for the main purpose of fingerprinting ambers based on the MS identity of the peaks generated by the volatile fraction, together with their relative percentual area within the chromatogram. Chromatographic data analysis was based entirely on Automated Mass Spectral Deconvolution & Identification System (AMDIS) software to produce deconvoluted mass spectra which were used to build-up a mixed mass spectra and relative retention scale library. Multivariate data analysis was further applied on AMDIS results with successful discrimination between Romanite and Baltic ambers. A special trial was conducted to generate pyrolysis “like” macromolecular structure breakdown to volatile compounds by gamma irradiation with a high absorbed dose of 500 kGy. Contrary to our expectations the volatile fraction fingerprints were not modified after irradiation experiments. A complementary non-destructive new approach by ESR spectroscopy was also proposed for discriminating between Romanite and Baltic ambers. 相似文献
173.
Filippo Cammaroto Andrei Catalioto Jack Porter 《Central European Journal of Mathematics》2011,9(6):1242-1251
In this article, we extend the work on minimal Hausdorff functions initiated by Cammaroto, Fedorchuk and Porter in a 1998
paper. Also, minimal Urysohn functions are introduced and developed. The properties of heredity and productivity are examined
and developed for both minimal Hausdorff and minimal Urysohn functions. 相似文献
174.
Fabien Durand Ai-Hua Fan Andrei Yu. Khrennikov Dongdai Lin Franco Vivaldi Yuefei Wang 《P-Adic Numbers, Ultrametric Analysis, and Applications》2011,3(4):359-362
On the occasion of the 60th birthday of Professor Vladimir Sergeevich Anashin, we present a review of his significant scientific
research and related activities. 相似文献
175.
Andrei Khrennikov 《Foundations of Physics》2011,41(3):317-329
The idea that quantum randomness can be reduced to randomness of classical fields (fluctuating at time and space scales which are essentially finer than scales approachable in modern quantum experiments) is rather old. Various models have been proposed, e.g., stochastic electrodynamics or the semiclassical model. Recently a new model, so called prequantum classical statistical field theory (PCSFT), was developed. By this model a “quantum system” is just a label for (so to say “prequantum”) classical random field. Quantum averages can be represented as classical field averages. Correlations between observables on subsystems of a composite system can be as well represented as classical correlations. In particular, it can be done for entangled systems. Creation of such classical field representation demystifies quantum entanglement. In this paper we show that quantum dynamics (given by Schrödinger’s equation) of entangled systems can be represented as the stochastic dynamics of classical random fields. The “effect of entanglement” is produced by classical correlations which were present at the initial moment of time, cf. views of Albert Einstein. 相似文献
176.
We find sufficient conditions for the absence of harmonic L 2 spinors on spin manifolds constructed as cone bundles over a compact Kähler base. These conditions are fulfilled for certain perturbations of the Euclidean metric, and also for the generalized Taub-NUT metrics of Iwai-Katayama, thus proving a conjecture of Vi?inescu and the second author. 相似文献
177.
Experiments using bovine semen reveal that the addition of a high-gain water soluble dye results in random laser action when excited by a Q-switched, frequency doubled, Nd:Yag laser. The data shows that the linewidth collapse of the emission is correlated to the sperm count of the individual samples, potentially making this a rapid, low sample volume approach to count determination. 相似文献
178.
Chen QF Troshyn A Ernsting I Kayser S Vasilyev S Nevsky A Schiller S 《Physical review letters》2011,107(22):223202
Using an ultrastable continuous-wave laser at 580 nm we performed spectral hole burning of Eu(3+):Y(2)SiO(5) at a very high spectral resolution. The essential parameters determining the usefulness as a macroscopic frequency reference, linewidth, temperature sensitivity, and long-term stability, were characterized using a H-maser stabilized frequency comb. Spectral holes with a linewidth as low as 6 kHz were observed and the upper limit of the drift of the hole frequency was determined to be 5±3 mHz/s. We discuss the necessary requirements for achieving ultrahigh stability in laser frequency stabilization to these spectral holes. 相似文献
179.
Luican A Li G Reina A Kong J Nair RR Novoselov KS Geim AK Andrei EY 《Physical review letters》2011,106(12):126802
We report high magnetic field scanning tunneling microscopy and Landau level spectroscopy of twisted graphene layers grown by chemical vapor deposition. For twist angles exceeding ~3° the low energy carriers exhibit Landau level spectra characteristic of massless Dirac fermions. Above 20° the layers effectively decouple and the electronic properties are indistinguishable from those in single-layer graphene, while for smaller angles we observe a slowdown of the carrier velocity which is strongly angle dependent. At the smallest angles the spectra are dominated by twist-induced van Hove singularities and the Dirac fermions eventually become localized. An unexpected electron-hole asymmetry is observed which is substantially larger than the asymmetry in either single or untwisted bilayer graphene. 相似文献
180.
Lanin AA Voronin AA Sokolov VI Fedotov IV Fedotov AB Akhmanov AS Panchenko VY Zheltikov AM 《Optics letters》2011,36(10):1788-1790
Slow-light effects induced by stimulated Raman scattering in polymer waveguides on a printed circuit board are shown to enable a widely tunable delay of broadband optical signals, suggesting an advantageous platform for optical information processing and ultrafast optical waveform transformation. 相似文献