全文获取类型
收费全文 | 7081篇 |
免费 | 285篇 |
国内免费 | 33篇 |
专业分类
化学 | 4906篇 |
晶体学 | 42篇 |
力学 | 210篇 |
数学 | 967篇 |
物理学 | 1274篇 |
出版年
2023年 | 77篇 |
2022年 | 87篇 |
2021年 | 129篇 |
2020年 | 164篇 |
2019年 | 161篇 |
2018年 | 125篇 |
2017年 | 107篇 |
2016年 | 260篇 |
2015年 | 197篇 |
2014年 | 257篇 |
2013年 | 401篇 |
2012年 | 433篇 |
2011年 | 494篇 |
2010年 | 263篇 |
2009年 | 225篇 |
2008年 | 447篇 |
2007年 | 455篇 |
2006年 | 418篇 |
2005年 | 334篇 |
2004年 | 287篇 |
2003年 | 251篇 |
2002年 | 223篇 |
2001年 | 71篇 |
2000年 | 69篇 |
1999年 | 69篇 |
1998年 | 65篇 |
1997年 | 65篇 |
1996年 | 87篇 |
1995年 | 63篇 |
1994年 | 48篇 |
1993年 | 43篇 |
1992年 | 36篇 |
1991年 | 51篇 |
1990年 | 47篇 |
1989年 | 29篇 |
1988年 | 26篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 43篇 |
1984年 | 39篇 |
1983年 | 26篇 |
1982年 | 30篇 |
1981年 | 35篇 |
1980年 | 40篇 |
1979年 | 29篇 |
1978年 | 34篇 |
1977年 | 39篇 |
1976年 | 28篇 |
1975年 | 23篇 |
1974年 | 24篇 |
排序方式: 共有7399条查询结果,搜索用时 15 毫秒
61.
Tomáš Skála František Šutara Kevin C. Prince Vladimír Matolín 《Journal of Electron Spectroscopy and Related Phenomena》2009
Cerium oxide layers grown on Cu(1 1 1) were studied by conventional X-ray and resonant photoelectron spectroscopy with synchrotron radiation. A quantitative method of determining the cerium chemical state from the Ce 3d photoelectron spectra is described in detail. After the preparation of the ceria layer, Sn films of different thickness were evaporated onto the surface at temperatures of 120, 300 and 520 K. In all three cases, the deposited Sn was oxidized, CeO2 was partially reduced, and a mixed Sn–Ce–O oxide was formed. The quantitative extent of these reactions was found to be determined by limited diffusion of the deposited Sn atoms into the ceria layer at low temperature. The excess of tin formed a metallic overlayer on the sample surface. 相似文献
62.
Mohsin Ali Chaudry Christian Woitzik Christian Weißenfels Alexander Düster Peter Wriggers 《PAMM》2016,16(1):311-312
In this contribution, a novel design strategy is investigated for improving the crashworthiness of double-hull vessels, which involves usage of granular materials. For numerical simulation, a framework based on coupling of the Discrete Element and the Finite Element Method is used to study load bearing capacity of granular materials during uniaxial compression. In addition, the effect of Young's modulus of particles is also investigated with respect to the load transferability. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
63.
The preparation of 7-ethoxy-5-fluoroquinazolin-4-one, starting from 3,5-difluorophenol, is described. Further reaction with alkoxide then gives differentially substituted 5,7-dialkoxyquinazolin-4-ones. 相似文献
64.
Vincent J. Kalish Robert L. Shone Steven W. Kramer Paul W. Collins Kevin A. Babiak Kathleen T. McLaughlin 《合成通讯》2013,43(11):1641-1645
Hydrozirconation-iodination of a terminal acetylene followed by lithium-iodide exchange and finally dilithio cyanocuprate mediated conjugate addition to an appropriate cyclopentenone is reported as an efficient method for the synthesis of prostaglandin analogues. 相似文献
65.
In the current contribution, we present a multi-scale constitutive model capturing macroscopic inelastic effects (like stress softening and permanent set) in soft tissues under cyclic loading. Soft biological tissues can be described as a biological composite material. The extracellular matrix is hereby reinforced by collagen fibers which themself are an assembly of collagen fibrils embedded in a proteoglycan (PG) rich matrix. Micro-damage induced by cyclic loading is treated by an interaction scenario between the fibrils and the PGs. At the low strain regime PGs promote sliding between fibrils [1] which leads to the yielding of statistical distributed overlapping segments. The breakage of the PG-bridges is defined by a decreasing PG-density. Due to the accumulated damage of the PG connections at high tissue strains, the strains at the fibril level increases. This finally drives the over-stretching of the fibrils, which is associated with a permanent rupture of the hydrogen bonds inside of the tropocollagen molecules [2]. The so obtained model is in line with recent experimental findings [1, 2] and was additionally validated against experimental data available in literature. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
66.
Andreas Leng Cornelius Weiß Nina Straßner Prof. Dr. Andreas Hirsch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(53):e202201446
An unprecedented compound class of functional organic hybrids consisting of a photoswitchable norbornadiene building block and a redoxactive chromophore, namely naphthalene diimide, were designed and synthesized. Within these structures the capability of rylene chromophores to function as a redox active catalyst upon their photoexcitation was utilized to initiate the oxidative back-conversion of the in situ formed quadricyclane unit to its norbornadiene analogue. In this way successive photoexcitation at two different wavelengths enabled a controlled photoswitching between the two isomerical states of the hybrids. Beyond this prove of concept, the dependency of the reaction rate to the intramolecular distance of the two functional molecular building blocks as well as the concentration of the photoexcited sample was monitored. The experimental findings and interpretations were furthermore supported by quantum chemical investigations. 相似文献
67.
Stefan Fritsch Nazli Aldemir Jan Balszuweit Kevin Bojaryn Prof. Dr. Jens Voskuhl Dr. Christoph Hirschhäuser 《ChemistryOpen》2022,11(7):e202200098
The first total synthesis of resveratrone and iso-resveratrone based on an epoxide olefination approach is described. The pivotal reaction proceeds by insertion of the lithiated epoxide into a boronic ester and subsequent syn-elimination. Resveratrone has been described to have remarkable photophysical properties, including two-photon absorption. Therefore, an azide derivative has been prepared to allow for use as a biological label. 相似文献
68.
We present a comparative study of the application of a recently introduced heuristic algorithm to the optimization of transport on three major types of complex networks. The algorithm balances network traffic iteratively by minimizing the maximum node betweenness with as little path lengthening as possible. We show that by using this optimal routing, a network can sustain significantly higher traffic without jamming than in the case of shortest path routing. A formula is proved and tested with numerical simulation that allows quick computation of the average number of hops along the path and of the average travel times once the betweennesses of the nodes are computed. Using this formula, we show that routing optimization preserves the small-world character exhibited by networks under shortest path routing, and that it significantly reduces the average travel time on congested networks with only a negligible increase in the average travel time at low loads. Finally, we study the correlation between the weights of the links in the case of optimal routing and the betweennesses of the nodes connected by them. 相似文献
69.
Jacob RE Laicher G Minard KR 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,188(2):357-366
In (3)He magnetic resonance images of pulmonary air spaces, the confining architecture of the parenchymal tissue results in a non-Gaussian distribution of signal phase that non-exponentially attenuates image intensity as diffusion weighting is increased. Here, two approaches previously used for the analysis of non-Gaussian effects in the lung are compared and related using diffusion-weighted (3)He MR images of mechanically ventilated rats. One approach is model-based and was presented by Yablonskiy et al., while the other approach utilizes the second order decay contribution that is predicted from the cumulant expansion theorem. Total lung coverage is achieved using a hybrid 3D pulse sequence that combines conventional phase encoding with sparse radial sampling for efficient gas usage. This enables the acquisition of nine 3D images using a total of only approximately 1 L of hyperpolarized (3)He gas. Diffusion weighting ranges from 0 s/cm(2) to 40 s/cm(2). Results show that the non-Gaussian effects of (3)He gas diffusion in healthy rat lungs are directly attributed to the anisotropic geometry of lung microstructure as predicted by the Yablonskiy model, and that quantitative analysis over the entire lung can be reliably repeated in time-course studies of the same animal. 相似文献
70.
Jaegeun Noh Soonmin Jang Donghyung Lee Seokmin Shin Young Joon Ko Eisuke Ito Sang-Woo Joo 《Current Applied Physics》2007,7(6):605-610
Adsorption of dimethyl disulfide (DMDS) on gold colloidal nanoparticle surfaces has been examined to check its binding mechanism. Differently from previous results, DMDS molecules adsorbed on the gold surface at high concentration showed the S–S stretching band at 500 cm−1 in surface-enhanced Raman scattering (SERS) spectra, which indicates the presence of intact adsorption of DMDS molecules. However, it was found that the S–S bond of disulfides was easily cleaved on the gold surface at low concentration. These behaviors were not observed for diethyl disulfide (DEDS) or diphenyl disulfide (DPDS). Our results indicate that DMDS molecules with the shortest alkyl chains on the gold surface can be inserted into self-assembled monolayers (SAMs) without the S–S bond cleavage during self-assembly due to insufficient lateral van der Waals interaction and the low adsorption activity of disulfides, whereas DEDS with longer alkyl chains or DPDS with the weak disulfide bond dissociation energy would not. These unusual DMDS adsorption behaviors were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We also compared the bonding dissociation energy of the S–S bonds of various disulfides by means of a density functional theory (DFT) calculation. 相似文献