全文获取类型
收费全文 | 5960篇 |
免费 | 114篇 |
专业分类
化学 | 3287篇 |
晶体学 | 30篇 |
力学 | 133篇 |
数学 | 1360篇 |
物理学 | 1264篇 |
出版年
2021年 | 39篇 |
2020年 | 45篇 |
2019年 | 54篇 |
2018年 | 141篇 |
2017年 | 133篇 |
2016年 | 203篇 |
2015年 | 148篇 |
2014年 | 199篇 |
2013年 | 480篇 |
2012年 | 294篇 |
2011年 | 399篇 |
2010年 | 217篇 |
2009年 | 181篇 |
2008年 | 337篇 |
2007年 | 334篇 |
2006年 | 309篇 |
2005年 | 226篇 |
2004年 | 202篇 |
2003年 | 142篇 |
2002年 | 141篇 |
2001年 | 96篇 |
2000年 | 80篇 |
1999年 | 57篇 |
1998年 | 50篇 |
1997年 | 49篇 |
1996年 | 47篇 |
1995年 | 47篇 |
1994年 | 30篇 |
1993年 | 42篇 |
1992年 | 56篇 |
1991年 | 43篇 |
1990年 | 47篇 |
1989年 | 51篇 |
1988年 | 48篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 61篇 |
1984年 | 67篇 |
1983年 | 65篇 |
1982年 | 61篇 |
1981年 | 41篇 |
1980年 | 53篇 |
1979年 | 47篇 |
1978年 | 68篇 |
1977年 | 39篇 |
1976年 | 52篇 |
1975年 | 42篇 |
1974年 | 49篇 |
1973年 | 41篇 |
1972年 | 33篇 |
排序方式: 共有6074条查询结果,搜索用时 0 毫秒
941.
In the setting of generalized metric spaces, so called G-metric spaced introduced by Z. Mustafa and B. Sims in 2006, some fixed point results for mappings with contractive iterate at a point and common fixed point results for infinite family of self mappings will be presented. The results are generalizations of well known results in the metric space. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
942.
Aleksandar Savić Roland Kardos Miklós Nyitrai Ksenija Radotić 《Journal of fluorescence》2013,23(3):605-610
Despite of widely application of multivariate analysis in chemometrics, problem of resolving closely positioned components in the fluorescence spectra remained unsolved, thus limiting the usage of fluorescence spectroscopy in analytical purpose. In this paper we have described a novel procedure, adapted especially for the analysis of complex fluorescence spectra with multiple, closely positioned components’ maxima. The method was first tested on the simulated spectra and then applied on the spectra of proteins whose fluorophores have similar properties of both the excitation and the emission spectra. In this paper, simple but efficient modification of the method was applied. Instead of analyzing full size emission matrix (12 spectra), 9 spectra wide windows were analyzed, and 4 factors (greatest possible number of factors with physical meaning both for actin and simulated spectra) were extracted in each pass. Obtained factor scores were grouped by using the K-means algorithm. Groups of factor scores obtained from K-means algorithm were passed through the one more factor analysis (FA) in order to find one factor that represents each group. Our approach provides resolution of extremely closed spectral components, which is a vital data for protein conformation analysis based on fluorescence spectroscopy. 相似文献
943.
The electronic bands appearing in the region 300–330 nm were produced in a low-pressure DC are with beryllium electrodes. The bands were obtained in the atmosphere of ordinary water vapour and heavy water vapour. From isotope shift studies, experimental conditions and the similarity with the bands of isoelectronic BeF, the emitting molecules were identified as BeOH and BeOD, respectively. 相似文献
944.
High-resolution data of online chats are studied as a physical system in the laboratory in order to quantify collective behavior of users. Our analysis reveals strong regularities characteristic of natural systems with additional features. In particular, we find self-organized dynamics with long-range correlations in user actions and persistent associations among users that have the properties of a social network. Furthermore, the evolution of the graph and its architecture with specific k-core structure are shown to be related with the type and the emotion arousal of exchanged messages. Partitioning of the graph by deletion of the links which carry high arousal messages exhibits critical fluctuations at the percolation threshold. 相似文献
945.
946.
947.
In this article we study the existence of range projections in rings with involution, relating it to the existence of the Moore–Penrose inverse. The results are applied to the solution of the equation xbx?=?x in rings with involution, extending the results of Greville for matrices. Simpler new proofs are given of the Moore–Penrose invertibility of regular elements in rings with involution, and of the Ljance's formula. 相似文献
948.
949.
Nanoparticles of zinc-doped maghemite were prepared using ultrasonic radiation. As a precursor, a suspension of maghemite in an alkaline aqueous solution of zinc nitrate at pH 9 was sonicated. The zinc-doped maghemite nanoparticles were investigated by X-ray diffraction, Mössbauer spectroscopy, high-resolution electron microscopy (HREM) and SQUID magnetometry. The Mössbauer measurements, which cover the temperature range 4.2 K to room temperature, were acquired in zero field and an applied field of 5 T. The results show that by using ultrasound radiation, zinc Zn2+ can substitute for Fe3+ up to a composition close to zinc ferrite (ZnFe2O4), which has a random distribution of Fe3+ ions over both A and B sublattices in the spinel structure with an inversity parameter of δ = 0.322. This leads to a maximum saturation magnetization (Ms) of 64.1 emu/g at 300 K and 73.5 emu/g at 2 K. 相似文献
950.
BaTiO3 (BT) powder, with average particle size of 1.4 microm, was synthesized by solid-state reaction. A high-intensity ultrasound irradiation (ultrasonication) was used to de-agglomerate micro-sized powder to nano-sized one. The crystal structure, crystallite size, morphology, particle size, particle size distribution, and specific surface area of the BT powder de-agglomerated for different ultrasonication times (0, 10, 60, and 180 min) were determined. It was found that the particles size of the BT powder was influenced by ultrasonic treatment, while its tetragonal structure was maintained. Therefore, ultrasonic irradiation can be proposed as an environmental-friendly, economical, and effective tool for the de-agglomeration of barium titanate powders. 相似文献